K. Kratzat et al., BRANCHED FLUORINATED NONIONIC Y-SHAPED SURFACTANTS - EFFECT OF MOLECULAR-GEOMETRY ON LIQUID-CRYSTALLINE PHASE-BEHAVIOR, Langmuir, 12(26), 1996, pp. 6346-6350
The synthesis of branched partially fluorinated nonionic Y-shaped surf
actants, with the general formula (CnC2N)-C-F(E(m)M)(2), where C-n(F)
denotes fluorinated alkyl chain F(CF2)(n) with n = 4-10, C-2 is C2H2,
and E(m)M is oligooxyethylene monomethyl ether with m = 2, 3, and thei
r hydrocarbon analogs Cn+2N(E(m)M)(2) (C-n equals hydrocarbon chain) i
s described. These surfactants are synthesized to analyze the influenc
e of the fluorinated alkyl chain on the packing effects to amphiphilic
layers in a binary surfactant/water system. The lyotropic phase behav
ior of these surfactants is investigated by polarizing microscopy. The
liquid crystalline (LC) phase polymorphism of the fluorinated (CnC2N)
-C-F(E(3)M)(2) surfactants strongly changes with n from hexagonal H-1
phase (n = 6) to lamellar L(alpha) phase (n = 10). In contrast to othe
r Y-shaped hydrocarbon oligooxyethylene surfactants C(m)G(E(m)M)(2) (w
here G denotes a glycerol unit) which form only cubic I-1 and H-1 phas
es for n = 12-16 and m = 3-5, the phase behavior of the (CnC2N)-C-F(E(
m)M)(2) surfactant/water systems shows a remarkable change in the LC p
hase polymorphism (from H-1 to L(alpha) phase) with n and m. Compared
to hydrocarbon surfactants these results distinctly confirm the influe
nce of more rigid fluorinated alkyl chain on the phase behavior.