聚二甲基二烯丙基氯化铵及其与CTAB混合物水溶液的吸附动力学

Adsorption Kinetics of Aqueous Poly(Diallyldimethylammonium Chloride) and Its Mixture with CTAB Solutions

用最大泡压法分别测定了聚二甲基二烯丙基氯化铵,十六烷基三甲基溴化铵以及两者混合物水溶液的动表面张力.十六烷基三甲基溴化铵的吸附服从扩散-动力学控制机理.发现聚二甲基二烯丙基氯化锭水溶液的表面张力具有独特的时间相关性.吸附的前期服从扩散控制机理,而在吸附的后期,即接近吸附平衡时服从扩散-动力学控制机理.混合物水溶液的整个吸附过程受扩散控制.

The dynamic surface tension of the aqueous solutions of cetyltrimethylammonium bromide(CTAB), poly( diallyldimethylammonium chloride )(PDADMAC) and their mixed solution were measured in the case of slow stretching surface by the maximum bubble pressure method at 30℃ . The adsorption of CTAB molecules follows a diffusion-kinetic-controlled adsorption mechanism. Dynamic surface tension isotherm of aqueous PDADMAC solution exhibits a peculiar feature. Each of the four sections in isotherm corresponds a special adsorption period. Increasing surface tension at the beginning of adsorption may be responsible for the adsorption of excess water at the interface. The existence of an induction period can be explained by the adsorption barrier due to polymer molecular characteristics. A marked reduction in surface tension in the time period t1 < t < t2 shows an actual adsorption process. A slow decrease in dynamic surface tension after the second critical time t2 brings adsorption into a prolonged mesoequilibrium period. A continuous conformational rearrangement and progressive ordering of polymer segments within the surface layer occur at this point. For the aqueous PDADMAC solution, the adsorption kinetics is time-dependent. In the limit of short time, it was controlled only by diffusion. At the later stages of adsorption, however, the kinetics of adsorption is governed by a diffusion-kinetic-controlled mechanism. Adding low-molecular weight surfactant CTAB to the aqueous PDADMAC solution leads to a change of adsorption mechanism from diffusion-kinetic-controlled to diffusion-controlled .