Dynamic stiffening and softening of a system of colloids cross-linked via polymers

With the goal of deciphering the design principles for biomimetic materials that can autonomously stiffen and soften, we investigate colloids as a model system that can dynamically transition between fluid-like and gel-like states when crosslinked with polymers. The model is first developed with a system of colloids interacting via Lennard Jones potential, a fraction of which are further connected via passive crosslinkers. We study this system using Brownian Dynamics simulations and obtain collective properties, such as the time needed to form system spanning networks and elastic moduli, for various colloid volume fractions, interaction strengths, and cross-linker concentrations. Using experimental parameters for polystyrene spheres and Bovine Serum Albumin (BSA) crosslinkers, we predict the behavior of real systems. Next, we replace the passive, one-shot crosslinkers in our model by active cross-linkers that can dynamically attach and detach, and characterize the degree of order and the mechanical response of the system as a function of time. Our results provide insights into the design of self-sustaining soft materials that can dynamically stiffen and soften, and how the properties of such materials can be tuned.