Polymer layers immobilized at the interface affect the stability and rheology of colloidal dispersions, the lubrication properties and the biocompatibility of artificial surfaces, and static and dynamic forces between coated surfaces. In this work we have investigated the behavior of surfaces coated with dense layers of thermoresponsive pNIPAM-based microgels under compression and shear produced by self-assembly and chemical grafting. We describe how the presence of a long-range repulsive interaction can modify the geometry of approaching surfaces, with significant consequences on the experimental determination of normal and friction forces. Local surface deformations as small as few nanometers must be considered for a complete description of the behavior of surfaces under compression and shear, in particular when the range of action of normal and friction forces are significantly different, as is often the case for macromolecular lubrication. In dynamic conditions we observed the presence of shear-induced lift forces, which are evidenced by a variable gap between the surfaces under shear. The origin and consequences of this force will be discussed in detail. All these findings suggest simple mechanisms for robust control of lubrication by properly tuning stiffness and geometry of the interacting bodies.

Soft and slippery: Microgel-coated surfaces under shear

2019 Fall National Meeting

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