The scientific observer of Nature is a kind of mystic seeker in the act of prayer.

-Allama Iqbal

I would like to dedicate this thesis to my parents and teachers. Their integrity, honesty and love for knowledge is exemplary.

List of Papers

This PhD thesis is based on the following papers, which are referred to in the text by their Roman numerals. Reprints were made with the permission of the respective publishers.

I Potential Controlled Anion Absorption in a Novel High Surface Area Composite of Cladophora Cellulose and Polypyrrole Kristina Gelin, Albert Mihranyan, Aamir Razaq, Leif Nyholm, Maria Strømme Electrochimica Acta (2009) 54, 3394-3401.

II Influence of the Type of Oxidant on Anion Exchange Properties

of Fibrous Cladophora Cellulose/Polypyrrole Composites Aamir Razaq, Albert Mihranyan, Ken Welch, Leif Nyholm, Maria Strømme Journal of Physical Chemistry B (2009) 113, 426-433.

III High-capacity Conductive Nanocellulose Paper Sheets for

Electrochemically Controlled Extraction of DNA Oligomers Aamir Razaq, Gustav Nyström, Maria Strømme, Albert Mihranyan, Leif Nyholm Submitted.

IV Spatial Mapping of Elemental Distributions in Polypyrrole-

Cellulose Nanofibers using Energy-Filtered Transmission Electron Microscopy Stefano Rubino, Aamir Razaq, Leif Nyholm, Maria Strømme, Klaus Leifer, Albert Mihranyan

Journal of Physical Chemistry B (2010) 114, 13644-13649.

V Ultrafast All-Polymer Paper-Based Batteries Gustav Nyström, Aamir Razaq, Maria Strømme, Leif Nyholm, Albert Mihranyan Nano Letters (2009) 9, 3635-3639.

VI Carbon Fiber-reinforced Polypyrrole-Cladophora Nanocellulose Composite for Paper-based Energy Storage Devices Aamir Razaq, Leif Nyholm, Martin Sjödin, Maria Strømme, Albert Mihranyan Submitted.

VII Electrochemically Controlled Separation of DNA Oligomers with High Surface Area Conducting Paper Electrode Aamir Razaq, Maria Strømme, Leif Nyholm, Albert Mihranyan ECS Transactions (2011) 35, 135-142.

Summary of my contribution to the papers included in this PhD thesis:

Paper I Part of the experimental work, analysis of results and part of the writing.

Paper II Experimental planning, experimental work, analysis of

results and part of the writing.

Paper III Experimental planning, experimental work, analysis of results and part of the writing.

Paper IV Sample preparation and part of the writing.

Paper V Experimental planning, initial experimental work, analysis

of results and writing of the first draft.

Paper VI Experimental planning, experimental work, analysis of results and part of the writing.

Paper VII Experimental planning, experimental work, analysis of

results and part of the writing.

Also published

Ionic Motion in Polypyrrole-Cellulose Composites: Trap Release Mechanism during Potentiostatic Reduction Maria Strømme, Göran Frenning, Aamir Razaq, Kristina Gelin, Leif Nyholm, Albert Mihranyan Journal of Physical Chemistry B (2009) 113, 4582-4589.

A Nanocellulose Polypyrrole Composite Based on Microfibrillated

Cellulose from wood Gustav Nyström, Albert Mihranyan, Aamir Razaq, Tom Lindström, Leif Nyholm, Maria Strømme Journal of Physical Chemistry B (2010) 114, 4178-4182.

The Salt and Paper Battery; Ultrafast and All-polymer Based

Gustav Nyström, Aamir Razaq, Albert Mihranyan, Leif Nyholm, Maria Strømme Mat. Res. Soc. Symp. Proc. (2009) 1197, 41-46.

Conference contributions

Nanostructured high surface area conducting paper composites for multiple purpose applications including extraction of DNA and energy storage devices Albert Mihranyan, Aamir Razaq, Gustav Nyström, Leif Nyholm, Maria Strømme

Nanotech Europe, Berlin, 28-30 September, 2009.

High surface area conducting paper materials composed of polypyrrole and Cladophora cellulose Albert Mihranyan, Aamir Razaq, Gustav Nyström, Maria Strømme, Leif Nyholm 216th ECS Meeting, Vienna, 4-9 October, 2009.

Salt and paper battery Albert Mihranyan, Gustav Nyström, Aamir Razaq, Leif Nyholm, Maria Strømme Printed Electronics/Photovoltaics Europe, Dresden, April 13-14, 2010.

Electrochemically controlled ion-exchange membrane based on high surface area conducting paper composite for separation of biomolecules Aamir Razaq, Gustav Nyström, Daniel O. Carlsson, Maria Strømme, Leif Nyholm, Albert Mihranyan Biosensors 2010 Congress, Glasgow, 26-28 May, 2010.

A battery from algae cellulose

Albert Mihranyan, Gustav Nyström, Aamir Razaq, Leif Nyholm, Maria Strømme PulpPaper 2010, Helsinki, 1-3 June, 2010.

Tracking ion distributions in polypyrrole coated cellulose nanofibers

by means of energy filtered transmission electron microscopy Stefano Rubino, Aamir Razaq, Maria Strømme, Leif Nyholm, Albert Mihranyan, Klaus Leifer Scandem 2010, Stockholm, 8-11 June, 2010.

Potential controlled ion-exchange membrane based on high surface

area conducting paper composite for DNA separation Aamir Razaq, Gustav Nyström, Daniel O. Carlsson, Maria Strømme, Leif Nyholm, Albert Mihranyan Materials for 21st Century Workshop, Uppsala, February 9, 2011 (won the best poster prize).

Carbon highways in high surface area conducting paper membranes

for efficient DNA separation Aamir Razaq, Maria Strømme, Leif Nyholm, Albert Mihranyan MRS spring meeting, San Francisco, 25-29 April, 2011.

Energy storage and biomolecular extraction using polypyrrole

coated cellulose nanofiber composites Maria Strømme, Martin Sjödin, Gustav Nyström, Daniel O. Carlsson, Natalia Ferraz, Henrik Olsson, Aamir Razaq, Albert Mihranyan, Leif Nyholm MRS fall meeting, Boston, 28 November - 02 December 2011, Submitted.

Contents

1. General Introduction .................................................................................13

2. Aims of the work ......................................................................................14

3. Conductive polymers ................................................................................15 3.1. Polypyrrole ........................................................................................15 3.2. Ion-exchange mechanism of PPy ......................................................17 3.3. Cellulose as a substrate for CP coatings............................................18

4. Extraction methods and spatial mapping of elemental distributions ........20 4.1. Electrochemical extraction methods .................................................20 4.2. Spatial mapping of elemental distribution.........................................20

5. Applications of conductive polymers .......................................................23 5.1. Extraction of biomolecules................................................................23 5.2. Energy storage...................................................................................24

6. Influence of additives................................................................................25

7. Experimental .............................................................................................26 7.1. Synthesis............................................................................................26

7.1.1. PPy-Cladophora cellulose composites.......................................26 7.1.2. PPy-Cladophora cellulose-CCF composites ..............................27

7.2. Primary material characterization .....................................................27 7.2.1. Scanning Electron Microscopy..................................................27 7.2.2. Transmission Electron Microscopy ...........................................27 7.2.3. Electronic conductivity..............................................................28 7.2.4. Specific surface area ..................................................................28 7.2.5. Apparent density and porosity ...................................................28

7.3. Electrochemical characterization ......................................................29 7.3.1. Cyclic voltammetry ...................................................................29 7.3.2. Chronoamperometry ..................................................................29 7.3.3. Chronopotentiometry.................................................................29

7.4. Spectrofluorometry............................................................................31

8. Results and discussion ..............................................................................32 8.1. General characterization....................................................................32 8.2. Applications of the PPy-Cladophora cellulose composites...............35

8.2.1. Potential-controlled anion exchange..........................................35 8.2.2. Current-controlled DNA extraction ...........................................39 8.2.3. Paper-based energy storage devices ..........................................44

8.3. Incorporation of CCFs in the PPy-Cladophora cellulose composite.47

9. Conclusions...............................................................................................53

10. Future work.............................................................................................55

Acknowledgements.......................................................................................56

Sammanfattning på Svenska .........................................................................58

References.....................................................................................................60

Abbreviations

ATP Adenosine Triphosphate CE Counter electrode CFs Carbon fibers CCFs Chopped carbon fibers CPs Conductive Polymers CV Cyclic voltammetry DNA Deoxyribonucleic acid EELS Electron energy loss spectroscopy EFTEM Energy-filtered transmission electron

microscopy ESPME Electrochemically controlled solid

phase micro-extraction EMLC Electrochemically modulated liquid

chromatography PANI Polyaniline PT Polythiophene PEDOT Poly(3,4-ethylenedioxythiophene) PMo Phosphomolybdic acid PPV Polyphenylene vinylene Py Pyrrole PPy Polypyrrole RE Reference electrode SEM Scanning Electron Microscopy SPME Solid phase micro-extraction TEM Transmission Electron Microscopy WE Working Electrode

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1. General Introduction

Polymers are commonly used by the electronics industry because of their insulating properties. However, polymers which can conduct electric current, i.e. conductive polymers (CPs) are also available and have been explored extensively in a variety of fields over the last few decades. CPs are an attrac-tive replacement for metals because of their light weight, ease of processing (low temperature processing), environmental friendliness (they are dispos-able, obtained from renewable sources, and their production leaves a low carbon footprint) and cost saving factors.

The applications of CPs fall into two main areas. The first utilizes their electrically conductive properties to produce such applications as electro-magnetic shielding1, printed circuit boards2, artificial nerves3 and antistatic clothing4. The second utilizes their electroactive properties for applications such as ion-exchange membranes5-7, energy storage devices8-10, molecular electronics11, electrical displays12, electrochemical actuators13, drug release systems14 and various types of sensory devices15, 16.

The work in this PhD thesis focuses on two applications of CP i) electro-chemically controlled extraction of biomolecules and ii) non-metal based energy storage devices. In particular, a composite conductive paper material composed of polypyrrole (PPy) and Cladophora algae cellulose, which was first described by Mihranyan et al17., is developed as a paper-based electrode material for ion-exchange.

