Graduate School of Environment and Information Sciences, Yokohama National University.
Research Institute for Bioscience Products & Fine Chemicals, Ajinomoto Co., Inc.
J Oleo Sci. 2022 Aug 4;71(8):1169-1180. doi: 10.5650/jos.ess22080. Epub 2022 Jul 6.
Hydrogels formed by low-molecular-weight gelators have reversible sol-gel transition and responsiveness to various stimuli, and are used in cosmetics and drug applications. It is challenging to obtain hydrogels using novel gelators because subtle differences in their molecular architecture affect gelation. Organogelators (which form organogels) are insoluble in water, and their use as hydrogelators has not previously been considered. However, a surfactant-mediated gelation method was reported in which organogelators were solubilized in water by surfactants to form hydrogels using 12-hydroxyoctadecanoic acid. To investigate whether this method can be applied with other organogelators, the formation of hydrogel using a glutamic-acid-based organogelator was studied here. Hydrogels were formed by solubilizing 1:1 mixtures of glutamate-based organogelators, N-lauroyl-L-glutamic acid dibuthylamide, and N-2-ethylhexanoyl-L-glutamic acid dibutylamide in aqueous micellar solutions of anionic surfactant (sodium lauroyl glutamate) and cationic surfactant (cetyltrimethylammonium chloride). The minimum gelation concentration of the hydrogel was ~0.2-0.6 wt%. By changing the molar fraction of cetyltrimethylammonium chloride in the mixed surfactant, either spherical or wormlike micelles were formed. The hydrogel with wormlike micelles had a higher sol-gel transition temperature than that with spherical micelles and formed fine self-assembled fibrillar networks. Additionally, the hydrogel with the spherical micelles was elastic, whereas that with wormlike micelles was viscoelastic, suggesting that networks of the organogelators and wormlike micelles coexisted in the hydrogel from the wormlike micellar solution. Moreover, the hydrogel suppressed the reduction in the storage modulus at higher temperatures compared with the micellar aqueous solution, indicating that the elastic properties of the organogelator networks were maintained at high temperatures. The gel fibers of the hydrogel partially formed a loosely aggregated structure as the temperature increased, the fibers bundled via hydrophobic interactions, and new cross-linking points formed spontaneously. This phenomenon corresponded with an inflection point in the temperature-dependent storage modulus of the hydrogel.
由低分子量凝胶剂形成的水凝胶具有可逆的溶胶-凝胶转变和对各种刺激的响应性，因此被应用于化妆品和药物领域。使用新型凝胶剂获得水凝胶具有挑战性，因为其分子结构的细微差异会影响凝胶形成。有机凝胶剂（形成有机凝胶）不溶于水，以前并未考虑将其用作水凝胶剂。然而，据报道有一种表面活性剂介导的凝胶化方法，其中通过表面活性剂将有机凝胶剂溶解在水中，然后使用 12-羟基十八酸形成水凝胶。为了研究该方法是否可以应用于其他有机凝胶剂，本文研究了使用基于谷氨酸的有机凝胶剂形成水凝胶的情况。通过在阴离子表面活性剂（谷氨酸钠）和阳离子表面活性剂（十六烷基三甲基氯化铵）的胶束水溶液中溶解 1:1 混合物的基于谷氨酸的有机凝胶剂、N-月桂酰基-L-谷氨酸二丁酰胺和 N-2-乙基己酰基-L-谷氨酸二丁酰胺，形成水凝胶。水凝胶的最低凝胶浓度约为 0.2-0.6wt%。通过改变混合表面活性剂中十六烷基三甲基氯化铵的摩尔分数，可以形成球形或蠕虫状胶束。具有蠕虫状胶束的水凝胶的溶胶-凝胶转变温度高于具有球形胶束的水凝胶，并且形成了精细的自组装纤维状网络。此外，具有球形胶束的水凝胶具有弹性，而具有蠕虫状胶束的水凝胶具有粘弹性，表明在从蠕虫状胶束溶液形成的水凝胶中，有机凝胶剂网络和蠕虫状胶束共存。此外，与胶束水溶液相比，水凝胶在较高温度下抑制了储能模量的降低，表明在较高温度下有机凝胶剂网络的弹性性质得以保持。随着温度的升高，水凝胶的凝胶纤维部分形成了松散聚集的结构，纤维通过疏水相互作用聚集在一起，并且新的交联点自发形成。这一现象与水凝胶的储能模量随温度变化的拐点相对应。
