| In the first study I investigated structure/property relationships in hydrophobically modified hydroxyethyl cellulose (HMHEC)/surfactant hydrogels. This study encompasses the effects of polymer degree of polymerization, side chain content, side chain length and structure, and surfactant structure on the gel forming ability and gel quality. Strong gels were characterized further in terms of rheology and hydrophobicity. Gel formation is favored when the side chain level on the polymer is below a critical number of side chains/backbone. This critical number lies between 210 and 390. In general, gel quality improves with increasing degree of polymerization, increasing solubility of the polymer side chains in water and decreasing critical micelle concentration (cmc) of surfactants.; In the second study I investigated the role of surfactants in enhancement of spreading of aqueous solutions over hydrophobic surfaces. Based on the differentiated form of Young's equation, spreading can be enhanced by using surfactants which pack very densely at the hydrophobic surface/water interface. To identify the structural parameters of surfactants, viz. size of hydrophilic and hydrophobic groups, which exhibit dense packing, packing densities of 2 members of a homologous series of surfactants were studied. My results show that for hydrocarbon based ethoxylated surfactants (CH{dollar}sb3{dollar}-(CH{dollar}rmsb2)sb{lcub}m-1{rcub}{dollar}-(OCH{dollar}rmsb2CHsb2)sb{lcub}n{rcub}{dollar}-OH) (designated {dollar}rm Csb{lcub}m{rcub}Esb{lcub}n{rcub}),{dollar} packing density increases with a decrease in n (n considered was 1 and 6). Furthermore I provide, for the first time, visual and quantitative evidence of dense packing ({dollar}sim{dollar}20 A{dollar}sp2{dollar}/molecule) for {dollar}rm Csb{lcub}14{rcub}Esb1.{dollar} Visual evidence is provided by using the technique of fluorescence microscopy while quantitative evidence is provided by using attenuated total reflection - Fourier transform infrared (ATR-FTIR) spectroscopy. |
