The shape memory and interface properties of graphene oxide enforced poly ( L -lactide-co- ɛ -caprolactone) by molecular dynamics simulation

Abstract This paper aims to explore the mechanism underlying the shape memory properties of poly ( L -lactide-co- ɛ -caprolactone) with graphene oxide (GO) modified by the hydroxyl functional groups. The interface performance has a particularly crucial impact on the performance of composite materials. By molecular dynamics method, the effect of different hydroxyl coverage of GO on the shape memory properties and the interface bonding properties is revealed. In the uniaxial tensile test of shape memory, the recovery rate in the direction parallel to GO surface increases with increasing hydroxyl coverage. There is a critical value near 7.5% hydroxyl coverage in the perpendicular direction (to GO surface) that causes the fixation rate and recovery rate to reach a relatively ideal state. In the interfacial separation of GO and polymer, the maximum pull-out forces increase with increasing hydroxyl coverage of GO in glass state and rubber state. The maximum force in the composite without oxygen is apparently lower than the ones with oxygen. Comparing the pull-out process at the glass and rubber states, the interface property at the glass state is obviously higher than that at the rubber state. The mechanical adhesion of the functional groups on the surface of graphene and the polymer plays an obvious role at high temperatures. Therefore, the functional group coverage rate is conducive to the shape recovery of the composite materials at high temperatures. The presence of graphene in the composite material with unmodified graphene surface will hinder the shape recovery of the polymer. These findings provide an important reference for the design of graphene-oxide composites.