Bai Guangyue, Catita José A M, Nichifor Marieta, Bastos Margarida
CIQ (UP), Department of Chemistry, Faculty of Sciences, University of Porto, R. Campo Alegre, 687, P-4169-007 Porto, Portugal.
J Phys Chem B. 2007 Oct 4;111(39):11453-62. doi: 10.1021/jp073530r. Epub 2007 Sep 7.
We synthesized and characterized a series of new polymers-hydrophobically modified cationic polysaccharides-based on dextran having pendant N-(2-hydroxypropyl)-N,N-dimethyl-N-alkylammonium chloride groups randomly distributed along the polymer backbone. These polymers are good candidates for studying the hydrophobic effect on polymer/surfactant association. In previous papers we reported their interactions with oppositely charged surfactants. For further insight into the relative importance of the hydrophobic interaction in the association process now we studied the thermodynamics of the interaction of these hydrophobically modified polymers with surfactants of the same charge (DMRX/CnTAC) by isothermal titration calorimetry (ITC). In order to try to discriminate the solution behavior of these polymer/surfactant systems, we analyzed separately the interaction of unmodified dextran with ionic surfactants and the interactions between the corresponding cationic surfactants. The interaction enthalpies for DMRX/CnTAC systems were derived from a proposed thermodynamic model with equations that describe the polymer-surfactant interactions. The thermodynamic parameters for the DMRX/CnTAC aggregation process as well as surfactant micellization in the presence of the polymer were also calculated. From all the results we were able to ascertain the effect on the interactions of changing the alkyl chain length of the polyelectrolyte pendant groups or the surfactant. The importance of the polymer aggregation state on the mechanism of interaction was also addressed.
我们合成并表征了一系列新型聚合物——基于葡聚糖的疏水改性阳离子多糖，其侧链N-(2-羟丙基)-N,N-二甲基-N-烷基氯化铵基团沿聚合物主链随机分布。这些聚合物是研究聚合物/表面活性剂缔合过程中疏水效应的良好候选物。在之前的论文中，我们报道了它们与带相反电荷表面活性剂的相互作用。为了进一步深入了解缔合过程中疏水相互作用的相对重要性，现在我们通过等温滴定量热法（ITC）研究了这些疏水改性聚合物与相同电荷表面活性剂（DMRX/CnTAC）相互作用的热力学。为了试图区分这些聚合物/表面活性剂体系的溶液行为，我们分别分析了未改性葡聚糖与离子表面活性剂的相互作用以及相应阳离子表面活性剂之间的相互作用。DMRX/CnTAC体系的相互作用焓来自一个提出的热力学模型，该模型包含描述聚合物-表面活性剂相互作用的方程。还计算了DMRX/CnTAC聚集过程以及聚合物存在下表面活性剂胶束化的热力学参数。从所有结果中，我们能够确定改变聚电解质侧链基团或表面活性剂的烷基链长度对相互作用的影响。还讨论了聚合物聚集状态对相互作用机制的重要性。
