Lee Hansol D, Estillore Armando D, Morris Holly S, Ray Kamal K, Alejandro Aldair, Grassian Vicki H, Tivanski Alexei V
Department of Chemistry, University of Iowa , Iowa City, Iowa 52242, United States.
J Phys Chem A. 2017 Nov 2;121(43):8296-8305. doi: 10.1021/acs.jpca.7b04041. Epub 2017 Oct 20.
Understanding the role of sea spray aerosol (SSA) on climate and the environment is of great interest due to their high number concentration throughout the Earth's atmosphere. Despite being of fundamental importance, direct surface tension measurements of SSA relevant sub-micrometer particles are rare, largely due to their extremely small volumes. Herein, atomic force microscopy (AFM) is used to directly measure the surface tension of individual sub-micrometer SSA particle mimics at ambient temperature and varying relative humidity (RH). Specifically, we probed both atmospherically relevant and fundamentally important model systems including electrolyte salts, dicarboxylic acids, and saccharides as single components and mixtures. Our results show that the single particle surface tension depends on RH or solute mole percentage and chemical composition. Moreover, for liquid droplets at and below 100 Pa s in viscosity, or at corresponding RH, we show good agreement between the AFM single particle and the bulk solution surface tension measurements at overlapping concentration ranges. Thus, direct surface tension measurements of individual particles using AFM is shown over a wide range of chemical systems as a function of RH, solute mole percentage, and viscosity than previously reported.
由于海喷雾气溶胶（SSA）在地球大气中数量浓度很高，了解其在气候和环境中的作用备受关注。尽管具有根本重要性，但对与SSA相关的亚微米颗粒进行直接表面张力测量却很少见，这主要是因为它们的体积极小。在此，原子力显微镜（AFM）用于在环境温度和不同相对湿度（RH）下直接测量单个亚微米SSA颗粒模拟物的表面张力。具体而言，我们探究了与大气相关且具有根本重要性的模型系统，包括电解质盐、二元羧酸和糖类作为单一成分以及混合物。我们的结果表明，单个颗粒的表面张力取决于相对湿度或溶质摩尔百分比以及化学成分。此外，对于粘度在100 Pa·s及以下的液滴，或在相应相对湿度下，我们发现在重叠浓度范围内，AFM单个颗粒测量结果与本体溶液表面张力测量结果吻合良好。因此，与之前报道相比，利用AFM在广泛的化学系统中作为相对湿度、溶质摩尔百分比和粘度的函数对单个颗粒进行直接表面张力测量得以实现。
