Changes of mesophase structure of BRIJ 96/water mixtures on addition of liquid paraffin

The influence of the addition of liquid paraffin (LP) on the structure of the lamellar (Lα) and hexagonal (H1) mesophases formed in mixtures of water (W) and BRIJ 96 (B) was studied. Mesophases were identified using polarization microscopy and small angle x-ray diffraction (SAXD). Repeat spacings were also determined with SAXD. Depending on theW/B ratio, addtion ofLP toLα gives a large, almost linear one-dimensional swelling or an initial swelling followed by a gradual transition to H1.Lα with a highLP-content gives a diffraction pattern showing only the first order diffraction maximum, possibly a result of undulations of the layers. The lamellar structure, however, was confirmed using freeze fracture electron microscopy (FFEM). Addition ofLP to H1 gives an initial swelling followed by a transition to a transparent, highly viscous, isotropic phase, called the gel-phase (G). The diffraction pattern obtained fromG yields little information on its structure. A large swelling ofG withLP was observed. From the degree of swelling as a function of hydrocarbon content it was inferred that this phase consists of spherical aggregates forming a close-packed structure. Using FFEM, textures were visualized resembling those obtained from the isotropic mesophase (I1) in water-surfactant mixtures. Finally, geometrical factors are discussed that may play a role in the formation of the gel-phase.