Physical and Theoretical Chemistry Laboratory, University of Oxford , South Parks Road, Oxford OX1 3QZ, U.K.
Rutherford-Appleton Laboratory, STFC , Chilton, Didcot, Oxfordshire OX11 0RA, U.K.
J Phys Chem B. 2017 Apr 6;121(13):2825-2838. doi: 10.1021/acs.jpcb.7b01337. Epub 2017 Mar 28.
The composition of the adsorbed layer of a ternary surfactant mixture at the air-water interface has been studied by neutron reflectivity. The adsorption of the ternary mixture of octaethylene monododecyl ether (CE) sodium dodecyl 6-benzene sulfonate (LAS), and sodium dioxyethylene glycol monododecyl sulfate (SLES), as well as each of the binary mixtures, at solution concentrations greater than the mixed critical micelle concentration is highly nonideal. In the ternary mixture, the surface adsorption is dominated by CE and LAS, and there is little SLES at the interface. The departure from ideality in the binary mixtures can be quantitatively described by applying the pseudophase approximation with quadratic and cubic terms in the excess free energy of mixing (G) both at the surface and in the micelles. The same parameters that describe the binary interactions give a quantitative fit to the adsorbed fractions in the ternary mixture over a wide range of composition. A similar analysis is effective for the mixture containing sodium dodecyl sulfate instead of SLES. Of the set of six G required to fit the ternary data, one is ideal (SLES-LAS) and three, LAS-CE (micelle) and CE-SLES (micelle and surface), have minima occurring at a composition (mole fraction) of the anionic species of 1/3.
通过中子反射率研究了三元表面活性剂混合物在气-水界面上吸附层的组成。在溶液浓度大于混合临界胶束浓度的情况下，辛基聚氧乙烯十二醚（CE）十二烷基硫酸钠（LAS）和二氧乙烯二醇单十二烷基硫酸盐（SLES）三元混合物以及每种二元混合物的吸附都是高度非理想的。在三元混合物中，表面吸附由 CE 和 LAS 主导，界面上几乎没有 SLES。二元混合物中偏离理想状态可以通过在表面和胶束中混合过剩自由能（G）中应用二次和三次项的拟相近似来定量描述。描述二元相互作用的相同参数可以在很宽的组成范围内对三元混合物中的吸附分数进行定量拟合。对于含有十二烷基硫酸钠而不是 SLES 的混合物，类似的分析是有效的。为了拟合三元数据，需要设置六个 G，其中一个是理想的（SLES-LAS），三个是 LAS-CE（胶束）和 CE-SLES（胶束和表面），它们的最小值出现在阴离子物质的摩尔分数为 1/3 的组成处。
