Epoxy adhesive with dynamic covalent bonds as a fully removable adhesive via photothermal effect of titanium nitride plasmonic nanoparticles

Conventional epoxies have a variety of features that make them appealing for adhesive purposes to almost any substrate. However, their thermosetting nature makes them permanent and nearly impossible to remove without damaging the adhered surfaces. Introduction of Diels-Alder (DA) dynamic bonds into the epoxy network is one way to overcome this limitation. The forward reaction at lower temperatures allows it to work as an adhesive. Above ~120oC, the reverse reaction breaks the dynamic bonds and depolymerizes the adhesive network. Plasmonic nanoparticles were incorporated for specific and localized depolymerization upon exposure to light, which enables removal of adhesive exclusively at a targeted area.

In this study, adhesive strengths of DA epoxy and plasmonic nanoparticle composite samples were studied by lap shear testing. First, adhesive strength of various DA epoxy samples were measured as a function of temperature. It did not show a noticeable change up to 120 ºC, but dropped greatly (~20 times) above 120 ºC because of the thermal dependence of the DA network. Next, adhesive strengths of DA epoxy and nanoparticle composite samples were measured at varying light intensities. It gave an instant drop in adhesive strength by heat generation through a photothermal conversion.