Electric birefringence of flexible polymers in high fields: Brownian dynamics simulation

Abstract

The dynamics of polyelectrolytes and other orientable polymers can be followed experimentally by electric birefringence. In this work, we examine the steady state and transient behavior of polymer chains in electric fields with a Brownian dynamics simulation. The polymers are modeled as bead‐spring chains with finitely extensible nonlinear elastic springs. Two models of the interaction between the electric field and the polymer chains are examined. The two models are a local mechanism which acts on individual chain segments, and a global mechanism which depends on the conformation of the entire chain. Steady‐state birefringence vs field strength results indicate that both mechanisms have an apparent coil‐stretch transition at some critical field strength. Observation of the steady‐state conformation of these chains reveals that the local mechanism does not truly uncoil the chain but rather stretches individual links, while the global mechanism results in the entire coil unraveling. The transient behavior is likewise affected by the orientation mechanism. Relaxation spectra for chains oriented by the different mechanisms reveal that the longest relaxation time is seen only for the unraveled chains that result from the global mechanism.