High Performance Natural Rubber Composites with Well-Organized ...
Supporting Information:
High Performance Natural Rubber Composites with Well-Organized Interconnected Graphene Networks for Strain-Sensing Application Bin Dong,† Sizhu Wu,†,‡ Liqun Zhang, †,‡ and Youping Wu*,†,‡ †
State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029, China
‡
Beijing Engineering Research Center of Advanced Elastomers, Beijing University of Chemical Technology, Beijing 100029, China
* Corresponding author. Tel.: +86-10-64442621; Fax: +86-10-64456158. E-mail address: [email protected] (Youping Wu).
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S1. Chemical Structure of Gelatin
Figure S1. Chemical structure of gelatin.1,2 S2. Reduction Level of Gel-RGO by HHA
Figure S2. Electrical conductivities of Gel-HHA-RGO with different RHHA/GO. For fabrication of highly conductive RGO, hydrazine hydrate (HHA) was further used to reduce Gel-RGO. However, considering the deoxidation reaction between HHA and gelatin molecules, the concentration of HHA on the reduction level of Gel-RGO was detailedly investigated. The mass ratio of HHA to GO (RHHA/GO) was varied from 0:1 to 50:1. The electrical conductivities of Gel-HHARGO with different reduction levels were measured. As shown in Figure S2, the electrical conductivity of resulting Gel-HHA-RGO increased with increasing RHHA/GO. However, when the RHHA/GO exceeded 10:1, the electrical conductivity was not changed with RHHA/GO, indicating the complete reaction between HHA and Gel-RGO.
S2
S3. Energy Dispersive X-ray Spectra (EDX) of GO and Gel-HHA-RGO
Figure S3. EDX for element analysis and its corresponding element weight and atom percentage content of (a) GO and (b) Gel-HHA-RGO. S4. TGA Curves
Figure S4. TGA curves of gelatin, GO, HHA-RGO, and Gel-HHA-RGO.
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S5. Self-Assembly Between Gel-HHA-RGO Nanosheets and NRL Particles
Figure S5. TEM micrographs of Gel-HHA-RGO and NRL particles.
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S6. Dynamic Viscoelastic Properties of Gel-HHA-RGO Composites
Figure S6. (a) Plots of loss modulus E'' versus temperature for Gel-HHA-RGO/NR composites; (b) Loss factor tan δ (tan δ =E''/E') versus temperature for Gel-HHA-RGO/NR composites. Commonly, the definition of glass transition temperature (denoted as Tg,1) as the temperature at which loss factor tan δ reaches its maximum is widely adopted in most literatures.3 The temperature dependence of tan δ of NR composites with various RGO content are presented in Figure S6b. Notable differences in tan δ peak shape and intensity were observed for all the samples. In accordance with other graphene/rubber composites, the reduction in peak intensity with increase in RGO content implied the restricted rubber chain mobility due to the strong interfacial interactions between RGO and NR. Obviously, the Tg,1 gradually decreased with increasing RGO content. However, some arguments were in favor of another fact that it was more suitable to definite the glass transition temperature (denoted as Tg,2) as the temperature at which loss modulus E'' (reflecting segmental relaxation process) exhibited a local maximum.3-5 Reasons can be ascribed that Tg,1 was influenced not only by local segmental mobility, but also by the filler reinforcement effects on both E' and E''.4 However, Tg,2 was only determined by the segmental dynamics of rubber chain. The temperature dependence of E'' with various RGO content are presented in Figure S6a. It was obvious to find that the E'' transition peak was not appreciably affected by the incorporation of RGO, and there was almost no change in Tg,2. The decrease in Tg,1 can be explained that the incorporation of RGO increased both E' and E'' in rubbery region; however, the E' was affected more obviously at the glass-to-rubber softening transition region, which was induced by the nature of the formed nanofiller network. In other words, the change in Tg,1 was mainly caused by the construction of interconnected RGO structure which resulted in obvious variations in E' at the transition region. In fact, the local segmental dynamics of NR composites was not influenced by the incorporation of RGO nanosheets. S5
S7. Electrical Properties of Gel-HHA-RGO/NR Composites Prepared by Latex Co-Coagulation
Figure S7. Electrical conductivities of Gel-HHA-RGO/NR composites prepared by latex compounding and co-coagulation.
