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Abstract:
The present work discusses the effects of reduced graphene oxide (rGO) on the nonlinear viscoelastic behavior, or the Payne effect, of silica/styrene-butadiene rubber compounds. The volume fraction of unmodified silica was constant, while the amount of rGO in these hybrid filler compounds varied. Dynamic-mechanical analysis (DMA) in strain sweep mode showed that adding a small quantity of rGO to the silica-filled compounds resulted in diminished network formation of unmodified silica as well as a reduced Payne effect and corresponding energy dissipation. The state of silica dispersion in the presence of rGO in the rubber matrix was predicted by calculating the work of adhesion in a three-component system and detected by scanning electron microscopy. It was observed that the dispersion of the unmodified silica was improved by the addition of only 0.25 or 0.5 phr rGO, which may be due to the improved silica-rubber interactions that occur during mixing and/or reduced silica flocculation after mixing, as measured by DMA in time sweep mode. The synergy between silica and small quantities of rGO (0.25 or 0.5 phr) resulted in an enhancement in mechanical strength (45%) and abrasion resistance (63%), as well as a reduction in heat build-up (23%). This hybrid system can be considered an alternative to silane modification of silica in green tire technology.

Abstract:
The present study discusses the effects of graphenic particles on the kinetics of sulfur vulcanization in styrene butadiene rubber composites. Using data obtained from a cure rheometer and fitted by an autocatalytic model, it was verified that graphenic particles follow our recently established catalytic-networking model for the effect of particles on the sulfur vulcanization of rubber, regardless of the type of particles. The magnitude of the catalytic and networking effects depends on surface chemistry and interfacial interactions of particles with rubber that can be tailored by the chemical reduction of graphene oxide. Accordingly, the reduction process decreased the catalytic effect due to the elimination of surface functional groups and increased the networking effect due to the enhancement of filler–rubber interactions and immobilization of rubber. The latter was verified by differential scanning calorimetry and bound rubber measurements.

Keywords:
graphene oxide, interfacial interactions, rubber composites, surface chemistry, vulcanization kinetics, wettability

Abstract:
The influence of reduction temperature on the electromechanical properties and actuation behavior of polydimethylsiloxane (PDMS) dielectric elastomer containing the thermally reduced graphene oxide (rGO) with different surface chemistry has been systematically investigated. A set of rGO nanosheets was prepared by thermal reduction of graphene oxide (GO) at four temperatures (150, 200, 300, and 400 °C). The dielectric permittivity, dielectric loss, and elastic modulus of PDMS composites were increased, while the electrical breakdown strength of composites was decreased with an increase of the reduction temperature of GO. A thermodynamic model applied for studying the electromechanical deformation and stability of PDMS/GO(rGO-x) dielectric elastomer composites showed that the optimum value of the break-point was observed in PDMS/rGO-300. It is shown for the first time that the variation of electromechanical instability and recovery behavior are attributed to the surface chemistry of rGOs. A critical reduction temperature is observed at 300 °C which can be considered as proper rGO nanosheets for electromechanical applications. By employing an equivalent circuit on impedance spectroscopy, the interfacial polarization is recognized as the dominant mechanism rather than the intrinsic polarization of the matrix and nanosheets. Noteworthy, PDMS composites containing rGO, reduced at higher temperatures, have more interfacial polarized charges at the interface.

Keywords:
Dielectric Elastomer ,Polymer Composite ,Graphene Oxide (GO),Thermally Reduced Graphene Oxide (rGO) ,Electromechanical Properties,Actuation Behavior,Electromechanical Instability

Abstract:
Various quantities of reduced graphene-oxide (rGO) were added into silica-filled styrene-butadiene rubber (SBR) to make hybrid-filler composites. The non-linear viscoelastic behavior and corresponding energy dissipation of silica/rGO hybrid-filler and silica-filled composites were compared. Dynamic-mechanical analysis (DMA) of the hybrid-filler composites in strain-sweep showed that adding small quantity of rGO results in diminished silica network and reduced storage and loss modulus in silica-filled composites. Moreover, the synergy between silica and small quantities of rGO results in reduction of heat build-up (23%). The hybridization of silica/rGO was done without surface modification. This hybrid-filler system can be considered as an alternative to silane-modification of silica in industry.