Generally, additives are the substances introduced to the host materials for improvement in the performance of the final products. The investigations in this thesis also address the effects of inclusion of an additive (chopped carbon fibers; CCFs) on the electrochemical performance of the paper-based electrode material for biomolecular extraction and energy storage applications.

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2. Aims of the work

The main aim of this work was to investigate the properties of the conductive composite paper composed of PPy and Cladophora cellulose for applications within electrochemically controlled ion extraction and non-metal energy storage devices.

Specific aims of the work were:

To investigate the potential controlled anion-exchange properties of the conductive paper composite for extraction of relatively small inorganic and organic anions (Paper I).

To evaluate how the potential controlled ion-exchange properties of

the conductive paper composite are influenced by the size of the oxidant anion, incorporated during the polymerization of the PPy coating (Papers II and IV).

To assess the efficiency of DNA oligomer extraction and release by

the conductive paper composite in an electrochemically controlled set-up (Papers III and IV).

To develop an environmentally friendly paper-based energy storage

device by utilizing the conductive paper composite as the electrode material (Paper V).

To examine the effects of incorporation of CCFs as an additive in

the composite paper material i) for enhanced electroactive perform-ance of paper-based energy storage devices (Paper VI) and ii) for enhanced release of DNA oligomers following electrochemically controlled extraction (Paper VII).

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3. Conductive polymers

The era of CPs was started in 1963, and Alan G. Heeger, Alan G. MacDiarmid and Hideki Shirakawa were subsequently awarded the Nobel Prize in Chemistry in 2000 "for the discovery and development of electrically conductive polymers". The discovery of CPs was important, be-cause they can be used as a substitute for metallic conductors and semicon-ductors. CPs lend themselves to enormous design flexibility; they are capa-ble of conducting an electric current, exhibit highly reversible redox behav-ior, and can act as functional materials18,19. Thanks to these inherent charac-teristics, CPs can be used in a wide range of applications in physics and biology. The most promising CPs, which include PPy, polyaniline (PANI), polythiophene (PT), poly (3,4-ethylenedioxythiophene) (PEDOT) and poly-phenylene vinylene (PPV), have relatively high electron conductivity, the oxidized state is relatively stable, and they are easy to process. Among the many available CPs, PPy is especially attractive because of its relatively high electrical conductivity at room temperature (varying from 10-4 to 102 S cm-1), facile synthesis in both aqueous and organic media, ability to switch efficiently between the red-ox states20 and good ion-exchange properties21.

3.1. Polypyrrole In 1968, Dall’Olio et al.22 synthesized films of black oxypyrrole on platinum (Pt) through electrochemical polymerization of pyrrole (Py) from a solution of sulfuric acid. Later, in 1979, Diaz et al. modified Dall’Olio’s approach by polymerizing Py onto Pt in acetonitrile, resulted in a black, adherent PPy film23. PPy is an amorphous24,25 but intrinsically conductive polymer, wherein electron conductivity is achieved due to inter-chain hopping of elec-trons through the polymer matrix in the oxidized form26.

PPy has been synthesized by both electrochemical and chemical polym-erization of Py, employing different protocols. In the electrochemical method, polymerization of PPy is achieved by the oxidation of Py in a solu-tion of suitable doping (oxidizing) anions27. A conductive substrate is needed for electrochemical polymerization, and several materials28 have been inves-tigated for this purpose, e.g. glassy carbon, platinum, gold, titanium, aluminum, brass, tin oxide, and silver. The relatively straightforward process of electrochemical synthesis can be used to obtain a thin PPy film, although

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this is difficult to peel from the underlying electrode substrate. The electro-chemical method is also not feasible for large-scale applications29.

PPy can also be synthesized by oxidative chemical polymerization in both aqueous30-32 and non-aqueous33,34 media. The iron (III) salts were most com-monly employed as the oxidizing agents35-37 whereas the use of halogens and organic electron acceptors as the oxidant for PPy synthesis has also been reported38,39. Generally, the conductivity and yield of chemically synthesized PPy depend on such factors as the choice of oxidant and solvent, the monomer to oxidant ratio, and the duration and temperature of the polymeri-zation reaction. The oxidant provides the doping anions for the polymeriza-tion of the Py monomer. Therefore, the nature of the anions from the oxidant plays a vital role in determining the conducting and electroactive properties of the forming polymer matrix40. The polymerization mechanism of Py is complicated and still not fully understood. The general suggested mechanism41 of Py polymerization consists of three main steps, as illustrated in figure 1.

Figure 1. Suggested polymerization scheme for polpyrrole41.

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It can be seen in figure 1 that during the first step of chemical oxidative polymerization, radical cations (C4NH5

+) are generated. In the second step, radical-radical coupling occurs between two radical cations, resulting in the formation of a dimer, followed by deprotonation. Finally, the dimer labeled as bipyrrole is re-oxidized and coupled with other radical cations consecu-tively during the chain propagation.

3.2. Ion-exchange mechanism of PPy In the inherent electroactive behavior of PPy films, the redox reaction in-volves the oxidation of the highly delocalized -system of the polymer back-bone42. During oxidation (doping) of the polymer film, -electrons are re-moved from the upper zone of the valence band with a simultaneous lower-ing of the boundary -levels. The band gap is reduced to less than or equal to 2.5 eV, and the polymer becomes semi-conducting43. The reduction process (dedoping) leads to insulation or the neutral state of the polymer. In practice, both anions and cations could participate in the charge compensation of CPs.

The electrochemical switching of the PPy redox state is accompanied by the movement of counter ions in and out of the polymer. During oxidation, PPy chains become positively charged and are often counterbalanced by the inflow into the polymer of negatively charged ions (anions) from the elec-trolyte or by positively charged ions (cations) moving out44,45. During reduc-tion of the PPy chains, incorporated anions diffuse out to the electrolyte. The electroneutrality during reduction can also be maintained by the insertion of cations from the electrolyte solution. The doping ions incorporated during synthesis of PPy films, generally determine the ion-exchange properties of the polymer46.

Anion-exchange5,21,47: If a small counter anion, e.g. chloride or nitrate, is incorporated into the PPy as a doping ion during polymerization, it will be generally expelled during the reduction process. Upon further oxidation and reduction in the presence of small mobile anions, the polymer will act as an anion-exchange membrane.

Cation-exchange48-50: If, during polymerization, a large, poorly mobile organic anion is immobilized in the structure of PPy, the ion exchange will be dominated by cation exchange during further oxidation and reduction processes. Also, the PPy film could start to exhibit progressively cation-exchange properties if it is repeatedly oxidized and reduced in the presence of relatively small but polyvalent-charged anions.

It has been found51 that the relative contribution of the anions or cations to the overall charge transport process associated with the ion-exchange capacities of the polymer depends upon various factors such as the oxidation state of the polymer, the nature of the intercalating ions and the thickness of the polymer film. Although the inherent capacity of PPy to be used as an

18

electrochemically controlled ion-exchanger can be increased by increasing the thickness of its film, however it has been observed52 that only the outer-most layer of the bulky, thick film will be electroactive during the extraction of ions. This effect is due to mass transport limitations, i.e. penetration of ions inside the bulk of thick PPy films.

3.3. Cellulose as a substrate for CP coatings CPs are generally difficult to process post-synthesis because of their brittle-ness, low solubility in most solvents, poor compactibility, and poor heat-annealing properties53,54. To overcome these problems, especially for large-scale applications, direct chemical polymerization on various substrate mate-rials is often employed to improve their mechanical properties. Polymer fibers used in textiles (e.g. silk55-57) have been chemically coated with PPy. Unlike wool or silk, cellulose fibers are remarkably easy to coat with PPy because of the strong chemical interaction between the NH groups in Py and the OH groups that are abundantly available on the surface of the cellulose fibers58.

Cellulose is known for its intrinsic mechanical strength and flexibility and is also attractive for its low cost and abundance in nature. An investigation of composites obtained by combining cellulose whiskers with CPs showed remarkable improvement in the mechanical characteristics of PPy59. The cellulose-based CP composites are typically flexible conductive paper mate-rials, which can be molded into different shapes. The obtained flexible con-ductive paper can be employed either directly as a working electrode (WE) for electrochemically controlled ion-exchange or can function as an underly-ing conductive substrate material for electrochemical deposition of various metals (e.g. copper or Ag)60. Recent advances in the production of cellulose nanofibers have enhanced the properties of PPy-cellulose composites not only by mechanically reinforcing the brittle CP structures but also by in-creasing the surface area for PPy coating. Several researchers have been coated wood plant cellulose with PPy58,61-68. Nanocellulose fibers from wood (e.g. microfibrillated cellulose) and other terrestrial plant sources can also be employed as a substrate for making composites with PPy58, 62, 69. PPy has also been coated onto high surface area Cladophora algae cellulose17.

Cladophora cellulose, extracted from green Cladophora sp. algae, displays distinct properties70 in comparison with cellulose derived from terrestrial plants. Cladophora cellulose has a high degree of crystallinity (95%), a large surface area (60-90 m2 g-1), and large crystallites (20-30 nm)70,71. This type of cellulose has been employed in a number of applications(as a tabletting aid for drug delivery72, as a thickener to improve the stability and texture of other dispersive systems73 and as a reinforcement in construction materials such as polyurethane foams74).

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The composite conductive paper of PPy and Cladophora cellulose is a black paper sheet which can be bent or twisted and can be cut easily with scissors. An insulating paper sheet made of only Cladophora nanocellulose fibers and a black conductive paper sheet obtained after PPy coating on nanocellulose fibers are shown in figure 2.

Figure 2. Cladophora cellulose sheet (left) and PPy-Cladophora cellulose composite sheet (right) obtained after polymerization of PPy on Cladophora nanocellulose fibers.

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4. Extraction methods and spatial mapping of elemental distributions

4.1. Electrochemical extraction methods Solid phase micro-extraction (SPME) is a sample preparation method, developed by Pawliszyn et al.75. In SPME, a small amount of extracting phase associated with a solid support is placed in the sample matrix for a pre-determined time. If the time is sufficient, concentration equilibrium is established between the sample matrix and the extraction phase. After extraction, the extracting phase is transferred to another compartment, where desorption of the analyte takes place, combined with chromatography76,77.

SPME in combination with electrochemistry is called electrochemically controlled solid phase micro-extraction (ESPME). ESPME is a technique in which sorption and desorption of electro-active species can be controlled by applying external potentials to the extracting phase52,78-82. Unlike SPME, in which the extracting phase has a fixed composition, i.e. a fixed number of exchange sites, in ESPME the number of exchange sites of the extracting phase can be externally controlled using a potential.

