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

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. Atomic force microscopy (AFM) investigated how water capillary forces affect polymer‐substrate adhesion in ambient conditions. When the polymer interacted with blank substrates, water capillary forces dominated adhesion, particularly on hydrophilic mica. However, when a blank AFM tip interacted with polymer‐coated substrates, water capillary forces were significantly reduced, and adhesion was the largest on hydrophobic graphite due to stronger polymer‐substrate interactions.