Switchable friction of stimulus-responsive hydrogels.

TitleSwitchable friction of stimulus-responsive hydrogels.
Publication TypeJournal Article
Year of Publication2007
AuthorsDP Chang, JE Dolbow, and S Zauscher
JournalLangmuir : the Acs Journal of Surfaces and Colloids
Start Page250
Pagination250 - 257
Date Published01/2007

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.

Short TitleLangmuir : the Acs Journal of Surfaces and Colloids