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As part of a study polyoxyethylene alkyl ethers (CmEOn), water and decane, the phase diagram and the structures of the mesophases of pure C~2EO 6 and technical grade C~2EO(75 were compared. The constructed phase diagrams of the two systems show a great resemblance except for one difference: the viscous isotropic phase is only present in the C12EO 6 phase diagram.The swelling behavior of the lamellar and hexagonal phases was studied with smallangle x-ray scattering. Both the lamellar and hexagonal phases showed an ideal swelling behavior and no differences between the lamellar and hexagonal phases of the two systems were detected.With freeze-fracture electron microscopy the hexagonal and lamellar phases were visualized. No differences in the textures of the lamellar phases were found, however, the micrographs of the hexagonal phases of the two systems clearly showed different textures. While in the hexagonal phase of the C12EO 6 system only infinite long rods were visualized, short interrupted rods were found in the hexagonal phase of the C12EO(7 ) system.

Abstract." Lamellar (L~) and hexagonal (Hi) mesophases, formed in mixtures of water and polyethylene oxide (PEO) oleylethers (average EO-numbers 5 (a), 8.5 (b) and 14 (c)) and pure hexaoxyethylene dodecylether (d), were investigated with small-an~e X-ray diffraction. Analysis of repeat spacings shows a deviation from linear one-and two-dimensional swelling of L~ and P/l, respectively, when a transition to a mesophase with a larger curvature of the interface is approached. With regard to L~, in this respect similar behaviour is observed for a pure surfactant (d) and a surfactant with an EO-length distribution (b). It is proposed that, through the formation of aggregates of limited extent, water filled pores in the mesophases arise. This is confirmed by analysis of the intensity ratio of diffraction maxima of first and second order in L~. Models for finite aggregates are introduced. These consist of (1) lamellae, infinite in one direction and with variable length L in a direction perpendicular to the first, with cylindrical edges and (2) cylinders with variable length L bounded by spherical caps. According to these models, under certain conditions, finite aggregates may be formed without an increase of the interfadal area per surfactant molecule. Applying the models to the regions where non-linear swelling is observed, reasonable values for L are found, which decrease progressively when the phase transition is approached.

The influence of the addition of liquid paraffin (LP) on the structure of the lamellar (L~) and hexagonal (H1) mesophases formed in mixtures of water (W) and BRIJ 96 (/3) was studied. Mesophases were identified using polarization microscopy and small angle x-ray diffraction (SAXD). Repeat spacings were also determined with SAXD. Depending on the W/B ratio, addtion of LP to L~ gives a large, almost linear one-dimensional swelling or an initial swelling followed by a gradual transition to H1. L~ with a high LPcontent 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 of LP 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 from G yields little information on its structure. A large swelling of G with LP 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.