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.
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