Unilever Research and Development, Port Sunlight Laboratory, Quarry Road East, Bebington, Wirral CH63 3JW, U.K.
ISIS Facility, STFC, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, OXON, U.K.
Langmuir. 2020 Jun 2;36(21):5997-6006. doi: 10.1021/acs.langmuir.0c00922. Epub 2020 May 18.
Saponins are highly surface active glycosides, derived from a wide range of plant species. Their ability to produce stable foams and emulsions has stimulated their applications in beverages, foods, and cosmetics. To explore a wider range of potential applications, their surface mixing properties with conventional surfactants have been investigated. The competitive adsorption of the triterpenoid saponin escin with an anionic surfactant sodium dodecyl sulfate, SDS, at the air-water interface has been studied by neutron reflectivity, NR, and surface tension. The NR measurements, at concentrations above the mixed critical micelle concentration, demonstrate the impact of the relative surface activities of the two components. The surface mixing is highly nonideal and can be described quantitatively by the pseudophase approximation with the inclusion of the quadratic and cubic terms in the excess free energy of mixing. Hence, the surface mixing is highly asymmetrical and reflects both the electrostatic and steric contributions to the intermolecular interactions. The relative importance of the steric contribution is reinforced by the observation that the micelle mixing is even more nonideal than the surface mixing. The mixing properties result in the surface adsorption being largely dominated by the SDS over the composition and concentration range explored. The results and their interpretation provide an important insight into the wider potential for mixing saponins with more conventional surfactants.
皂苷是高度表面活性的糖苷，源自广泛的植物物种。它们产生稳定泡沫和乳液的能力激发了它们在饮料、食品和化妆品中的应用。为了探索更广泛的潜在应用，研究了它们与传统表面活性剂的表面混合特性。通过中子反射率（NR）和表面张力研究了三萜皂苷 escin 与阴离子表面活性剂十二烷基硫酸钠（SDS）在气-水界面的竞争吸附。在混合临界胶束浓度以上的浓度下进行的 NR 测量表明了两种成分相对表面活性的影响。表面混合是高度非理想的，可以通过包括混合过剩自由能中的二次和三次项的拟相近似来定量描述。因此，表面混合非常不对称，反映了分子间相互作用的静电和空间贡献。混合的高度非理想性表明，胶束混合比表面混合更不对称，这进一步证实了空间贡献的重要性。混合特性导致表面吸附在探索的组成和浓度范围内主要由 SDS 主导。这些结果及其解释为皂苷与更常规表面活性剂混合的更广泛潜力提供了重要的见解。
