New adaptable adhesive could be consumer product game-changer
Kim’s paper, with first author and former MechSE graduate student Jeffrey Eisenhaure, “High-strain shape memory polymers as practical dry adhesives,” was published in the International Journal of Adhesion and Adhesives. Their new findings are based on work resulting in multiple journal publications from 2014, including “An internally heated shape memory polymer dry adhesive” in Polymers.
“This is an invention of a dry adhesive using shape memory polymer (SMP). This means that it is sometimes highly adhesive (~15 vacuum) but sometimes adhesive-less when you want. It’s also reusable and dry, not tacky—which means it can be used repeatedly as a wall mount, for instance,” said Kim.
The adhesive benefits of incorporating shape memory polymers (SMPs) in various dry adhesive designs have been well documented in recent years. Chemically cross-linked SMPs can possess remarkable shape fixity and recovery ability, chemical and thermal stability, a sharp glass transition, and other desirable qualities. However, low failure strain and a relatively rigid rubbery state limit their performance as a dry adhesive component in many practical applications. Kim’s work explores the adhesive benefits of using an epoxy-based SMP that has been modified to maintain a softer rubbery state and an increased maximum strain before failure.To achieve his results, Kim successfully modified a well-known epoxy SMP formula, using a heavier (longer) epoxy monomer and greatly increasing the concentration of the curing, or crosslinking, agent. Since SMP is dry and rigid at room temperature but becomes soft when heated, he used internal Joule heating elements to soften it, allowing strong conformal contact upon preloading, then cooled down to become rigid (and thus, more adhesive). The resulting SMP was found to be both softer in its rubbery state and substantially more stretchable, while retaining its superlative shape memory properties.
Kim plans to investigate the effects of the formula modifications on dry adhesive performance, and to produce a prototype practical dry adhesive.