Effects of interfacial interaction on chain dynamics of rubber/graphene oxide hybrids: A dielectric relaxation spectroscopy study

Hybrids consisting of graphene oxide (GO) sheets and butadiene-styrene- vinyl pyridine rubber (VPR) were prepared by a co-coagulation process with different flocculants, hydrogen chloride and calcium chloride, in order to form two kinds of bonding interfaces, namely ionic bonding (HVPR) and hydrogen bonding (CaVPR) interfaces. To reveal the effects of interfacial interaction on the chain dynamics, the dielectric relaxation spectra of these hybrids have been investigated. The results show that all hybrids exhibit two distinct relaxation processes, segmental relaxation and interfacial relaxation. The concentration of GO has no impact on the segmental dynamics of CaVPR, but the segmental dynamics of HVPR slow down at 1.5 vol% of GO. Meanwhile, the segmental relaxation of HVPR is always a little faster than its CaVPR counterpart. In the temperature range of 5-35°C, a new relaxation mode, which is slower than the segmental relaxation and attributed to the interphase with restricted chain dynamics, has been observed for all the hybrids with a GO loading lower than 2.5 vol%. The interfacial relaxation time of HVPR decreases with decreasing GO concentration. However, in CaVPR it first decreases and then increases with decreasing GO concentration. Most interestingly, the interfacial relaxation of HVPR is slower than that for CaVPR. The dielectric strength (Δε), the calculated fragility parameter and the effective activation enthalpy of the interfacial chains in HVPR are always higher than those in CaVPR with the same GO concentration. All the evidence indicates the stronger interfacial interactions in HVPR than in CaVPR.