Figure S8. TEM graphs of Gel-HHA-RGO/NR composites prepared by latex co-coagulation. The Gel-HHA-RGO filled NR composites were also prepared by latex compounding and cocoagulation, where the curing agents were incorporated into NR by two-roll mill processing. The electrical and thermal conductivities of NR composites were measured and presented in Figure S7. It clearly suggested that there was very limited enhancement in electrical conductivity, compared with the corresponding properties of NR composites prepared by solution-casting method. The slight improvement in electrical properties can be explained that latex co-coagulation would cause serious aggregation of RGO nanosheets; meanwhile the two-roll mill treatment disordered and broke down the interconnected RGO network, resulting in a dramatic decrease in electrical conductivity. The typical TEM graphs are presented in Figure S8. Serious aggregation of nanofiller and absence of interconnected RGO network were observed. S6
S8. Electrical Response of Bending Movements of Index Finger Joints
Figure S9. Further mensurements of electrical response of strain sensor for motion detection of fingers (90o bending angle). REFERENCES (1) Peña, C.; De la Caba, K.; Eceiza, A.; Ruseckaite, R.; Mondragon, I. Enhancing water repellence and mechanical properties of gelatin films by tannin addition. Bioresource Technol. 2010, 101, 6836. (2) Ge, Y.; Wang, J.; Shi, Z.; Yin, J. Gelatin-assisted fabrication of water-dispersible graphene and its inorganic analogues. J. Mater. Chem. 2012, 22, 17619. (3) Rieger, J. The glass transition temperature Tg of polymers-comparison of the values from differential thermal analysis (DTA, DSC) and dynamic mechanical measurements (torsion pendulum). Polym. Test. 2001, 20, 199. (4) Robertson, C. G.; Lin, C. J.; Rackaitis, M.; Roland, C. M. Influence of particle size and polymerfiller coupling on viscoelastic glass transition of particle-reinforced polymers. Macromolecules 2008, 41, 2727. (5) Robertson, C. G.; Roland, C. M. Glass transition and interfacial segmental dynamics in polymerparticle composites. Rubber Chem. Technol. 2008, 81, 506.
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High Performance Natural Rubber Composites with Well-Organized Interconnected Graphene Networks for Strain-Sensing Application Bin Dong,† Sizhu Wu,†,‡ Liqun Zhang, †,‡ and Youping Wu*,†,‡ †
State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029, China
‡
Beijing Engineering Research Center of Advanced Elastomers, Beijing University of Chemical Technology, Beijing 100029, China
* Corresponding author. Tel.: +86-10-64442621; Fax: +86-10-64456158. E-mail address: [email protected] (Youping Wu).
S1
S1. Chemical Structure of Gelatin
Figure S1. Chemical structure of gelatin.1,2 S2. Reduction Level of Gel-RGO by HHA
Figure S2. Electrical conductivities of Gel-HHA-RGO with different RHHA/GO. For fabrication of highly conductive RGO, hydrazine hydrate (HHA) was further used to reduce Gel-RGO. However, considering the deoxidation reaction between HHA and gelatin molecules, the concentration of HHA on the reduction level of Gel-RGO was detailedly investigated. The mass ratio of HHA to GO (RHHA/GO) was varied from 0:1 to 50:1. The electrical conductivities of Gel-HHARGO with different reduction levels were measured. As shown in Figure S2, the electrical conductivity of resulting Gel-HHA-RGO increased with increasing RHHA/GO. However, when the RHHA/GO exceeded 10:1, the electrical conductivity was not changed with RHHA/GO, indicating the complete reaction between HHA and Gel-RGO.
S2
S3. Energy Dispersive X-ray Spectra (EDX) of GO and Gel-HHA-RGO
Figure S3. EDX for element analysis and its corresponding element weight and atom percentage content of (a) GO and (b) Gel-HHA-RGO. S4. TGA Curves
Figure S4. TGA curves of gelatin, GO, HHA-RGO, and Gel-HHA-RGO.
S3
S5. Self-Assembly Between Gel-HHA-RGO Nanosheets and NRL Particles
Figure S5. TEM micrographs of Gel-HHA-RGO and NRL particles.