PPy has also been used in chromatographic separation systems such as electrochemically modulated liquid chromatography (EMLC)83-87 as a sta-tionary phase for the separation of biomolecules. However, this application has not found widespread use, most likely due to the relatively complex ex-perimental set-up and problems associated with the packing of efficient columns. The stationary phase for these columns should consist of uniform (2-10 µM) conductive particles with a large (150-200 m2 g-1) surface area.

4.2. Spatial mapping of elemental distribution Electron energy loss spectroscopy (EELS) and energy-filtered transmission electron microscopy (EFTEM) are techniques that enable visualization of the distributions of various chemical elements with nanometer resolution and short acquisition times88. The scattering contrast between two non-crystalline objects observed in TEM is caused by thickness or density differences. The interaction between an incident electron beam and the sample leads to ionization of the involved atoms, giving rise to an energy loss that is

21

characteristic of the ionized atom. The chemical composition of the object can be obtained by measuring the electron energy loss signal. Figure 3 schematically depicts the principles of chemical element mapping with EFTEM in a sample with a circular cross section.

Figure 3. Schematic drawing of possible element distribution maps when the elec-tron beam e- passes through a rod-like specimen: a) cross-section and element map profile of a homogeneous solid rod of 100 nm in diameter; b) cross-section and element map profile of a solid rod with a cylindrical core of 5 nm in diameter; c) cross-section and element map profile of a solid rod with a cylindrical core of 80 nm in diameter. Reprinted from Paper IV with the permission of the publisher.

If the specimen under study has the appearance of a solid rod with a di-ameter of e.g. 100 nm and homogeneous distribution of the chemical ele-ment throughout its bulk, the EFTEM profile will simply reflect the thick-ness of the sample, as shown in figure 3a. If, however, the 100 nm specimen contains a 5 nm diameter core of a different material, the EFTEM profile will correspond to that depicted in figure 3b because of the density differ-ences between the core and the rest of the specimen. Similarly, if the diame-ter of the core is 80 nm, the EFTEM profile will resemble that depicted in figure 3c. In this way, the distribution maps of chemical elements can be obtained. If the distribution of the element is not uniform within the outer region (for example, if there is a higher concentration of the elements at the surface than closer to the core), the element profile will correspond to an

22

intermediate case with respect to the profiles in figures 3a and 3c. The EFTEM technique has obvious potential for studying ion-exchange proc-esses in oxidized and reduced CPs by visualizing the spatial distribution of chemical elements within the samples. EELS89-91 measurements can thus be used to obtain spatial distributions of chemical elements in the sample, particularly for light elements such as carbon, nitrogen, oxygen, etc. Among others, the technique under study has also been used for investigation of polymeric materials92, 93.

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5. Applications of conductive polymers

5.1. Extraction of biomolecules CPs have been extensively investigated in the fields of controlled drug deliv-ery, biomedical engineering and diagnostics29,94-96. Examples of interactions between biomolecules and CPs that have been studied include the binding and release of relatively small biomolecules such as the neurotransmitter dopamine97, cochlear neurotrophines98, the antipsychotic drug risperidone99 and adenosine triphosphate (ATP)48. The interactions between deoxyribonu-cleic acid (DNA) molecules and CPs have also been the focus of research for applications in biosensors100,101, nanowires102,103 and clinical diagnos-tics104,105. In these designs, the DNA strands were often immobilized or in-serted inside the structure of a CPs such as PPy or on its surface. Immobilization was commonly achieved either by simple non-specific adsorption106-108 or by in situ polymerization of CP monomers (chemical or electrochemical) in the presence of DNA molecules105,109-111. The use of CP monomers substituted with DNA strands (which had been immobilized by in situ polymerization) has also been studied104. It was reported that when DNA molecules are immobilized inside the structure of PPy, the latter acts as a cation-exchange membrane during electrochemical oxidation and reduction109.

The good ion-exchange and cycling-stability properties of PPy make it an interesting candidate for the extraction of large biomolecules such as DNA106,112 or proteins113. Thus, when PPy is electrochemically oxidized, DNA strands can attach to the positively charged PPy chains to maintain the electroneutrality of the system114. DNA, thanks to the phosphate groups pre-sent on its backbone, exhibits an inherently poly-anionic nature. It should also be possible to release the extracted DNA quantitatively by reducing PPy in a pure buffer solution, as this removes the positive charges on the poly-mer. The efficiency of the latter step will most likely depend on the thick-ness of the PPy film. As discussed earlier, sufficiently thick PPy films doped with large anions generally serve as cation exchangers, i.e. the electroneu-trality of the reduced PPy films is maintained by the inflow of cations into the PPy films rather than by the outflow of the large anions115,116.

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5.2. Energy storage The use of CPs for energy storage is at the forefront of research because of their potential for electron conductivity, pseudo-capacitance, red-ox switch-ing, and chemical stability in the ambient environment. Further, their low cost, light weight and environmentally friendly characteristics are appealing. According to Rüetschi, the determining factors for a successful energy stor-age system are the 3-E criteria: Energy-Economics-Environment117. There-fore, there is particular interest in cost-efficient, thin, flexible, light-weight, environmentally friendly CP-based energy storage devices for both miniatur-ized and large-scale applications. The foremost hindrances for the develop-ment of CP-based batteries and supercapacitors are poor cycling stability10,18,118, high self-discharge rates119-122, low capacities due to poor degrees of attainable doping123, and mass transport limitations due to thick polymer layers124-126 of investigated materials.

Several investigations into the development of flexible, versatile energy storage devices have been carried out; in these, the electrode material was made either purely of CPs or a combination of CPs8,124,127,128 with various types of carbon materials [e.g. carbon nanotubes (CNTs)129-131]. Recently, composites obtained by coating cellulose paper sheets with carbon nanotubes (CNTs) have also been investigated132-134. However, CNTs mainly rely on double layer capacitance of carbon materials whereas CP composites gener-ally have higher theoretical capacitance due to the presence of both faradic and double layer capacitance135. Of the available CPs, PPy is often investi-gated for energy storage applications, particularly because of its compatibil-ity with a large variety of substrates10,43,136. PPy has also been directly chemically polymerized onto graphite fibers to yield an electrode material with a high charge capacitance [400 F g-1 at 10 mV s-1 from cyclic voltammetry]137. For a paper-based flexible energy storage device, compos-ites of PPy and cellulose are particularly interesting. The development of novel PPy-Cladophora cellulose composites offers the possibility of using them as versatile electrode materials for lightweight, fully recyclable, flexi-ble energy storage devices.

For the construction of CP-based electrochemical energy storage devices, both symmetric (i.e. both anode and cathode made of identical material) and asymmetric designs have been considered118,138.

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6. Influence of additives

An additive is generally a substance added in minor quantities to the host-substance (i.e. the major component) to amplify the desired function of the final product. Any kind of substance can act as an additive as long as it is present in minor quantities and improves the functionality of the product. For instance, conductive materials such as carbon fibers (CFs), metal nanowires or CPs can be incorporated into the insulating paper to provide it with conductive properties. One such example comprises a low cost conduc-tive paper material [developed by Kimberly-Clark Worldwide, Inc. (USA), under the trade-name of cNonwoven™] which consists of cellulose pulp fibers and CCFs. CCFs are composed of mechanically comminuted fibers made entirely of carbon (graphite) or containing carbon in amounts suffi-cient to conduct an electric current, and are between 1 and 12 mm in length and between 3 and 15 µM in diameter139. The cNonwoven™ conductive paper is used in various applications such as electronics (keypads) or anten-nas140, diapers, incontinence products for clinical use, or training garments with an integrated moisture or wetness indicator, such as an audible or radio signal139,141.

It should be mentioned that the addition of conductive components to an already conductive matrix is also not uncommon. Single and multi-walled CNTs have been embedded in a CP matrix for sensory applications142. Furthermore, PPy has recently been used as an additive in a lithium ion battery to enhance the performance of its electrodes143. It has been concluded that, in all these examples, inclusion of an additive drastically influenced the performance of the final product.

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7. Experimental

7.1. Synthesis The nanocellulose fibers employed as substrate in the present study were extracted from Cladophora algae144. Cladophora sp. algae were collected from the Baltic Sea. Most of the reagents were obtained from Sigma-Aldrich, Germany. The CFs (C005715/1, Grade XAS, number of filaments 6000, filament diameter 0.007 mm) were purchased from Goodfellow, UK. Fluorophore-tagged oligonucleotides (oligomers) of varying length were synthesized by Biomers.net, Germany. The oligomers were single-stranded sequences of thymine (T) with no internal modifications. Oligomers of (dT)6, (dT)20 and (dT)40 were tagged at the 3´-position with 6-FAM, TexRed and Cy3 fluorophores, respectively. Graphite foil was obtained from VTT, Finland.

7.1.1. PPy-Cladophora cellulose composites Oxidative chemical polymerization of Py monomer was employed to coat the novel Cladophora cellulose fibers, using iron (III) chloride as oxidant. The following protocol was employed for the synthesis of the PPy-Cladophora cellulose composite:

300 mg of Cladophora cellulose was dispersed for 8 min in 100 mL of de-ionized water using high-energy ultrasonic treatment (VibraCell 750W, Son-ics, USA) at room temperature. A water jacket was used for cooling during sonication of the cellulose fibers. 3 mL of Py was pipetted into a volumetric flask and the final volume was brought to 100 mL by adding deionized wa-ter. To enhance the solubility of Py in water, one drop of Tween-80 was added and stirred for 5 min. The cellulose dispersion was stirred for 5 min with the diluted Py solution. 8 g of iron (III) chloride (oxidant) was dis-solved in 100 mL of deionized water and added to the cellulose and Py mix-ture. The reaction was allowed to continue for 30 min to induce oxidative polymerization. The resultant product was in the form of a fluffy sponge-like suspension. The suspension was thoroughly rinsed with water on filter paper fixed in a Buchner funnel under vacuum to remove un-reacted species and intermediate species such as the monomer, oxidant and oligomers. After washing, the suspension was transferred to a beaker and redispersed for 1 min; the water was then removed using filter paper. The final product, in the

27

form of a paper sheet, was subsequently dried in air. A similar protocol was followed, with some alterations, for synthesis of the composite paper sheets in all the appended papers.

