Asymmetrically Branched Nonionic Oligooxyethylene Va-Surfactants: Effect of Molecular Geometry on Liquid-Crystalline Phase Behavior, 5
✍ Scribed by Krystyna Kratzat; Heino Finkelmann
- Publisher
- Elsevier Science
- Year
- 1996
- Tongue
- English
- Weight
- 326 KB
- Volume
- 181
- Category
- Article
- ISSN
- 0021-9797
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✦ Synopsis
on temperature, concentration, and, mainly, the structure of This work describes the synthesis of new branched, nonionic Vthe molecules. The influence of the molecular structure on surfactants, with the general formula C k C n GE 8 M, where C k and the shape of the micelles in the absence of micellar interac-C n denote different alkyl chains, with k Å 4 for n-butyl (C 4 ) or tions has already been introduced by Israelachvili et al. (2).
tert-butyl (C t 4 ) and n Å 10, 12, G denotes a triglyceryl unit, and These authors defined a critical packing parameter F, E 8 M denotes octaoxyethylene monomethyl ether. These surfactants with an asymmetrically branched lipophilic moiety are synthesized to analyze the influence of the hydrocarbon part structure
on the packing effects on amphiphilic layers in a binary surfactant/ water system. The lyotropic LC-phase behavior of these surfacwhere V l denotes the volume of the lipophilic moiety, l c the tants is investigated by polarizing microscopy and X-ray diffraction. They consist of hexagonal, bicontinuous cubic, and lamellar critical lipophilic chain length, and A the surface area of the phases. The structural differences between n-or tert-butyl chain surfactant at the interface. In view of this model, the shapes within the asymmetrical V-isomers leads to a different phase beof micelles (spherical, cylindrical, or bilayer) depend on the havior, especially in view of the existence region of the lamellar value of F. Therefore, in a given system any variation of phase. Compared to other branched oligooxyethylene surfactants V l , l c , or A is directly reflected in the micellar shape and of the same apolar-polar volume ratio but different molecular should also influence the LC-phase structure at higher surfacarchitecture, the phase diagrams of the asymmetrically branched tant concentrations.
surfactant/water systems show a stabilization of the hexagonal
To elucidate pure packing effects on the micellar shape phase. These results confirm clearly the influence of molecular and the LC-phase structures, we previously presented a congeometry on the lyotropic phase behavior. Furthermore, the influcept (3) which allows us to modify the molecular structure ence of the different hydrocarbon part structures of double-alkyl
and, therefore, the packing parameter F without affecting chain surfactants on the self-organization in water is discussed and a structure parameter for these surfactants is defined. ᭧ 1996 the apolar-polar volume ratio (V l /V h ) and the hydrophilic-Academic Press, Inc.