Rheodialysis: A Platform for Probing Rheology in Evolving Chemical Environments

Abstract

Many soft and complex materials exhibit rheological behaviour that evolve spatially in response to changes in their chemical environment, particularly at interfaces. Examples include biopolymer coatings, food products during digestion and personal care products.   However, conventional rheological techniques typically operate under static conditions, limiting their ability to capture these coupled time and spatial effects. This presents a significant challenge for understanding processes such as gelation, transport-driven structuring, and interfacial material evolution. Here, we present rheodialysis as an experimental platform that enables in situ rheological measurements under dynamically controlled chemical conditions. The approach integrates a modified rheometer geometry with a membrane-separated flow system, allowing reagents to be introduced non-invasively via diffusion while continuously monitoring rheological properties. This configuration provides precise control over the local chemical environment without disrupting the sample structure. Using alginate hydrogels as a model systems undergoing chemically induced transformations, we demonstrate how rheodialysis can resolve both time-dependent rheological evolution. This work highlights the potential of rheodialysis as a versatile tool for studying soft matter in non-equilibrium conditions. The approach is broadly applicable to systems where external stimuli drive changes in structure and mechanics, offering new opportunities to investigate and optimise processes relevant to formulations, biological systems, and advanced materials.