Adsorption Kinetics of Polyelectrolyte onto Monolayers

用衰减全反射（ATR）方法研究了电解质聚合物在溶液上单层的吸附动力学。聚合物为PSSK（聚苯乙烯磺酸钾）阴离子和DOAB（二十八烷基二甲基溴化铵阳离子）单层聚合物。将斜边表面涂有薄（-500 A） Ag膜的SFS-1玻璃棱镜压在铺在纯水上的DOAB单层上。对银/单层界面表面等离子激元（SPP）产生的ATR信号进行了监测。然后用不同浓度的聚合物溶液慢慢取代亚相水。ATR倾角的变化表示聚合物吸附在单层上的厚度，宽度表示聚合物层的不均匀性。我们发现吸附分两步进行；首先吸附层为单分子（厚度- 5A），然后逐渐生长为厚而不均匀的薄膜。初始层厚度与聚合物的分子量无关。然而，最终厚度对分子量的依赖性较弱（当n=3500时d=16A，当n=42000时d=33A，其中n为聚合度），表明在这一阶段薄膜中存在环状和尾部。我们还发现，在我们方法的分辨率范围内，非阳离子单层（硬脂酸）上完全没有吸附。结论：聚合物在扩散单层上的吸附完全受电荷中性的支配（至少在吸附的早期），正如长期以来所推测的那样，在溶液/单层界面上确实形成了1:1的多离子复合物。

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.