Institute of Physical and Theoretical Chemistry, University of Regensburg, Universitätsstrasse 31, D-93040 Regensburg, Germany.
Langmuir. 2013 Feb 26;29(8):2506-19. doi: 10.1021/la304431c. Epub 2013 Feb 12.
In preceding studies, we demonstrated that choline carboxylates ChC(m) with alkyl chain lengths of m = 12 - 18 are highly water-soluble (for m = 12, soluble up to 93 wt % soap and 0 °C). In addition, choline soaps are featured by an extraordinary lyotropic phase behavior. With decreasing water concentration, the following phases were found: micellar phase (L(1)), discontinuous cubic phase (I(1)' and I(1)"), hexagonal phase (H(1)), bicontinuous cubic phase (V(1)), and lamellar phase (L(α)). The present work is also focused on the lyotropic phase behavior of choline soaps but with shorter alkyl chains or different alkyl chain properties. We have investigated the aqueous phase behavior of choline soaps with C(8) and C(10) chain-lengths (choline octanoate and choline decanoate) and with a C(18) chain-length with a cis-double bond (choline oleate). We found that choline decanoate follows the lyotropic phase behavior of the longer-chain homologues mentioned above. Choline octanoate in water shows no discontinuous cubic phases, but an extended, isotropic micellar solution phase. In addition, choline octanoate is at the limit between a surfactant and a hydrotrope. The double bond in choline oleate leads also to a better solubility in water and a decrease of the solubilization temperature. It also influences the Gaussian curvature of the aggregates which results in a loss of discontinuous cubic phases in the binary phase diagram. The different lyotropic mesophases were identified by the penetration scan technique with polarizing light microscope and visual observations. To clarify the structural behavior small (SAXS) and wide (WAXS) angle X-ray scattering were performed. To further characterize the extended, isotropic micellar solution phase in the binary phase diagram of choline octanoate viscosity and conductivity measurements were also carried out.
在之前的研究中，我们证明了具有 12-18 个烷基链长的胆碱羧酸盐 ChC(m) 具有很高的水溶性（对于 m = 12，在 0°C 下可溶解高达 93wt%的肥皂）。此外，胆碱皂还具有非凡的溶致相行为。随着水浓度的降低，发现了以下相：胶束相（L(1)）、不连续立方相（I(1)' 和 I(1)“）、六方相（H(1)）、双连续立方相（V(1)）和层状相（L(α)）。本工作也集中在胆碱皂的溶致相行为上，但具有较短的烷基链或不同的烷基链性质。我们研究了具有 C(8)和 C(10)链长（辛酸胆碱和癸酸胆碱）以及具有顺式双键的 C(18)链长（油酸胆碱）的胆碱皂在水中的相行为。我们发现癸酸胆碱遵循上述较长链同系物的溶致相行为。水合辛酸胆碱没有不连续立方相，而是具有扩展的各向同性胶束溶液相。此外，辛酸胆碱处于表面活性剂和水溶助长剂的界限之间。油酸胆碱中的双键也导致在水中的溶解度增加和增溶温度降低。它还影响了聚集物的高斯曲率，导致在二元相图中失去不连续立方相。不同的溶致中间相通过偏光显微镜和目视观察的穿透扫描技术来识别。为了澄清结构行为，进行了小角（SAXS）和广角（WAXS）X 射线散射。为了进一步表征二元相图中辛酸胆碱的扩展各向同性胶束溶液相的结构行为，还进行了粘度和电导率测量。
