Fabrication and Modeling of a Thermoreversible Modular Core-Shell Colloidal System.

A widely used model system in rheological studies of colloidal gels consists of octadecyl-coated silica particles that undergo thermoreversible gelation in specific suspending media. Their standard synthesis protocol involves an etherification of octadecanol and suffers from poor reproducibility with varying grafting densities and, therefore, transition temperatures. To overcome this limitation, we present here an alternative approach using an amine-yne click-like reaction to graft octadecyl chains onto the particle surface with high fidelity. Suspended in tetradecane, these particles exhibit a reversible liquid-solid transition below 20 °C─making them ideal for comparative studies, particularly by avoiding complications in the rheological characterization due to loading history or thixotropic effects. By fine-tuning the reaction conditions, we precisely control the grafting density─and thus the gelation. The resulting interparticle interactions can be described as a superposition of temperature-dependent forces: repulsion at high temperatures, van der Waals attraction, and temperature-dependent chain-chain interactions, and their resulting potentials can be validated with AFM measurements. The accurate tuning of interparticle potentials makes this model system ideally suited for quantitative comparisons between experiments and simulations across relevant length scales.