Division of Physical Chemistry 1, Center for Chemistry and Chemical Engineering, Lund University, POB 124, SE-221 00 Lund, Sweden.
Langmuir. 2010 Jun 15;26(12):9357-67. doi: 10.1021/la1003353.
The adsorption to hydrophilic silica surfaces in relation to the bulk phase behavior was investigated by in situ null ellipsometry and bulk turbidity measurements for four cationic copolymers of varying hydrophobicity in mixtures with anionic surfactant sodium dodecylsulfate (SDS). The purpose was to reveal the effect of polyion hydrophobicity on the association with surfactant at surfaces and in the bulk. All polyelectrolytes contained 20 wt % cationic units and had similar molecular weights. An increase in surfactant concentration by the stepwise addition of SDS to a dilute polyelectrolyte solution led to an increase in both the adsorbed amount and bulk turbidity, starting at a defined SDS concentration, as a result of the formation of insoluble polyion-surfactant ion complexes. At some higher SDS concentration, the formed aggregates started to redissolve gradually in the bulk and desorb from the surface because of the overcharging of the complexes. The SDS concentration at which the maxima in adsorption and turbidity occurred increased with decreasing polyion hydrophobicity; the more hydrophobic polyions bound excess SDS more readily, and the aggregates therefore redissolved at a lower SDS concentration. The adsorption from polyelectrolyte-SDS solutions, premixed at SDS concentrations above the adsorption maximum, which occurred on diluting the solution by "rinsing" the ellipsometer cuvette with 1 mM NaCl, was also investigated. On dilution, both the turbidity and the adsorbed amount increased as the excess surfactant in the polyion-surfactant ion complexes progressively decreased. More efficient deposition was achieved if the initial SDS concentration was close to the adsorption maximum. The latter situation could be achieved either by adjusting the SDS concentration or, at a fixed SDS concentration, by choosing a polyion with the appropriate hydrophobicity.
采用原位无椭圆法和体相浊度法研究了四种不同疏水性的阳离子共聚物在与阴离子表面活性剂十二烷基硫酸钠（SDS）混合时在亲水性硅胶表面的吸附与体相行为的关系。目的是揭示聚离子疏水性对与表面活性剂在表面和体相中的缔合的影响。所有聚电解质都含有 20wt%的阳离子单元，分子量相似。通过逐步向稀聚电解质溶液中添加 SDS 来增加表面活性剂浓度，导致吸附量和体相浊度增加，起始于定义的 SDS 浓度，这是由于形成了不溶性聚电解质-表面活性剂离子复合物。在某些较高的 SDS 浓度下，由于复合物的过充电，形成的聚集体开始在体相逐渐重新溶解并从表面解吸。在吸附和浊度出现最大值时的 SDS 浓度随聚离子疏水性的降低而增加；疏水性更强的聚离子更容易结合过量的 SDS，因此在较低的 SDS 浓度下聚集体就会重新溶解。通过用 1mM NaCl“冲洗”椭圆仪池来稀释溶液，还研究了在 SDS 浓度高于吸附最大值的条件下预先混合的聚电解质-SDS 溶液的吸附。稀释时，由于聚电解质-表面活性剂离子复合物中的过量表面活性剂逐渐减少，浊度和吸附量都增加。如果初始 SDS 浓度接近吸附最大值，则可以实现更有效的沉积。后一种情况可以通过调节 SDS 浓度或在固定 SDS 浓度下选择具有适当疏水性的聚离子来实现。
