Natural and Biological Inspired Nanocomposites

Noraiham Mohamad, PhD

Department of Engineering Materials

Faculty of Manufacturing Engineering

Universiti Teknikal Malaysia Melaka

Chapter 10

INTRODUCTIONWhat is Biology?

• the science of life or living matter in all its forms and phenomena, especially with reference to origin, growth, reproduction, structure, and behavior.

• is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy.

• Biology is a vast subject containing many subdivisions, topics, and disciplines. Among the most important topics are five unifying principles that can be said to be the fundamental postulates of modern biology:

• Cells are the basic unit of life• New species and inherited traits are the product of evolution• Genes are the basic unit of heredity• An organism regulates its internal environment to maintain a

stable and constant condition• Living organisms consume and transform energy.

Subdisciplines of biology are recognized on the basis of the scale at which organisms are studied and the methods used to study them: biochemistry examines the rudimentary chemistry of life;

molecular biology studies the complex interactions of systems of biological molecules;

cellular biology examines the basic building block of all life, the cell;

physiology examines the physical and chemical functions of the tissues, organs, and organ systems of an organism; and

ecology examines how various organisms interact and associate with their environment.

Biological nanocomposite materials

Can be divide into three: Entirely inorganic

Entirely organic

Mixture of inorganic and organic materials

What is unique about synthetic process? “even final material may be entirely one class of material,

multiple classes of materials may be involved in the synthetic process, which may or may not remain in the final structure”.

Example of biological nanocompositesThe organic material does not remain in the final product: Enamel of the mature human tooth

95wt% consist of hydroxyapatite

During tooth formation;

Enamel consist of proteins (primarily amelogenin and enamelin) and hydroxyapatite.

But the proteins removed as the tooth develop.

Presence of protein and self-assembled structures they form with other biological macromolecules – help generate the minerl cross-ply structure of the enamel (plays a major part in its toughness)

Tooth Enamel

Tooth enamel formation. Coloured scanning electron micrograph (SEM) of a freeze-fractured section through a tooth, showing the enamel-forming cell layer (blue). This epithelium comprises a single layer of column-like cells called ameloblasts. Enamel (green, top) is a hard ceramic layer that covers and protects the teeth. The end of the ameloblasts can be seen originating in the internal tooth tissue (brown, bottom). Magnification x2700 when printed at 10 centimetres wide.

Tooth enamel. Coloured scanning electron micrograph (SEM) of a section through tooth enamel. The enamel is the outer covering the crown (visible part) of the tooth. It is the hardest substance in the human body. It is composed of rows of calcium and phosphorous salts (light brown) embedded in a protein matrix (grey). Magnification: x1400 when printed at 10 centimetres wide.

Example of biological nanocomposites

Inorganic/organic structural composite for both phases remain in the final product

Aragonitic nacreous layer of the abalone shell It is exceptionally strong because of its organic/inorganic

layered nanocomposite structure

Crystalline ceramic layers are separated by highly elastic organic layers

Synthetic efforts have been made for more than 10 years- their properties have been inferior

Abalone

Biological systems are known to self-assemble into organized structures at many length scales. At the smallest levels, the resulting structures sometimes act as templates for the growth of other materials. The end result is a layered composite with several levels of structural organization. For example, the structure of an abalone shell consists of layered plates of CaCO3 (~200 nm) held together by a much thinner (<10 nm) "mortar" of organic template.

Factors of failure in attempts to copy biology

Disconnect between needs of engineering materials and biological materials: Biological materials generally form over a period of days to

years, use a limited set of elements, and are designed to be used within a limited temperature range.

Practical engineering must be made rapidly (hours or minutes); generally, must operate over a wide range of temperature and other environmental conditions

Scientists conclude: “rather than attempting to directly copy biology, a much better

philosophy is to learn from biology and use the knowledge to create synthetic materials”

“this may or may not involve the use of some biological molecules”

“But, no attempt is made to ‘copy’ specific biological processes”

1. NATURAL NANOCOMPOSITE MATERIALS

Natural composite materials with structure on the nanoscale

2. BIOMIMETIC NANOCOMPOSITES

Synthetic nanocomposite materials formed through processes that mimic biology as closely as possible

3. BIOLOGICALLY INSPIRED NANOCOMPOSITES

• Composite materials with nanoscale order created through processes that are inspired by a biological process or a biological material

• Without attempting to mimic or directly copy the mechanism of formation of the biological materials

Natural nanobiocomposite materials Natural composite materials with structure on the

nanoscale

All the functionality provided by these materials- direct consequence of the nanoscale dimensions of the structure.