In Paper II, phosphomolybdic acid (PMo) was employed as an oxidant in the place of iron (III) chloride to investigate the influence of an oxidant on the anion-exchange properties of the composite materials.

7.1.2. PPy-Cladophora cellulose-CCF composites The cake of PPy and cellulose obtained after synthesis was divided into two equal parts and both were washed first with 2.5 L of 0.3 M HCl and then with 0.5 L of 0.1 M sodium chloride. After rinsing with acid and salt, one half of the PPy-Cladophora cellulose nanofibers was mixed with 0.4 g of CCFs using a mechanical homogenizer(IKA T25 Ultra-Turrax, Germany) at 6200 rpm for 10 min, whereas second half kept without incorporation of CCFs (reference sample). The mixture was subsequently drained on a poly-propylene filter to form a filter cake and then dried to form a paper sheet.

7.2. Primary material characterization

7.2.1. Scanning Electron Microscopy Scanning Electron Microscopy (SEM) was used to obtain information about the organization and dimensions of PPy-coated cellulose fibers. The samples were mounted on aluminum stubs using double-sided adhesive tape. Prior to imaging, Au/Pt was sputtered onto the samples to minimize charging effects. Micrographs were taken with an environmental SEM (FEI/Philips XL 30, The Netherlands) and SEM (Leo Gemini 1559 FEG, UK) in the high-vacuum mode.

7.2.2. Transmission Electron Microscopy Transmission Electron Microscopy (TEM) was conducted with a JEOL-3010 microscope, operating at 300 kV (Cs 0.6 mm, resolution 1.7 Å). Images were recorded using a CCD camera (model Keen View, SIS analysis, size 1024 × 1024, pixel size 23.5-23.5 µM) at 30 000-100 000 times magnification using low-dose conditions on as-synthesized samples. Samples were sonicated for 5 min prior to transfer to the TEM grid.

28

7.2.3. Electronic conductivity The resistance of the samples was measured at room temperature using a semiconductor device analyzer (B1500A, Agilent Technologies, USA). Prior to the measurements, silver paint was pasted on the ends of the rectangular samples to ensure good contact. The voltage U, which was scanned between -1 and +1 V, was applied and the resulting dc current I was measured. The conductivity was then calculated using equation 1.

wd

L

U

I (1)

where U

I denotes the conductance of the sample obtained as the slope of

the current versus voltage curve, L is the length , w is the width and d is the thickness of the sample.

7.2.4. Specific surface area The specific surface areas of the composites were measured using multi-point BET N2 gas adsorption analysis (ASAP 2020 Micromeritics, USA). N2 gas adsorption and desorption isotherms were obtained with an ASAP 2020 (Micromeritics, USA). The specific surface area was obtained according to the BET method145.

7.2.5. Apparent density and porosity He-pycnometry (AccuPyc 1340, Micromeritics, USA) was used to measure the apparent (true) densities of the composites. The total porosity of the composite paper sheets was estimated from equation 2 as:

1001 )(%t

b (2)

where % is the total porosity, B is the bulk density, and T is the true den-sity. The bulk density, i.e. the ratio of the mass of the sample to its volume, was estimated from the dimensions of a piece of composite paper sheet, us-ing a high precision digital caliper (Mitutoyo, Japan).

29

7.3. Electrochemical characterization The electrochemical characterization was performed using a potentiostat equipped with an Autolab/GPES interface (ECO Chemie, The Netherlands).

7.3.1. Cyclic voltammetry Cyclic voltammetry (CV) measurements were performed in a standard three-electrode electrochemical cell, where the composite sample was used as the WE, a Pt wire as the counter electrode (CE), and an Ag/AgCl electrode as the reference electrode (RE). The composite samples were cut into rectangu-lar pieces with scissors. The samples were contacted using a Pt wire that was coiled around the sample to obtain good ohmic contact and then immersed in the electrolyte. For investigations in Papers I and II, the samples were wrapped with Pt foil on one side of the sample, clipped with alligator steel clips, and used as WEs. The potential sweep window was carefully chosen for each measurement; to avoid overoxidation of PPy, the potential sweep was reversed during the anodic scan immediately prior to the onset of the second (overoxidation) peak. In the cyclic voltammograms, the values were normalized with respect to the total weight of the composite.

7.3.2. Chronoamperometry Chronoamperometry/potential step measurements were performed in a stan-dard three-electrode electrochemical cell, where the composite sample was used as the WE, a Pt wire as the CE and an Ag/AgCl electrode was used as the RE. As in the CV measurements, the samples were wrapped with Pt foil and clipped in alligator steel clips, which were used as working electrodes in Papers I and II.

7.3.3. Chronopotentiometry Chronopotentiometry (galvanostatic) measurements were performed in two-electrode or three-electrode setups in the energy storage and DNA extraction studies, respectively. a) Two-electrode setup

Coffee-bag: A symmetric device, hermetically heat-sealed in a coffee-bag arrangement, was made by employing composite samples as both cathode and anode. A piece of ordinary filter paper, used as a separator, was sand-wiched between the two electrodes. The battery device was soaked with 2 M sodium chloride solution to function as the electrolyte. The Pt foil and

30

graphite paper were used as the current collectors in Papers V and VI, respectively. Plastic cell: A piece of ordinary filter paper, used as a separator, was sandwiched between two circular pieces of the composite paper material. The electrochemical cell was contacted using two glassy carbon plates to cover the entire surface of the paper electrode, and these in turn were connected to the current collector using strips of Pt foil. To ensure good con-tact, the entire device was then tightly clamped between two plastic plates leaving a small (1-2 mm) gap between the plastic plates. The entire cell was then immersed into 40 mL of 2 M sodium chloride solution and the current collectors were connected to the galvanostat. The cell capacitances in were calculated from the slope of the potential-time response by using equation 3:

t

V

m

iC

12 (3)

where i is the applied current, m1 is the mass of the smaller, limiting elec-

trode and t

V is the slope of the potential vs. time response.

b) Three-electrode setup

The electrochemically controlled extraction and release measurements of DNA oligomers were performed in a standard three-electrode electrochemi-cal mini-cell utilizing an Autolab/GPES instrument (ECO Chemie, The Netherlands) with the PPy-Cladophora cellulose composite sample as the WE, a Pt wire as the CE and an Ag/AgCl electrode as the RE. The electro-chemical cell was fitted with a Teflon cap and a glass tube with a frit (Bio-analytical Systems, UK) to obtain separate anode and cathode compartments. The latter was done to minimize the changes in the pH within the WE com-partment as a result of the oxidation/reduction of water taking place on the Pt counter electrode. A schematic diagram of the electrochemical mini-cell used is shown in figure 4.

The samples were contacted and immersed in the electrolyte using a Pt wire, which was coiled around the sample to obtain good ohmic contact. Different applied currents and intervals were employed for the extraction and release of the DNA oligomers, as explained in Paper III.

31

Figure 4. Schematic diagram of the electrochemical mini-cell used for galvanostatic extraction of DNA oligomers. Reprinted from the supporting information in Paper III.

7.4. Spectrofluorometry The changes in the concentrations of DNA in the solutions following the electrochemical extraction and release experiments were monitored using a spectrofluorometer (TECAN Infinite M200, Austria). Black Corning 96-well plates with flat bottoms (Corning, Lowell, MA) were used, and the gain-value was fixed at 100 in all measurements. Three 100 µL samples were taken for each analysis. For determination of the galvanostatic extraction and release yield in the (dT)6 tagged 6-FAM oligomer experiments, were em-ployed together with an excitation wavelength of 460 nm and emission spec-trum between 505 and 560 nm. As well as in the extraction experiments in-volving the mixtures of the 6-FAM, Texas Red and Cy3 tagged oligomers, were employed together with an excitation wavelength of 460 nm and emis-sion spectrum between 505 and 650 nm For the release experiments involv-ing the 6-FAM, Texas Red and Cy3 fluorophore-tagged DNA, the emission and excitation wavelengths varied with the fluorophore. The excitation wavelengths 460, 573 and 523 nm and emission spectral ranges 505-560, 600-650 and 556-586 nm were thus used for 6-FAM, Texas Red and Cy3 fluorophores, respectively. Calibration curves were constructed for each specific fluorophore based on the respective gain-values, excitation wave-lengths, and emission spectra.

32

8. Results and discussion

8.1. General characterization Figure 5 displays the morphology of the PPy-Cladophora cellulose compos-ite prepared by oxidative chemical polymerization of Py on Cladophora nanocellulose fibers. The SEM micrograph in figure 5a clearly shows a fine fibril structure of composite nanofibers with no apparent PPy islands.

a)

1 µm

a)

1 µm

50 nm

b)

50 nm50 nm

b)

Figure 5. PPy-Cladophora cellulose composite: a) SEM and b) TEM images. Figure 5b was reprinted from Paper II with the permission of the publisher.

33

The PPy-Cladophora cellulose nanofibers were intertwined to form a 3-dimensional network. The SEM micrograph does not suggest any promi-nent degradation of cellulose fibers during PPy polymerization. In fact, the Cladophora cellulose fibers retained their typical pore network after chemi-cal synthesis of PPy70. In figure 5b, the TEM image of the PPy-Cladophora cellulose composite shows a homogeneous PPy coating on the nanocellulose fibers with an overall thickness of ~90-100 nm. The original PPy layer ap-peared to be ~40-50 nm in thickness, wrapping around the ~20-30 nm cellu-lose fibers. Based on the thickness ratio between the PPy layer and the cellu-lose fibers, it can be concluded that the major constituent of the composite nanofibers is PPy.

The solid-state characterizations of the PPy-Cladophora cellulose com-posite showed the apparent density of the composite to be ~1.65 g cm-3 and the total porosity to be ~80%. The measured specific surface area of the composite was ~60-80 m2 g-1, and the total pore volume (for pores less than 124 nm) was 0.37 cm3 g-1, as estimated from N2, BET gas adsorption iso-therms. The electronic conductivity of the composite paper sheets was in the range of 0.65 to 2 S cm-1 at room temperature, dependent on the synthesis conditions.

