Soft colloids enable the exploration of states with densities exceeding that of random close packing, but it remains unclear whether softness controls the dynamics under these dense conditions. Experimental studies have reported conflicting results, and numerical studies have so far focused primarily on simple models that allow particles to overlap, but neglect particle deformations. This makes the concept of softness in simulations and experiments difficult to compare. Here, we propose a model system consisting of polymer rings with internal elasticity. At high packing fractions, the system displays compressed exponential decay of the intermediate scattering functions and super-diffusive behaviour of the mean-squared displacements. These features are explained in terms of the complex interplay between particle deformations and dynamic heterogeneities, which gives rise to persistent motion of ballistic particles. We also observe a striking variation of the relaxation times with increasing particle softness, clearly demonstrating the crucial role of deformation in the dynamics of realistic soft colloids.

Polymer membranes are employed in several critical sustainability applications involving the separation of gas mixtures based on size differences. In spite of their widespread use, important performance challenges remain outstanding - the need to dramatically affect the transport of a desired mixture component and improving mechanical resilience relative to the current state-of-the-art. Here, we develop novel membranes based on polymer-grafted nanoparticles (GNPs) which possess controllable, spatially inhomogeneous gas transport behavior. We show that smaller gases are transported more uniformly than larger solutes in the polymer layer of pure GNPs; these larger gases preferentially move through the interstices between the NPs. Free chains added to these GNPs preferentially segregate into these interstices where they selectively hinder large solute motion and thus yield dramatic performance improvements for several industrially relevant gas pairs. The magnitude of these effects are controlled by grafting parameters and the length of the free chains. Our ability to create and tune spatial inhomogeneities in GNPs, apparently through judicious manipulation of chain entropy, is thus a new, apparently general, physics-based paradigm to design membranes with unprecedented performance even using common polymers.

Collaborators: Connor Bilchak, Yucheng Huang, Daniele Parisi, Zaid Abbas, Werner Egger, Ferruccio Doghieri, Matteo Minelli, Marcel Dickmann, Brian Benicewicz, Jacques Jestin, Michael Rubinstein, Dimitris Vlassopoulos, Ludwik Leibler, Christopher Durning