Example of nanoscale materials in biology: Lipid cellular membranes

Ion channels

Proteins

DNA

Actin

Spider silk and etc.

Lipid cellular membranes

A: The fluid mosaic model of membrane structure. The membrane consists of a phospholipid double layer with proteins inserted in it (integral proteins) or bound to the cytoplasmic surface (peripheral proteins). Integral membrane proteins are firmly embedded in the lipid layers. Some of these proteins completely span the bilayer and are called transmembrane proteins, whereas others are embedded in either the outer or inner leaflet of the lipid bilayer. The dotted line in the integral membrane protein is the region where hydrophobic amino acids interact with the hydrophobic portions of the membrane. Many of the proteins and lipids have externally exposed oligosaccharide chains. B: Membrane cleavage occurs when a cell is frozen and fractured (cryofracture). Most of the membrane particles (1) are proteins or aggregates of proteins that remain attached to the half of the membrane adjacent to the cytoplasm (P, or protoplasmic, face of the membrane). Fewer particles are found attached to the outer half of the membrane (E, or extracellular, face). For every protein particle that bulges on one surface, a corresponding depression (2) appears in the opposite surface. Membrane splitting occurs along the line of weakness formed by the fatty acid tails of membrane phospholipids, since only weak hydrophobic interactions bind the halves of the membrane along this line. (Modified and reproduced, with permission, from Krstíc RV: Ultrastructure of the Mammalian Cell. Springer-Verlag, 1979.)

Phospholipids, the lipid type that constitutes the majority of the cell membrane, are made up from a phosphate head (circles) that like water and lipid tail (lines) that hate it. These so-called amphipathic molecules line up so as to limit the exposure of the hydrophobic portions to the aqueous phase that is found on both sides of the membrane.

Characteristics of natural nanocomposites

Dimension characteristic of the structure- at least in 1D and often in 3D is on the order of a few nanometers

Composed of discrete nanoscale building block

In their active form, when folded: proteins are composed of domains with varying hydrophilic

and hydrophilicity

as well as, domains with structural features as alpha helixes, beta sheets and turns

It has complex structures containing nanometer-sized domains of varying chemical properties Because of chemically diverse regions- can exhibit acidic,

basic, hydrogen-bonding, hydrophilic or hydrophobic behavior

They can interact in exceedingly diverse ways with precursors for mineral compounds and the final mineral product

Completely organic nanocomposites (Spider silk) Dragline spider silk which makes up the spokes of a spider

web

Criteria: Strong core that composed of primarily of two protein

components that self assemble into crystalline and amorphous regions

Crystalline regions- alternating alanine-rich crystalline forming block; impart hardness

Amorphous regions- glycine-rich amorphous blocks; provide elasticity

Properties: Five times tougher than steel by weight

Can stretch 30-40% without breaking

Elastic modulus is significantly less than of steel

For application in which flexibility and toughness are the primary need (bullet proof vest) synthetic route to create material with properties equivalent to spider silk

15

Primary structure of spider dragline silk

Hinman, M.B.; Jones, J. A.; Lewis, R. TIBTECH 2000, 18, 374-379. Vollrath, F.; Knight, D. P. Nature 2001, 410, 541-548.Simmons, A. H.; Michal, C. A.; Jelinski, L. W. Science 1996, 271, 84-87.

