Topological adhesion. I. Rapid and strong topohesives

Topological adhesion, or topohesion for brevity, links two polymer networks, to be called adherends, even when the adherend networks carry no functional groups for chemical coupling. Uncrosslinked polymers, called stitch polymers, are spread between the two adherends. In response to a trigger, the stitch polymers form a stitch network in topological entanglement with both adherend networks. It is commonly believed that topohesion always takes a long time, but this is a misconceived myth. In principle, two adherends topohere strongly even when the stitch network entangles with each adherend network by a single polymer mesh size. The shallowness of this requirement dictates that topohesion is rate-limited by the gelation of the stitch network, not by the diffusion of the stitch polymers into the adherend networks. We illustrate this concept using two pieces of polyacrylamide hydrogels as adherends, an aqueous solution of cellulose as stitch polymers, and a change in the pH in the cellulose solution as a trigger. By varying the thickness of the cellulose solution, the time to topohere is tunable from seconds to hours. For a solution of thickness of 50 microns adhesion energy of 50 Jm(-2) is attained in 60 s. These experimental findings dispel the myth, and shed light on the times to topohere reported in the literature. The art and science of topohesion provide fertile grounds for fundamental discovery and practical invention to enable unusual applications. (C) 2020 Elsevier Ltd. All rights reserved.