Investigation of microgel monolayers with the colloidal probe technique: how concentration and temperature allow tuning the properties of a microgel coating

Microgels are soft nanometer-sized polymer systems that show high potential as responsive functional coatings. Here, we report colloidal probe measurements with a silica particle and thermo-responsive PNIPAM-<i>co</i>-APMH microgels adsorbed to a solid substrate immersed in water at different surface concentrations and at different temperatures. We show that the increase in the microgel concentration allows for a higher deformation leading to an effective softer microgel monolayer. We attribute this to a lower lateral expansion of the microgel on the substrate leading to a higher protrusion of the soft microgel corona into the water phase. Further, it is shown that even a small number of charged functional groups significantly impacts the properties of the microgel coating. As the microgels collapse, the viscoelastic properties of the network change and the microgels become stiffer. Additionally, the surface charge density increases. Thus, adjusting the concentration of the microgels at the interface as well as the temperature allows controlling the viscoelastic properties of the monolayer as well as the steric and electrostatic interactions perpendicular to the interface.