Connection-improved conductive network of carbon nanotubes in the rubber crosslink network

Transcription

1 Supporting Information Connection-improved conductive network of carbon nanotubes in the rubber crosslink network Lin Gan, Ming Dong, Ying Han, Yanfang Xiao, Lin Yang, Jin Huang* School of Chemistry and Chemical Engineering, Southwest University, No. 2, Tiansheng Road, Beibei District, Chongqing , China. Corresponding author * Jin Huang, huangjin2015@swu.edu.cn. Tel.: ; fax: S-1

2 1.TEM images of CNTs The dimeter of those kinds of CNTs was investigated by TEM and the diameters of these three CNTs were counted. Figure S1. TEM images of three kinds of CNTs (a) NC7000, (b) TNSM2, (c) TNSM3. 2. The critical exponent of the PDMS/NC7000 nanocomposites calculated by Statistics percolation theory Table S1. The critical exponent of the PDMS/NC7000 nanocomposites Crosslink density (mol/m 3 ) Critical exponent S-2

3 3. Crosslink density measured by DMA Figure S2. The cross-linking density of PDMS at different curing temperatures was measured by DMA The cross-link density is closely related to the elastic modulus of the elastomer. According to the theory of cross-linked networks, as the cross-linking density increases, the molecular chains become more compact and restrict the movement of the molecular chains. Therefore, the cross-linked polymer under certain stress produces less deformation and the modulus can be improved. In Roger Hagen's work 1, DMA data was used to calculate the crosslinking density of the rubber. Calculation formula as follows 2 : D = E 6RT (S1) Where E is the storage modulus, Pa, R is the gas constant, J/(mol K), T is absolute temperature, K. DMA test results showed in Fig. S3: S-3

4 Figure S3. The storage modulus (a) and Tan δ (b) of PDMS at different curing temperatures tested by DMA 4. Crosslink density measured by equilibrium swelling experiments Equilibrium swelling experiments is a classic method for testing crosslink density. The following formula can be used to calculate the crosslink density: ln D V (S2) 1 Where D is crosslink density, mol/m 3, χ is Flory-Huggins parameters, V 1 is solvent molar volume, ie toluene, ml / mol, φ is the volume fraction of polymer in the swollen body which could be calculated by: m m m (S3) In which ρ 1 refers to the solvent density, ρ 2 is the polymer density, m 0 is the mass before swelling, m is the mass after swelling. As we all known, χ is a parameter of polymer-solvent interaction and has been proved by many theories and experiments that it is not a constant in most cases and S-4

5 dependent on the volume fraction of the polymer. There was the formula for χ: (S4) By the above calculation method can be drawn at different curing temperatures PDMS crosslinking density. Figure S4. The cross-linking density of PDMS at different curing temperatures was measured by equilibrium swelling experiments S-5

6 5. Resistance at different points of the same sample surface (PDMS/CNT(NC7000) with the crosslink density of 182mol/cm 3 ) tested via a multimeter. Table S2. Resistance of PDMS/CNT(NC7000) with 0.5wt%, 1wt% CNTs at different points of samples sample 1(MΩ) 2(MΩ) 3(MΩ) 4(MΩ) 5(MΩ) Error bar(mω) PDMS/CNT-0.5% PDMS/CNT-1% Mechanical properties of PDMS/CNT (NC7000) at the crosslink density of 182 mol/cm 3 Figure S5. Mechanical properties of PDMS/CNT (NC7000) (a) Young s modulus, (b) Tensile strength, (c) the elongation at break S-6

7 7. The relationship between the resistance of PDMS/CNT composites and temperature Figure S6. The relationship between the resistance of PDMS/CNT composites and temperature of the PDMS/CNT nanocomposties that were cured at 70 o C and 150 o C The relationship between the resistance of PDMS/CNT composites and temperature was also measured with PDMS/CNT nanocomposties that were cured at 70 o C and 150 o C (shown in Fig. S6). Both their percolation values were 0.1 wt%. When the CNT content (0.12 wt%) was near percolation value of double-network structure, the resistance varied little. This result suggested that the connection between CNTs in PDMS crosslink network was stable at the percolation content of CNTs. In contrast, when the CNT content (0.3 wt% and 0.5 wt%) was much higher than the percolation value and was in the plateau region, the resistance can increase rapidly with the temperature. Those results indicated that the double-network structure can stabilize the conductive network and improve the connection between CNTs in the PDMS crosslink network. S-7

8 Reference 1. Hagen, R.; Salmen, L.; Stenberg, B., Effects of the Type of Crosslink on Viscoelastic Properties of Natural Rubber. J. Polym. Sci. Pol. Phys. 1996, 34, Saville, B.; Waston A. A. Structural Characterization of Sulfur-Vulcanized Rubber Networks. Rubber Chem. Technol. 1967, 40, Chassé, W.; Lang, M.; Sommer, J. U.; Saalwächter, K. Cross-Link Density Estimation of PDMS Networks with Precise Consideration of Networks Defects. Macromolecules 2012, 45, S-8