Polymer effects on microemulsions and lamellar phases

Abstract: The main part of this thesis deals with the effects of adsorbing and non-adsorbing polymers when mixed with microemulsion droplets and bilayers in a lamellar phase. The phase behaviour, microstructure and interactions in a nonionic surfactant/ water/ oil-system, comprising penta ethylene oxide dodecyl ether (C12E5) and decane, was investigated. The microemulsion phase was studied by small angle neutron scattering (SANS), and was shown to contain spherical oil-swollen micelles with a radius =80Å, having a low size polydispersity. The interactions between the micelles basically resemble that between hard spheres, as was shown by osmometry. The surfactant film was made weakly charged by incorporating an ionic surfactant, and the impact on phase behaviour and interactions was studied. The introduction of electrostatics affected both droplet stability and interactions, which are well described by the Poisson-Boltzmann equation. The main part of the experimental work concerns the addition of polymer and polyelectrolyte to the surfactant/water/oil system. Two types of polymers were used, poly ethylene oxide (PEO) and poly sodium acrylate (PA), and their hydrophobically modified analogues, HM-PEO and HMPA, onto which hydrophobic octadecyl chains had been anchored. While PEO and PA are non-adsorbing with respect to the surfactant film, HM-PEO and HMPA are adsorbing. Polymeric additives in most cases changed the phase behaviour. Moreover, in the case of HM-PEO and HMPA also the droplet interactions and self-diffusion were influenced, as was evidenced by SANS, NMR self-diffusion and rheology measurements. The lamellar (La) phase was studied with small angle X-ray scattering (SAXS). HM-PEO and HMPA dissolve in the La phase and lower the swelling capacity. PA and PEO are not soluble in the La phase. This polymer-incompatibility was used in an osmotic stress study of the La phase, the results of which gave support for the concentration dependence of the Helfrich undulation force and providing a value for the bilayer bending modulus.