Department of Applied Mathematics, Research School of Physics and Engineering, Australian National University, Canberra 0200 ACT, Australia.
J Phys Chem B. 2012 May 24;116(20):6059-65. doi: 10.1021/jp302055e. Epub 2012 May 14.
The adsorption of nonionic surfactants such as poly(ethylene oxide) alkyl ether surfactant (C(n)E(m)) and polysorbate (commonly referred to as Tween) was studied at the titania-water interface using optical reflectometry and atomic force microscopy (AFM). Previous reports have indicated little to no adsorption of these surfactants to titania, however under certain conditions, the surface excess was high. Typically significant adsorption was only observed when the titania surface was not strongly hydrated, that is, at point of zero charge and under low ionic strength conditions. For these amorphous titania surfaces prepared using atomic layer deposition, the pzc was at pH 5.1. Furthermore, the adsorbed amount of nonionic surfactant decreased with increasing ionic strength. This was attributed to the increased hydration of the titania interface from the specific adsorption of ions inhibiting the adsorption of the strongly hydrated ethylene oxide headgroup of the surfactant. AFM force measurements at the pzc in the presence of the surfactant as a function of concentration confirmed adsorption of the surfactant. Furthermore, soft contact imaging suggests that there was a spherical aggregate adsorbed layer structure above the critical surface aggregation concentration at pH 5.1 and no additional background electrolyte. No structure was observed at lower concentrations or under other solution conditions.
使用光反射法和原子力显微镜（AFM）研究了非离子表面活性剂（如聚（氧化乙烯）烷基醚表面活性剂（C(n)E(m)）和聚山梨酯（通常称为吐温））在二氧化钛-水界面上的吸附。以前的报告表明，这些表面活性剂对二氧化钛的吸附很少或没有，但在某些条件下，表面过剩很高。通常只有在二氧化钛表面没有强烈水合时，即零电荷点和低离子强度条件下，才会观察到显著的吸附。对于使用原子层沉积制备的这些无定形二氧化钛表面，pzc 为 pH 5.1。此外，随着离子强度的增加，非离子表面活性剂的吸附量减少。这归因于离子的特异性吸附增加了二氧化钛界面的水合作用，从而抑制了表面活性剂中强水合乙氧基头基的吸附。在存在表面活性剂的情况下，在 pzc 处进行的 AFM 力测量随浓度变化证实了表面活性剂的吸附。此外，软接触成像表明，在 pH 5.1 和没有额外背景电解质的情况下，在临界表面聚集浓度以上存在球形聚集吸附层结构。在较低浓度或其他溶液条件下未观察到结构。