QGAGAAAAAAGGAGQGGYGGLGGQGAGQGGYGGLGGQGAGQGAGAAAAAAAGGAGQGGYGGLGGLGGYGGQGAGGAAAAAAGAGQGGRGAGQS

SQGAGRGGLGGQGAGAAAAAAAGGAGQGGYGGLGGLGGYGGQGAGGAAAAAAGQGGRGAGQNSQGAGRGGLGGQAGAAAAAAGGAGQGGYGGLGGQGAGQGGYGGLG

GLGGYGGQGAGGAAAASAGAGQGAGQGGLGGQGAGGAAAAAAAGAGQGGLGGRGAGQSSQGAGRGGEGAGAAAAAAGGAGQGGYGGLGGQGAGQGGYGGLG

GLGGYGGQGAGGAAAAAAGAGQGAGQGGLGGQGAGGAAAAGAGQGGLGGRGAGQSSQGAGRGGLGGQGAGAVAAAAGGAGQGGYGGLG

GLGGYGRQGAGGAAAAAAGAGQGGRGAGQSNQGAGRGGLGGQGAGAAAAAAAGGAGQGGYGGLG

GLGGYGGQGAGGAAAAAGQGGRGAGQNSQGAGRGGQGAGAAAAAAVGAGQEGIRGQGAGQGGYGGLG

GAGGYGGQRVGGAAAAAAGAGQGAGQGGLGGQGAGGAAAAAAGAGQGGLGGRGSGQSSQGAGRGGQGAGAAAAAAGGAGQGGYGGLGGQGVGRGGLGGQGAGAAAAGGAGQGGYGGVG

SSLRSAAAAASAASAGS

Fibrous protein composed of Spidroin 1 (MaSp1) and Spidroin 2 (MaSp2)- Sequences highly conserved- Repetitive stretches of poly(Ala) and (GlyGlyXaa)n sequences (Xaa = Tyr, Leu, Gln)- MW of MaSp1 ~ 275-320 kDa; Sp1+Sp2 ~ 700-750 kDa

Repeating sequence of MaSp1

16

Proposed secondary structure and mode of elasticity

Kubik, S. Angew. Chem. Int. Ed. 2002, 41, 2721-2723.Van Beek, J. D.; Hess, S.; Vollrath, F. Meier, B. H. Proc. Nat. Acad. Sci. 2002, 99, 10266-10271.

• Poly(Ala) modules form anti-parallel β-sheets (~30-40%)• Glycine-rich, amorphous regions are thought to be helical

Disordered chain region

Strain

Crystalline region with-sheet structure

17

The classic strong synthetic fiber

Material Strength (GPa)Elasticity (%)Energy to break (J/kg)

Dragline Silk 1.1 35 4 x 105

Kevlar 3.6 5 3 x 104

Rubber 0.001 600 8 x 104

Nylon, type 6 0.07 200 6 x 104

Fiber axis

Kevlar®: Dupont (1960s) Uses

- Bulletproof vests and helmets- Automobile brake pads- Ropes and cables- Aerospace components

Lewis, R. Chem. Rev. 2006, 106, 3762-3774. Vollrath, F.; Knight, D.P. Nature 2001, 410, 541-548.Tanner, D.; Fitzgerald, J.A.; Phillips, B.R. Angew. Chem. Int. Ed. Engl. Adv. Mater. 1989, 5, 649-654.Kubik, S. Angew. Chem. Int. Ed. 2002, 41, 2721-2723.

18

Spider silks have potential in many applications

Surgical sutures Scaffolds for tissue engineering

Biomedical applications

Parachutes

High strength ropes/cables

Fishing line

Technical and industrial applications

Ballistics

Naturally production of spider silk

Inside the spider; The silk precursor exists as a lyotropic liquid crystal that is

approximately 50%.

As the silk excreted, the protein molecules that make up silk fold and aligned as they approach and then pass through the spinneret forming a complex insoluble nanostructured.

Limitation for sufficient application: Spiders cannot be kept in close quarters and harvested;

they eat one another

The only route: need to be produced synthetically.

20

Vollrath, F. J. Biotechnol. 2000, 74, 67-83.Hu, X. et al. Cell. Mol. Life Sci. 2006, 63, 1986-1999.

Spiders spin 6 different fibers

Web reinforcement (Minor ampullate 1 and 2) Dragline (major

ampullate 1 and 2)

Wrapping and egg case fiber (aciniform)

Pyriform silk (?)

Acini-form

Capture Spiral(Flagelliform)

Glue coating(Aggregate silk) (?)

