Compression-enhanced mobility during finite-cluster growth in a soft colloidal SALR fluid.

Abstract

Short-range-attractive, long-range-repulsive (SALR) interactions generate organization over multiple length scales, making the relation between aggregation and particle transport inherently nontrivial. Here, we use molecular-dynamics simulations to investigate how compression affects structure and mobility in a three-dimensional soft-colloidal SALR fluid derived from polymer-grafted nanoparticles. The self-diffusion coefficient exhibits a pronounced minimum followed by an extended regime of compression-enhanced mobility. This crossover does not coincide with cluster dissolution, system-scale connectivity, or a sharp exchange between competing local coordination environments. Instead, compression promotes finite-cluster growth while predominantly weakening intermediate-range SALR correlations. Direct tracking of local cluster neighborhoods further shows that particle exchange becomes systematically more frequent across the diffusion minimum. Thus, enhanced long-time mobility develops in a fluid that becomes more locally associated while simultaneously reorganizing at larger length scales. For the effective interaction investigated here, these results reveal a scale-dependent structure-dynamics relationship in which aggregation, mesoscopic organization, and particle transport need not evolve in parallel.