Controlling the flexible polymer - hard colloid duality of temperature-responsive microgels at interfaces by the adsorption pathway

We study the effect of the adsorption pathway on the morphology and temperature-induced collapse of PNIPAM microgels at the solid/liquid interface by means of atomic force microscopy (AFM). Two samples with extreme differences in softness are probed: i) regularly 5 mol% BIS, and ii) ultra-low cross-linked microgels (ULC). ULC microgels are strongly deformed when being deposited either by spin-coating or by Langmuir-Blodgett technique from an oil-water interface. After rehydration, the ULC microgels cannot collapse as entire objects instead small globules are formed. Such a strong deformation can be avoided by in-situ adsorption to the substrate. Then, the ULC microgels exhibit half-ellipsoidal shapes with a smooth surface similar to more cross-linked microgels. Due to the extreme softness of ULC microgels, they can be selectively trapped either in a more particle-like or in a more polymer-like behavior. Coatings with strongly different topographies and properties can be prepared by one and the same ultra-low cross-linked microgel.