Supporting Information

Transcription

1 Supporting Information Knitted Fabrics made from Highly Conductive Stretchable Fibers Rujun Ma,, Jiyong Lee,, Dongmin Choi, Hyungpil Moon, and Seunghyun Baik*,, IBS Center for Integrated Nanostructure Physics (CINAP), Institute of Basic Science (IBS), Daejeon, , Korea Department of Energy Science, Sungkyunkwan University, Suwon, , Korea School of Mechanical Engineering, Sungkyunkwan University, Suwon, , Korea * 1

2 Figure S1 Fibers synthesized by wet spinning using different coagulants. Fibers synthesized by wet spinning using different coagulants are shown in Figure S1. The diameter was not uniform and ionic liquid was not contained inside the fiber except hexane. 2

3 Relative density calculation The relative density (RD) of composite fibers was calculated using Eq. (S1). (S1) where is the experimentally measured density of the fiber, and is the theoretical maximum density S1,S2. The was experimentally measured by the Archimedes method (Electronic densimeter MD-300S). The was calculated using Eq.(S2) assuming complete removal of the solvent during the wet spinning and curing process. The silver (Ag) particles, carbon nanotubes, ionic liquid, and PVDF-HFP in the initial mixture were assumed to be retained in the fiber without any loss. (S2) where m is the mass and v is the volume. The subscript indicates each material. 3

4 Conductivity simulation of the composite fiber using 3-dimensional percolation theory The conductivity of composites can be theoretically described using the power law relationship as shown in Eq. (S3) S3,S4. (S3) where σ is the electrical conductivity of the composite, is the electrical conductivity of the conductive filler, V f is the volumetric fraction of the conductive filler, V c is the volumetric fraction at percolation threshold, and s is the fitting exponent. The 100~150 nm Ag particles were considered as primary conductive fillers and modeled as spheres with a diameter of 120 nm (see inset of Figure 1a). The conductivity of Ag particles ( ) was 630,000 S cm -1 S5. V c was calculated using the average inter-particle distance model S3-S5. (S4) where D is the diameter of Ag particles, and is the distance between conductive fillers for the tunneling of electron. V c = was obtained by assuming = 15 nm S3,S4. The exponent s=1.63 was obtained by fitting the experimental data. There was a good agreement between the data and theoretical prediction as shown in Figure 2a. The stretching induces the volume change of the composite fiber (V matrix ) whereas the volume of Ag particles (V silver ) is fixed. This leads to the change of V f in Eq.(S3) S4. V matrix can be described as a function of the axial strain (ε) using Eqs. (S5~S8). / / (S5) 4

5 (S6) (S7) 1 1 (S8) where L 1 and D 1 are the length and diameter of the fiber before stretching, and L 2 and D 2 are the length and diameter of the fiber after stretching. The poisson s ratio in the radial direction was experimentally determined (ν = 0.243) by Eq. (S5). Finally, V f was calculated using Eq. (S9) S4. (S9) The simulated of the fiber as a function of is shown in Figure 2b (initial Ag particle concentration = 10.4 wt%, V silver = cm 3 ). The decreasing of the fiber with increasing could be well predicted by the theory. 5

6 Figure S2. Fibers with 4 different diameters (70, 100, 190, and 380 µm) were synthesized by changing the diameter of nozzles of wet spinning apparatus (100, 200, 310, and 500 µm). The 100~150 nm Ag particle concentration in the initial mixture was 8.5 wt% for all fibers. (a) SEM images. (b) The conductivities of fibers are shown as a function of tensile strain. As shown in Figure S2, the conductivity-tensile strain characteristics were similar for all 4 fibers although the diameter of fibers was different (70~380 µm). 6

7 Conductivity (S/cm) sample 1 sample 2 sample Tensile strain (%) Figure S3. The conductivities of three single fibers are shown as a function of tensile strain. The fibers were synthesized under identical conditions (Ag: 8.5 wt%). The conductivity-tensile strain characteristics were similar for all 3 fibers. 7

8 Figure S4 SEM images of fibers before and after stretching. (a) Fiber without the hot-rolling process (Ag: 7.4 wt%). (b) Hot-rolled fiber (Ag: 7.4 wt%). Figure S4 shows SEM images of fibers before and after stretching (0 and 150% strain). As shown in Figure S4a, the diameter of the fiber decreased after stretching due to the Poisson effect. The Ag particles were more uniformly embedded in the polymer matrix after the hot-rolling process as shown in Figure S4b. The increased distance between Ag particles along the length axis could be observed for both fibers after stretching. 8

9 Figure S5 Fabrics made from the conductive stretchable fiber. (a) Low and high magnification optical images of the plain weave fabric. (b) Low and high magnification optical images of the sparsely woven fabric after the hot-rolling process. Figure S5 shows plain weave fabrics made from the conductive stretchable fiber. However, the stretchability was not enhanced. 9

10 Figure S6 Schematics of the weft knitted fabric (purl stitch) before and after stretching. The schematics of the weft knitted fabric (purl stitch) were drawn using a 3D software (SketchUp). 10

11 Figure S7 A schematic of the dissembled robot finger. The distortion of a sensor frame was detected using 6 semiconductor strain guages when the robot finger-tip was touched by an object S6,S7. The quantitive information on the exerted force and moment was calculated by an embedded microprocessor (STMicroelectornics, STM32F103T6) in the finger-tip sensor cover using the data from 6 strain guages S6,S7. A detailed description of the robot finger was provided elsewhere S6. The processed signal was transmitted through the conductive stretchable fabric to the main controller via the CAN interface at a sampling rate of 100 Hz. Finally, the touch position information was analyzed using a customized software in the main controller. The joint was actuated by a DC motor with a 100:1 gear ratio, and its motion was controlled by a customized DC motor drive S6. 11

12 Figure S8. Optical microscopic images of the PDMS-coated fiber at 0 and 40 % tensile strain. The optical microscopic images of the PDMS-coated fiber before and after stretching are shown in Figure S8. The measured effective Poisson s ratio was

13 References S1 Kim, S. W., Khalil, K. A., Cockcroft, S. L., Hui, D. & Lee, J. H. Sintering behavior and mechanical properties of HA-X% mol 3YSZ composites sintered by high frequency induction heated sintering. Compos Part B-Eng 45, (2013). S2 Sridhar, I. & Fleck, N. A. Yield behaviour of cold compacted composite powders. Acta Mater 48, (2000). S3 Li, J. & Kim, J. K. Percolation threshold of conducting polymer composites containing 3D randomly distributed graphite nanoplatelets. Compos Sci Technol 67, (2007). S4 Chun, K. Y. et al. Highly conductive, printable and stretchable composite films of carbon nanotubes and silver. Nat Nanotechnol 5, (2010). S5 Park, M. et al. Highly stretchable electric circuits from a composite material of silver nanoparticles and elastomeric fibres. Nat Nanotechnol 7, (2012). S6 Jung, K. et al. Evaluation of fingertip F/T sensor for dexterous manipulation th International Conference on Ubiquitous Robots and Ambient Intelligence (URAI), (23-26 Nov. 2011). S7 Butterfass, J., Grebenstein, M., Liu, H. & Hirzinger, G. DLR-Hand II: Next Generation of a Dextrous Robot Hand. Proceedings of the 2001 IEEE International Conference on Robotics and Automation, (21-26 May 2001). 13