S4
S6. Dynamic Viscoelastic Properties of Gel-HHA-RGO Composites
Figure S6. (a) Plots of loss modulus E'' versus temperature for Gel-HHA-RGO/NR composites; (b) Loss factor tan δ (tan δ =E''/E') versus temperature for Gel-HHA-RGO/NR composites. Commonly, the definition of glass transition temperature (denoted as Tg,1) as the temperature at which loss factor tan δ reaches its maximum is widely adopted in most literatures.3 The temperature dependence of tan δ of NR composites with various RGO content are presented in Figure S6b. Notable differences in tan δ peak shape and intensity were observed for all the samples. In accordance with other graphene/rubber composites, the reduction in peak intensity with increase in RGO content implied the restricted rubber chain mobility due to the strong interfacial interactions between RGO and NR. Obviously, the Tg,1 gradually decreased with increasing RGO content. However, some arguments were in favor of another fact that it was more suitable to definite the glass transition temperature (denoted as Tg,2) as the temperature at which loss modulus E'' (reflecting segmental relaxation process) exhibited a local maximum.3-5 Reasons can be ascribed that Tg,1 was influenced not only by local segmental mobility, but also by the filler reinforcement effects on both E' and E''.4 However, Tg,2 was only determined by the segmental dynamics of rubber chain. The temperature dependence of E'' with various RGO content are presented in Figure S6a. It was obvious to find that the E'' transition peak was not appreciably affected by the incorporation of RGO, and there was almost no change in Tg,2. The decrease in Tg,1 can be explained that the incorporation of RGO increased both E' and E'' in rubbery region; however, the E' was affected more obviously at the glass-to-rubber softening transition region, which was induced by the nature of the formed nanofiller network. In other words, the change in Tg,1 was mainly caused by the construction of interconnected RGO structure which resulted in obvious variations in E' at the transition region. In fact, the local segmental dynamics of NR composites was not influenced by the incorporation of RGO nanosheets. S5
S7. Electrical Properties of Gel-HHA-RGO/NR Composites Prepared by Latex Co-Coagulation
Figure S7. Electrical conductivities of Gel-HHA-RGO/NR composites prepared by latex compounding and co-coagulation.
Figure S8. TEM graphs of Gel-HHA-RGO/NR composites prepared by latex co-coagulation. The Gel-HHA-RGO filled NR composites were also prepared by latex compounding and cocoagulation, where the curing agents were incorporated into NR by two-roll mill processing. The electrical and thermal conductivities of NR composites were measured and presented in Figure S7. It clearly suggested that there was very limited enhancement in electrical conductivity, compared with the corresponding properties of NR composites prepared by solution-casting method. The slight improvement in electrical properties can be explained that latex co-coagulation would cause serious aggregation of RGO nanosheets; meanwhile the two-roll mill treatment disordered and broke down the interconnected RGO network, resulting in a dramatic decrease in electrical conductivity. The typical TEM graphs are presented in Figure S8. Serious aggregation of nanofiller and absence of interconnected RGO network were observed. S6
S8. Electrical Response of Bending Movements of Index Finger Joints
Figure S9. Further mensurements of electrical response of strain sensor for motion detection of fingers (90o bending angle). REFERENCES (1) Peña, C.; De la Caba, K.; Eceiza, A.; Ruseckaite, R.; Mondragon, I. Enhancing water repellence and mechanical properties of gelatin films by tannin addition. Bioresource Technol. 2010, 101, 6836. (2) Ge, Y.; Wang, J.; Shi, Z.; Yin, J. Gelatin-assisted fabrication of water-dispersible graphene and its inorganic analogues. J. Mater. Chem. 2012, 22, 17619. (3) Rieger, J. The glass transition temperature Tg of polymers-comparison of the values from differential thermal analysis (DTA, DSC) and dynamic mechanical measurements (torsion pendulum). Polym. Test. 2001, 20, 199. (4) Robertson, C. G.; Lin, C. J.; Rackaitis, M.; Roland, C. M. Influence of particle size and polymerfiller coupling on viscoelastic glass transition of particle-reinforced polymers. Macromolecules 2008, 41, 2727. (5) Robertson, C. G.; Roland, C. M. Glass transition and interfacial segmental dynamics in polymerparticle composites. Rubber Chem. Technol. 2008, 81, 506.
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