Supporting Information

Transcription

1 Supporting Information All Solid State Carbon Nanotube Torsional and Tensile Artificial Muscles By Jae Ah Lee, Youn Tae Kim, Geoffrey M. Spinks, Dongseok Suh, Xavier Lepró, Marcio D. Lima, Ray H. Baughman and Seon Jeong Kim*, Center for Bio-Artificial Muscle and Department of Biomedical Engineering, Hanyang University, Seoul , Korea IT Fusion Technology Research Center and Department of IT Fusion Technology, Chosun University, Gwangju , Korea Intelligent Polymer Research Institute, ARC Centre of Excellence for Electromaterials Science, University of Wollongong, Wollongong, NSW, 2522, Australia Department of Energy Science, Sungkyunkwan University, Suwon , Korea The Alan G. MacDiarmid NanoTech Institute, University of Texas at Dallas, Richardson, TX 75083, USA Experimental Methods Materials: Well-aligned MWNT sheets were drawn from a MWNT forest that was grown on a Si wafer by using the previously reported chemical vapor deposition. 16 Tetraethyl ammonium tetrafluoroborate (TEABF 4, M w : g/mol), polyvinyl alcohol (PVA, Mw 146, ,000), propylene carbonate (PC, anhydrous, 99.7%), ethylene carbonate (EC) 1

2 and poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-co-HFP, M w : ~455,000, average M n ~110,000, pellets) were purchased from Sigma-Aldrich (USA). 2N sulfuric acid solutions (1M H 2 SO 4 ) were purchased from Daejung Chemicals (South Korea). Preparation of organic-based solid gel electrolyte: Acetone (30 g) and PVdF-co-HFP (3 g) were mixed using a stirring bar for 2 hours at ~60 C in an oil bath. The concentration of PVdF-co-HFP/acetone was 10 wt%. Organic electrolyte solution was prepared by dissolving 1 M TEABF 4 (6.52 g) in PC (30 ml) using a stirring bar for 30 min. PVdF-co-HFP/acetone and TEABF 4 /PC solutions were mixed at a ratio of 1:3. Preparation of aqueous-based solid gel electrolyte: Water (30 ml) and sulfuric acid (1.67 ml) were mixed using a stirring bar for 10 minutes in a 50 ml glass bottle (1 M sulfuric acid solution). Three grams of PVA (M w : 146, ,000) was added to the solution, and the mixture was then stirred for 1h at ~90 C. This solution was deposited and dried, as described above, to obtain the solid gel electrolyte. Fabrication of non-coiled yarns and torsional artificial muscle: Non-coiled yarns were prepared by twist insertion in a ~2 cm wide MWNT sheet, using an inserted twist of 12,000 to 15,000 turns/meter (based on initial sheet length), to generate a ~29 µm diameter yarn. After twist insertion, both ends of two identical yarns (the muscle anode and cathode) were fixed to a glass slide using double-sided tape, so that the yarns were parallel and closely separated. A copper wire was attached to an end of each yarn by using silver paste, and then the interconnects were coated with epoxy adhesive to ensure reliable electrical and mechanical connection between the copper wires and the MWNT yarn electrodes. The two parallel yarns were then dipped into the mixed organic-based solid gel electrolyte solution for min. After drying, the two parallel yarns (now infiltrated and coated with solid gel 2

3 electrolyte) were plied together and coated with organic-based solid gel electrolyte again to form the final torsional actuator. Fabrication of coiled yarns and tensile artificial muscle: Coiled yarn was fabricated from non-coiled yarn by inserting sufficient additional twist to provide complete yarn coiling. Thirty MWNT sheets, which were 6-7 mm wide, were stacked and then twisted using a motor. A constant load was applied to the twisted yarns while inserting additional twist until the yarn contracted to 30% 40% of its original length, reaching a coiled diameter of ~95 µm. Conversion of the two segments of coiled yarn to a plied yarn containing coiled anode and cathode that are infiltrated and coated with electrolyte was conducted analogously to the above case of for fabrication of torsional muscles. Characterization: Electrochemical measurements deployed a Gamry instrument (Reference 600 TM Potentiostat/Galvanostat), wherein the reference and counter electrode were combined to contact with one yarn electrode and the working electrode was contacted to the other yarn electrode to perform symmetric two-electrode analysis. A 30 frames/s movie camera was used to record paddle rotation from images taken parallel to the rotation axis. Tensile actuation stroke was measured using a non-contact linear displacement sensor (LD 701), which can sense metal targets, puchased from Omaga. About 20 training cycles were performed before the start of muscle characterization. Cross-sections for SEM imaging analysis were prepared by ion milling a 2-plied electrolyte infiltrated-coiled MWNT yarn in a Focus Ion Beam (FIB, FEI Nova 200) using ion currents ranging from 7.0 to 0.5 na. 3