Large diameter eggCase fiber (Tubuliform)

Aggregate TubuliformFlagelliform

Pyriform

Minor ampullate

Major ampullate

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Forced silking to obtain silk fibers

Spiders are anesthetized with CO2

and secured ventral side up

Silk is pulled from the spinneret,

attached to a reel, and drawn at a

specified speed

Work, R. W.; Emerson, P. D. J. Arachnol. 1982, 10, 1-10.Elices, M.; Perez-Rigueiro, J.; Plaza, G. R.; Guinea, G. V. JOM 2005, 57.

22

Spiders are highly developed fiber “spinners”

Lewis, R. Chem. Rev. 2006, 106, 3762-3774.Dicko, C.; Vollrath, F.; Kenney, J.M. Biomacromolecules 2004, 5, 704-710.

Spidroin secretion

Lumen

Spinneret

Duct

Fiber alignment

Duct

Tail

Funnel

1 mm

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Antiparallel and parallel -sheet structure

Poly(alanine) segment

Rotondi, K. S.; Gierasch, L. M. Biopolymers 2005, 84, 13-22. Simmons, A.; Ray, E.; Jelinski, L. W. Macromolecules 1994, 27, 5235-5237.

N-terminus

N-terminus

C-terminus

C-terminus

N-terminus

N-terminus

C-terminus

C-terminus

N C

NC

N C

N C

24

Solid state 13C-NMR and FT-IR spectroscopy

Marcotte, I.; van Beek, J. D.; Meier, B. H. Macromolecules 2007, 40, 1995-2001.Simmons, A.; Ray, E.; Jelinski, L.W. Macromolecules 1994, 27, 5235-5237.Dong, Z.; Lewis, R.; Middaugh, C. R. Arch. Biochem. Biophys. 1991, 1, 53-57.

13C-NMR chemical shifts (ppm)

13C-labeledAlanine

Wavenumber (cm-1)

1700 1600 15000.1550

0.2800

0.4050

Ab

sorb

an

ce

1691

1666

1637

1612

Infrared spectrum of silk from Nephila clavipes

Amide I (antiparallel-sheet)

-carbon

-carbon

Anti-parallel β-sheet

Parallel β-sheet

α-helixAla C

α-helix

Ala C

Ala CC=O

-sheet

20.1 15.1

48.7 52.5

171.9 176.5

Infrared wavelengths (cm-1)

1630, 1685

1630, 1645

1650, 1560

Synthetically production of spider silk

First, synthesis of silk precursor Created by expressing two of the dragline silk genes in

mammalian cells

Cannot be created by conventional organic synthesis due to high complexity

Second, silk precursor (soluble recombinant dragline silk proteins) is wet spun into fibers of diameters ranging from 10-40 m

Third, a postspinning draw produced fibers with mechanical properties approaching those of natural silk

Synthetic approaches to spider dragline silk

Biosynthesis Chemical Synthesis

Protein sequences

BioSteel is a trademark name for a high-strength based fiber material made of the recombinant spider silk-like protein extracted from the milk of transgenic goats, made by Nexia Biotechnologies. [1]

The company has created lines of goats that produce recombinant versions of either the MaSpI[expand acronym] or MaSpII[expand acronym] dragline silk proteins in their milk.[2][3] When the female goats lactate, the milk, containing the recombinant silk, is harvested and subjected to chromatographic techniques to purify the recombinant silk proteins.

The purified silk proteins are then dried, dissolved using solvents (DOPE formation) and transformed into microfibers using wet-spinning fiber production methodologies. The spun fibers so far have tenacities in the range of 2 - 3 grams/denier and elongation range of 25-45%. The "Biosteel biopolymer" has been transformed into nanofibers and nanomeshes using the electrospinning technique.[4]

Biosteel and other biopolymers are being researched to provide lightweight, strong, and versatile materials for a variety of medical and industrial applications.[5] Nexia Biotechnologies plans to use the spider silk from the milk of transgenic goats for bulletproof vests and anti-ballistic missile systems.

No one has been able to produce the silk in commercial quantities. Nexia is the only company which has successfully produced fibres from recombinant spider silk and is currently in the process of developing commercial quantities of BioSteel using its transgenic goat technology.[6] The Company was founded in 1993 by Dr. Jeffrey Turner and Mr. Paul Ballard, and was sold in 2005 to PharmAthene.

