The phase behavior of aqueous mixtures of a nonionic surfactant, hexaethylene glycol dodecyl ether (C12E6), was investigated by means of differential scanning calorimetry (DSC), Fourier transform infrared (FT-IR) spectroscopy, and 13Cnuclear magnetic resonance (13CNMR)spectroscopy. TheT-Xphase diagram of this system was constructed from theDSCresults. Comparison of the phase diagram with those previously obtained for C12E7 and C12E8 demonstrates that with the decrease in the polyoxyethylene (POE) chain length, the region of LR phase expands toward higher temperature, whereas the H1 region shrinks toward lower temperature. This behavior is well explained in terms of the change in the critical packing parameter of the surfactant molecules associated with the change in the POE chain length. FT-IR results indicate that the ordered conformational structure of both the hydrocarbon and POE chains is kept after the transformation from solid to mesophases. The order-to-disorder transformation of the conformational structure of the chains takes place rather gradually within mesophases with the increase in temperature. This behavior of the chain melting associated with the temperature rise is common to aqueous mixtures of POE-type nonionic surfactants. 13C NMR line widths depend strongly on the phase structure formed by this mixture system: quite broad signals are observed for H1 and LR phases, whereas the signals for V1 phase are rather sharp. According to the two-step model for NMR relaxation in aqueous surfactant systems, the line broadening observed inH1 and LR phases is attributed to the anisometry of the molecular assemblies in these phases.

Salt and pH can induce reversible aggregation of vesicles composed of a nonionic synthetic glycolipid, 1,3-di-o-phytanyl-2-o-(-maltotriosyl) glycerol. The aggregation of the vesicles appears reversible with respect to a change in the pH value of the medium as seen from the reversible change in the turbidity. It was also found that in an acidic region (pH 4-6), the size of the aggregated vesicles are well above 1000 nm, an indication of vesicle aggregation. But in an alkaline region (pH 8-10), the sizes are 110-130 nm, close to their original size of 100-110 nm, which strongly suggests the reversible disaggregation and also confirms the lack of vesicle fusion. The potentials of vesicles are measured in the presence of NaCl with the pH changes of the vesicle suspension. It is seen that the potential of vesicles changes with the pH value. The surface charges of the Mal3(Phyt)2 vesicles arise from two independent mechanisms; one is excess ‘adsorption’ of OH ions at the vesicle-water interfaces and the other is dissociation of hydroxyl groups in a high pH region (pH 11). The changes of the surface charges are thought to be the major factor which induces the aggregation and disaggregation of this nonionic glycolipid vesicle.

The kinetic studies of the acrylic octadecyl ester and styrene polymerization in microemulsion systems, (1) cetyl pyridine bromide (CPDB)/t-butanol/styrene/water; (2) CPDB/t-butanol/toluene+acrylic octadecyl ester (1:1, w/v)/water; (3) cetyl pyridine bromide/styrene/formamide, were made by using dynamic laser light scattering techniques (DLS). The mechanisms of nucleation of latex particles were discussed. The most possible nucleation location of the styrene and acrylic octadecyl ester microlatex particles in aqueous microemulsion system is in aqueous phase via homogeneous nucleation. Meanwhile, parts of microlatex particles are possibly produced via swollen micelles (microemulsions) and monomer droplets nucleation. On the other hand, the most possible nucleation location of the styrene microlatex particles in nonaqueous microemulsion system is inside monomer droplets. The relationship between the amount of monomer and the size of microlatex was also investigated. It has been found that the size of microlatex particles could be controlled by changing the amount of monomer. © 2002 Elsevier Science B.V. All rights reserved.

13C NMR was applied to investigate the various phases formed in aqueous mixtures of heptaethylene glycol dodecyl ether (C12E7). On the basis of the analysis of NMR line width, a qualitative picture was drawn concerning the molecular motion of C12E7 in some mesophases as follows. In the H1 and LR phases, the motion of the alkyl chain of the surfactant molecule is rather restricted, whereas the polyoxyethylene (POE) chain can undergo segmental motion to some extent. The molecular motion of the surfactants in the V1 phase, which appears between the H1 and LR phases, is quite rapid and is close to that in the liquid phase. The V1 phase is known to show the highest bulk viscosity in the mesophases due to the network structure constituted by the surfactant bilayer. The rapid motion of C12E7 in the V1 phase suggests that the surfactant molecules are packed rather loosely in the surfactant bilayer. The signal of carbon atoms in the POE chain was shifted upfield by the addition of water in a manner that the extent increased with the increase in water content in the mixture, which reflects the hydration of the POE chain. In addition, the signal of thePOEcarbons was shifted downfield rather continuously by the temperature rise, suggesting that the dehydration of the POE chain proceeds with the increase in temperature.

Large unilamellar vesicles composed of a nonionic synthetic glycolipid, 1,3-di-O-phytanyl-2-O-(¯-D-maltotriosyl)glycerol exhibited a pH-dependent aggregation-disaggregation process; vesicle aggregation occurred in a lower pH region and vesicle disaggregation occurred in a higher pH region. This process was almost reversible and the aggregation threshold pH increased as NaCl concentration increased. Electrophoretic mobility measurements revealed that the glycolipid vesicles are negatively charged in the range pH 1.6-13. The change in ³-potentials as functions of pH and NaCl concentration could be well described by the Gouy-Chapman expression of the surface charges with an assumption that the interfacial charges arise from the "adsorption" of OH¡ at the vesicle-water interface and the dissociation of hydroxyl groups of the sugar headgroup in a higher pH regime (>pH 10). The pHdependent aggregation process was reasonably well described by the classical DLVO theory. Thus, the double-layer repulsive forces appear to be a major factor in stabilizing the glycolipid vesicle suspension.