Kinetic Limitation to Inorganic Ion Diffusivity and to Coalescence of Inorganic Inclusions in Viscous Liquid–Liquid Phase-Separated Particles,The Journal of Physical Chemistry A

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Kinetic Limitation to Inorganic Ion Diffusivity and to Coalescence of Inorganic Inclusions in Viscous Liquid–Liquid Phase-Separated Particles
The Journal of Physical Chemistry A ( IF 2.7 ) Pub Date : 2017-11-22 00:00:00 , DOI: 10.1021/acs.jpca.7b05242
Mehrnoush M. Fard ₁ , Ulrich K. Krieger ₁ , Thomas Peter ₁

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Mixed organic/inorganic aerosols may undergo liquid–liquid phase separation (LLPS) when the relative humidity drops in the atmosphere. Phase-separated particles adopt different morphologies, which will have different consequences for atmospheric chemistry and climate. Recent laboratory studies on submicron particles led to speculation whether LLPS observed for larger drops might actually be suppressed in smaller droplets. Here, we report on micron-sized droplets of a ternary mixture of ammonium sulfate (AS), carminic acid, and water at different temperatures, which were exposed to typical atmospheric drying rates ranging from 0.34 to 5.0% RH min^–1. Our results reveal that increasing the drying rate and lowering the temperature results in different morphologies after LLPS and may suppress the growth and coalescence of the inorganic-rich phase inclusions due to kinetic limitations in a viscous matrix. The coalescence time was used to estimate the viscosity of the organic-rich phase within a factor of 20, and based on the Stokes–Einstein relationship, we estimated AS diffusivity. Furthermore, we evaluated the initial growth of inclusions to quantitatively determine the AS diffusivity in the organic-rich phase, which is about 10^–8 cm² s^–1 at room temperature. Extrapolation of diffusivity to lower temperatures using estimations for the diffusion activation energy leads us to conclude that the growth of the inorganic phase is not kinetically impeded for tropospheric submicron particles larger than 100 nm.

中文翻译：

粘稠液-液相分离颗粒中无机离子扩散性和无机夹杂物聚结的动力学极限

当大气中的相对湿度下降时，有机/无机混合气溶胶可能会发生液相-液相分离（LLPS）。相分离的颗粒采用不同的形态，这将对大气化学和气候产生不同的影响。最近对亚微米颗粒的实验室研究导致人们猜测，观察到的较大液滴的LLPS是否实际上可以在较小液滴中被抑制。在这里，我们报告了在不同温度下，硫酸铵（AS），氨基甲酸和水的三元混合物的微米级液滴，这些液滴暴露于0.34至5.0％RH min ^–1的典型大气干燥速率下。我们的结果表明，提高干燥速率和降低温度会导致LLPS后形成不同的形貌，并且由于粘性基质中的动力学限制，可能会抑制富含无机物的夹杂物的生长和聚结。聚结时间用于估计富含有机物相的粘度在20倍以内，并基于Stokes-Einstein关系，我们估计了AS扩散率。此外，我们评估了夹杂物的初始生长，以定量确定富含有机物的相的AS扩散率，即约10 ^–8 cm ² s ^–1在室温下。使用对扩散活化能的估计将扩散率外推至较低温度，这使我们得出结论，对于大于100 nm的对流层亚微米颗粒，无机相的生长不会受到动力学阻碍。

更新日期：2017-11-23

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