Steck Katja, Schmidt Claudia, Stubenrauch Cosima
Institute of Physical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany.
Department of Chemistry, University of Paderborn, Warburger Straße 100, 33098 Paderborn, Germany.
Gels. 2018 Sep 12;4(3):78. doi: 10.3390/gels4030078.
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⁻CE₇ (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⁻CE₇ 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⁻-decane, and large amounts of gelator are required for gels to form, especially in the lamellar phase.
通过向表面活性剂和溶剂的混合物中添加胶凝剂，可以形成凝胶状溶致液晶。如果凝胶网络和液晶相共存且互不影响，则这种自组装被称为正交。在本研究中，研究了有机胶凝剂12-羟基十八烷酸（12-HOA）对二元体系H₂O⁻CE₇（七甘醇单十二烷基醚）的层状和六方液晶相的影响。更确切地说，我们添加了质量分数为0.015至0.05的12-HOA，并通过双折射的目视观察和²H NMR光谱研究了所得的H₂O⁻CE₇体系相图。此外，测量了样品的动态剪切模量以检查其凝胶特性。结果表明，12-HOA部分充当了共表面活性剂，表现为六方相的不稳定和层状相的稳定。总表面活性剂浓度越高，12-HOA掺入表面活性剂层中的量就越多。因此，与12-HOA⁻癸烷体系相比，其在表面活性剂溶液中的胶凝能力大幅降低，形成凝胶需要大量的胶凝剂，尤其是在层状相中。
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