Simulations of Non-equilibrium Processes in Polymer-based Materials*

Polymer-based materials range from adhesives to associative polymeric networks and mucus hydrogels. Non-equilibrium processes include stick-slip behavior, energy dissipation (as underlies adhesive strength), shear-induced structural transition, and memory effects. In this talk, I will discuss my contributions to the field over the years, starting with simulations I performed as a postdoctoral associate in Mark Robbins’ lab. Next, I will describe how these studies inspired my subsequent scientific work.

In the 1996 paper on “why glue glues” we showed that adhesive strength is due to energy dissipation in rapid slip events during which the polymeric substance restructures and creates gradually larger voids.

I studied associative polymeric networks under an oscillatory shear deformation with large strain amplitude later in my career. These show similar sudden transitions. In our hybrid molecular dynamics (MD), Monte Carlo (MC) algorithm polymer chains are modeled as a coarse-grained bead-spring system. Functionalized end groups at both ends can form and break reversible bonds according to MC rules. As the system moves away from the zero-strain position,  reversible bonds are broken and chains stretch. During the movement to the other extreme of the cycle, first a stress overshoot occurs, then a yield accompanied by shear-banding. Finally, the network restructures. Interestingly, the system periodically restores bonds between the same associating groups and its network topology.

Finally, I will discuss the extension of these simulations of associating polymers to current work on mucus hydrogels. In these, hydrogen, as well as disulfide bonds, form.