Tuning Interparticle Interactions in Graphene Oxide Dispersions for Enhanced Shear-Induced Alignment.

Abstract

The macroscopic behavior of colloidal materials is governed by interactions between their microscopic building blocks. In anisotropic colloidal systems, subtle variations in interparticle forces can lead to dramatic changes in phase behavior, flow response, and alignment under shear. Here, we systematically investigate how ionic strength controls the structural state, rheology, and alignment dynamics of aqueous graphene oxide (GO) dispersions, and how these effects translate into the performance of wet-spun fibers. By varying the NaCl concentration, we tune the GO system across three regimes: a jammed repulsive glass state at low salt, an aggregation-dominated state at high salt, and a relaxed soft glassy state that allows for structural rearrangement. In this intermediate regime (∼1-5 mM NaCl), the dispersions exhibit the lowest yield stress and the fastest domain reorientation under shear, as observed via shear polarized optical microscopy (shear-POM) and rheo-small-angle X-ray scattering (rheo-SAXS). When processed into fibers via wet spinning, dispersions from this regime yield markedly higher alignment, tensile strength, and electrical conductivity than those from either the jammed or the aggregated state. These findings establish a multiscale structure-rheology-alignment-property relationship in GO dispersions, in which shear-induced alignment is determined by the balance of interparticle interactions and the resulting structural state.