Diffusion of prodan on self-assembled monolayers and grafted polymer layers

This thesis explores 2-D, solid state diffusion of small organic molecules, both on several chemically functionalized surfaces and through thin layers of polymer grafted to a surface, as a means for directed molecular transport. Toward this end diffusion rates of a dye molecule, prodan, were quantified for naked glass, three surfaces chemistries and two different polymer brushes; additionally, surfaces and brushes were patterned.; Fluorescence recovery after photobleaching (FRAP) was the primary experimental technique. Circular areas were bleached with multi-photon IR utilizing an electo-optical modulator (EOM) and the region of interest (ROI) capabilities of a commercial confocal microscope. Diffusion constants were extracted by comparing FRAP data to curves generated from Fick's second law and from linear fits of variance verses time plots. Diffusion constants from the two methods generally agreed well.; Prodan diffusion rates were quantified for clean glass, SAMs formed from chlorotrimethyl silane (CTS) and octadecyltrichlorosilane (OTS), and poly(ethylene glycol) (PEG) grafted to silica. Similar diffusion constants, ∼1--3 x 10-7 cm2/s, were found for the CTS and PEG layers; this is thought to be due to the intermediate surface polarity and the ability of prodan to partially intercalate. Very little fluorescence recovery is observed on the OTS SAM or on the clean silica surface; dye is thought to aggregate on the former and form hydrogen bonds with the latter.; Two grafted polymer layers were synthesized, for diffusion studies, with surface-initiated polymerization (SIP). The results suggest that there is very little bulk translational diffusion in first layer, poly (N-isopropylacrylamide) (PNIPAM). Rather, fluorescence recovery is thought to be due to either rotational diffusion or a combination of fast surface diffusion and slow bulk diffusion. Increasing relative humidity enhanced recovery. FRAP results for prodan on the second grafted layer, poly (oligoethylene glycol acrylatmide) (POEGA) indicate that there is indeed bulk diffusion; D is calculated to be ∼1--3 x 10-8 cm2/s. Directed diffusion is accomplished by patterning lines on a sample with reactive ion etching (RIE). This method greatly reduces recovery due to surface diffusion, but rotational diffusion still occurs. Increasing relative humidity or ethanol vapor increased the recovery rate.