Branched Fluorinated Nonionic Y-Shaped Surfactants. Effect of Molecular Geometry on Liquid Crystalline Phase Behavior

Abstract

The synthesis of branched partially fluorinated nonionic Y-shaped surfactants, with the general formula CFnC2N(EmM)2, where CFn denotes fluorinated alkyl chain F(CF2)n with n = 4−10, C2 is C2H2, and EmM is oligooxyethylene monomethyl ether with m = 2, 3, and their hydrocarbon analogs Cn+2N(EmM)2 (Cn equals hydrocarbon chain) is described. These surfactants are synthesized to analyze the influence of the fluorinated alkyl chain on the packing effects to amphiphilic layers in a binary surfactant/water system. The lyotropic phase behavior of these surfactants is investigated by polarizing microscopy. The liquid crystalline (LC) phase polymorphism of the fluorinated CFnC2N(E3M)2 surfactants strongly changes with n from hexagonal H1 phase (n = 6) to lamellar Lα phase (n = 10). In contrast to other Y-shaped hydrocarbon oligooxyethylene surfactants CnG(EmM)2 (where G denotes a glycerol unit) which form only cubic I1 and H1 phases for n = 12−16 and m = 3−5, the phase behavior of the CFnC2N(EmM)2 surfactant/water ...