Interfacial Interactions in a Model Composite Material: Insights into α → β Phase Transition of the Magnetite Reinforced Poly(Vinylidene Fluoride) Systems by All-Atom Molecular Dynamics Simulation

Poly(vinylidene fluoride) (PVDF) is identified as a piezoelectric polymer and has attracted a great deal of attention for various applications. It has been proved experimentally that adding Fe₃O₄nanoparticles improves β phase contribution, which has the highest piezoelectric coefficient among all the PVDF crystalline forms. Here, we used molecular dynamics simulation to investigate the physical properties and conformational changes of α-PVDF in the presence of magnetite slabs with different surface chemistry. The results show that H-bond interactions between OH groups on the surface of magnetite and PVDF chains stabilize the system and cause the α → β phase transition of the polymer. Moreover, replacing 20% of hydroxyl groups by carboxylic acids reduces the extent of the phase transition. In turn, hexanoic acid grafting induces the highest boosting effect, among all the carboxylic acid modifications of the magnetite, and the interaction of PVDF chains with the magnetite slab increases as the hexanoic acid:OH ratio decreases.