Supporting Information. Mussel-Inspired Cellulose Nanocomposite Tough Hydrogels with

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1 Supporting Information Mussel-Inspired Cellulose Nanocomposite Tough Hydrogels with Synergistic Self-Healing, Adhesive and Strain Sensitive Properties Changyou Shao, a Meng Wang, a Lei Meng, a Huanliang Chang, a Bo Wang, a Feng Xu a, Jun Yang, a * Pengbo Wan b a Beijing Key Laboratory of Lignocellulosic Chemistry, Beijing Forestry University, No 35, Tsinghua East Road, Haidian District, Beijing, , China b Center of Advanced Elastomer Materials, State Key Laboratory of Organic Inorganic Composites, Beijing University of Chemical Technology, Beijing , China * Corresponding author: yangjun11@bjfu.edu.cn. Tel:

2 Table S1. Compositions of the ionic gels. code (wt%) (mg) AA (g) APS (mg) MBA (mg) Water (ml) PAA TA@CNC TA@CNC TA@CNC TA@CNC TA@CNC TA@CNC Table S2. Mechanical properties summary of the ionic gels. code Fracture elongation (%) Fracture strength (kpa) Young s modulus (kpa) Toughness (MJ/m 3 ) PAA 504± ± ± ±0.02 TA@CNC ± ± ± ±0.05 TA@CNC ± ± ± ±0.15 TA@CNC ± ± ± ±0.22 TA@CNC ± ± ± ±0.20 TA@CNC ± ± ± ±0.18 TA@CNC ± ± ± ±0.16 The details of mechanical tests of ionic gels. All mechanical tests were performed at room temperature using a universal mechanical tester (Zwell/Roell) equipped with a 200 N load cell. To minimize water evaporation, silicone oil was coated on the hydrogel surface during the testing and storage time. The uniaxial tensile test was performed on the rectangular-shape specimens (10 2

3 mm in width, 6 mm in depth, and 35 mm in length). The initial distance (L 0 ) between two clamps was 15 mm, and the constant stretching rate was 120 mm/min. The nominal tensile stress (σ) was obtained by dividing the force (F) by the initial cross-sectional area (A 0 ) of the specimen (σ = F/A 0 ). The tensile strain (ε) was defined as the ratio of gauge length (L) to the initial gauge length (L 0 ) (ε = (L L 0 )/L 0 ). Toughness (T) was estimated by the area under the stress strain curves until fracture point by following equation: = ( ) (1) where and corresponded to the initial stretch and fracture stretch, respectively. The Young s modulus (E) was calculated from the slope of the initial linear region of the stress-strain curves (5-15% strain). The fracture energy (τ), a parameter to characterize the toughness of the sample, was determined by the area under the stress strain curve. The strain-rate-dependent tensile test was conducted at the strain rates ranging from 60 to 180 mm/min. For recovery experiment, the specimen was initially stretched to a predetermined strain (1200%) and then unloaded at the same velocity (120 mm/min) at room temperature. Then, the successive loading-unloading tensile tests were conducted for five cycles without intervals between consecutive cycles. The residual strain ratio was defined by a ratio of length change along the direction of stress after removal of stress with respect to the original length of the specimen. The recovery ratio was defined by a ratio of energy dissipation after each cycle to the initial cycle. The hysteresis test was performed under different strain from 400% to 1600% at a 3

4 constant stretching rate (120 mm/min). The dissipated energy ( Ui) for the i th cycle, is defined as the area of hysteresis loop encompassed by the loading unloading curve, which is calculated by integrating the area under the stress-strain curve: Ui= (2) The energy dissipation ratio (δ), measures how efficiently a material dissipates energy and is calculated as below: δ= Ui Ui (3) σ Ui max = σdε 0 (4) where Ui is the elastic energy stored in the materials when it is loaded elastically to a stress σ max in the i th cycle. The unconfined compression tests of the cylindrical sample (30 mm height and 20 mm diameter) were conducted at a crosshead speed of 10 mm/min. The raw data were recorded as force versus displacement and converted to stress versus strain with respect to the initial dimensions. The compression hysteresis was measured at the same conditions at compression deformation of 85% strain. 4

5 Figure S1. Dimension distribution histograms of CNCs and The average dimensions of CNCs and were measured to be 200 ± 10 nm long 20 ± 5 nm wide and 210 ± 15 nm long 40 ± 5 nm wide, respectively. It is noted that the individual TA@CNC exhibits a much remarkably thicker walls after the assembly coating process. Figure S2. The Young s modulus and toughness of ionic gels as a function of TA@CNC content. 5

6 Figure S3. Critical strain and fracture energy for notched ionic gels as a function of TA@CNC content, measured by pulling the notched gels to rupture. The ionic gel exhibited extremely notch-insensitivity, that is, when we cut a notch (as the insets) into the gel and then pulled it to a stretch, the notch was remarkably blunted and remained stable. Figure S4. Stress-time tensile curves during a cyclic loading unloading process at 1200% strain. Figure S5. Recovery ratio and residual strain ratio of ionic gels in cyclic tensile curves at 1200% strain without resting time. 6

7 Figure S6. Dissipated energy of ionic gels in cyclic tensile tests under different strains (400%, 800%, 1200%, 1600%) and corresponding energy dissipation ratio. Figure S7. The time-dependent self-healing behaviors of the ionic gels with a two-stage process distinguished by the increase amplitude of healing efficiency. Figure S8. The adhesive ionic gel could easily adhere to (a) glasses (supporting a load of 350 g), (b) polytetrafluoroethylene (PTFE), (c) rubbers, (d) wood and (e) carnelian. 7

8 Figure S9. There is no stripping lag process for the pristine PAA gels so that the crack can easily propagate along the interface without kinking or significantly deformation. Figure S10. Effects of various tensile strains on the resistance. Figure S11. The variation of LED bulb for undamaged, cut, and self-healed ionic gel in the electric circuit. 8

9 Figure S12. Time evolution of the electrical self-healing process for the conductive gel by the real-time relative resistance change measurements. Figure S13. Schematics of tensile-adhesion testing. 9