Surfactant fluid microstructure and surfactant aided spreading

Spin-echo-pulsed-field-gradient NMR (NMR) and dynamic light scattering (DLS) have been used to study the microstructure-forming ability of ethoxylated alcohols C{dollar}sb{lcub}rm i{rcub}{dollar}E{dollar}sb{lcub}rm j{rcub}{dollar} in C{dollar}sb{lcub}rm i{rcub}{dollar}E{dollar}sb{lcub}rm j{rcub}{dollar}/octane/water systems in isotropic one phase regions and to distinguish the solution behaviors of C{dollar}sb{lcub}12{rcub}{dollar}E{dollar}sb5{dollar}, C{dollar}sb{lcub}10{rcub}{dollar}E{dollar}sb4{dollar}, C{dollar}sb8{dollar}E{dollar}sb3{dollar}, C{dollar}sb6{dollar}E{dollar}sb2{dollar} and C{dollar}sb4{dollar}E{dollar}sb1{dollar}. As temperature is approached either from below or above to the regions near the lamellar liquid crystal phase at fixed composition in C{dollar}sb{lcub}12{rcub}{dollar}E{dollar}sb5{dollar} system, the NMR self-diffusivity results show that the microstructure changes either from oil-in-water to bicontinuous or from water-in-oil to bicontinuous, and the DLS results show that the droplet diffusivity changes from two well separated modes to either a single or two not well separated modes; while the slow mode diffusivity (comparable to NMR droplet diffusivity) is approaching to the fast mode diffusivity and its contribution is decreased. The slow mode is the droplet self diffusion mode and the fast mode the collective mode according to the Pusey et al. model. Similar results are obtained with C{dollar}sb{lcub}10{rcub}{dollar}E{dollar}sb4{dollar} system but the microstructure changes are less drastic. The NMR diffusivity results reveal, however, that in the C{dollar}sb6{dollar}E{dollar}sb2{dollar} and C{dollar}sb4{dollar}E{dollar}sb1{dollar} systems, the solutions are molecular mixture and the DLS results give single mode. We conclude that the amphiphilicity decreases in this order: C{dollar}sb{lcub}12{rcub}{dollar}E{dollar}sb5{dollar}, C{dollar}sb{lcub}10{rcub}{dollar}E{dollar}sb4{dollar}, C{dollar}sb8{dollar}E{dollar}sb3{dollar}, C{dollar}sb6{dollar}E{dollar}sb2{dollar}, C{dollar}sb4{dollar}E{dollar}sb1{dollar}.; The second part of the thesis is about surfactant aided spreading on hydrophobic surfaces. A droplet of an aqueous two phase dispersion of SS1 spreads spontaneously and rapidly on Parafilm and polystyrene surfaces. We observed a surface covering rate on Parafilm of about 10 cm{dollar}sp2{dollar}/min for a 0.0078 gram aqueous drop (0.1wt% SS1) and a rate on polystyrene of about 60 cm{dollar}sp2{dollar}/min for an aqueous drop (0.17wt% SS1). The covered area in the early stage of spreading increases monotonically with increasing SS1 concentration and time. The equilibrium spreading area is proportional to concentration. The results suggest that spreading stops when all of the surfactant is deposited as a monolayer at the interfaces. The spreading is faster when a rougher surface or an ultra-sonicated dispersion is used and when the surrounding has higher water vapor pressure.; The dispersed droplets of SS1-rich phase are found to play a special role in the observed superspreading. A mechanism to explain the observed results is proposed.