Supplementary Information

Development of Reversibly Compressible Feather-like

Lightweight Chitosan/GO Composite Foams and Their

Mechanical and Viscoelastic Properties

Stephanie K. Lee1, Mei Wang2, Jin Hyun Lee3,*, and Jonghwan Suhr1,4,5,*

1 Department of Energy Science, Sungkyunkwan University, 2066 Seobu-ro, Jangan-gu,

Suwon-si, Gyeonggi-do 16419, Republic of Korea

2 State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser

Spectroscopy, Collaborative Innovation Center of Extreme Optics, Shanxi University,

Taiyuan, Shanxi 030006, China

3 Polymer Research Center, Inha University, 100 Inha-ro, Michuhol-gu, Incheon 22212,

Republic of Korea

4 Department of Polymer Science and Engineering, Sungkyunkwan University, 2066 Seobu-

ro, Jangan-gu, Suwon-si, Gyeonggi-do 16419, Republic of Korea

5 School of Mechanical Engineering, Sungkyunkwan University, 2066 Seobu-ro, Jangan-gu,

Suwon-si, Gyeonggi-do 16419, Republic of Korea

*Corresponding authors. Tel: +82) 32-860-7488. E-mail: hannahlee@inha.ac.kr (Jin Hyun Lee); Tel: +82) 31-290-7290. E-mail:

suhr@skku.edu (Jonghwan Suhr)

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Table S1Assignment of the FT-IR characteristic bands of CS/GO foams [1-6].

Wavenumber (cm-1) Chemical Group Type of Vibration

650 C–O–C Symmetric stretching1028 C–OH Stretching of primary alcohol group1060 C–OH Stretching of secondary alcohol hydroxyl group1151 C–O–C Symmetric stretching1380 C–H3 Bending of CH3 in amide group1404 C–H Symmetric stretching1548 N–H Bending of amino groups of CS1637 C=O Stretching of carbonyl group in the amide group2880 C–H Symmetric stretching2920 C–H Symmetric stretching3356 N–H Stretching of amino groups of CS3450 N–H & O–H Stretching of amino groups of CS or water

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Table S2Molar ratios, apparent densities, pore sizes, and porosities of the CS/GO foams prepared with various CS concentrations (5, 8, 10, 15, 20, and 40 mg/mL).

SampleConcentration

(mg/mL) Molar ratio(CS : GO)

Apparent density(mg/cm3)

Pore size(µm)

Porositya

(%)CS GO

CS5/GO1 5 1 1 : 7.175 4.178 - 92.14

CS8/GO1 8 1 1 : 4.577 6.268 - 91.22

CS10/GO1 10 1 1 : 3.661 7.523 - 90.83

CS15/GO1 15 1 1 : 2.364 9.535 60 ~ 200(Mean = 121) 90.79

CS20/GO1 20 1 1 : 1.831 13.87 85 ~ 300(Mean = 173) 84.92

CS40/GO1 40 1 1 : 0.9153 24.53 120 ~ 400(Mean = 245) 61.48

a Porosity (%): Pt = Vp/Vt 100%, Vp (pore volume) = Vt (total volume) - Vc (volume of completely compressed foam)

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Fig. S1. Custom-built micro-indenter apparatus for monotonic compression and stress-relaxation tests.

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Fig. S2. Schematic of the generalized SLS model referred to as the generalized Maxwell model. In this model, four springs (elastic elements) and three dashpots (viscous dampers) are assembled in parallel, where the springs E∞, E1, E2, and E3 ensure an instantaneous response to a step load, while the dashpots τ1, τ2, and τ3 denote a time-dependent delay upon the application of the step load.

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Fig. S3. Schematic of the compressive stress-strain profile of a foam material. Regime I, II, and III represent the elastic, plateau, and densification regions, respectively, and E, E*, E**, Ɛ , Ɛ**, and σ* are the elastic modulus, collapse modulus, densification modulus, critical strain, densification strain, and collapse strength of the material, respectively.

Definitions of the six parameters: - Elastic modulus ( E ) is the ratio of stress to the corresponding strain in the elastic

region (regime I), where associated with the bending of cell walls. (Ex. The elastic modulus of CS15/GO1 is 55.18 kPa, and it was measured in the range of linear proportionality of stress to strain (~ 13.30%)).

- Collapse modulus ( E * ) is the ratio of stress to the corresponding strain in the plateau region (regime II), where associated with the collapse of the cells by elastic buckling in the foams. (Ex. The collapse modulus of CS15/GO1 is 28.52 kPa, and it was measured in the range of linear proportionality of stress to strain (13.30% ~ 67.25%)).

- Densification modulus ( E ** ) is the ratio of stress to the corresponding strain in densification region (regime III), where the cells have almost completely collapsed opposing cell walls touched and further strain compresses the solid itself, giving the final region of rapidly increasing stress. (Ex. The densification modulus of CS15/GO1 is 395.6 kPa, and it was measured in the range of linear proportionality of stress to strain (68% ~)).

- Critical strain ( Ɛ ) is defined as the critical point of the true strain at which incipient bulking occurs from uni-axial tests. (Ex. The critical strain of CS15/GO1 is at 13.30%).

- Densification strain ( Ɛ ** ) is the critical strain when the cell walls have collapsed. (Ex. The densification strain of CS15/GO1 is at 67.25%).

- Collapse strength ( σ * ) is defined as the stress at which a material begins to deform plastically. (Ex. The collapse strength of CS15/GO1 is 7.780 kPa at 13.30%).

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