Polarizability in graphene increases nanoscale friction by amplifying interfacial energy corrugation

Early classical molecular dynamics simulations utilizing non-polarizable force fields estimated the water-graphene friction coefficient to be ∼1.4×104Nsm-3. However, recent studies have demonstrated that electric polarization and quantum effects beyond the Born-Oppenheimer approximation are crucial for accurately describing nanoscale friction. Observations from recent models suggest that incorporating electric polarization leads to higher predicted friction coefficients. This study evaluates the water-graphene friction coefficient using the SWM4-NDP polarizable water model interacting with both polarizable and non-polarizable graphene models. The friction coefficient is initially computed via equilibrium molecular dynamics (EMD) utilizing the Green-Kubo relation. Given the ongoing debate regarding the application of this methodology, the friction coefficient of the fully polarizable system is also evaluated using non-equilibrium molecular dynamics. Our EMD calculations show that incorporating explicit electric polarization in graphene increases the interfacial friction coefficient by 23%. Using enhanced-sampling simulations, we found that the free-energy landscape of a water monomer is more corrugated on polarizable graphene compared to the non-polarizable model. Quantitative analysis of these landscapes reveals that the friction increase caused by incorporating explicit polarization arises exclusively from a larger lateral force amplitude, which results directly from enhanced energetic surface corrugation.