Yoshii Noriyuki, Iwahashi Kensuke, Okazaki Susumu
Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan.
J Chem Phys. 2006 May 14;124(18):184901. doi: 10.1063/1.2179074.
Free energy of micelle formation has been evaluated for spherical sodium dodecyl sulfate (SDS) in water by a thermodynamic integration method combined with a series of large-scale molecular dynamics calculations following the chemical species model. In particular, free energy change delta mu(n+1)0 with respect to the addition of one surfactant molecule to the spherical micelle of size n was obtained as a function of n. The free energy profile showed a minimum followed by a maximum, which corresponds to a peak in the size distribution. The calculated peak size n = 57 near its critical micelle concentration is in good agreement with the experimental averaged aggregation number n = 55-75 of the SDS micelle. The distribution showed a rather sharp peak, indicating that the size is almost a monodisperse one. The size is likely to be insensitive to the total concentration of the surfactant.
通过热力学积分方法结合一系列遵循化学物种模型的大规模分子动力学计算，评估了水中球形十二烷基硫酸钠（SDS）形成胶束的自由能。特别地，获得了相对于向大小为n的球形胶束中添加一个表面活性剂分子的自由能变化Δμ(n+1)0作为n的函数。自由能分布呈现出一个最小值后接着一个最大值，这对应于尺寸分布中的一个峰值。在其临界胶束浓度附近计算得到的峰值尺寸n = 57与SDS胶束的实验平均聚集数n = 55 - 75吻合良好。该分布显示出一个相当尖锐的峰值，表明尺寸几乎是单分散的。尺寸可能对表面活性剂的总浓度不敏感。