The analysis of the cyclic voltammograms is probably one of the most important characterizations of the composite material. It should be men-tioned that the shape of the voltammograms varies depending on the contact between the WE and the current collector. In Papers I and II, the contacts for the composite, which acted as the WE, were Pt foil and an alligator clip made of steel. However, in Papers III-VII, the contacts were more refined; a Pt wire was coiled around the composite, rather than using Pt foil. Figure 6 presents high quality CV images of PPy-Cladophora cellulose in 2 M KNO3

solution at four different scan rates, with Pt wire contacts. This figure is im-portant for discussion of the ion-exchange processes occurring in the anodic and cathodic scans. The first cycle of CV at each scan rate is plotted in fig-ure 6a, but part of the CV between 0 and -0.3 V was omitted for clarity.

In figure 6a, two clearly visible peaks were observed at scan rates of 2.5, 5 and 10 mV s-1, whereas only one big halo was observed at 20 mV s-1. During the anodic scan, for the interval between -1 and -0.4 V, a steady pla-teau was observed and the current value was approximately zero. This stage corresponds to the non-conductive, neutral form of PPy. At around -0.4 V, a steep increase in the current was seen; this corresponds to a build-up of con-ducting paths inside the polymer, i.e. polaron formation, and oxidation of PPy chains. The current reached its first maximum between -0.1 and +0.1 V, depending on the scan rate, after which it started to decay as the process became controlled by diffusion of dopant anions into the polymer to maintain electroneutrality. The onset of the second peak was detected at around +0.4 V, most likely due to irreversible overoxidation. The magnitude of the current in the second anodic peak was larger than that in the

34

first one (Figure 6a). Such a high charge consumption during overoxidation has previously been ascribed to partial cleavage of the PPy chains, in addi-tion to oxidation of the Py rings inside the chain146.

Figure 6. Cyclic voltammograms of the PPy-Cladophora cellulose composite in 2 M KNO3 solutions during the a) first and b) fifth cycles.

Figure 6b shows the fifth cycle from CV measurements of the PPy-Cladophora cellulose composite samples in 2 M KNO3 solution as described earlier. The transition of PPy from the fully reduced, non-conductive state to the oxidized conductive state occurred at more anodic potentials than during the first cycle. This can be related to the increasingly resistive behavior of PPy due to overoxidation147. For instance, the top of the first peak during the first and fifth cycles at 2.5 mV s-1 occurred at around -0.1 and +0.5 V, re-spectively, whereas for 10 mV s-1 it occurred at around +0.1 and +0.4 V, respectively. Thus, during anodic polarization at lower scan rates, the time-window and therefore the probability of irreversible overoxidation of PPy is large. Furthermore, compared to the first cycle, the second peak of PPy during the anodic scan was almost entirely absent at all scan rates.

35

8.2. Applications of the PPy-Cladophora cellulose composites

8.2.1. Potential-controlled anion exchange In Paper I, the ion-exchange properties of the PPy-Cladophora cellulose composite were investigated in electrolytes containing different concentra-tions of nitrate, chloride and p-toluene sulfonate. The oxidation mechanism and the dependence of the oxidation behavior of PPy, which was obtained by oxidation of Py with iron (III) chloride, on the anion type and concentration was studied.

0

5 1020

1 1021

1.5 1021

2 1021

0 1 2 3 4 5 6

Cl- IN

Cl- OUT

NO3

- IN

NO3

- OUT

CH3C

6H

4SO

2O- IN

CH3C

6H

4SO

2O- OUTN

o. o

f ion

s in

sert

ed/e

xtra

cted

duri

ng o

xida

tion

/red

uctio

n [#

/g]

Concentration [M]

Figure 7. Number of ions entering and leaving the composite during the oxidation (+0.7 V for 300 s) and reduction (-0.8 V for 300 s) steps as a function of electrolyte concentration. The number of ions in/out was normalized with respect to the sample weight and the displayed error bars represent maximum variations over five meas-urements. Reprinted from Paper I with the permission of the publisher.

Figure 7 shows that the total number of ions incorporated in the compos-ite under applied constant potential increased with increasing electrolyte concentrations and that the results leveled out at concentrations around 1 M for all three anion types under study. Generally, smaller ions are more mo-bile in the polymer layer and these should be able to progress further into the

36

PPy layer covering the cellulose fibers during oxidation. The number of p-toluene sulfonate ions which entered into the composite at high electrolyte concentrations was only about 50% of the number of nitrate ions. For large anions, the charge compensation can occur via cation exchange. The chemi-cal element analysis of sulfur in the composite samples following electro-chemical ion-exchange of p-toluene sulfonate verified that the latter mole-cule was indeed reversibly extracted and released from/into the electrolyte, see table 1. Figure 7 also shows that the number of ions released from the composite during reduction was approximately 20-30 % less than the num-ber of ions inserted during oxidation. This difference in the number of ions participating in the oxidation and reduction processes most likely stems from overoxidation of the composite at anodic potential of +0.7 V.

The main conclusion from Paper I is that the composite material functions as an excellent reversible potential-controlled ion-exchange membrane for a range of inorganic and organic molecules and exhibiting ion extraction ca-pacities of 1.7 to 3.3 mmol g-1.

Table 1. Chemical sulfur elemental analysis following electrochemical extraction and release of p-toluene sulfonate. Reprinted from supporting information in Paper IV with the permission of the publisher.

S element content, % wt

Reference (PPy-Cladophora cellulose composite synthesized with iron (III) chloride)

0.05

Oxidized 6.1

Reduced 1.6

8.2.1.1. Influence of type of oxidant on anion exchange In Paper II, influence of oxidant’s anions differing in sizes and mobilities for the electrochemically controlled ion-exchange properties of PPy-Cladophora cellulose composites have been investigated. In general, by employing an oxidizing agent with a large anion, the network spacing of PPy chains in-creased as a result of the incorporation of the anions during polymerization. For this purpose, PMo and iron (III) chloride were employed as oxidizing

37

agents, since PMo has a molecular weight that is 11 times larger than that of iron (III) chloride.

Figure 8 shows the elemental distributions for carbon, oxygen, molybde-num and phosphorus within PPy-coated nanofibers prepared using PMo as the oxidizing agent (Paper II) as investigated using EFTEM in Paper IV. In the elemental map of figure 8, [PMo12O40]

3- anions are shown as inclusions of nanoparticles of two distinct types. In the first group, the nanoparticles were about 5 nm in diameter and were randomly distributed within the PPy coating. The second group comprised large agglomerates with diameters of 15-30 nm which were predominantly positioned on the outside of the com-posite fibers or adjacent to the fiber surface.

Figure 8. Intensity profiles and elemental maps for carbon (C), oxygen (O), molyb-denum (Mo) and phosphorus (P) in the PPy-Cladophora cellulose composite synthe-sized with PMo. The blue arrows point to artifacts originating from beam damage. Reprinted from supporting information in Paper IV with the permission of the pub-lisher.

The arrows pointing to dark spots in the carbon profile in figure 8 high-light some of the [PMo12O40]

3- nanoparticles. The intensity of phosphorus was too low to give information about the distribution of the [PMo12O40]

3- anions within the composite. Based on the molybdenum maps and the sharp contrast of the [PMo12O40]

3- nanoparticles in the TEM micrographs, it can be concluded that the [PMo12O40]

3- anions were randomly distributed within the PPy bulk matrix in the form of particles of a few nanometers (in diameter) without any preferential distribution at the periphery.

The electrochemically controlled ion-exchange properties of PMo and iron (III) chloride-synthesized composites at different oxidation potentials in electrolytes containing sodium chloride, aspartic acid, glutamic acid and Na-p-toluene sulfonate were studied in Paper II. The electronic conductivity appeared to be five times larger for the iron (III) chloride compared to the PMo-synthesized samples (Paper II). To evaluate the anion-exchange

38

capacities of the composite samples under study, different potential step measurements were performed in four different electrolytes, using the com-posite sample as WE. Generally, the number of unit charges participating in the oxidation and reduction processes (reflecting the number of anions ab-sorbed and expelled, respectively) were plotted as a function of the applied oxidation potentials in figure 9. The number of extracted and released anions per sample mass was then found to be larger for the iron (III) chloride-synthesized sample than for the PMo-synthesized sample for all four electro-lytes. Figure 9 shows that the number of unit charges was significantly higher for chloride than for the other larger anions for both composite sam-ples, which is not surprising considering the difference in the size of the anions.

Figure 9a shows that, in 2.0 M sodium chloride, the number of unit charges for the iron (III) chloride-synthesized sample initially increased with ascending oxidation potential to reach a maximum of 3.3 x1021 units g-1 sample at an oxidation potential of 1.1 V. The lower value for the number of unit charges (1 x 1021 units g-1) at 1.2 V can be ascribed to overoxidation of the sample (discussed in section 8.1). A corresponding increase in the num-ber of unit charges with increasing potential was also seen for the PMo sam-ple in 2.0 M sodium chloride for potentials larger than 1 V. The higher po-tential needed in this case can be explained by the higher iR (voltage) drop for the less conducting or high resistive PMo sample. For the larger anions, an increase in the number of unit charges absorbed and expelled with in-creasing potential was only seen for the glutamate anions at the lowest po-tentials with the iron (III) chloride-synthesized sample. The constant number of unit charges for different oxidation potentials in figure 9 b-d clearly shows that the number of anions taking part in the oxidation and reduction processes was independent of the applied potential as long as this was suffi-ciently high to oxidize both samples. This means that the oxidation currents in these cases were practically independent of the oxidation potential.

The comparison of ion-exchange properties between the two composite samples under study showed that the number of absorbed ions per sample was larger for the iron (III) chloride-synthesized composite than for the PMo-synthesized composite in all four electrolytes. The relatively high elec-tronic conductivity and high surface area of the iron (III) chloride-synthesized composite suggest more efficient ion-exchange capacities. The results also imply that the composite material would be suitable for reversi-ble extraction of biomolecules such as amino acids, suggesting that this ma-terial can potentially be used for sample preparation (pre-concentration) or purification of biological solutions.

39

Figure 9. Number of unit charges participating in the oxidation (OX) and reduction (RED) of the iron (III) chloride and PMo-synthesized samples as a function of the oxidation potential. Each data point represents the average of the number of charges in steps 2 and 3 for the three-step procedures. The deviations between the values for each potential were always less than 6%. The number of charges was normalized with respect to the mass of the sample material. Reprinted from Paper II with the permission of the publisher.

