Equilibrium and Nonequilibrium Properties of Nonionic Surfactant Membranes

Sammanfattning: An extensive investigation of the multilamellar vesicles (La'), lamellar (La), and multiply connected sponge (L3) phase formed in surfactant systems is presented in this thesis. These membrane structures were studied using surfactant systems containing poly(oxyethylene) alkyl ethers, n-CnH2n+1(OCH2CH2) mOH, commonly abbreviated as CnEm. This class of nonionic surfactants, often viewed as short AB block copolymer, is ideal for use as model systems since the hydrophilic head group, m, or the hydrophobic tail, n, can be varied systematically. An important feature of the CnEm surfactants is the significant temperature dependence arising from the temperature-sensitive nature of the water-polyethylene oxide interaction. Making use of these unique properties, the C12E5-n-decane-water system was selected to investigate the thermodynamics and kinetics of the multiply connected (sponge-like) membrane using static light scattering (SLS), dynamic light scattering (DLS), and joule heating temperature jump (JHTJ); the C10E3-water system to investigate the topological transformation from multilamellar vesicles to planar lamellar to sponge structure under shear using small-angle neutron scattering (SANS) and small-angle x-ray scattering (SAXS); and the C12E4-water system to investigate the packing states of the shear-induced multilamellar vesicles using SANS. Measurements from scattering methods and from phase equilibria were analyzed within the framework of the elastic curvature energy concept. In this thesis, we report the thermodynamics, kinetics, effect of shear, shapes and sizes, membrane rigidity, stability, and instability of these membrane structures.