Dynamical scaling of coarse-grained ionic liquid under shear flow

Abstract

Room-temperature ionic liquids exhibit unique physicochemical properties, making them ideal for processing materials under non-equilibrium conditions. Taking shear flow as a representative case, we use molecular dynamics simulations to examine the shear dependence of both all-atom and coarse-grained (CG) models of [C4mim]+[PF6]−. Both models show comparable trends in structural distortion and molecular orientation with increasing shear, although the CG model exhibits milder responses due to its reduced resolution. In line with our earlier observation of a low critical shear rate marking the onset of shear-induced changes in structure and dynamics, the present study identifies a high critical rate beyond which the CG dynamical rescaling plateaus. For example, the CG model’s speed-up factor, ∼3 at equilibrium for distinct dynamical properties, systematically decreases with shear and plateaus at ∼1.5 beyond the high critical shear rate. The same critical shear is observed across dynamical observables that probe distinct timescales, and for both cations and anions, marking the regime where external forces dominate, and rendering the CG dynamical rescaling insensitive to specific molecular interactions. These findings clarify the fidelity and limitations of CG models under non-equilibrium conditions and guide their use for efficient investigations of ionic-liquid-based processes.