Nonequilibrium structure and fluctuation of soft matter under shear flow

Abstract

Shear flow can change not only the structure of soft matter but also the nature of fluctuation and response by breaking the time-reversal symmetry. We constructed a system combining a rheometer and a confocal laser scanning microscope to observe three-dimensional structure under shear flow and measure shear stress at the same time. Here, we present our results. First, we investigated the structural change of an immiscible blend subjected to a step electric field under shear flow. The relation between the structural change and the transient shear stress was discussed in terms of the interface tensor charactering the orientation distribution of interfaces. Next, Brownian motion in a simple shear flow was investigated by using a new method for observation and analysis. We found that the mean-square displacement consists of an anomalous t3 term in addition to the normal Einstein diffusion term linear in t. Last, we investigated the linear response of shear stress to ac electric fields under shear flow in a nematic liquid crystal. Although the Debye-type response was obtained at low shear rates, discrepancies were observed at high shear rates. Nonconservative forces were found to play an important role in determining the fluctuation dynamics.