Langmuir. 2018 Jul 17;34(28):8379-8387. doi: 10.1021/acs.langmuir.8b01455. Epub 2018 Jul 3.
Monoglycerides form lipophilic liquid-crystalline (LC) phases when mixed with water. The corresponding LC nanostructures coexist with excess water, which is a necessary condition for the formation of internally nanostructured dispersed particles. These nanostructures comprise bicontinuous cubic phases, inverted hexagonal phases, and inverted micellar cubic phases. The dispersed particles are therefore named cubosomes, hexosomes, or micellar cubosomes. Such dispersions are usually stabilized by hydrophilic high-molecular-weight triblock (TB) copolymers. Another way to stabilize such dispersions is by forming the so-called Pickering or Ramsden emulsions using nanoparticles as stabilizers. In this contribution, we explore the possibility of forming and stabilizing inverted or reverse systems, that is, dispersions of hydrophilic LC phases in an excess oil phase like tetradecane. Our aim was to change from oil-in-water emulsions to water-in-oil emulsions, where the water phase is a LC phase in equilibrium with excess oil and where the oil is nonpolar, for example, an alkane. This work consists of three parts: (1) to find a hexagonal hydrophilic LC phase that can not only incorporate a certain amount of tetradecane but can also coexist with excess tetradecane in the case of higher oil concentration, (2) to find a suitable stabilizer-either polymeric or nanoparticle type-that can stabilize the emulsion without destroying the hexagonal LC phase, and finally (3) to check the stability of this reverse hexosome emulsion. We discovered that it is possible to create a hexagonal hydrophilic LC phase with short-chain nonionic surfactants such as polyethylene glycol alkyl ethers or with high-molecular-weight TB copolymers of type A-B-A. Furthermore, it is possible to successfully stabilize the reverse hexosomes with low hydrophilic-lipophilic balance TB copolymers-either synthesized in our laboratory or commercially available ones-as well as with hydrophobized, commercially available silica nanoparticles.
单甘油脂与水混合时会形成亲脂性液晶（LC）相。相应的 LC 纳米结构与过量的水共存，这是形成内部纳米结构分散颗粒的必要条件。这些纳米结构包括双连续立方相、反相六方相和反相胶束立方相。因此，分散颗粒被命名为立方溶胶囊、六方溶胶囊或胶束立方溶胶囊。这些分散体通常由亲水性高分子量三嵌段（TB）共聚物稳定。另一种稳定此类分散体的方法是使用纳米颗粒作为稳定剂形成所谓的 Pickering 或 Ramsden 乳液。在本贡献中，我们探索了形成和稳定反相或反向系统的可能性，即亲水性 LC 相在过量油相（如十四烷）中的分散体。我们的目的是将油包水乳液转变为水包油乳液，其中水相是与过量油相平衡的 LC 相，而油相是非极性的，例如烷烃。这项工作分为三个部分：（1）找到一种可以不仅包含一定量的十四烷，而且在较高油浓度下也可以与过量的十四烷共存的六角亲水 LC 相；（2）找到一种合适的稳定剂-无论是聚合物还是纳米颗粒类型-可以在不破坏六角 LC 相的情况下稳定乳液；最后（3）检查这种反向六方溶胶囊乳液的稳定性。我们发现，使用短链非离子表面活性剂（如聚乙二醇烷基醚）或高分子量的 A-B-A 型 TB 共聚物，可以形成六角亲水 LC 相。此外，使用低亲水-亲油平衡 TB 共聚物-无论是在我们实验室合成的还是市售的-以及经过疏水化处理的市售二氧化硅纳米颗粒，都可以成功地稳定反向六方溶胶囊。
