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

Abstract

The influence of the addition of liquid paraffin (LP) on the structure of the lamellar (L _α) 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 toL _α gives a large, almost linear one-dimensional swelling or an initial swelling followed by a gradual transition to H₁.L _α 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.