Friction controlled by ferroelectric polymer at β-phase PVDF/graphene van der Waals interfaces

Despite the rapid development in tribology, the frictional characteristics influenced by ferroelectric materials remain largely unexplored. Here, through first-principle calculations, we demonstrate that the interfacial electronic structures in polar β-phase poly(vinylidene fluoride) (PVDF)/graphene van der Waals (vdW) heterostructures can be effectively tuned by varying the thickness and polarization of ferroelectric polymer β-PVDF. Our potential energy surface (PES) calculations reveal that the sliding friction at β-PVDF/graphene interfaces can be modulated by altering the polarization of β-PVDF. Specifically, reversing the polarization of β-PVDF from upward to downward, pointing towards graphene, results in an enhancement of the PES amplitude and the frictional shear strength. Additionally, we observe a significant increase in energy corrugation of the PES at polar β-PVDF/graphene sliding interfaces as the number of polar β-PVDF molecular layer increases. As a comparison, no thickness-dependent friction behavior is observed in non-polar α-PVDF/graphene interfaces. This tunable frictional behavior is attributed to the controlled internal electric field within β-PVDF, which is governed by its thickness and polarization. Then, the internal electric field substantially influences the interfacial electronic structures, leading to the tunable PES that governs the friction properties. Our study reveals the potential of ferroelectric polymers for controlling friction, offering significant promise for novel tribological applications.