Interfacial Engineering of Thermoresponsive Microgel Capsules: Polymeric Wetting vs Colloidal Adhesion

Abstract

Control of the microstructure of microgels adsorbed on solid surfaces plays an essential role in various fields, including lithography, optical sensing, and biocatalysis. Here, we adopt an experimentally validated molecular dynamics simulation approach to investigate the structural properties and deswelling dynamics of thermoresponsive microgel capsules on solid substrates. Specifically, by examining the interfacial elastocapillarity of the adsorbed microgel capsules, we find that the poorly cross-linked microgel capsules (i.e., cross-link density ψ ≤ 0.0217) display a crossover adsorption regime between polymeric wetting and colloidal adhesion, whereas the highly cross-linked microgel capsules present only colloidal adhesion adsorption. As the system temperature increases, the microgel capsules progressively transform from the fully swollen state to the fully collapsed state on the solid substrates, whereas the capsule architecture remains. The adsorption regime of the microgel capsule is mutually determined by the elastic deformation and surface attraction strength. In addition, the elastic deformation is attributed to the internal structure of the microgel capsule, which varies with the system temperature and cross-link density. Aiming to identify the adsorption regime over wider ranges of the control variables, a machine learning study on an artificial neural network is further carried out and a three-dimensional phase diagram of the adsorption regime and multiple control variables is constructed, unraveling the comprehensive relationship among the adsorption regime and the operational parameters.