Lagerge S, Keh E, Partyka S, Lindheimer M
Laboratoire des Agrégats Moléculaires et Matériaux Inorganiques, C.N.R.S., UMR 5072, Université de Montpellier II, Case 015, Place E. Bataillon, Montpellier Cedex 05, 34095, France
J Colloid Interface Sci. 2000 Jul 15;227(2):412-420. doi: 10.1006/jcis.2000.6901.
The behavior of two polydisperse nonionic surfactants, poly (oxyethylene) glycol alkylphenyl ether TX-35 and TX-100, at the prewetted silica gel/n-heptane and dried silica gel/n-heptane interfaces has been compared by the determination of the average adsorption isotherms of the polydisperse surfactants and of displacement enthalpies. From HPLC experiments, we could also separately quantify the adsorption of each ethyleneoxide (EO) fractions for silica gel from the polydisperse surfactant solution. The adsorption isotherms clearly indicate an incomplete preferential adsorption of the large (EO) chains over the small ones, as well on dried silica gel as on a prehydrated sample. This preferential adsorption and its driving force follow the solubility rules of the poly(oxyethylene) glycol alkylphenyl ether in an apolar solvent and support the idea of a solubility-limited adsorption: solubility in organic solvents of the smaller (EO) chains is much more significant than that of the longer ones and hence prevents adsorption of the smaller species. Consequently, it is observed that the presence of interfacial water decreases the affinity of TX-35 molecules for the hydrophilic silica surface due to the hydration of (EO) chains. In contrast, for TX-100 adsorption after the prewetting treatment the clearest trend is a drastic increase of the adsorption ascribed to the additional solubilization (and micellization) of the TX-100 molecules in the interfacial aqueous phase. The differential molar enthalpies of displacement show a change in the adsorption mechanism, depending on the presence of molecular water on the surface. In the initial part of the adsorption isotherm, a prevailing exothermic process is obtained with prehydrated silica and suggests that hydration of the polar heads of TX-35 and the solubilization of the TX-35 in interfacial water are occurring. For higher equilibrium concentrations, the enthalpies of displacement observed with the prehydrated adsorbent become slightly lower than those obtained with dry silica gel. It may be that this difference is due to the micellization phenomenon of the surfactant species with longer EO chains in interfacial water. These features emphasize the influence of interfacial water on the adsorption of EO fractions from organic solvent. Copyright 2000 Academic Press.
通过测定多分散表面活性剂的平均吸附等温线和置换焓，比较了两种多分散非离子表面活性剂聚（氧乙烯）二醇烷基苯基醚TX - 35和TX - 100在预湿硅胶/正庚烷界面和干燥硅胶/正庚烷界面的行为。通过高效液相色谱实验，我们还可以从多分散表面活性剂溶液中分别定量硅胶对每个环氧乙烷（EO）组分的吸附。吸附等温线清楚地表明，无论是在干燥硅胶还是预水合样品上，大的（EO）链相对于小的链都存在不完全的优先吸附。这种优先吸附及其驱动力遵循聚（氧乙烯）二醇烷基苯基醚在非极性溶剂中的溶解度规则，并支持溶解度限制吸附的观点：较短（EO）链在有机溶剂中的溶解度比长链的溶解度大得多，因此阻止了较小物种的吸附。因此，可以观察到，由于（EO）链的水合作用，界面水的存在降低了TX - 35分子对亲水性硅胶表面的亲和力。相反，对于预湿处理后的TX - 100吸附，最明显的趋势是吸附量急剧增加，这归因于TX - 100分子在界面水相中的额外增溶（和胶束化）。置换的微分摩尔焓表明吸附机制发生了变化，这取决于表面上分子水的存在。在吸附等温线的初始部分，预水合硅胶获得了主要的放热过程，这表明TX - 35的极性头发生了水合作用，并且TX - 35在界面水中发生了增溶。对于较高的平衡浓度，预水合吸附剂观察到的置换焓略低于干燥硅胶获得的置换焓。这种差异可能是由于界面水中具有较长EO链的表面活性剂物种的胶束化现象。这些特征强调了界面水对有机溶剂中EO组分吸附的影响。版权所有2000年学术出版社。
