Surface-enhanced Raman and surface plasmon resonance measurements of Case II diffusion events on the nanometer length scale

A study of spatially-localized phenomena associated with Case II transport is reported. Steady-state aspects of viscoelastic diffusion were investigated with the aid of SERS-active planar films implanted in $\mu$m-scale polymer films. The use of Au rather than Ag metal-island films is shown to eliminate spectral interference resulting from photolytic degradation reported in typical SERS studies of glassy polymers. A sample probe consisting of an Au metal film sandwiched between polymer thin films was shown to provide a spatial resolution of less than 30 nm in the direction of penetrant motion i.e. normal to the plane of the superstrate-polymer interface. This high resolution probe may be used to generate SERS spectra of the polymer/penetrant system during permeation experiments. Penetrant motion and polymer relaxation processes may be simultaneously monitored in situ by interpretation of vibrational mode evolution. Polymer relaxation and deformation in response to osmotic stress caused by the presence of permeant molecules appears to lag behind solvent arrival and continue long after the diffusion front has passed.Surface plasmon resonance position measurements were used to study permeant-induced interfacial swelling processes in ultra-thin ($\le$350 A) poly(methylmethacrylate) films. A one-dimensional swelling model was developed and used in conjunction with Fresnel reflectivity relationships for multilayer systems to relate observed shifts in surface plasmon resonance position to changes in sample thickness and dielectric profile. Precision control of sample thermal history was accomplished with a feedback temperature regulation system based on a digital velocity PID control algorithm. Changes in sample thickness of less than 1A were easily observed. The swelling behavior of films in the 10 to 30 nm thickness range immediately subsequent to permeant introduction was investigated. Evidence that penetrant molecules are incorporated directly from the vapor stream, rather than from an adsorbed surface layer is reported. Sample thickness modulations at 0.3 Hz and of amplitude ca. 1A were observed at penetrant volume fractions between 0.08 and 0.12. The initial evolution of permeant concentration profiles on this length scale appears to be generally well described by the Thomas and Windle model, however, a strong temperature dependence is observed.U of I OnlyETDs are only available to UIUC Users without author permissio