28

Two biosynthetic routes to spidroin proteins

Vendrely, C.; Scheibel, T. Macromol. Biosci. 2007, 7, 401-409.Altman, G.H. et al. Biomaterials 2003, 24, 401-416.

Synthetic DNA

Spider cDNA

Flexibility withhost

Protein fibers

Reverse transcription

Eukaryotic host (insect cells)

Spider silk protein sequences/mRNA

Gene design

Nephila clavipes

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Expression of spider silk cDNA in mammalian cells

Lazaris, A. et al. Science 2002, 295, 472-476.

Dragline silk gene sequencefrom A. diadematus

Gene sequence inserted intoexpression vector

Transformation of vector in mammalian cells

protein synthesis

Protein purification, and characterization

Protein: MW ~ 60-140 kDa Fiber diameter ~ 40 μm Yield ~ 37 mg/L

Mechanical Properties:

Protein sample Toughness(MJ/m3)

Modulus(GPa)

Elasticity(%)

Strength(GPa)

Actin depolymerizing factor 3 (ADF-3)

A. diadematus dragline

85 13 43.4 0.26

130 10 30 1.1

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Recombinant expression of synthetic silk genes

DNA fragment

Fahnestock, S. R.; Irwin, S. L. Appl. Microbiol. Biotechnol. 1997, 47, 23-32. Stephens, S.J. et al. Mat. Res. Soc. Symp. Proc. 2003, 774, 2.3.1-2.3.10.Fahnestock, S. R.; Bedzyk, L. A. Appl. Microbiol.Biotechnol. 1997, 47, 33-39.O’Brien, J. P.; Fahnestock, S. R.; Termonia, Y.; Gardner, K. H. Adv. Mater. 1998, 10, 1185-1195.

AGQGGYGGLGSQG--------------------------------------------AGQGGYGGLGSQGAGRGGLGGQGAGAAAAAAAGGAGQG-------GLGSQGA---------- GQGAGAAAAAA----GGAGQGGYGGLGSQGAGRG-----GQGAGAAAAAA---GG

Spidroin 1 analog: DP-1B[

]n=8-16

Ligate 8 or 16DNA fragments

DNA duplex

Hybridize complementary

strands

Premature termination with expression in E. coli

High MW polymers from yeast

Transform inEscherichia coli

Insert gene into plasmid vector

Or transform inyeast

Protein fibers1 g/L

Protein fibers300 mg/L

170 nm diameter fibers

31

Summary of biosynthetic pathways

Biosynthetic Method Advantages Disadvantages

Spider Silk cDNA Difficulty with protein

purification (aggregation)Produce proteins most

like native silk

High MW polymers

are readily attainable

Eukaryotic hosts are expensive

Synthetic DNA Polymer structure can

be tuned based on

DNA sequence used

Flexibility with

expression host

Truncated syntheses in many hosts

Natural organic/inorganic Nanocomposites

Also formed through self-assembly

Two extremes of the formation mechanism: 1st route- The organic matrix form first followed by

mineralization (biologically directed nucleation and growth of a mineral phase); organic matrix restructures and reorganizes continuously as the mineral deposits

2nd route- Organic and inorganic materials coassemble into nanostructured composite

No evidence in which inorganic structure forms first followed by organic structure formation.

Natural organic/inorganic Nanocomposites3 types according to level of complexity:

Simplest example- those in which mineral phase is simply deposited onto or within an organic structure (1st route). Eg: Grasses – many species precipitate SiO2 within their cellular structures

Bacteria- magnetic bacteria has internal chain of magnetite (Fe3O4) nanocrystals running down their long axis.

