Control of dispersion stability of colloidal systems by the adsorption layers of amphiphilic molecules

1.测定了带负电荷的聚苯乙烯胶乳（PSL）分散液在烷基三甲基溴化铵溶液中的浊度和浊度-电位随表面活性剂浓度的变化。由于阳离子表面活性剂的吸附作用，聚苯乙烯颗粒的静电势随表面活性剂浓度的增加而增大。当表面活性剂浓度约为0.05时，PSL具有快速凝固特性。2 μM时，PSL的表面电位和表面电荷仍为负。同时，通过AFM直接力测量证实，在阳离子表面活性剂溶液中，聚苯乙烯微球与硅胶板之间的粘附能在该表面活性剂浓度（2 μM）下最大。提出了吸附阳离子表面活性剂分子的聚苯乙烯颗粒表面结构模型.本文以磷脂在胶体颗粒表面的吸附层为模型，研究了磷脂在水介质中形成的双层膜的力学性质。采用交流电电铸法制备了磷脂巨囊泡，并在光学显微镜下进行了微吸管抽吸实验，测定了磷脂巨囊泡的面积膨胀模量。据证实，通过引入一个疏水肽，短杆菌肽A，到脂质双层，膨胀模量降低，而它增加时，胆固醇加入到双层。从这些结果，我们可以预期，短杆菌肽A的加入磷脂可能会导致积极的效果的胶体稳定性的分散体系，因为来自于吸附的脂质层的波动的胶体颗粒之间的排斥力增强。

1. Turbidity and ζ-potential of negatively charged polystyrene latex (PSL) dispersions in alkyltrimethylammonium bromide solutions were measured as a function of the surfactant concentration. By the adsorption of the cationic surfactants, the ζ-potential of polystyrene particles increased with the surfactant concentration. The rapid coagulation of PSL was observed when the surfactant concentration was ca. 2 μM where ζ-potential and the surface charge of PSL were still negative. Also, it was confirmed by the direct force measurements using AFM that the adhesion energy between a polystyrene micro-sphere and silica plate in cationic surfactant solution was the largest at this surfactant concentration (2 μM). We proposed a model for the surface structure of polystyrene particles adsorbing cationic surfactant molecules.2. Mechanical properties of bilayer membranes made of phospholipids in aqueous medium were studied as a model system of the adsorbed layers of amphiphilic molecules on colloidal particles. Giant vesicles of phospholipids were prepared by the so-called alternative current electroformation method, and the micropipet aspiration experiments were performed under the optical microscope observation to estimate the area expansion modulus of the bilayer. It was confirmed that by introducing a hydrophobic peptide, gramicidin A, into the lipid bilayers, the expansion modulus was decreased whereas it was increased when cholesterol was added into the bilayers. From these results, we could expect that the addition of gramicidin A to phospholipids may lead the positive effect for the colloidal stability of the dispersion systems because of the enhanced repulsive force between the colloid particles which originated from the undulation of adsorbed lipid layers.