Probing polymer surface and interface dynamics

Polymeric materials generally exhibit various molecular motions and relaxations. Such relaxation processes, which include the glass transition temperature, have significant effects on physical and mechanical behavior. Polymer molecules and segments at surfaces and interfaces also exhibit motions and relaxations. In air or vacuum, such motions ‘permit’ the surface to restructure to minimize the surface free energy. In aqueous solution, the polymer surface restructures and reorients to optimally interact with the aqueous solvent, thereby minimizing the interfacial free energy. XPS and related high vacuum techniques probe the vacuum‐equilibrated surface. The best way to probe the polymer‐liquid interface is via dynamic contact angle or wetting methods. A number of issues and concerns are discussed: (1) the size or hierarchy of structures: (2) the time course of surface dynamic processes; (3) theory, modeling, and simulation of surface dynamics; and (4) experimental methods.