Enhancing Adhesion On-Demand in Bottlebrush Pressure Sensitive Adhesives

There is significant interest in pressure sensitive adhesives that can alter their tackiness on demand. It is particularly desirable to switch adhesion without using additives and chemical agents. In this article, we explore the potential of altering bottlebrush network architecture, via a mild external stimulus, to induce shifts in the viscoelastic properties of a material. Specifically, we controllably decrease the cross-link density of a bottlebrush network via exposure to UV light over a short period of time, leading to quantitatively predictable shifts in the network's plateau modulus and Rouse relaxation time. This was achieved through the incorporation of <i>o</i>-nitrobenzyl ester groups into the cross-links of a poly(<i>n</i>-butyl acrylate) brush network, which cleave in response to UV light. Concurrently enhancing softness and dissipation allowed enhancement of the work of adhesion by more than 3 orders of magnitude for peel rates ranging from ca. 10^-3 to 10 s^-1. The work of adhesion measured as a function of the deformation rate covers three distinct regimes from viscoelastic bulk- to interface-dominated adhesion with increasing network's cross-linking density.