8.2.2. Current-controlled DNA extraction The results presented in Paper III served as a foundation for continued attempts to design an efficient and reversible electrochemically controlled ion-exchange membrane suitable for highly specific batch-wise extraction and release of DNA molecules in the presence of excess amounts of buffer ions. Figure 10 displays the electrochemically controlled uptake of (dT)6 oligomers tagged with 6-FAM by employing the PPy-Cladophora cellulose composite as the WE. Figure 10a shows the results of chronopotentiometric (galvanostatic) experiments, performed to extract the (dT)6 oligomers tagged with 6-FAM fluorophore using a constant current of 1.2 mA to oxidize the

40

Figure 10. Time-dependent extraction of tagged (dT)6 oligomers from a 1 µM solution employing a constant anodic current of 1.2 mA: a) Potential of the PPy-Cladophora cellulose composite versus time; b) tagged (dT)6 oligomer uptake during different time intervals with no applied current and with an applied current of 1.2 mA, respectively: the dashed line represents the average uptake during all inter-vals with no applied current; and c) amount of tagged (dT)6 oligomers in the com-posite as a function of the applied charge for the initial four fixed time intervals (i.e. 600-1800 s). The results were normalized with respect to the weight of the compos-ite sample and the error bars represent the standard deviation (n=3). Reprinted from Paper III.

41

PPy-Cladophora cellulose composite for varying time intervals ranging from 600 to 4000 s. During oxidation, the PPy chains became positively charged, and anions entered to maintain charge neutrality within the film. As a result of oxidation, the potential of the PPy composite increased with time, as seen in figure 10a. The potential increased almost linearly with time during the first 1800 s, after which a potential plateau, starting at around 0.7 V vs. Ag/AgCl, developed. The plateau can be explained by the onset of PPy overoxidation, which has been discussed earlier. A significant decrease in the pH of the solution was found for oxidation times longer than 1800 s, most probably as a result of the protons liberated during the overoxidation of PPy. No such change in the pH was observed for shorter oxidation times. In subsequent experiments, care was therefore taken to ensure that the potential was always significantly below 0.7 V.

These results indicate that the charge consumed during the 1800 s ex-periment (viz. 2.16 C) corresponded to the ion-extraction capacity of the PPy film that is practically available. It is seen in figure 10c that the uptake of oligomers increased approximately linearly with applied charge up to 2.16 C (1.2 mA for 1800 s). Figure 10b also supported the above hypothesis, al-though there was uncertainty among the DNA uptake results above the 1800 s interval under an applied current of 1.2 mA. This indicates that the amount of DNA oligomers extracted can be controlled by tuning the extraction time, but more importantly that the fraction of the total charge compensated by the DNA oligomers remains constant under these extraction conditions. This latter point is important, as it suggests that there are no mass transport re-strictions for the DNA oligomers within the PPy film during the extraction step. Figure 10 clearly demonstrates the advantages of using these high sur-face area PPy-Cladophora cellulose paper sheets for direct batch-wise ex-tractions of DNA in the presence of an excess of buffer ions.

The results described in figure 10 were also supported by the results of Paper IV, which investigated the distribution of the DNA oligomers within the PPy film on samples enriched with (dT)6 by employing EFTEM. The EFTEM results suggest that (dT)6 did indeed penetrate into the structure of the PPy film following the current-controlled oxidation step. Figure 11 shows the chemical element maps for carbon, nitrogen, boron, and phospho-rus in the composite PPy-Cladophora cellulose fibers used for current-controlled (1.2 mA for 800 s) extraction of DNA hexamers dissolved in bo-rax buffer solution. During oxidation of the PPy-Cladophora cellulose com-posite, it was expected that both tetraborate (buffer anions) and DNA hexamers would enter into the film as counter ions. Based on the larger size of the 6-FAM fluorophore-tagged DNA hexamers, it might be anticipated that the DNA oligomers would not be able to compete with the relatively smaller tetraborate ions, especially since the concentration of the tetraborate ions was several orders of magnitude higher than that of the DNA hexamers (Paper III); however, this was not established.

42

Figure 11. Intensity profiles and elemental maps for carbon (C), nitrogen (N), boron (B) and phosphorus (P) for the PPy-Cladophora cellulose composite synthesized with iron (III) chloride. The composite was oxidized in a solution containing DNA hexamers and borax buffer. Reprinted from Paper IV with the permission of the publisher.

The elemental map of carbon in figure 11 shows its overall distribution throughout the PPy-Cladophora cellulose nanofibers. This occurred because carbon is the main constituent of the cellulose core and PPy coating as well as of the DNA hexamers. Nitrogen is a characteristic element of both PPy and the DNA hexamers and is consequently expected to be present through-out the PPy layer but not in the cellulose core of the composite. The nitrogen map supports this assumption as a small dip in the center is visible in some parts. No conclusions could, however, be drawn from the nitrogen map con-cerning the distribution of DNA hexamers in the composite. Boron, how-ever, is only present in the tetraborate anions and can therefore be used to map the distribution of these ions within the composite. The boron map shows that the tetraborate anions are randomly distributed as patches of boron at the edges (i.e. the surface) of the PPy coating. The real space distri-bution of DNA hexamers can be obtained from the corresponding phospho-rus maps in figure 11, as this element is characteristic of DNA hexamers. The phosphorus element maps were somewhat noisier than the chemical element maps of carbon or nitrogen due to the much lower concentration of phosphorus in the PPy coated nanofibers. However, the element distribution maps clearly show that phosphorus was distributed throughout the entire PPy coating, except within the core where the cellulose fibers were located. The results of the EFTEM analysis show that the DNA hexamers readily pene-trated into the bulk of the PPy coating during the electrochemically con-trolled extraction process even in the presence of large quantities of buffer anions.

To fully realize the potential of the PPy-Cladophora cellulose composite material for the extraction of biomolecules, it is important to demonstrate the

43

Figure 12. Extraction and release of a mixture of DNA oligomers: a) fluorescence emission spectra of mixtures of tagged (dT)6, (dT)20 and (dT)40 oligomers following galvanostatic extraction for the indicated number of extraction cycles. The emission curves recorded for a concentration of 0.5 µM of each tagged DNA oligomer are also displayed. Cumulative b) uptake and c) release of the tagged DNA oligomers. The results have been normalized with respect to the weight of the composite sample and the error bars represent the standard deviations (n=2). Reprinted from Paper III.

44

possibility of performing repeated and reversible DNA extraction and release, as well as extractions of DNA oligomers of varying length from the same solution. The release of DNA oligomers extracted into the PPy-Cladophora cellulose composite is discussed in Paper III. To investigate the selective extraction capacity of the PPy-Cladophora cellulose composite for anions of particular size and charge, uptake and release measurements in mixtures containing three oligonucleotides of different size were performed, as shown in figure 12.

Figure 12a displays typical fluorescence emission spectra obtained during galvanostatic extraction of DNA oligomers from a solution containing equal concentrations of (dT)6, (dT)20 and (dT)40 tagged with 6-FAM, Texas Red and Cy3 fluorophore, respectively, after four consecutive extraction cycles. It can be seen that the fluorescence intensities decreased for all three DNA oligomers after each extraction cycle. Figure 12b shows the cumulative number of DNA oligomers extracted from the solution after the second and fourth cycles, respectively. Although it can clearly be seen that all three oli-gomers were extracted during oxidation of the PPy film, it is difficult to draw any definitive conclusions regarding any preferential extraction of any of the oligomers due to the uncertainties in the data. The apparent preference for extraction of the (dT)20 oligomer, at least with respect to the (dT)6

oligomer, is thus not statistically significant. On the other hand, significantly different results were obtained for the oligomers during the subsequent re-lease experiments. Figure 12c clearly shows that only the (dT)6 fraction could be released to any substantial extent [the released amounts of the (dT)20 and (dT)40 oligomers were thus found to be negligible even after four consecutive release cycles].

The fact that the (dT)20 and (dT)40 oligomers could be extracted at least as well as the (dT)6 oligomers can be explained by the ion-exchange process in which the oligomers replace some of the buffer anions as counter ions in the oxidized PPy film. The finding that only the (dT)6 oligomer could be re-leased during the subsequent reduction of the oxidized PPy film suggests that the specific interactions between the oligomers and the PPy composite106 increase with increasing oligomer size. To be able to release the larger oli-gomers (and to increase the release efficiency in general) it is thus necessary to overcome these interactions. This could possibly be accomplished using a release approach in which the negatively charged oligomers are driven out of the PPy composite using an external electric field. The results do, however, indicate that it is possible to employ the PPy-Cladophora cellulose compos-ite to separate small DNA oligomers from larger ones to a certain extent.

8.2.3. Paper-based energy storage devices The results in Paper V indicated that the PPy-Cladophora cellulose conduc-tive composite paper material may also be suitable electrode material for

45

water-based, lightweight, flexible and environmentally friendly energy stor-age devices. To evaluate the PPy-Cladophora cellulose composite as an elec-trode material for energy storage, an electrochemical cell was assembled in which the composite paper was employed as both the anode and the cathode. Filter paper soaked with 2.0 M sodium chloride solution was placed as a separator between the electrodes. A schematic illustration of the paper-based energy storage cell is presented in figure 13.

The embedded graph in figure 14 shows the galvanostatic charge-discharge curves of the paper-based energy storage device for different ap-plied charging or discharging currents. To avoid problems with overoxida-tion of the PPy coating, the charging and discharging were interrupted at voltages below those at which overoxidation was found to take place for the different applied currents. The results clearly showed that the PPy coatings could be reversibly oxidized and reduced even at very high rates. With in-creasing charging currents, the charging time of the energy storage cell could be reduced from 8 min at 10 mA to only 11.3 s at a current of 320 mA (cor-responding to a current density of 600 mA cm-2). These currents correspond to rates of 7.5 C and 320 C, respectively. These results confirm the expected behavior for a high surface area electrode material coated with a thin elec-troactive layer.

Figure 14 shows the charge capacities calculated from the charging curves in the embedded figure after normalization with respect to the total dry weight of the composite material. It is seen that 72% of the electrode capac-ity obtained with a current of 10 mA was maintained when increasing the current to 320 mA. This demonstrates the outstanding ability of the PPy-Cladophora cellulose composite material to undergo rapid oxidation and reduction.

