Scanning probe microscopy studies of polymer dispersed liquid crystals and polyelectrolyte-surfactant complexes

Near field scanning optical microscopy (NSOM) and atomic force microscopy (AFM) are used to characterize polymer dispersed liquid crystals (PDLCs) and polyelectrotyte-surfactant complexes (PSCs). This dissertation includes a general overview of near-field techniques and details about experimental methods. The experiments presented in this dissertation clearly show the power of NSOM and AFM to provide information on the nanometer variation of material properties.;PDLC materials consist of micron-sized, birefringent liquid crystal droplets dispersed in an optically transparent and uniform polymer film. Field-induced reorientation methods were explored in PDLCs. Faster reorientation dynamics were observed in the edge region of the droplets. Dye-doped PDLCs were used to study the local interactions between dye dopants and liquid crystals. Simultaneous recording of fluorescence and birefringence images showed that the ordered and disordered states of liquid crystal and dye, respectively. NSOM studies of electric-field-induced reorientation show the interactions between dye dopants and liquid crystals play a substantial role in the reorientation process. Analysis of the simultaneously recorded birefringence and fluorescence data shows the dye is strongly reoriented via its interaction with the reorienting liquid crystal and via its independent interactions with the applied field.;PSCs films were prepared from a complex formed between poly(vinyl sulfate) (PVS) and a cationic indocarbocyanine surfactant dye (DiI). Local film morphology and chemical composition were studied as a function of dye/anionic-site stoichiometry by NSOM and AFM. AFM images show that overall film morphology changes modestly with dye content. Fluorescence NSOM images reveal that at lowest PVS loading, the films are extremely heterogeneous, exhibiting round fluorescent regions 100--250 nm in size. As the dye content is increased, the fluorescent regions increase in number but remain of similar sizes.;Nonstoichiometric PSCs formed between PVS and alkyltrimethylammonium bromide (CnTAB) were also studied. AFM studies showed that the morphology of the PSC films evolves with the surfactant loadings (i.e. surfactant/anionic-site stoichiometries). PSC films changed from relatively uniform films at 1%, to spheroidal and/or discoidal polyelectrolyte-surfactant micelles structures at 10%, and finally to lamellar bilayer structures at 25--50%. It is clear that longer alkyl chain surfactants formed lamellar phases at lower surfactant loadings.