Cao Fangyu, Liu Ying, Xu Jiajun, He Yadong, Hammouda B, Qiao Rui, Yang Bao
Department of Mechanical Engineering, University of Maryland, College Park, MD 20742, USA.
Department of Mechanical Engineering, Virginia Tech, Blacksburg, VA 24061, USA.
Sci Rep. 2015 Nov 4;5:16040. doi: 10.1038/srep16040.
Surfactant solutions typically feature tunable nanoscale, internal structures. Although rarely utilized, they can be a powerful platform for probing thermal transport in nanoscale domains and across interfaces with nanometer-size radius. Here, we examine the structure and thermal transport in solution of AOT (Dioctyl sodium sulfosuccinate) in n-octane liquids using small-angle neutron scattering, thermal conductivity measurements, and molecular dynamics simulations. We report the first experimental observation of a minimum thermal conductivity occurring at the critical micelle concentration (CMC): the thermal conductivity of the surfactant solution decreases as AOT is added till the onset of micellization but increases as more AOT is added. The decrease of thermal conductivity with AOT loading in solutions in which AOT molecules are dispersed as monomers suggests that even the interfaces between individual oleophobic headgroup of AOT molecules and their surrounding non-polar octane molecules can hinder heat transfer. The increase of thermal conductivity with AOT loading after the onset of micellization indicates that the thermal transport in the core of AOT micelles and across the surfactant-oil interfaces, both of which span only a few nanometers, are efficient.
表面活性剂溶液通常具有可调节的纳米级内部结构。尽管很少被利用，但它们可以成为一个强大的平台，用于探测纳米尺度区域内以及跨越半径为纳米级的界面的热传输。在这里，我们使用小角中子散射、热导率测量和分子动力学模拟，研究了正辛烷液体中AOT（二辛基磺基琥珀酸钠）溶液的结构和热传输。我们首次通过实验观察到在临界胶束浓度（CMC）处出现热导率最小值：随着AOT的添加，表面活性剂溶液的热导率降低，直到胶束化开始，但随着更多AOT的添加，热导率又会增加。在AOT分子以单体形式分散的溶液中，热导率随AOT负载量的降低表明，即使是AOT分子的单个疏油头基与其周围非极性辛烷分子之间的界面也会阻碍热传递。胶束化开始后热导率随AOT负载量的增加表明，AOT胶束核心内以及跨表面活性剂 - 油界面（两者都仅跨越几纳米）的热传输是高效的。