To test the long-life cycling properties of the PPy-Cladophora cellulose composite electrodes, 100 consecutive galvanostatic charge/discharge cycles were performed using the highest reported charging currents in Paper V. It was found that the energy storage cell under study also cycled well at this high rate (i.e. 320 C); a 6% decrease in charge capacity over the 100 cycles was obtained. The aqueous-based energy storage devices, which are entirely based on cellulose and PPy, exhibited charge capacities between 38 and 50 mAh g-1 per weight of the active material and open up new possibilities for the production of environmentally friendly, cost-efficient, up-scalable, lightweight energy storage applications. The performance of the PPy-Cladophora cellulose composite-based energy storage device was further improved by incorporation of the CCFs in the polymer matrix.

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Figure 13. Schematic image of the PPy-Cladophora cellulose composite paper-based energy storage device. Reprinted from Paper V with the permission of the publisher.

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Figure 14. Charge capacities obtained with the conductive paper composite cell for currents ranging from 10 to 320 mA. The capacities were normalized with respect to the total amount of PPy-Cladophora cellulose composite used in the cell. The embedded graph represents the charge/discharge curves of composite samples under applied currents from 10 to 320 mA. Reprinted from Paper V with the permission of the publisher.

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8.3. Incorporation of CCFs in the PPy-Cladophora cellulose composite In Paper VI, micrometer thick CCFs were incorporated as an additive in the PPy-Cladophora cellulose matrix after the polymerization to boost the charg-ing rates of the paper-based energy storage device. One reason for low elec-troactivity at higher charging rates could be insufficient charge transfer be-tween the current collector and the polymer redox sites. Thus, the electrons need to travel to the current collector through an intricate web of CP-based electrode material with relatively low conductivity leading to an overall high distributed resistance. The electron transfer becomes hindered during reduc-tion of the CP layer due to the increased resistance of the latter state. Follow-ing the incorporation of CCFs, however, the electrons only need to travel to the nearest “exit” CF junction from which they can rapidly transfer to the current collector. The CCFs thus facilitate the electron transfer in the host material without contributing to the overall charge capacity. The incorpora-tion of CCFs was highly beneficial in both the energy storage device and the efficiency of DNA release.

Figure 15. SEM images of the PPy-Cladophora cellulose composite reinforced with CCFs. Reprinted from Paper VI.

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Figure 15 shows typical SEM micrographs of the PPy-Cladophora cellu-lose composite samples after incorporation of CCFs. In figure 15a, an open structure can be seen in which 7-8 µM thick carbon rods randomly pierce the web-like structure of the PPy-coated Cladophora cellulose nanofibers. This distribution favors unhindered electron transfer within the composite. In figure 15b, the intricate, web-like structure of PPy-Cladophora cellulose composite nanofibers enveloping an individual carbon rod is depicted more clearly. Further, the individual CCFs appear to be straight and rather stiff, whereas the PPy-Cladophora cellulose nanofibers appear more flexible.

To investigate the electrochemical performance of the PPy-Cladophora cellulose-CCF composites as electrode material for the energy storage device after adding various amounts of CCFs, two electrode galvanostatic meas-urements under different applied currents were performed in Paper VI. In this paper, 0 g CCF composite represents the reference. PPy-Cladophora cellulose composite (without CCFs) and 0.4 g CCF composite represents the PPy-Cladophora cellulose-CCF composite containing 47 wt. % CCFs in the PPy matrix after polymerization of PPy. The synthesized composites were washed with water or acid and labeled as water washed (WW) or acid washed (AW), respectively.

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Figure 16. Cell capacitance of 0 and 0.4 g CCF AW composite-based devices for applied currents ranging from 10 to 700 mA during the charge/discharge cycles. The values were normalized with respect to the weight of PPy. The cut-off potential value was set at 0.6 V. Reprinted from Paper VI.

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Figure 16 shows the cell capacitance plotted against the charging current (10 to 700 mA), normalized with respect to the PPy weight in the composite. It had already been concluded from the CV measurements (Paper VI) that CCFs incorporated in cellulose fibers showed negligible charge capacity; cell capacitance was therefore normalized with respect to the percentage of active PPy in the composite. The percentage of PPy was determined by the CHN analysis as described in Paper VI. It is evident from the plot in figure 16 that the cell capacitance for the 0.4 g CCF AW sample remained virtually unchanged at ~60 F g-1 over the entire region of tested charging currents between 10 and 700 mA (i.e. current densities from 1.4 to 99 mA cm-2), whereas the cell capacitance decreased with increasing charging currents above 100 mA for the 0 g CCF AW sample. It should be noted that while the cell capacitance remained unchanged even when employing the charge cur-rent of 700 mA (cut-off at 0.6 V, current density 99 mA cm-2). The latter effect represents remarkable progress for paper-based energy storage devices intended for high power applications.

Figure 17. Cell capacitances of the 0.4 g CCF AW composite sample for applied currents of + 50 and +150 mA for consecutive 1500 charge/discharge cycles. The cut-off value was set at 0.6 V. The charge capacitance is normalized with respect to the weight of PPy. The embedded graphs show the first and last five charge/discharge cycles performed with an applied current of +50 mA (right panel) and +150 mA (left panel), respectively. Reprinted from Paper VI.

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The drastic improvement in the charge-discharge properties of the device upon inclusion of CCFs is further illustrated by the significant cycling stabil-ity upon charge and discharge. Figure 17 shows the cycling stability for a 0.4 g CCF AW based device following 1500 charge/discharge cycles at 50 and 150 mA (i.e. current densities of 16 and 48 mA cm-2). It can clearly be seen from the graph that the energy storage paper device retained its cell capacitance unchanged even after a three-fold increase in the applied current. The cell capacitance increased by 2% at a 50 mA charge and discharge cur-rent and decreased by 0.25% at 150 mA following 1500 cycles. It could be concluded that the observed stable charge capacity of the paper electrode material at faster rates is mainly due to the improved accessibility of the PPy active sites provided by the CCFs acting as electronic highways in the composite material. The results represent a significant step forward in the development of environmentally friendly paper-based energy storage devices

Higher release efficiency was also observed (Paper VII) during DNA re-lease by employing the PPy-Cladophora cellulose-CCF composite as elec-trode material for galvanostatic extraction and release of DNA hexamers (dT)6 tagged with 6-FAM fluorophore. One problem limiting a fully reversi-ble DNA exchange was the poor electron transfer properties of the PPy composite in the reduced state. Thus, may be pockets of electro-active PPy material that remained embedded in the insulating matrix were not accessi-ble for electron transfer during reduction. Therefore, a composite material which also exhibited good conductivity in the reduced state would be valu-able, since these CCFs can act as electron transfer highways by facilitating electron transfer between the current collector and the PPy-Cladophora cel-lulose composite nanofibers. In fact, the incorporation of the CCFs improved the conductivity during reduction of the composite material, and this resulted in increased release efficiency of DNA oligomers.

Figure 18 from Paper VII, shows the results of galvanostatic oxidation and reduction of PPy in the presence of (dT)6 hexamers in buffer solutions. It is seen from figure 18 that the potential increases almost linearly during the entire oxidation interval for the samples containing CCFs whereas, in the reference sample, the potential response clearly is non-linear. The linear response observed for the CCF samples indicates facilitated electron transfer throughout the entire electrode material. The effect of inclusion of the CCFs on the electroactivity of the paper electrode material became even more pro-nounced during the reduction experiments. It was clearly seen that the char-acteristic drop in the potential at around 1500 s for the reference sample occurred at around 2000 s for the sample containing CCFs, suggesting im-proved reduction of PPy. However, galvanostatic curves do not allow the amount of DNA extracted during oxidation and released during reduction of PPy to be quantified. Therefore, the efficiency of DNA extraction and re-lease was quantified using Spectrofluorometry as summarized in figure 19.

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Figure 18. Comparison of electrochemical oxidation and reduction curves (2nd cycle) of the 0 g and 0.4 g CCF composites. The oxidation cycles were performed in 10 mL of 1 nmol of (dT)6 DNA dissolved in phosphate-buffered saline (PBS) solu-tion while the reduction cycles were performed in 10 mL of borax buffer solution with zero concentration of (dT)6 at a temperature of 70 oC. Reprinted from Paper VII with the permission of the publisher.

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Figure 19 summarizes quantitatively the results of (dT)6 extraction and release as normalized with respect to the total weight of the active PPy con-stituent in the composite samples. The efficiency of (dT)6 release was sig-nificantly better for the sample containing CCFs. A DNA recovery of ~45% was observed in the first cycle for the CCF sample whereas, for the corre-sponding sample without CCF, the DNA recovery level was ~25%.

Further, the efficiency of DNA extraction was also better for the sample containing CCFs. Thus, the facilitated electron transfer inside the electrode material favored more efficient recovery of DNA oligomers. It can be seen in figure 19 that the efficiency of the release was significantly improved, whereas fully reversible extraction of DNA was not achieved. It can thus be concluded that the limited conductivity of the PPy-Cladophora cellulose composite in the reduced state is only one of several limiting fac-tors. The observed improvement is, however, promising for further devel-opment of PPy composite paper electrode materials as a new technology platform for electrochemically-controlled extraction techniques in biotechnology, nanoanalytical systems, paper-based diagnostic devices and immunosensors.

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9. Conclusions

The development of conductive PPy-Cladophora cellulose composite paper sheets obtained by combination of PPy and Cladophora cellulose17 has been addressed for high-tech applications. The characteristics of the PPy-Caldophora cellulose composite enabled it to be used as an electrode mate-rial which can be directly immersed in electrolyte solutions for batch-wise electrochemically controlled ion-exchange.

The electrochemical properties of the PPy-Cladophora cellulose paper composite were investigated in electrolytes containing three different types of anion (chloride, nitrate and p-toluene sulfonate). It was found that nitrate ions are more readily extracted by the composite than chloride ions whereas the capacity of the composite to host large p-toluene sulfonate ions was about half of that of the smaller ions under the oxidation conditions used in the study.

