Stochastic thermodynamics of a confined colloidal suspension under shear flow

Abstract

Based on Brownian dynamics simulations, we investigate the thermodynamic signatures of nonequilibrium steady states in a confined colloidal suspensions under shear flow. Specifically, we consider a thin film consisting of charged particles in narrow slit-pore confinement, forming two layers with quadratic in-plane structure in equilibrium. This many-body system displays three distinct steady states, characterized by unique dynamical and rheological response to the applied shear flow. Calculating the work and heat, we find that both quantities indicate the different states by their mean and by their distributions. A particularly interesting situation occurs at large shear rates, where the particles perform a collective zig-zag motion. Here, we find a bistability regarding the degree of phase synchronization of the particle motion. It turns out that this bistability is key to understanding the resulting ensemble-averaged work distributions. For all states, we compare the work and heat distributions to those of effective single-particle systems. By this, we aim at identifying the many-body character of the stochastic thermodynamic quantities. arXiv:1809.01978v1 [cond-mat.soft]

Dynamical modes of sheared confined microscale matter

“…Interestingly, the nonequilibrium transition between the two steady states is most clearly reflected by the heat distributions, displaying a marked behavior with respect to its mean and the strength of its fluctuations. This is somewhat different to our findings for a planar slit pore system, 40 where we have found the opposite, namely that a most marked response for the stochastic work distributions.…”

“…Interestingly, we did not observe a direct correspondence between the work rate and the shear stress, as we have reported for a planar slit pore system. 40 Overall, we find a very good agreement between numerical simulations and experiments not only with respect to the mean values but also the fluctuations of the mean angular velocity as well as the azimuthal-and radial displacements. One open question is the importance of the magnetic torque dependency of the dipole-dipole interactions exerted between the paramagnetic particles.…”

“…As discussed in our earlier study of a planar slit pore system, 40 the work and heat distributions are in general time dependent and the same behavior occurs here. Regarding the mean values, we find a linear increase in time for both the work and the heat, that is, hw(t)i E h : wit and hq(t)i E h : qit, and the functions are fully determined by their respective mean rates, as expected for a steady state.…”

“…This comparison is motivated by our results for a planar slit pore system, where these two quantities are closely related. 40 However, the same does not hold true for the sheared circular system, which deviates from the expected relation for B 0 4 B 0,c .…”

“…Note that, in contrast to systems driven by a linear shear flow, the work rate does not trivially reduce to the virial expression for the configurational shear stress, as reported in previous studies. 40 All integrals and derivatives are evaluated using the Stratonovich calculus.…”