Molecular Dynamics Simulations to Study Response to Perturbation of Polymer Melts, Polymer Solutions, and Colloidal Gels

Soft matter systems can be characterized by observing their responses to perturbations that induce changes in their structure or dynamics.

For instance, the application of shear reveals material properties, while changes in temperature or solvent quality change phases or trap systems into dynamically arrested states.

Molecular Dynamics (MD) simulations are the ideal tool to perform these studies: provided a suitable energy function and a model for perturbation any system can be simulated at arbitrary temporal and spatial resolutions.

Here, I illustrate three applications of MD simulations of soft matter systems responding to external perturbations.

I will briefly discuss the initial stages of weld formation when two polymer films prepared at different temperatures are juxtaposed -- a problem inspired by additive manufacturing.

Next, I will sum up the variety of the structures and rheological responses of interpenetrating colloidal gels generated by changing only two parameters of the energy function.

Finally, I will focus on polymer nanoprecipitation triggered by changes in solvent quality.

In experiments, a solution of polymer and good solvent is injected into a non-solvent bath, leading to solvent exchange and the formation of polymer nanocapsules.

Here, I focus on the response of polymer solution to the sudden change in solvent quality.

Following an experimental setup, I sampled independent conformations of polymers in good solvent, and then I initiated the mixing with poor solvent.

Monitoring the polymers during solvent exchange, I observed transient states generated by the interplay between timescales for polymer diffusion, conformational changes in the polymer chain, and diffusion of the solvent into the non-solvent bath.

In this talk, I will describe these transients, how they are affected by changes in parameters describing the interaction between the model components (e.g. solvent and non-solvent), and the implications for experiments.