The influence of different sized oxidants used during polymerization on the electrochemically controlled anion extraction capacity of the composite was also studied. The composites synthesized with two different oxidizing agents, i.e. iron (III) chloride and PMo, were investigated in 2.0 M electro-lytes for their ability to extract anions of different sizes (chloride, aspartate, glutamate and p-toluene sulfonate). It was established that the surface area and electronic conductivity of the iron (III) chloride-synthesized sample were almost twice and five times, respectively, as large as those of the PMo-synthesized sample. Both samples absorbed significantly higher amounts of chloride ions than the larger anions. The number of absorbed ions per sample mass was larger for the iron (III) chloride-synthesized sample than for the PMo-synthesized sample for all four electrolytes studied. The iron (III) chlo-ride-synthesized sample (PPy-Cladophora cellulose composite) showed a considerable absorption capacity for various anions, including amino acids and p-toluene sulfonate.

It was demonstrated that the PPy-Cladophora cellulose composite can be used as a solid phase extraction material for batch-wise extraction and re-lease of different sized DNA oligomers. The (dT)20 and (dT)40 oligomers were extracted at least as well as the (dT)6 oligomers, while the diffusion of only the smallest (dT)6 oligomers was established during release experi-ments. The results clearly indicated that the present combination of high surface area and thin PPy films, yielding both high capacity and rapid diffu-sion into the PPy layer, is very promising for the development of

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inexpensive, electrochemically controlled ion-exchange membranes for batch-wise extraction of a range of different biomolecules.

It was also shown that the mechanically robust and light-weight PPy-Cladophora cellulose composite can act as an electrode material in symmet-ric non-metal-based energy storage devices. The presented paper-based energy storage system was also shown to be compatible with high charging rates with a reasonable cycling stability; the presented energy storage cell thus holds great promise for applications in areas where lithium ion batteries are difficult to use, e.g. in inexpensive large-scale devices or flexible energy storage devices to be integrated into textiles or packaging materials.

Micron-sized CCFs incorporated as an additive were shown to improve the charge-discharge rates of paper-based energy storage devices and to en-hance the DNA release efficiency. The results showed that the internal resis-tance of the PPy paper electrode was reduced after incorporation of CCFs, and the entire volume of PPy could remain active yielding retained charge capacitances for current densities up to 99 mA cm-2. The cycling stability measurements showed only 0.2 % loss even after 1500 charge-discharge cycles. Incorporation of CCFs also improved the efficiency of DNA release from 25 to 45%. It is concluded that the CCFs acted as electron transfer highways, remarkably facilitating electron transfer between the current col-lector and the PPy composite nanofibers.

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10. Future work

It is concluded that the combination of the high surface area and thin PPy coating on Cladophora cellulose nanofibers was reasonably successful in the early development of electrochemically controlled batch-wise extraction /release of DNA oligomers and paper-based energy storage devices. The limited conductivity of the PPy-Cladophora cellulose composite in the reduced state during release of DNA oligomers was only one of several lim-iting factors for preventing DNA release, and 100% release efficiency is hence yet to be achieved. It is suggested that future work includes studies utilizing an external electric field to be applied in the vicinity of the oxidized and DNA containing PPy-Cladophora cellulose composite, to facilitate migration of the DNA oligomers. In the presence of an electric field, it may in fact be possible to obtain sequential release of oligomers of different sizes by varying the imposed electric field strength. The limitations of PPy-Cladophora cellulose-based energy storage devices in terms of degradation of PPy and self-discharge should also be addressed in future in order to enable industrial scale applications.

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Acknowledgements

All praises are due to Allah, most merciful and beneficial, Who blessed me ample strength to complete this work. I cannot thank Him enough. All of my devolutions and tributes to His Holy Prophet Muhammad (peace be upon him) for teaching us to recognize our Creator.

My main supervisor Dr. Albert Mihranyan is greatly acknowledged for his guidance and continuous support in my PhD studies. He has shown me how to approach the research problems and the importance of being persis-tent with the research goals. Many thanks to Professor Maria Strømme, my co-supervisor and leader of NFM group, for providing me the opportunity in her research group to do PhD studies in an outstanding environment. I am grateful for your motivation, guidance and cheerful words to make the things working when nothing seems to work. My second co-supervisor, Professor Leif Nyholm, is also greatly acknowledged for providing the vital guidance in electrochemistry related problems during my PhD studies. The quality of the work always improved immensely after the critical reviews by Leif. I am especially thankful to all my supervisors for always being there when I needed the support during my PhD studies. My research skills are developed quite extensively under the trio of these supervisors.

Thanks to all my colleagues; Ken, Alf, Mattias, Martin, Christian, Saad, Natalia, Erik, Johan, Gustav, Teresa, Yanling, Daniel, Henrik and Christoffer, for your cooperation in the laboratory and fun during the out-door events. I am also thankful to my former colleagues, especially Dr. Ulrika and Dr. Rambabu, for supporting with the constructive reflections in the beginning of my studies. Special thanks to my office mate Dr. Mattias Strömberg for the academic and cultural discussions. I would like to thank Dr. Christian Pedersen for his help in translating the thesis summary into Swedish. Many thanks to the administrative and technical staff at the department of engineering sciences; Ingrid, Eva, Maria Melin, Maria Skoglund, Jonatan and Enrique, for your wonderful support.

I would like to thank all of my friends in Uppsala, especially Junaid, Jawad, Hassan, Sultan, Qaiser, Ramzan, Salman, Taqi, Tanveer, Nadeem, Shafiq, Shahid, Ahson and Zubair, for arranging nice gatherings. During my stay here, I had never felt being away from home. No one is forgotten if you are not mentioned here.

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Higher Education Commission (HEC) of Pakistan is greatly acknowl-edged for providing the financial support for this PhD studies. Many thanks to Swedish Institute (SI) for monitoring the PhD studies and providing the administrative help concerning the residence permits.

I am really grateful to my parents for their love and support throughout my studies. I am especially thankful to my mother for her permission to allow me for higher studies outside the country.

Last but not least I would like to thank my wife, Sehar, for her love, patience, allowing me to concentrate fully on my research work and particu-larly providing the company during work in office on weekends. Finally, I am thankful to my daughter, Urwah, for her innocent smiles and unfathomable love. Aamir Razaq Uppsala, October 2011

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Sammanfattning på Svenska

Det har länge varit känt att polymera material är goda elektriska isolatorer vilken är en egenskap som utnyttjas i många applikationer. Mycket forskning har fokuserat på polymerers elektriska egenskaper och nya möjligheter upp-stod inom polymervetenskapen när det upptäcktes att man även kan tillverka polymerer som är elektriskt ledande. Forskarna Alan J. Heeger, Alan G. MacDiarmid och Hideki Shirakawa fick Nobelpriset i kemi år 2000 för den-na upptäckt. Polymerer med god förmåga att leda elektrisk ström har sedan dess kallats ledande polymerer. Ledande polymerer har kunnat ersätta metal-ler som det ledande materialet i många applikationer eftersom polymererna väger relativt lite samt kan tillverkas på ett enkelt och kostnadseffektivt sätt.

En ledande polymer kan göras elektriskt laddad genom att en spänning appliceras och genom att variera spänningen kan polymerens laddningsgrad kontrolleras. På så vis kan även polymerens förmåga att locka till sig och fånga upp laddade molekyler i en vattenlösning kontrolleras. Polypyrrol (PPy) är ett exempel på en ledande polymer med hög elektrisk ledningsför-måga och som dessutom är lätt att syntetisera i både vattenlösning och orga-niska lösningsmedel. PPy är därtill en av de grundligast undersökta ledande polymererna och har använts i batterier, solceller, sensorer, läkemedelsbe-redningar, jonbytesmembran och för elektromagnetisk skärmning.

Några svagheter hos ledande polymerer är att de oftast är spröda och me-kaniskt svaga material som inte tål att kompakteras och är svårlösliga i de flesta lösningsmedel. Därför syntetiseras ofta den ledande polymeren på ytan av ett mekaniskt starkt material (ett substrat). Resultatet är en så kallad kom-posit (d.v.s. ett material som består av minst två olika komponenter) som både är elektriskt ledande och har tillfredsställande mekaniska egenskaper. Cellulosa är ett material som är känt för sin inre mekaniska styrka och har därför i många sammanhang använts som ett substrat som täckts med en yta av en ledande polymer. Cellulosa har många andra fördelar i detta samman-hang såsom att den är miljövänlig och kostnadseffektiv.

I denna avhandling har cellulosa från grönalgen Cladophora använts som substrat för PPy. Cellulosa från Cladophora har stor ytarea och hög grad av kristallinitet. Kompositen bestående av PPy och Cladophora cellulosa har utformats som ett pappersark vilket är svart samt relativt starkt och böjligt. I avhandlingen har kompositen använts i två sammanhang: (1) som grundma-terial i ett miljövänligt och cellulosabaserat batteri samt (2) för extraktion av biomolekyler.

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I avhandlingsarbetet har kompositen studerats i närvaro av en mängd oli-ka joner och laddade molekyler. Experimenten visar att kompositen är väl lämpad för reversibel extraktion av DNA-molekyler i lösning. I stora drag kan processen beskrivas enligt följande: (1) Kompositen sänks ner i en lös-ning med DNA-molekyler, (2) kompositen laddas upp genom att en elektrisk spänning appliceras vilket i sin tur leder till att kompositen fångar upp de motsatt laddade DNA-molekylerna, (3) kompositen sänks ner i en annan lösning där kompositens laddningsgrad sänks vilket ger frisättning av DNA-molekylerna. Resultaten innebär ett stort steg framåt mot projektets långsik-tiga mål vilket är att ta fram en kompositbaserad metod för att extrahera DNA och proteiner ur biologiska vätskor.

I avhandlingsarbetet har kompositen även utvärderats som material för miljövänliga batterier. Ett batteri har designats där kompositmaterialet utgör både anod och katod och ett filterpapper fungerar som separator mellan elek-troderna. Lösningen som systemet befinner sig i är rent saltvatten. Resultaten visar att kompositen med fördel kan användas som en komponent i ett miljö-vänligt cellulosabaserat batteri vilket kan laddas upp väldigt snabbt.

I ett av delprojekten har mikrometerstora kolfibrer tillsatts till kompositen för att förbättra dess prestanda. Resultaten visar att tillsats av kolfibrer mins-kar kompositens elektriska resistans och därmed kan det cellulosabaserade batteriet laddas upp och ur ett mycket stort antal gånger utan att batteriet egenskaper försämras nämnvärt. Dessutom ger tillsatsen av kolfibrer en be-tydligt effektivare frisättning av DNA-molekyler från kompositmaterialet.

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