Head group effects on molecular packing in lamellar liquid crystals.

In this study, molecular packing in lamellar liquid crystals in poly(oxyethylene) dodecyl ether(C(12)EO(n)) pure systems and the two surfactant mixtures of C(12)EO(8)/1-dodecanol(C(12)EO(0)), C(12)EO(8)/lipophilic sucrose laurate (L-595), hydrophilic sucrose laurate (L-1695)/C(12)EO(2) is investigated in terms of mean molecular area and partial molecular area (PMA). Lamellar liquid crystals formed in the C(12)EO(8)/C(12)EO(0) mixed system show higher melting temperatures than those in the C(12)EO(n) pure systems, even though the average number of EO units in the mixed surfactant system is the same as in the pure system. We compared the mean molecular area at the interface between hydrophilic and lipophilic moieties in the lamellar liquid crystals in each system. In the mixed system, the molecules are packed more tightly than in the pure system. Among the C(12)EO(n) and sucrose laurate mixtures, the L-1695/C(12)EO(2) mixed system showed a smaller mean molecular area per lipophilic chain than the C(12)EO(8)/L-595 mixed system. We investigated the effect of mixing two surfactants with different head group geometry on molecular packing by comparing the PMA of each surfactant.