In this work we investigated phase diagrams of CTAB and different polar solvents such as water, formamide, and glycerol in order to compare the effects of a nonaqueous solvent on the existence of intermediate phases. A small-angle X-ray scattering setup was used to observe the diffraction peak corresponding to the high values of the phase parameters and their transformations. We developed a method for rapid and continuous observation of the surfactant-solvent system over their transitions from the micellar to the lamellar phase. The following sequence of intermediate phases was identified in the CTAB/water system: hexagonal-monoclinic (close to a centered rectangular phase)-cubic-lamellar. Comparison with the results from CTAB/formamide and CTAB/glycerol systems showed the same sequence (except that the monoclinic phase existence was only found with water), but the existence regions of these phases are different and the parameters are smaller.

In this work we investigate lyotropic phases in different sugar-based surfactantlwater systems. Studies are carried out with the (N-alky1amino)-1-deoxylactitols (CS, C10, CIZ) and P-dodecyl maltoside. Liquid crystal phases are detected and lattice parameters determined by X-ray diffraction. The phases observed are the normal phases found in binary ionic or nonionic surfactantlwater systems. Schematic diagrams show the sequences of the lyotropic phases formed by these disaccharide surfactants. The difference in behavior is accounted for by the difference in chain length, hydrophilic ability, and steric hindrance of the polar head. IntroductionSurfactants derived from sugars form a large class of amphiphiles, which are currently receiving attention in view of their excellent biocompatibility and biodegradabi1ity.l Among the numerous applications of these compounds mention can be made of extraction and crystallization of membrane proteins2 and emulsification of substrates for enzymatic reaction^.^The first studies on the associative properties of these compounds were devoted to the solid-solid phase transitions and the liquid crystal properties of alkyl derivatives of carbohydrates in which the alkyl chain contained generally a t least eight carbon a t o m~.~-l~ Micellization of compounds of this family has been the subject of a few studies.13-15 More recently the surface properties of monolayers and the forces between bilayers of gangliosides

From the solution of the creeping-flow equations, the drag force on a sphere becomes infinite when the gap between the sphere and a smooth wall vanishes at constant velocity, so that if the sphere is displaced towards the wall with a constant applied force, contact theoretically may not occur. Physically, the drag is finite for various reasons, one being the particle and wall roughness. Then, for vanishing gap, even though some layers of fluid molecules may be left between the particle and wall roughness peaks, conventionally it may be said that contact occurs. In this paper, we consider the example of a smooth sphere moving towards a rough wall. The roughness considered here consists of parallel periodic wedges, the wavelength of which is small compared with the sphere radius. This problem is considered both experimentally and theoretically. The motion of a millimetre size bead settling towards a corrugated horizontal wall in a viscous oil is measured with laser interferometry giving an accuracy on the displacement of 0.1 $\mu$m. Several wedge-shaped walls were used, with various wavelengths and wedge angles.From the results, it is observed that the velocity of the sphere is, except for small gaps, similar to that towards a smooth plane that is shifted down from the top of corrugations. Indeed, earlier theories for a shear flow along a corrugated wall found such an equivalent smooth plane. These theories are revisited here. The creeping flow is calculated as a series in the slope of the roughness grooves. The cases of a flow along and across the grooves are considered separately. The shift is larger in the former case. Slightly flattened tops of the wedges used in experiments are also considered in the calculations. It is then demonstrated that the effective shift for the sphere motion is the average of the shifts for shear flows in the two perpendicular directions. A good agreement is found between theory and experiment.

A fast method for the analysis of the phase diagrams of lyotropic compounds was employed to study the formation of liquid crystals from two surfactants, cetyltrimethylammonium bromide (CTAB) and cetylpyridinium bromide (CPBr) in water. Studies were also carried out in the protic solvents, glycerol (G), formamide (FA), ethylene glycol (EG), and N-methylformamide (NMF), and the aprotic solvents, dimethylformamide (DMF) and N-methylsydnone (NMS). While the normal succession of ordered phases appeared to be governed by geometric constraints of interface curvature, the differences in behavior were accounted for by the differences in cohesion energy of the solvents and the different natures of the polar heads of the two surfactants. In DMF, a solvent with low cohesion energy, both surfactants showed only lamellar phases, whereas CPBr with a highly delocalized charge on the polar head displayed a succession of conventional phases in all the other solvents. CTAB with a localized charge formed only lamellar phases in NMF and NMS. This behavior was interpreted as resulting from headgroup solvation due to dipoledipole interactions or hydrogen bonding. The particular case of NMS was accounted for by better stacking between the planar molecules of this solvent and the pyridinium rings of CPBr.

