Characterization of reactive dissolution and swelling of polymer films using a quartz crystal microbalance and visible and infrared reflectance spectroscopy

Dissolution and swelling of thin films of ionizable polymers in contact with aqueous alkaline solutions are examined using a quartz crystal microbalance, while simultaneously recording the visible reflectivity and infrared absorption of the evolving films. From these data changes in the thickness, depth structure, composition, mass, and mechanical properties of the polymer film during its interaction with the aqueous solution can be detected. Analysis of these provides evidence for the formation of interfacial gel layers resulting from acid-base reaction of the polymer with the hydroxide solution and yields information on the kinetics of transport and chemical reaction that control the overall process. Kinetics simulations indicate that the most important factors influencing observed behaviors are the intrinsic reactivity of ionizable groups on the polymer and the response of the film's mechanical properties, which determine the ability of small molecules to move through it, to incorporation of water. © 2005 American Chemical Society.