Adhesion and Detachment Mechanisms between Polymer and Solid Substrate Surfaces: Using Polystyrene-Mica as a Model System

The adhesion and detachment of polymer and solid substrate surfaces play important roles in many engineering applications such as for designing adhesives, biomedical adhesives, adhesive tapes, robust protective coatings, biomedical scaffolds, prosthetic devices (e.g., artificial joints and implants), and fabrication of micro- and nanoelectromechanical devices. In this work, a surface forces apparatus (SEA) coupled with top-view optical microscopy was employed to measure the adhesion between thin polystyrene (PS) films and a mica substrate to probe their detachment behaviors. Various factors, including molecular weight (MW), contact time, and polarity-enhancing UV/ozone treatment, were examined. The results show that increased chain-end density, chain mobility, and segment polarity can all contribute to enhanced adhesion strength for both the "symmetric" PS PS and "asymmetric" PS mica systems but attributed to different adhesion/detachment mechanisms. For the asymmetric PS mica system, the increased chain-end density (lower MW), increased chain mobility, and increased polarity (induced by UV/ozone treatment) facilitate the rearrangement of the polystyrene chains and the development of mainly "polar" interactions such as dipole dipole, dipole induced dipole, and attractive hydrogen bond interactions between the polar groups on the UV-treated PS (the pi-electron clouds of the phenyl rings) and the highly polar mica surface. For the symmetric PS PS system, the enhanced adhesion is mainly due to the interdiffusion, interdigitation, interpenetration, and entanglement of chains across the polymer polymer contact interface. Importantly, during the separation of a UV/ozone-treated PS surface from mica, "stick slip" detachment was observed, resulting in a residue of concentric polymer rings left on the mica surface. Our results provide new fundamental and practical insights into the adhesion, detachment, and damage (wear) mechanisms of polymer polymer and polymer solid surfaces.