Tracer diffusion in crowded solutions of sticky polymers

Abstract

Macromolecular diffusion in strongly confined geometries and crowded environments remains as a open subject in soft matter Physics. Unveil the diffusion regimes in these conditions is essential for a complete understanding of several biological process. In this sense, we employ large scale Langevin Dynamics simulations to understand how the spherical tracer volumetric properties affects the diffusive properties. Two species of tracers are studied. One tracer particle is a standard soft-core particle modeled by the well known Weeks-Chandler-Andersen soft-core potential. The second is modeled as a Core-Softened particle. Core-softened macromolecules includes globular proteins, charged colloids and nanoparticles covered by polymeric brushes. These systems are characterized by the presence of two length scales in the interaction and can show waterlike anomalies regarding on the competition existent in the potential. In this work we study the diffusion and structure of these two tracer species in a polymeric crowded environment. We analyze how the tracer-polymer affinity and the system density affect the transport and aggregation properties. Surprisingly, the soft-core tracer particle shows a increase in the diffusion as we increase its volume occupancy – similar to the waterlike diffusion anomaly. Even the mechanism is similar to the observed in waterlike systems. We discuss our results based in the competitions in the interaction potentials and the competition induced by the crowded media.