Supporting Information Programmable and Bidirectional Bending of Soft Actuators Based on Janus Structure with Sticky Tough PAA-clay Hydrogel Lei Zhao, Jiahe Huang, Yuancheng Zhang, Tao Wang,*, Weixiang Sun, and Zhen Tong*,, Research Institute of Materials Science and State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China. *E-mail: E-mail: fetwang@scut.edu.cn (T. Wang) E-mail: mcztong@scut.edu.cn (Z. Tong) Tel: (86)-20-87112886; Fax: (86)-20-87110273 1
Figure S1. Photo of the as-prepared PAA-clay hydrogel. 2
The Fourier transformed infrared (FT-IR) spectra of dried and milled hydrogel samples were detected by a Nicolet 6700 spectrometer with the conventional KBr pellet method at room temperature. Monomer AA and clay were also measured for comparison. The energy-dispersive X-ray spectroscopy (EDS) was obtained using a Phenom Pro desktop scanning electron microscope (SEM) operated at 15.0 kv. Hydrogel samples were quickly frozen in liquid nitrogen and then freeze-dried for 3 d to remove water thoroughly. Before observation, the gel samples were carefully sliced and sputtered with gold. A AA B Au Transmittance (%) clay 1702 1635 1712 1613 1432 1297 1241 1410 1455 1250 1033 1162 2000 1800 1600 1400 1200 1000 800 600 Wavenumber (cm -1 ) C O Si Au Cl Fe F- A4C2 A4B3 0 2 4 6 8 10 12 14 Energy (kev) Figure S2. (A) FT-IR spectra of the hydrogel, clay and monomer AA. (B) Energy-Dispersive X-ray Spectroscopy (EDS) of the indicated hydrogels. For the gel, disappearance of the ν C=C at 1635 and 1613, and appearance of ν C-O at 1250 and 1162 with the ν C=O at 1712 prove the formation of PAA. 1 The broad shoulder peak around 1050 of the hydrogel indicates the presence of ν Si-O in the hydrogel. The existence of Si element in the EDS spectra of A4C2 and gels confirms the presence of the clay in these hydrogels. While the appearance of Fe and Cl signals in the F- gel verifies the existence of Fe 3+ in the hydrogel after the immersing treatment. 3
Dynamic moduli were measured with a stress controlled rheometer AR-G2 using a parallel plate with diameter of 25 mm. The angular frequency ω ranged 0.1 100 rad/s at a strain of 0.1% for the frequency sweep. The effective network chain density N was calculated from G e = NRT, where G e, R and T were the equilibrium shear modulus taken from the plateau of storage modulus G', gas constant and absolute temperature, respectively. 2-3 10 5 A 50 40 B Effective network chain density N Molecular weight between cross-linkers M c 60 50 G',G'' (Pa) 10 4 10 3 A4B3 F- N (mol/m 3 ) 30 20 10 40 30 20 10 Mc /103 (g/mol) 10-1 10 0 10 1 10 2 ω (rad/s) 0 A4B3 F- 0 Figure S3. (A) Storage modulus G' (solid symbols) and loss modulus G" (open symbols) of the indicated PAA hydrogels at strain amplitude of 0.1% and 25 C, the F- gel was gained by immersing in FeCl 3 /HCl solution for 5 h; (B) effective network chain density N of the hydrogels. The molecular weight between cross-linkers M c was estimated as M c = ρ*/n, where ρ* was the polymer density in the hydrogel calculated from the density of pure PAA (1.22 g/cm 3 ) 4 and volume fraction of PAA in the as-prepared hydrogel (ca. 0.23). 4
Stress (MPa) 4 2 0.1 M HCl 0.2 M HCl 0.3 M HCl 0.4 M HCl 0 0 1000 2000 Strain (%) Figure S4. Stress-strain curves of the hydrogel after immersed in the indicated FeCl 3 -HCl solutions for 5 h. Figure S5. The bending and recovery actuation of the bilayer hydrogel immersed in the indicated solutions. 5
Figure S6. Schema of designed assembly of multilayer hydrogel consisting of F-PAA gel (yellow) and PAA gel (light blue) strips for presenting the word hydrogel. References: (1) Otsu, T.; Quach, L. Head-to-head vinyl polymers. III. Preparation and characterization of head-to-head poly(acrylic acid) and its esters. Journal of Polymer Science: Polymer Chemistry Edition 1981, 19, 2377-2389. (2) Wang, T.; Liu, D.; Lian, C.; Zheng, S.; Liu, X.; Tong, Z. Large Deformation Behavior and Effective Network Chain Density of Swollen Poly(N-isopropylacrylamide)-Laponite Nanocomposite Hydrogels. Soft Matter 2012, 8, 774-783. (3) Xiong, L.; Hu, X.; Liu, X.; Tong, Z. Network Chain Density and Relaxation of in situ Synthesized Polyacrylamide/Hectorite Clay Nanocomposite Hydrogels with Ultrahigh Tensibility. Polymer 2008, 49, 5064-5071. (4) James, M. E. Polymer data handbook, Oxford University Press: Oxford, 1999. 6