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-principles 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 the 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 increase in the PES amplitude and frictional shear strength. Additionally, we observe a significant increase in the energy corrugation of the PES at the polar β-PVDF/graphene sliding interfaces as the number of polar β-PVDF molecular layers increases. In comparison, no thickness-dependent friction behavior is observed at the nonpolar 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. The internal electric field substantially influences the interfacial electronic structures, leading to a 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.