Diffusion and reactivity in ultraviscous aerosol and the correlation with particle viscosity.
Diffusion and reactivity in ultraviscous aerosol and the correlation with particle viscosity.
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DOI：
10.1039/c5sc03223g
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发表时间：
2016-02-01
期刊：
影响因子：
8.4
通讯作者：
Dutcher CS
中科院分区：
文献类型：
--
作者：
Marshall FH;Miles REH;Song YC;Ohm PB;Power RM;Reid JP;Dutcher CS
利用光镊悬浮的三元组分单气溶胶粒子的扩散系数和粘度的直接比较。水、有机物和氧化剂在粘性气溶胶中的缓慢传输可导致气溶胶以瞬态存在，这不仅由热力学原理控制，而且由气-粒分配的动力学控制。分子扩散常数和颗粒粘度之间的关系（例如，如斯托克斯-爱因斯坦方程中所反映的）经常被认为提供了将气溶胶转化的动力学与气溶胶的材料性质相关联的近似指导。我们报告的直接研究的分子扩散和粘度在气溶胶相的三元系统水/马来酸/蔗糖，考虑与水分配的变化，马来酸的挥发，马来酸的臭氧分解动力学和颗粒粘度的吸湿响应之间的关系。尽管水明显地充当增塑剂，但添加少量其它有机部分可类似地导致粘度与形成有机基质的主要组分（蔗糖）预期的粘度相比发生显著变化。在这里，我们强调，水的扩散常数和颗粒的粘度之间的斯托克斯-爱因斯坦关系可能是一个数量级以上的误差，即使在粘度低至1帕秒。我们表明，吸湿响应的热力学关系，支持这样的动力学测定必须准确地知道检索准确的扩散常数值，这样的数据往往是不可用的。此外，我们表明，缩放的有机分子的扩散常数的大小相似的那些形成的矩阵与颗粒粘度可以很好地表示由斯托克斯-爱因斯坦方程，抑制半挥发性组分的表观挥发性。最后，氧化剂和小的弱相互作用分子的吸收系数和扩散常数的变化可能比更强相互作用的分子如水的扩散常数更少地依赖于粘度。
Direct comparison of diffusion coefficients and viscosities of ternary component single aerosol particles levitated using optical tweezers. The slow transport of water, organic species and oxidants in viscous aerosol can lead to aerosol existing in transient states that are not solely governed by thermodynamic principles but by the kinetics of gas-particle partitioning. The relationship between molecular diffusion constants and particle viscosity (for example, as reflected in the Stokes–Einstein equation) is frequently considered to provide an approximate guide to relate the kinetics of aerosol transformation with a material property of the aerosol. We report direct studies of both molecular diffusion and viscosity in the aerosol phase for the ternary system water/maleic acid/sucrose, considering the relationship between the hygroscopic response associated with the change in water partitioning, the volatilisation of maleic acid, the ozonolysis kinetics of maleic acid and the particle viscosity. Although water clearly acts as a plasticiser, the addition of minor fractions of other organic moieties can similarly lead to significant changes in the viscosity from that expected for the dominant component forming the organic matrix (sucrose). Here we highlight that the Stokes–Einstein relationship between the diffusion constant of water and the viscosity of the particle may be more than an order of magnitude in error, even at viscosities as low as 1 Pa s. We show that the thermodynamic relationships of hygroscopic response that underpin such kinetic determinations must be accurately known to retrieve accurate values for diffusion constants; such data are often not available. Further, we show that scaling of the diffusion constants of organic molecules of similar size to those forming the matrix with particle viscosity may be well represented by the Stokes–Einstein equation, suppressing the apparent volatility of semi-volatile components. Finally, the variation in uptake coefficients and diffusion constants for oxidants and small weakly interacting molecules may be much less dependent on viscosity than the diffusion constants of more strongly interacting molecules such as water.
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