Fluctuations of driven probes reveal nonequilibrium transitions in complex fluids
Marco Baiesi
(Dept. of Physics and Astronomy, University of Padova)
Complex fluids under localized microscopic energy inputs exhibit nonequilibrium behaviors only partially understood. To identify changes in the fluid’s microstructural conformation, we introduce a general method grounded in the breakdown of the equipartition theorem for laser-trapped probes dragged at a mean constant speed. Specifically, we link the different scaling regimes in the probe’s position variance, obtained through large-scale Brownian simulations of a polymeric fluid, to transitions from diffusive to jump dynamics, where the fluid intermittently relaxes accumulated stress. This view suggests that stored elastic stress is a relevant physical mechanism behind recently measured nonlinear friction curves. Our approach overcomes some limitations of continuum macroscopic descriptions and introduces an empirical method to experimentally detect nonequilibrium transitions in the fluids’ structure.