Field-induced alignment dynamics in suspensions of polarizable rods.

Abstract

Fluids composed of polarizable particles exhibit tunable structural and functional properties when subjected to external electric fields, as the particles tend to reorient and align along the field direction. This field-induced anisotropy leads to pronounced changes in macroscopic properties, rendering these systems highly relevant for applications in nanotechnology. Understanding the dynamics of their response to external fields is crucial for designing responsive materials with fast and controllable actuation. In this work, we employ molecular simulation to study the behavior of suspensions of polarizable rodlike particles under the action of a uniform electric field, with particular attention given to the transient dynamics associated with the switching on and off of the field. Induced dipoles are modeled by independently varying charge magnitude and field strength, yielding a variable effective polarizability. The induced dipole moment of each rod is treated as an effective, externally controlled parameter, and collective polarization effects arising from local electric fields generated by neighboring particles are not explicitly included. The system is studied in a dense regime, where interparticle interactions play a significant role and are implicitly controlled via pressure. We investigate how the characteristic response time depends on the competition between thermal motion and electric forces across a range of temperatures and field strengths. Our results reveal a rich dynamical behavior: at low to moderate field intensities, increasing the temperature significantly reduces the response time, as thermal agitation facilitates reorientation. However, beyond a critical field strength, the response time plateaus, becoming effectively temperature-independent. This saturation indicates a regime where the aligning torque from the field dominates over thermal fluctuations, setting a lower bound for how fast the system can respond. More specifically, we show that the alignment dynamics cannot be inferred from single-particle behavior alone, but emerges from a nontrivial interplay of field-induced dipolar torques, thermal fluctuations, and steric interactions at finite density, producing strongly temperature-dependent and nonlinear trends in both the nematic order parameter and response times.