Medium level- in which the structure of mineral phase is clearly determined by the organic matrix (1st route). Bacteria S-layer- serves as protein template for the formation of thin film of

mesostructured gypsum

Highest level- in which the structure of mineral is intimately associated with the organic phase to create a structure with properties superior to those of either the mineral or organic phases (2nd route) Sea urchin spine- single crystal essentially composed of calcite, containing

only about 0.02% glycoproteins trapped within the crystal lattice of the spine

Nacreous (mother-of-pearl) layer of the abalone shell- alternating layers of 500 nm thick aragonite platelets and ~30 nm thick sheets of an organic matrix

Bone- Complex structure and function

Schematic drawing of the isolation of S-layer proteins from bacterial cells and their reassembly into crystalline arrays in suspension (a), at solid supports (b), at the air-water interface (c), on lipid films (d) and on liposomes (e). The orientation of the recrystallized lattice is determined by the physicochemical properties of the surfaces.

Fig.8 Transmission electron micrograph of palladium (Pd) nanoparticles precipitated on a S-layer with square lattice symmetry. Bar, 20nm

Transmission electron micrograph of palladium (Pd) nanoparticles precipitated on a S-layer with square lattice symmetry. Bar, 20nm

Biologically Inspired Nanocomposites

Inspired by properties of biocomposites & synthetic pathways for their formation

Rationale: Not always necessary or even desirable to use biologically

derived materials for many applications

May be possible to simply use biology as an inspiration for totally synthetic nanocomposites system

Many lessons can be learned from biology (how to form complicated nanostructures & potential properties of synthetic nanostructured materials)

Learn from biological system

To develop synthetic approach to form complex inorganic structures

Example of routes to nanostructure formation; Producing nanoparticles

Producing thin film

Production of II-IV semiconductor nanoparticles

Example: formation of metal sulfide and selenide

Semiconducting nanoparticles can be synthesized through:

1st method: Grinding of large chunks- rarely done for nanoparticle,

grinding process is poor regulated,

generally generating very polydisperse population of particles

Introduces too many contaminates

2nd method: Gas phase synthesis – is a vaporation and condensation process

Crucible containing the desired semiconductor (@ other materials) is heated until it is start to sublime

Then, inert gas is flowed over the material

Carrier gas heads to cool region where the gaseous semiconductor atoms or molecules condense into nanoparticles collated

Advantages: It is versatile

Disadvantages: operates under conditions of high temperature; generally produces solid spherical particles

3rd method: Solution based synthetic routes for nanoparticles- range from simple precipitation reactions to much more complex self-assembly based routes.

Simple precipitation:

Results in agglomerates of nanoparticles

Size distribution varies widely

To prevent aggregation and to narrow down size distribution-to use self-assembly-based techniques

Self-assembly based routes: resemble nanostructure development in biological systems (biomineralization, cell membrane development, other biological structure formation)

Solution-phase synthesis of semiconductor Often preferred over other techniques

Generally mild (even being carried out at room T and P)

Can be used to create reasonable volumes of materials

Has been widely used to grow semiconductor quantum dots (Cd3P2)

Solution-based chemical synthesis are very attractive- allow for direct control over actual concentrations of the chemical precursors

Even possible to cap the surface with organic molecules – allows for further solution-based processing

More conventional route to creating nanostructured materials- through top-down lithographic methods:

Extreme UV lithography

Electron beam writing

Focused ion-beam lithography

X-ray lithography

Scanning probe lithography and

Micro-contact printing

Can form nanostructures on scale of 10 to 100 nm

Disadvantages;

Generally on flat surface/substrate

Can be quite slow

Often very expensive

Formation through self-assembly based routes: Not limited to feature

generation on flat surface

It can be massively parallel

Disadvantages;

It is not possible to highly regulate the exact spatial position of the nanostructure

We are still many years away from creating highly functional self-assembled electronic circuits

Another example of self-assembly based route to produce nanoparticle- Micellar routes Micelles are self-assembled from surfactant molecules +

solvent (that contains at least one of the precursors for the inorganic nanoparticles in solution)

Solution- that contains vast numbers of discrete nanoreactors (individually contain only a finite number of precursor species for the inorganic phase)

Reduction/oxidation

Ions are converted to mineral one nanoparticle per micelle

If possible to create a suspension of monodisperse micelles; it will a straightforward process to create nanoparticle with a very narrow distribution

Micellar routes

A lesson from biology: the process might be possible through the use of complex macromolecules that organize into particles of only a specific size.

