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Supporting Information

A Comparative Study on Microstructure, Physical-Mechanical Properties,

and Self-healing Performance of Two Differently Synthesized Nanocomposite

Double Network Hydrogels based on -Car/PAm/GO

Sara Tarashi,a Hossein Nazockdast,*

a Gholamhossein Sodeifian

b,c

a Polymer Engineering Department, Amirkabir University of Technology, P.O.B. 15875-4413, Tehran, Iran b Chemical Engineering Department, Faculty of Engineering, University of Kashan, P.O.B. 87317-53153, Kashan, Iran c Laboratory of Advanced Rheology and Rheometry, Faculty of Engineering, University of Kashan, P.O.B. 87317-53153,

Kashan, Iran

*Correspondence to Prof. Hossein Nazockdast;

E-mail: nazdast@aut.ac.ir

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Table S1. Position of the bands and intensity ratio between the D band and G band in the Raman spectra

of the GO and NCDN hydrogels prepared by different synthesis methods.

Wavenumber (cm-1

)

Sample Code D band G band ID/IG

GO 1359 1598 0.97

UV-DNGO0.3 1358 1601 0.96

Thermal-DNGO0.3 1358 1606 0.93

Table S2. Characteristic peaks of PAm SN hydrogel, DN hydrogel and NCDN hydrogels prepared by

different synthesis methods according to the FTIR spectra.

Absorption Peak (cm-1

)

Sample Code N-H

stretching

C-H

stretching

C=O

stretching

C-N

stretching

Glycosidic

linkage

D-galactose-

4-sulfate

UV-PAm 3435 2937 1629 1444 - -

UV-DN 3420 2916 1618 1421 1084 795

UV-DNGO0.3 3407 2898 1602 1410 1072 790

Thermal-PAm 3436 2928 1641 1457 - -

Thermal-DN 3433 2924 1634 1457 1112 808

Thermal-DNGO0.3 3429 2918 1629 1452 1109 799

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Table S3. Results of DSC thermograms for the UV-DN, UV-DNGO0.3, Thermal-DN, and Thermal-

DNGO0.3 DN and NCDN hydrogels.

Results of DSC thermogram

Sample Code Hm (J/g) Wfree (wt.%) Wbound (wt.%)

UV-DN 119.03 34.94 47.06

UV-DNGO0.3 104.79 30.76 51.24

Thermal-DN 136.55 40.09 41.91

Thermal-DNGO0.3 129.31 37.97 44.03

Table S4. Quantitative values of the tensile properties for the healed UV-cured and thermally-cured DN

and NCDN hydrogels.

Tensile properties

Sample Code σf (MPa) εf (%) E (MPa) W (MJ/m3)

Healed-UV-DN 0.055 147 0.05 0.055

Healed-UV-DNGO0.3 0.12 275 0.073 0.24

Healed-Thermal-DN 0.029 141 0.02 0.02

Healed-Thermal-DNGO0.3 0.044 165 0.026 0.04

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Figure S1. Stress-strain curves under uniaxial tensile for the DN hydrogel prepared by (a) UV-curing

method at different UV curing time and (b) thermal-curing method at different thermal curing time.

Comparison of (c) elastic modulus and fracture energy and (d) stress and strain at failure point between

the hydrogels.

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Thermally-cured hydrogels were prepared by graft polymerization of Am onto the -Car backbones using

the MBA cross-linker. First of all, APS, as a thermal-initiator, can decompose under heating and the

resultant radicals extracted hydrogen from the hydrogen groups of the -Car backbone to form

corresponding macro-initiators. This persulfate-saccharide redox system thus results in active centers

capable of initiating radical polymerization of Am to give a grafted polymer. In the presence of a cross-

linking agent (MBA), the cross-linking reaction can occur, and finally, a three-dimensional network is

produced. A simple scheme for the synthesis of thermally-cured hydrogel was illustrated in Figure S2. It

should be noted that this mechanism is based on the known reactions discovered basically by other

research groups [1-3].

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Figure S2. Proposed mechanism for grafting reaction in the hydrogels prepared by the thermal-curing

method. (i) Production of initiator free radicals, (ii) production of -carrageenan free macro-radicals and

(iii) initiation of vinyl monomers by free macro-radicals for polymerization.

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Actually, the states of water in the hydrogels can be categorized as (i) free water, which does not form

hydrogen bonds or interacts weakly with polymer chains and (ii) bound water, which interacts with the

polymer chains through hydrogen bonding [4]. In contrary to the free water, the bound water cannot

crystallize under normal conditions due to the bounding to the polymer chains [4]. Therefore, in order to

investigate the free water content in the hydrogels, the DSC experiments were performed on the samples

by using a first cooling mode up to -80 °C and then heating mode up to 40

°C. Figure S3 presents the DSC

thermograms obtained for the DN and NCDN hydrogels prepared by two different synthesis methods.

