Investigation On The Self-assembled Structures And Rheological Properties Of Mixed Systems Containing Siloxane Surfactants

In surfactant sciences, investigations on the phase behavior, self-assembled structures, and macroscopic properties of surfactants in aqueous solutions are one of the most important research subjects. Both in single surfactant systems and mixed systems, surfactants could self-aggregate into various kinds of aggregates, while in applications, mixed surfactant systems are more economical and effective than systems containing only one kind of surfactant. Generally in a lot of fields, they are used with some different kinds of surfactants mixed, so investigations on the phase behavior, aggregates, and macroscopic properties such as surface and rheological properties of surfactant mixed systems have been one of the most important issues in colloid and interface sciences. Nonionic surfactants (mainly polyoxyethylene nonionic surfactants) show rich phase behavior in water or organic solvents, self-aggregating into aggregates like micelle, hexagonal phase, cubic phase and lamellar structure, etc. Investigations on nonionic surfactant mixed systems may enrich the research contents of aggregation behavior of surfactants, settling certain theoretical bases for some surfactant application fields, such as cosmetics, coatings, oil exploration and nanometer materials with surfactant aggregates as the templates.In this thesis, we focused on the investigations of polyoxyethylene nonionic mixed system and the combination of trisiloxane nonionic surfactant with anionic hydrocarbon surfactant. With the applications of cryo-TEM, FF-TEM, small angle X-ray scattering (SAXS), and2H NMR etc, we investigated the phase behavior, self-assembled structures and the properties of the mixed solutions. The main contents are shown as follows:In the first chapter, we briefly introduced the basic knowledge referred in this thesis, technological means generally used in surfactant sciences, the areas of the research topic, and the research contents and significances of this paper.In Chapter2we studied the phase behavior, self-assembly, and the rheological properties of C12EO4/APTES/H2O system. With the variation of the composition, rich aggregation behavior can be obtained. The transition of self-assembled structures from vesicle with higher curvatures to planar lamellar structure with low curvatures at the addition of APTES to C12EO4aqueous solution was observed and the viscoelasticity decreases. At a fixed APTES concentration, when C12EO4concentration increases, a transition from vesicle to the co-existence of vesicles and planar lamellae occurs.In the third chapter, the phase behavior, microstructures of the aggregates and surface and rheological properties in M(D’EO5.5)M/AOT/H2O mixed system were investigated. M(D’EO5.5)M molecules could form planar lamellar phase and vesicles, while planar lamellar phase could be formed in AOT/H2O system during a wide concentration range. In the mixed system of M(D’EO5.5)M/AOT/H2O, two transition processes occurred as vesicles to the coexistence of vesicles and planar lamellae and planar lamellae to the coexistence of vesicles and planar lamellae. The interaction between the two surfactants was found to be much weaker. γcmc and cmc of the mixrures with different ratios of the two surfactants were both higher than single surfactant, and closer to those of M(D’EO5,5)M, indicating that M(D’EO5.5)M molecules are easier to be adsorbed at the interface, while AOT is more favorable to construct aggregates with long-range order.