Mass transport properties in thin ion-exchange polymer films and related phenomena

Thin ion-exchange polymer films (henceforth polyelectrolytes) have recently acquired substantial research interest. This is due in large part to the great promise demonstrated by the effective uptake and large preconcentration ratios of the ions from a liquid environment. The nanostructured porous film is an essential element of the spectroelectrochemical sensors. One fundamental aspect of the research involves molecular mass transport at the liquid/solid interface and associated film dynamics. These were studied using spectroscopic ellipsometry and quartz crystal microgravimetry and a good overall agreement between methods has been confirmed. The methodology for diffusion modeling was developed and demonstrated using several polyelectrolyte film materials. Three different theoretical models that account for non-ideal behaviors were employed to solve for the correct mechanism. Slow polymer relaxations coupled with ideal Fickian diffusion caused anomalies. The mass transport of model analytes was characterized by relatively slow diffusion constants (D = 10-12 - 10 -14 cm2/s) and relaxation rate constants (kR = 10-4 - 10-5 s-1). Anomalous diffusion in poly(vinyl alcohol)-poly(acrylic acid) (PVA-PAA) composite thin films and the structure-property relationship were studied in detail. The results of in situ complexation between Fe2+ and ligand (2,2'-bipyridine) in thin Nafion films gave important insight into the set of chemical reactions for aqueous iron detection. The last chapter focuses on dynamics of a novel polyelectrolyte film material for chemical sensing, namely, partially sulfonated polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SSEBS). The physico-chemical phenomenon of molecular aggregation was studied using rhodamine 6G laser dye and the SSEBS film material. It was demonstrated for the first time how spectroscopic ellipsometry could be effectively used in studying such a subtle process in thin films. The two thesis appendices are devoted to surface studies. The ultra-thin polyelectrolyte films (5-12 nm) were imaged using atomic force microcopy (AFM) and the results revealed "island-like" structures. The luminescence quenching of the laser dyes at the semiconductor indium tin oxide (ITO) surfaces was demonstrated using evanescent wave spectroscopy. The results of investigation showed that within the first few nanometers from the ITO surface the luminescence was significantly reduced. In conclusion, the work gives important new insight into fundamental aspects of the spectroelectrochemical sensors.