title: Switchable friction of stimulus-responsive hydrogels.
abstract: Poly(N-isopropylacrylamide) (pNIPAAm) gels are stimulus-responsive hydrogels that exhibit large reversible changes in their volume and surface physicochemical properties near the lower critical solution temperature (LCST) in response to external stimuli, such as a change in temperature or solvent composition. Here we report how different phase states, induced isothermally by changes in the solvent composition, affect the tribological properties of pNIPAAm hydrogels. Our measurements indicate that gels in a collapsed conformation (above the LCST) exhibit significantly more friction than swollen gels (below the LCST) at low shear rates. These differences arise from changes in the surface roughness, adhesive interactions, and chain entanglements of the gel surfaces associated with the phase transition. Importantly, we show that the changes in friction, triggered by an external stimulus, are reversible. These reversible and possibly tunable changes in friction may have a significant impact on the design of coatings for biosensors and for actuation devices based on stimulus-responsive hydrogels.
authors.affiliation: Department of Mechanical Engineering & Materials Science, Center for Biologically Inspired Materials and Material Systems, Duke University, Durham, North Carolina, USA.
authors.forename: Debby P
authors.initials: DP
authors.lastname: Chang
authors.forename: John E
authors.initials: JE
authors.lastname: Dolbow
authors.forename: Stefan
authors.initials: S
authors.lastname: Zauscher
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry; D017276:Friction; D020100:Hydrogels; D008422:Materials Testing; D013499:Surface Properties
chemical_list: D000180:Acrylic Resins; D020100:Hydrogels; C052970:poly-N-isopropylacrylamide