Effects of Hydration on the Interfacial Structure of Confined Acrylate Resin Studied by the Surface Forces Apparatus

While photocurable materials are widely utilized in precision coatings and 3D printing owing to their tunable properties, the performance and reliability of applications depend fundamentally on molecular interactions at the polymer–substrate interface. Here, we investigated how water hydration influences the interfacial dynamics of a common acrylate resin, 1,6-hexanediol diacrylate (HDDA), confined between mica substrates using the surface forces apparatus. Our results show that under humid exposure the adsorbed HDDA layers became shrunken and denser, along with an enhanced interlayer cohesion reaching ∼−37 mN/m(−7.9 mJ/m 2 ). Complementary atomic topography imaging clearly revealed a morphological transition from discrete protrusions to densely packed island-like domains, suggesting hydration-induced aggregation and subsequent interfacial phase separation. These structural changes can be attributed to the progressive development of a hydrogen-bond network among the polymer matrix, which modulates both interpolymer associations and adhesion to the substrate. Analysis of interference spectra further demonstrates that the observed cohesive forces originate from the capillary condensation of water molecules within the confined gap between HDDA layers. Furthermore, the resulting capillary interaction is primarily governed by surface roughness because of localized water bridging. Our findings shed light on the role of molecular interactions at resin interfaces, hopefully offering mechanistic guidance for optimizing interfacial engineering in high-resolution manufacturing.