Abstract
Gelled lyotropic liquid crystals can be formed by adding a gelator to a mixture of surfactant and solvent. If the gel network and the liquid-crystalline phase coexist without influencing each other, the self-assembly is called orthogonal. In this study, the influence of the organogelator 12-hydroxyoctadecanoic acid (12-HOA) on the lamellar and hexagonal liquid crystalline phases of the binary system H2O–C12E7 (heptaethylene glycol monododecyl ether) is investigated. More precisely, we added 12-HOA at mass fractions from 0.015 to 0.05 and studied the resulting phase diagram of the system H2O–C12E7 by visual observation of birefringence and by 2H NMR spectroscopy. In addition, the dynamic shear moduli of the samples were measured in order to examine their gel character. The results show that 12-HOA is partly acting as co-surfactant, manifested by the destabilization of the hexagonal phase and the stabilization of the lamellar phase. The higher the total surfactant concentration, the more 12-HOA is incorporated in the surfactant layer. Accordingly, its gelation capacity is substantially reduced in the surfactant solution compared to the system 12-HOA–n-decane, and large amounts of gelator are required for gels to form, especially in the lamellar phase.
Highlights
Gelled complex fluids [1], in which the mechanical stability of a gel is combined with the microstructure of a complex fluid, are interesting candidates fordermal drug delivery systems and tissue healing applications [1,2]
Its gelation capacity is substantially reduced in the surfactant solution compared to the system 12-hydroxyoctadecanoic acid (12-HOA)–n-decane, and large amounts of gelator are required for gels to form, especially in the lamellar phase
The visual phase studies allowed us to determine the occurrence of lyotropic liquid crystals via optical birefringence
Summary
Gelled complex fluids [1], in which the mechanical stability of a gel is combined with the microstructure of a complex fluid, are interesting candidates for (trans-)dermal drug delivery systems and tissue healing applications [1,2]. Additional applications of this class of materials can be found in a recent review by Stubenrauch and Gießelmann [1]. Examples of gelled Lα phases, known in literature are the cell [3], lamellar biogels [4], and gelled lamellar phases of synthetic surfactants.
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