4 Figure S1. SEM images at different magnifications (revealed by ion milling) of the crosssection of a plied, coiled yarn that provides tensile actuation, which shown yarn filling with the PVA/H 2 SO 4 gel electrolyte. 4

5 Figure S2. (a) Rotation and angular velocity versus time driven by a 0.8Hz, 5 V square-wave voltage with 50% duty cycle. (b) Maximum rotation speed (dark solid squares) and the peak torque versus applied square-wave voltage (2.5, 3, 4, 5V) for a two-ply, twist-spun, ZS MWNT yarn that is impregnated with PVDF-co-HFP/TEABF 4 /PC solid gel electrolyte. 5

6 Figure S3. (a) Tensile actuation in air as a function of time for 100 actuation cycles of the plied, coiled muscle of Figure 1h when driven by a 1 V square wave-voltage to lift an 11 MPa load. (b,c) The first 20 and last 20 actuator strokes of (a) are pictured using an expanded time scale. The electrolyte in the plied identical yarn electrodes in the muscle is PVA/H 2 SO 4. 6

7 Figure S4. The dependence of tensile stroke on time for different applied loads (7.4, 10.1, and 17.8 MPa) and an applied square-wave potential of 2.5 V. The electrolyte used was PVA/H 2 SO 4. 7

8 Figure S5. (a-e) The time dependence of tensile stroke for a 1 V applied square-wave pulse that is between 5s and 40s long. The electrolyte used was PVA/H 2 SO 4 and the applied tensile stress was 11 MPa. Note that the tensile stroke is independent of pulse length for pulses that are 20s or longer. 8

9 Figure S6. Retention of initial capacitance during electrochemical cycling of the tensile (a) and torsional (b) muscles. The insets provide the CV cycles used to obtain capacitances. 9

10 Table S1. Summary of our torsional and tensile actuation results and comparison with other artificial muscle systems providing both torsional and tensile actuation. Material CNT yarn BM500 series piezoelectric material NiTiCu shape memory alloy CNT yarn CNT/polymer hybrid yarn Input stimuli 5V/2.5V square wave (2-electrode electrochemical, in solid electrolyte) ~32V/mm (electrical impedance) 200 o C (thermal) 5 V square wave (3 electrode electrochemical, in liquid electrolyte) 40 V/cm / 15 V/cm (electro-thermal) Torsional Stroke/ Tensile Contraction 53 o /mm / 1.3% o /mm / -N/A o /mm / 3% 250 o /mm / ~1% 17.4 o /mm / ~10% Ratio of current results to previous studies -N/A- 6,625 times / -N/A- 350 times / 0.4 times 0.21 times / 1.3 times 3.0 times / 0.13 times Ref. In this paper [13] [12] [4] [11] REFERENCES (4) Foroughi, J.; Spinks, G. M.; Wallace, G. G.; Oh, J.; Kozlov, M. E.; Fang, S.; Mirfakhrai, T.; Madden, J. D. W.; Shin, M. K.; Kim, S. J.; Baughman, R. H. Science 2011, 334, (11) Lima, M. D.; Li, N.; Andrade, M. J. D.; Fang, S.; Oh, J.; Spinks, G. M.; Kozlov, M. E.; Haines, C. S.; Suh, D.; Foroughi, J.; Kim, S. J.; Chen, Y.; Ware, T.; Shin, M. K.; Machado, L. D.; Fonseca, A. F.; Madden, J. D. W.; Voit, W. E.; Galvão, D. S.; Baughman, R. H. Science 2012, 338, (12) Keefe, A. C.; Carman, G. P. Smart Mater. Struct. 2000, 9, (13) Kim, J.; Kang, B. Smart Mater. Struct. 2001, 10, (16) Zhang, M.; Atkinson, K. R.; Baughman, R. H. Science 2004, 306,