十二烷基三甲基溴化铵在聚苯乙烯胶乳粒子上的吸附

实验测得C~1~2TAB在PS胶乳粒子表面的吸附等温线呈L型的二阶段吸附特征,这表明初始的C~1~2TA^+离子是将其季铵正电性头基吸引在PS链的负电性硫酸根端基上,并将碳氢链通过疏水相互作用吸附在PS链上。结合光子相关谱测得胶乳粒子流体力学半径R~H的变化,表明第I阶段围绕着这些初始吸附位的聚集吸附,产生平均聚集数为4.0的松散小聚集体,此时对应的浓度c/cmc=0.32是文献通常所指的临界表面胶团浓度csmc。其后的进一步聚集吸附最终生成了附着在PS链端基处且平均聚集数为19.5的球形吸附胶团。这一饱和吸附的结果增加了胶乳粒子在水溶液中的分散稳定性。

Adsorption of dodecyltrimethylammonium bromide on polystyrene latex particles

The adsorption of cationic surfactant dodecyltrimethylammonium bromide (C~1~2TAB) on polystyrene (PS) latex particles has been investigated by estimation of the hydrodynamic radius using dynamic light scattering measurements as well as by determination of the adsorption isotherm using a surface tension technique. The surface of the latex particle has a hairy characteristic and the pendant PS chains terminate in sulfate groups. Initially, C~1~2TA^+ ions were bound at the extremities of the PS chains through both electrostatic attraction between the quaternary ammonium head groups of C~1~2TA^+ ions and the terminal sulfate entities of the PS chains and hydrophobic interaction between the alkyl tails and the PS backbone. Combination of both forces led to L-type isotherm. At the stage I, adsorption yielded small aggregates with average aggregation number of 4.0 on the entities of PS chains. Further significant adsorption (the stage II) of C~1~2TA^+ ions subsequently occurred around the small aggregates formed initially through hydrophobic interaction between the hydrocarbons, finally leading to formation of globular micelles anchored at the extremities of PS chains with average aggregation number of 19.5 (the stage III). In comparison with the previous. SDS case, the present result indicated that the adsorption sites occupied initially are an important factor for determining the structure of surface micelles adsorbed on the pendant polymer chains. Whereas the initial adsorption sites are dominated by the interaction forces between the surfactant molecules/ions and the polymer chains.