A nanoreactor with tight size distribution is –virus particles

Load the interior of the virus particles with precursors for nanoparticles

Type of nanoparticles produced by self-assembly based routes

Cadmium Sulphide (CdS): Dendritic structure were generated

Others: resulted in rod-like and even complex nanoparticles

Cadmium Selenide (CdSe) Nanorods with aspect ratio of 30:1 (arrow-, teardrop- and

branched tetrapod-shaped nanocrystals)

Production of nanostructure thin film Next level complexity in nanostructure formation- creation

nanostructures with complex, predefined morphologies

In biology- common to have complex predefined structures on nanometer scale

But, exceedingly difficult to syntheticly produced

Possible: power of assembly + materials synthesis strategies known today: Liquid crystal templating

Colloidal particle templating

Block copolymer templating

Surfactant inorganic self-assembly (most famous in producing mesoporous silica)

A liquid crystal is a substance that flows like a liquid but maintains some of the ordered structure characteristic of crystals.

Under certain circumstances, phases, liquid crystals have a liquid-like behaviour and during others they have the opposite behaviour.

Liquid crystals are partly ordered materials, somewhere between their solid and liquid phases. Their molecules are often shaped like rods or plates or some other forms that encourage them to align collectively along a certain direction. The order of liquid crystals can be manipulated with mechanical, magnetic or electric forces.

Liquid Crystal

Melt

Solidify

Intermediate Phase

Heat

Cool

Heat

Cool

What are Liquid Crystals?

Liquid Crystals (LCs)

LCs are orientationally ordered fluids with anisotropic properties

A variety of physical phenomena makes them one of the most interesting subjects of modern fundamental science.

Their unique properties of optical anisotropy and sensitivity to external electric fields allow numerous practical application.

Finally, liquid crystals are temperature sensitive since they turn

into solid if it is too cold, and into liquid if it is too hot.

What is so special about liquid crystals?

Types of Liquid Crystals

Liquid crystals

Lyotropic Thermotropic

Calamitic Polycatenar Discotic Banana-shaped

Nematic (N)

Smectic (S)

Nematic Discotic(ND)

Columnar (Col)

Lyotropic Liquid-Crystal Templating

Nanostrcture & nanocomposites formation that utilizes the self-assembled structure of a iquid crystal to regulate the structure of growing inorganic material

When processed correctly, structure of inorganic phase directly replicates the structure of the liquid crystal

Liquid crystal is “template’ for the inorganic

Lyotropic liquid crystal composed of at least two covalently linked components: One is usually amphiphile (molecule that has two or more

physically distinct components)

Other one- solvent

Lyotropic LCsLyotropic LCs are two-component systems where an amphiphile is dissolved in a solvent. Thus, lyotropic mesophases are concentration and solvent dependent.

The amphiphilic compounds are characterised by two distinct components, a hydrophilic polar“ head” and a hydrophobic “tail”.

Examples of these kinds of molecules are soaps (Figure-a) and various phospholipids like those present in cell membranes (Figure-b).

[a]

[b]

General concept of liquid-crystal templating First, form a liquid crystal that contains at least one of

the precursors of the mineral phase

Then, induce a mineral phase to precipitate in ONLY one chemical region of the liquid crystals – by applying perturbation.

Formation of nanostructures

Type of nanostructures according to the type of liquid crystal: Hexagonal

Lamellar

Cubic phases

Bicontinouous phase

Advantages of liquid crystal templating vs lithographic Dimensions of the synthesized materials smaller than

obtainable by lithographic

Often attainable through bulk synthesis, which obviously not possible via lithography

Generates semiconductor/organic superlattice containing both the symmetry and the long-range order of the precursor liquid crystal

Large number of amphiphilic liquid crystals with lattice constant from a few nanometers to tens of nanometers

Many of the amphiphilic system can be mineralized- produce materials with an array of novel structures and properties.

Example of the process

Grown of body-centred phase CdS

Using a triblock copolymer of poly(oxyethylene)-poly(oxypropylene)-poly(oxyethylene) as the amphiphile

Mix with water, PO segment is only weakly solveted, but EO is highly solvated.

The molecule is hydrated to form micelles which closely pack, forming cubic phase

Precipitation in the cubic phase formation of hollow nanospheres of CdS