Abstract
Nonequilibrium work relations have fundamentally advanced our understanding of molecular processes. In recent years, fluctuation theorems have been extensively applied to understand transitions between equilibrium steady-states, commonly described by simple control parameters such as molecular extension of a protein or polymer chain stretched by an external force in a quiescent fluid. Despite recent progress, far less is understood regarding the application of fluctuation theorems to processes involving nonequilibrium steady-states such as those described by polymer stretching dynamics in nonequilibrium fluid flows. In this work, we apply the Crooks fluctuation theorem to understand the nonequilibrium thermodynamics of dilute polymer solutions in flow. We directly determine the nonequilibrium free energy for single polymer molecules in flow using a combination of single molecule experiments and Brownian dynamics simulations. We further develop a time-dependent extensional flow protocol that allows for probing viscoelastic hysteresis over a wide range of flow strengths. Using this framework, we define quantities that uniquely characterize the coil-stretch transition for polymer chains in flow. Overall, generalized fluctuation theorems provide a powerful framework to understand polymer dynamics under far-from-equilibrium conditions.
Highlights
Accepted: 21 December 2021Understanding the dynamics of soft materials and complex fluids is of fundamental interest to materials scientists, engineers, and rheologists [1]
We use a combination of single molecule experiments and Brownian dynamics (BD) simulations to explore the existence of a generalized polymer viscoelastic hysteresis at the molecular level
The Crooks fluctuation theorem (CFT) is applied to analyze nonequilibrium steady-states (NESSs) of polymer chains based on a time-dependent planar extensional flow protocol
Summary
Accepted: 21 December 2021Understanding the dynamics of soft materials and complex fluids is of fundamental interest to materials scientists, engineers, and rheologists [1]. Soft materials processing often involves highly nonequilibrium conditions that are difficult to model using the standard framework of equilibrium thermodynamics [2] Processes such as flow-guided printing of semiconducting polymers [3], flow-assisted nonequilibrium assembly of hybrid synthetic oligopeptides [4,5], or flow-induced phase separation of colloidal particles [6] are governed by an interplay between far-from-equilibrium structure and dynamics. In order to understand and effectively control material properties during flow processing, it is essential to develop new molecular-level approaches that connect the nonequilibrium energetics of soft materials to transient flow conditions. From this view, the development of new molecular-level thermodynamic frameworks for flowing systems will allow researchers to fundamentally understand the nonequilibrium processes governed by thermodynamics and rheology [2]
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