Investigating the impact of water capillary forces on polymer-substrate adhesion using force spectroscopy

Abstract

Atomic force microscopy (AFM) was used to characterize how water capillary forces impact polymer-substrate adhesion in ambient conditions. We analyzed hydrophobic poly(styrene-co-butadiene) interacting with mica, silicon, and graphite substrates, each with distinct surface properties. Using polymer-coated AFM tips/blank substrates, and vice versa, we explored the roles of water capillary forces and polymer-substrate interactions on adhesion. When force spectroscopy experiments were conducted using polymer-coated tips, adhesion was the largest on mica due to substantial water capillary forces between the tip and hydrophilic substrate. However, when using a blank tip and polymer-coated substrates, the adhesion was largest on graphite and smallest on mica. This is because the blank tip interacted with the same hydrophobic polymer film for each experiment; therefore, water capillary forces had an equal magnitude on each substrate, allowing polymer-substrate interactions to be compared even within ambient conditions. Moreover, single-chain desorption events were consistently observed in these force-distance curves since water capillary forces were significantly reduced. This study elucidated several aspects of how water capillary forces impact polymer-substrate adhesion, which benefits applications reliant on polymer adhesion in ambient conditions and contributes to the fundamental understanding of polymer interface interactions.