Adsorption Kinetics of Polyelectrolyte onto Monolayers

用衰减全反射(ATR)法研究了电解质聚合物在溶液单分子膜上的吸附动力学。聚合物为PSSK(聚苯磺酸钾：阴离子)和单层DOAB(双十八烷基二甲基溴化铵：阳离子)。将斜边表面涂有一层(-500A)银膜的玻璃棱镜(SFS-1玻璃)压在铺在纯水上的DOAB单层上。监测了由表面等离子体激元(SPP)在银/单分子膜界面产生的ATR信号。然后用不同浓度的聚合物溶液慢慢取代亚相水。ATR倾角的移动表示吸附在单分子膜上的聚合物的厚度，宽度表示多聚物层的不均匀。我们发现，吸附分两步进行：首先是单分子(厚度-5A)的吸附层，然后是厚的、不均匀的薄膜。初始层厚与聚合物的相对分子质量无关。然而，最终厚度对分子量的依赖很弱(n=3500时d=16A，n=42000时d=33A，其中n是聚合度)，表明在这个阶段膜中存在环状和尾状。我们还发现，在我们方法的分辨率范围内，在非阳离子单层(硬脂酸)上完全没有吸附。结论：聚合物在分散的单分子膜上的吸附完全受电荷中性(至少在吸附的早期阶段)所支配，正如长期以来所推测的那样，在溶液/单分子膜界面确实形成了1：1的多离子络合物。

The adsorption kinetics of an electrolyte polymer onto a monolayer spread on the solution has been studied by means of the attenuated total reflection (ATR) method. The polymer was PSSK (potassium poly-(Stylenesulfonate) : anion) and the monolayer DOAB (dioctadecyl-dimethyl-ammonium-bromide : cation). A glass prism (SFS-1 glass) whose hypotenuse surface was coated with a thin (-500 A) Ag film was pressed onto a monolayer of DOAB spread on pure water. The ATR signal caused by the SPP (surface plasmon polariton) at the Ag/monolayer interface was monitored. The subphase water was then slowly replaced with the polymer solution of varing concentration. The shift of the ATR dip indicates the thickness of the polymer adsorbed onto the monolayer and the width signals the inhomogeneity of the polyemer layer. We found that the adsorption occurred in two steps ; first the adsorbed layer was monomolecular (thickness - 5A), then it grew into a thick and inhomogeneous film. The initial layer thickness was independent of the molecular weight of the polymer. The final thickness, however, depended on the molecular weight weakly (d=16A for n=3500 and d=33A for n=42000, where n is the degree of polymerization) suggesting loops and tails in the film at this stage. We also found that the adsorption was completely absent onto a non-cationic monolayer (stearic acid) within the resolution of our method. CONCLUSION : The polymer adsorption onto a spread monolayer is completely governed by the charge nutrality (at least in the early stage of the adsorption) and a 1 : 1 polyion complex is indeed formed at the solution/monolayer interface as has long been speculated.