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Asymmetrically Branched Nonionic Oligooxyethylene Va-Surfactants: Effect of Molecular Geometry on Liquid-Crystalline Phase Behavior, 5

Journal of Colloid and Interface Science
Publication Date
DOI: 10.1006/jcis.1996.0411
  • Nonionic Surfactant
  • Lyotropic Liquid Crystal
  • Phase Behavior
  • Mathematics


Abstract This work describes the synthesis of new branched, nonionic V-surfactants, with the general formula C k C n GE 8M, where C k and C n denote different alkyl chains, with k= 4 for n-butyl (C 4) or tert-butyl (C t 4) and n= 10, 12, G denotes a triglyceryl unit, and E 8M 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 surfactants is investigated by polarizing microscopy and X-ray diffraction. They consist of hexagonal, bicontinuous cubic, and lamellar phases. The structural differences between n- or tert-butyl chain within the asymmetrical V-isomers leads to a different phase behavior, especially in view of the existence region of the lamellar phase. Compared to other branched oligooxyethylene surfactants of the same apolar–polar volume ratio but different molecular architecture, the phase diagrams of the asymmetrically branched surfactant/water systems show a stabilization of the hexagonal phase. These results confirm clearly the influence of molecular geometry on the lyotropic phase behavior. Furthermore, the influence of the different hydrocarbon part structures of double-alkyl chain surfactants on the self-organization in water is discussed and a structure parameter for these surfactants is defined.

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