The exothermic peak observed in the cooling curves and endothermic peak in the heating curves of

hydrogels represent the crystallization and melting of free water, respectively [5]. The free water

percentage (Wfree) can be calculated according to the following formula [5-7]:

where Hm is the melting enthalpy of free water in the hydrogel (calculated from the area under the

endothermic peak of hydrogel), Hf is the heat of fusion for pure water (340.6 J/g) [7]. Therefore, the

bound water percentage (Wbound) was evaluated by the difference between the total water percentage (~ 82

%) and the amount of free water. The quantitative values of Wfree and Wbound for the hydrogels are listed in

Table S3. From these results, the free water content in the UV-DN hydrogel was found to be lower than

Thermal-DN hydrogel. This could be attributed to the lower contribution of O-H content in the thermally-

cured hydrogel as a result of the grafting reaction. Moreover, it was found that the introduction of GO

nanosheets into both DN hydrogels has an enhancing effect on the bound water. This could be explained

in terms of an increase in the hydrophilic potential of DN hydrogels due to the presence of GO with the

high amount of oxygen-containing groups.

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Figure S3. The DSC thermograms for DN and NCDN hydrogels prepared by two different synthesis

methods.

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Figure S4. Equilibrium swelling ratio and equilibrium water loss in hydrogels prepared by two different

synthesis methods.

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Figure S5. Digital photograph of (a) UV-DN, (b) Thermal-DN, (c) UV-DNGO0.3, and (d) Thermal-

DNGO0.3 hydrogels during tensile stretching at a constant strain.

Figure S6. Stress-strain curves under uniaxial tensile for the Thermal-DNGO1 NCDN hydrogel.

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Figure S7. Dependence of tan δ = G" / G' on temperature during a rheological temperature sweep at a

cooling and heating rate of 2 °C/min with a fixed angular frequency of 1 rad/s and a strain amplitude of

1% for the DN and DNGO0.3 NCDN hydrogels prepared by different methods.

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Figure S8. Dependence of G' (solid symbols) and G" (open symbols) on time during a rheological time

sweep at a fixed temperature of (a) 20 °C and (b) 70

°C with a strain amplitude of 1 % and constant

angular frequency of 1 rad/s for hydrogels prepared by different methods.

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Figure S9. G' (solid symbols) and G" (open symbols) during strain sweep from 0.001 % to 1000 % at a

constant angular frequency of 1 rad/s and at 20 °C for UV-cured PAm, thermally-cured PAm, and CAR

SN hydrogels.

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Figure S10. G' (solid symbols) and G" (open symbols) during frequency sweep in the angular frequency

range of 0.01 – 100 rad/s and at a constant strain amplitude of 1 % at a fixed temperature (a) 20 °C and (b)

70 °C for hydrogels prepared by different methods.

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References

[1] G. R. Mahdavinia, A. Asgari, Synthesis of kappa-carrageenan-g-poly(acrylamide)/ sepiolite

nanocomposite hydrogels and adsorption of cationic dye, Polym. Bull. 70 (2013) 2451–2470.

[2] B. Cheng, B. Pei, Z. Wang, Q, Hu, Advances in chitosan-based superabsorbent hydrogels, RSC Adv.

7 (2017) 42036.

[3] H. Salimi, A. Pourjavadi, F. Seidi, P. Eftekhar Jahromi, R. Soleyman, New Smart Carrageenan-Based

Superabsorbent Hydrogel Hybrid: Investigation of Swelling Rate and Environmental Responsiveness, J.

Appl. Polym. Sci. 117 (2010) 3228–3238.

[4] Y.Q. Xiang, Y. Zhang, D. Chen, Novel dually responsive hydrogel with rapid deswelling rate, Polym.

Int. 55 (2006) 1407–1412.

[5] A.W. Braszak, M. Kazmierczak, M. Baranowski, K. H. Natkaniec, K. Jurga, The aging process of

hydrogel contact lenses studied by H NMR and DSC methods, Eur. Polym. J. 76 (2016) 135-146.

[6] K. Krzysztofiak, A. Szyczewski, Study of dehydration and water states in new and worn soft contact

lens materials, Optica Applicata 2 (2014) 237–250.

[7] I. Tranoudis, N. Efron, Water properties of soft contact lens materials, Contact Lens Anterior Eye 27

(2004) 193–208.