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In this study, we investigated the micellization in water of four surfactants from the series of (N-alkylamino)lactitols by small angle neutron and X-ray scattering. These four surfactants differed from one another by the number of carbon atoms in their alkyl chain:  8, 9, 10, or 12. The comparison of the I(q) curves of the intensity scattered from micellar solutions as a function of concentration indicated that the micelle size was weakly dispersed at small concentrations. The C8 derivative presented a singular behavior which may be attributed to the formation of premicellar aggregates. The characteristic dimensions of the micelles are derived from the I(q) curve fittings. For the calculation of scattered intensity from the micelles, three models of micelles were considered:  spherical, oblate ellipsoidal, and prolate ellipsoidal. These models take into account particularities of the studied surfactants, in particular, the size of the sugar head group, which leads us to consider a nonuniform penetration of the solvent into the polar outer layer. On the other hand, the width of the polar head layer is assumed to be the same along the short and long axes of the ellipsoidal models. This means that the ellipticity of the external surface of the micelle is different from the ellipticity of the core which contains the alkyl chains. The best fit of the scattered intensity curves for the four surfactants was obtained with an oblate ellipsoidal model. The model produced a constant value of 0.55 for the ellipticity of the cores of the models. We pointed out how this particular packing is adapted to the characteristics of the (N-alkylamino)lactitol polar head, and we compared it to the other models of micelles:  spherical and prolate ellipsoidal. We also studied the evolution of several parameters (aggregation number, radius of the core, ...) as a function of the number of carbon atoms in the alkyl chain.

The motion of a spherical particle (with radius 1 to 6 mm) in a viscous fluid is measured using laser interferometry. The typical sensitivity on the measured displacement of the sphere is of the order of 50 nm. The particle is moving on the axis of a closed cylinder. The hydrodynamic interactions between the particle and the walls of the cylinder are compared with the theoretical result of Sano [J. Phys. Soc. Jpn. 56, 2713 (1987)] valid for a very small sphere. The agreement is excellent for the smallest sphere used in the experiment. The experiment also agrees with the result from the theory of lubrication when the sphere is close to a plane end wall. The effect of the particle roughness appears at small distances. Laser interferometry appears as a useful tool to study particle–wall hydrodynamic interactions when the geometry is cumbersome.

We present a comparative study of the thermotropic and lyotropic phases of 5 surfactants with an aliphatic chain of 12 carbon atoms and a cyclic or acyclic sugar head with different linkages between the two moieties. These linkages can concern different chemical groups or different orientations between the head and the chain. The compounds included the α-and β-N dodecyl-D-maltosides, N-dodecylamino-1-deoxylactitol, N-dodecyl lactobionamide and N-acetyl N-dodecyl lactosylamine. The influence of the polar head (with closed-and opened-type sugars) and the linkage with the hydrocarbon chain on the phases obtained by the heating of the anhydrous compounds and after addition of water was studied by X-ray diffraction and optical microscopy. In the anhydrous state, the surfactants were either crystalline or amorphous. On heating, they went through a liquid crystal smectic phase which, in some cases, was preceded by solid-to-solid transitions. On addition of water, the sequence of phases from the micellar phase to the lamellar phase was accounted for in terms of the geometric model of Sadoc and Charvolin. However, with certain surfactants this sequence was not complete, and the domains of existence of phases were altered. PACS. 61.30.Eb Experimental determination of smactic, nematic, cholesteric and other structures -61.10.Nz Single crystal and powder diffraction -64.70.Md Transitions in liquid crystals