Nonequilibrium domain formation by pressure fluctuations

Abstract

Fluctuations in thermal many-particle systems reflect fundamental dynamical processes in both equilibrium and nonequilibrium (NEQ) physics. In NEQ systems \cite{ritort} fluctuations are important in a variety of contexts ranging from pattern formation \cite{hohenberg,vdbroeck} to molecular motors \cite{schaller,kierfeld,narayan,prost}. Here, we address the question if and how fluctuations may be employed to characterize and control pattern formation in NEQ nanoscopic systems. We report computer simulations of a liquid crystal system of prolate molecules (mesogens) sandwiched between flat walls, and exposed to a time-dependent external field. We find that a switchable smectic domain forms for sufficiently high frequency. Although pressure and temperature are too low to induce an equilibrium smectic phase, the fluctuations of the pressure in the NEQ steady state match the pressure fluctuations characteristic of the equilibrium smectic phase. Furthermore, the {\it wall-normal} pressure fluctuations give rise to a {\it tangential} "fluctuation-vorticity" tensor that specifies the symmetry-breaking direction of the smectic layers. Our calculations demonstrate a novel method through which nanomaterials with a high degree of molecular order may be manufactured in principle.