Garg Gunjan, Hassan P A, Aswal V K, Kulshreshtha S K
Novel Materials and Structural Chemistry and Solid State Physics Divisions, Bhabha Atomic Research Centre, Mumbai-400 085, India.
J Phys Chem B. 2005 Feb 3;109(4):1340-6. doi: 10.1021/jp0472663.
The growth behavior of aggregates formed in aqueous solutions of the anionic surfactant sodium dodecyl sulfate (SDS) in the presence of the cationic hydrophobic salts o-toluidine hydrochloride (OTHC) and m-toluidine hydrochloride (MTHC) has been studied by dynamic light scattering (DLS) and small-angle neutron scattering (SANS) techniques. DLS studies indicate a progressive growth of SDS micelles with addition of less than equimolar concentrations of hydrophobic salts. A prolate ellipsoidal model is used to analyze the DLS data, which is further supported by SANS measurements. We explain the propensity for the strong growth of micelles in the presence of OTHC and MTHC by the high charge neutralization provided by these salts as the aromatic counterions are adsorbed on the surface of the micelles. When the substitution is at the meta position, i.e., for MTHC, micellar growth is favored at lower salt concentrations than for OTHC. The variation in growth behavior is explained in terms of the difference in the chemical environments of the substituents at the ortho and meta positions. Micellar parameters obtained from SANS data at elevated temperature also support enhanced growth of micelles in the presence of MTHC as compared to OTHC.
通过动态光散射（DLS）和小角中子散射（SANS）技术，研究了在阳离子疏水盐邻甲苯胺盐酸盐（OTHC）和间甲苯胺盐酸盐（MTHC）存在下，阴离子表面活性剂十二烷基硫酸钠（SDS）水溶液中形成的聚集体的生长行为。DLS研究表明，加入小于等摩尔浓度的疏水盐时，SDS胶束会逐渐生长。使用长椭球体模型分析DLS数据，SANS测量进一步支持了该模型。我们解释了在OTHC和MTHC存在下胶束强烈生长的倾向，这是因为这些盐提供了高电荷中和作用，芳香反离子吸附在胶束表面。当取代基位于间位时，即对于MTHC，与OTHC相比，在较低盐浓度下有利于胶束生长。根据邻位和间位取代基化学环境的差异解释了生长行为的变化。在高温下从SANS数据获得的胶束参数也支持与OTHC相比，MTHC存在下胶束的生长增强。
