Li Ningning, Thomas Robert K, Rennie Adrian R
Physical and Theoretical Chemistry Laboratory, Oxford University,, Oxford OX1 3QZ, UK.
J Colloid Interface Sci. 2012 Jul 15;378(1):152-8. doi: 10.1016/j.jcis.2012.04.026. Epub 2012 Apr 20.
The role of ionic interactions between sodium dodecyl sulfate, SDS, and sapphire surfaces have been studied using specular neutron reflection to determine the structure and composition of adsorbed surfactant layers. Increasing the pH of the solution from 3 to 9 reduces the adsorption by reversing the charge of the alumina. This occurs at lower pH for the R-plane (1102) than the C-plane (0001), corresponding to the different points of zero charge. The largest surface excess is about 6.5 μmol m(-2), the thickness of the adsorbed layer is about 24 Å and it contains roughly 20% water. The hydrocarbon tails of the surfactant molecules clearly interpenetrate rather than form an ordered bilayer. The structure is similar in either pure water or in 0.1 M NaCl when the surfactant is at the respective critical micelle concentration. Different structures were seen with lithium and cesium dodecyl sulfate. The CsDS forms dense layers with little or no hydration and a surface excess of about 10.5 μmol m(-2). The metal cation strongly influences the hydration of the adsorbed surfactant. An overall picture of 'flattened micelles' for the structure of the adsorbed layer is observed.
利用镜面中子反射研究了十二烷基硫酸钠（SDS）与蓝宝石表面之间离子相互作用的作用，以确定吸附的表面活性剂层的结构和组成。将溶液的pH值从3提高到9，通过使氧化铝的电荷反转来减少吸附。对于R平面（1102），这种情况在比C平面（0001）更低的pH值下发生，这与不同的零电荷点相对应。最大表面过剩量约为6.5 μmol m⁻²，吸附层厚度约为24 Å，且其中约含20%的水。表面活性剂分子的烃链明显相互渗透，而非形成有序的双层结构。当表面活性剂处于各自的临界胶束浓度时，在纯水或0.1 M NaCl中结构相似。用十二烷基硫酸锂和十二烷基硫酸铯观察到了不同的结构。CsDS形成致密层，几乎没有水合作用，表面过剩量约为10.5 μmol m⁻²。金属阳离子强烈影响吸附的表面活性剂的水合作用。观察到吸附层结构的整体图景为“扁平胶束”。
