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PRESSURE-SENSITIVE CONTROL OF ADHESION IN WRINKLED SOFT POLYMERS [2007]

Edwin P. Chan, Graduate Research Assistant, University of Massachusetts, Amherst, MA
Alfred J. Crosby, Assistant Professor, University of Massachusetts, Amherst, MA

ABSTRACT

Nature has demonstrated that a powerful way for enhanced control of adhesion lies in the use of patterned interfaces. In many of these systems (i.e. geckos and insects), a primary strategy is the incorporation of topographic patterns to ingeniously maximize adhesion forces while maintaining ease of release. Motivated by these natural attachment devices, significant research has been devoted towards understanding and developing synthetic analogs. Although the results of these synthetic analogs hold significant potential for the enhanced control of polymer adhesion, however, fabrication challenges still remain that limit commercial applications of these materials. In this work, we provide two alternative strategies to generating patterned soft polymer adhesives with well- defined pattern structures and demonstrate how the patterns can be intelligently designed to control polymer adhesion.

In the first part of this work, we provide a sequential fabrication approach based on lithographic patterning and conformal coating to generate a patterned, laterally confined thin acrylate adhesive. We illustrate how the lithographically prepared post patterns can tune the adhesion of the acrylate adhesive through 3 mechanisms of adhesion including 1) altering the local separation mode through lateral confinement, and 2) controlling the initiation and propagation of fracture instabilities, and 3) changing the local crack velocity to alter global viscoelastic response.

For the second part of this contribution, we provide a simple and elegant approach to generating a patterned adhesive based on surface wrinkling. We show a robust methodology to generating surface wrinkling based on swelling of a laterally confined acrylate elastomer. More importantly, we demonstrate how a wrinkled PnBA elastomer can provide a significant increase in adhesion relative to the smooth, non-wrinkled PnBA surface.