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.

Structures formed by self-assembly of α- and β-1-n-dodecyl d-maltosides in water depend on the configuration at the anomeric center. The α-anomer forms quasi-spherical aggregates, while the β-maltoside forms larger oblate ellipsoidal micelles. This difference in behavior suggests that the configuration of the head group influences the orientation of the polar residue and hence the packing of monomers during self-assembly.

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

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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