【摘要】 以羧甲基纤维素钠(Na CMC)-烷基三甲基溴化铵(CnTAB)复合体系为研究对象,在Na CMC亚浓缠结溶液中考察了CnTAB烷基尾链长度对CnTAB临界缔合浓度(cac)及溶液流变行为的影响.采用荧光探针法测得cac值,根据吉布斯自由能定量分析了烷基尾链对胶束缔合行为的影响.稳态流变测试结果表明,较高浓度CnTAB对Na CMC亚浓缠结溶液有强烈的增黏作用.显微观察表明,低浓度CnTAB形成孤立胶束(约5nm),而较高浓度CnTAB则形成胶束复合聚集体(约30 nm).扣除胶束电荷中和所致降黏作用后,孤立胶束表现为等效刚性球,Na CMC亚浓缠结溶液的黏度变化符合Einstein方程;相反,胶束在临界浓度以上发生逾渗,形成胶束复合聚集体,进一步形成贯穿于Na CMC分子缠结网路的胶束逾渗网络.首次揭示了复合体系增黏的实质是胶束网络逾渗,而不是由胶束吸附聚电解质链形成物理网络.增黏阶段Na CMC亚浓缠结溶液的黏度变化符合逾渗模型和平均场理论.长程静电相互作用控制胶束缔合与逾渗行为,逾渗临界胶束体积分数随CnTAB尾链长度增加而降低,临界胶束表面间距随CnTAB尾链长度增加而增大.更多还原

【Abstract】 Influence of alkyl trimethylammonium bromide( CnTAB) on rheological behavior of sodium carboxymethylcellulose( Na CMC) in entangled semi-dilute solution was investigated with respect to tail length of CnTAB. Both critical aggregation concentration( cac) and viscosity were studied. cac was achieved by steady-state fluorescence using pyrene as a probe. Effect of CnTAB tail length on formation of micelles in water and Na CMC solution were quantified by calculating the Gibbs free energy. A strong thicken effect of CnTAB at high concentrations on the entangled semi-dilute solution of Na CMC was found. According to transmission electron microscopy images,both isolated micelles( ca. 5 nm) at low Na CMC concentrations and large aggregates( ca. 30 nm) at high Na CMC concentrations can be seen. Excluding the viscosity reduction by the neutralization of charges induced by Na CMC,the isolated micelles act as hard spheres,causing a viscosity change of the Na CMC solution following Einstein law. On the other hand,percolation appears at high CnTAB concentrations and the micellar aggregates spread to form a network penetrating the entanglement network of Na CMC macromolecules. It is found for the first time that the viscosity of entangled semi-dilute solution increases according to the percolation theory with mean-field calculation. This indicates that long range interaction dominates in the aggregation and percolation behavior of micellar aggregates. At the onset of micellar percolation,critical volume fraction of micelles increases while mean distance between micelle surfaces decreases with increasing tail length of CnTAB.更多还原