Alshawa Ahmad, Dopfer Otto, Harmon Christopher W, Nizkorodov Sergey A, Underwood Joelle S
Department of Chemistry, University of California, Irvine, California 92697-2025, USA.
J Phys Chem A. 2009 Jul 2;113(26):7678-86. doi: 10.1021/jp809869r.
Aerosolized nanoparticles of NaCl coated with variable amounts of surfactant AOT were generated by electrospraying AOT/NaCl aqueous solutions, followed by neutralizing and drying the resulting particles. A tandem differential mobility analyzer was used to select a narrow size distribution of particles with mobility equivalent diameters below 20 nm and monitor their hygroscopic growth as a function of relative humidity. Effects of the particle size and relative amount of surfactant on the hygroscopic growth of NaCl were studied. For pure NaCl nanoparticles, the deliquescence relative humidity (DRH) increased as the particle size was decreased, in full agreement with previous measurements. Below the DRH the NaCl nanoparticles had an equivalent of one-four monolayers of water adsorbed on the surface. The addition of a sub-monolayer AOT coating reduced the DRH and suppressed the hygroscopic growth of the NaCl core. At AOT coverage levels exceeding one monolayer, a clear deliquescence transition was no longer discernible. The Zdanovskii-Stokes-Robinson (ZSR) model failed to predict the observed growth factors of mixed AOT/NaCl nanoparticles reflecting a large contribution of the interfacial interactions between NaCl and AOT to the total free energy of the particles. There were indications that AOT/NaCl nanoparticles prepared by the electrospray aerosol source were enhanced in the relative mass fraction of AOT in comparison with the solution from which they were electrosprayed.
通过电喷雾AOT/NaCl水溶液生成涂覆有不同量表面活性剂AOT的雾化NaCl纳米颗粒，然后对所得颗粒进行中和与干燥。使用串联差分迁移率分析仪选择迁移率等效直径低于20nm的窄尺寸分布颗粒，并监测其作为相对湿度函数的吸湿增长。研究了粒径和表面活性剂相对含量对NaCl吸湿增长的影响。对于纯NaCl纳米颗粒，潮解相对湿度（DRH）随着粒径减小而增加，这与先前的测量结果完全一致。在DRH以下，NaCl纳米颗粒表面吸附有相当于四分之一单层的水。添加亚单层AOT涂层降低了DRH并抑制了NaCl核的吸湿增长。当AOT覆盖水平超过一个单层时，不再能明显看出潮解转变。Zdanovskii-Stokes-Robinson（ZSR）模型未能预测观察到的混合AOT/NaCl纳米颗粒的生长因子，这反映出NaCl与AOT之间的界面相互作用对颗粒总自由能有很大贡献。有迹象表明，通过电喷雾气溶胶源制备的AOT/NaCl纳米颗粒与从中电喷雾的溶液相比，AOT的相对质量分数有所提高。
