Abstract. Atmospheric aerosol particles span orders of magnitude in size. In ultrafine particles, the energetic contributions of surfaces and interfaces to the Gibbs energy become significant and increase in importance as particle diameter decreases. For these particles, the thermodynamic equilibrium state depends on size, composition, and temperature. Various aerosol systems have been observed to undergo liquid–liquid phase separation (LLPS), impacting equilibrium gas–particle partitioning, modifying physicochemical properties of the particle phases, and influencing cloud droplet activation. Numerous laboratory experiments have characterized the onset relative humidity of LLPS in larger aerosol particles and macroscopic bulk systems. However, in sufficiently small particles, the interfacial tension between two liquid phases constitutes an energetic barrier that may prevent the formation of an additional liquid phase. Determining said small-size limit is a key question. We introduce a predictive droplet model based on the Aerosol Inorganic–Organic Mixtures Functional groups Activity Coefficients model. This model enables size-dependent computations of surface and interfacial tension effects on bulk–surface partitioning within phase-separated and single-phase particles. We evaluate four approaches for computing interfacial tension in multicomponent droplets, including a new method introduced in this work. Of the approaches tested, Antonov's rule best matches observed liquid–liquid interfacial tensions in highly immiscible mixtures, while a modified Butler equation fits well in more miscible systems. We find that two approaches substantially lower the onset relative humidity of LLPS for the studied systems.

中文翻译：

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界面张力在大气气溶胶颗粒尺寸依赖性相分离中的作用


摘要。大气气溶胶颗粒的尺寸跨越几个数量级。在超细颗粒中，表面和界面对吉布斯能量的能量贡献变得显着，并且随着颗粒直径的减小而变得更加重要。对于这些颗粒，热力学平衡状态取决于尺寸、成分和温度。已观察到各种气溶胶系统经历液-液相分离（LLPS），影响平衡的气体-颗粒分配，改变颗粒相的物理化学性质，并影响云滴活化。许多实验室实验已经表征了较大气溶胶颗粒和宏观散装系统中 LLPS 的起始相对湿度。然而，在足够小的颗粒中，两个液相之间的界面张力构成了能量屏障，可能阻止额外液相的形成。确定所述小尺寸限制是一个关键问题。我们引入了基于气溶胶无机-有​​机混合物官能团活性系数模型的预测液滴模型。该模型能够计算尺寸相关的表面和界面张力对相分离和单相颗粒内体表面分配的影响。我们评估了计算多组分液滴界面张力的四种方法，包括本工作中引入的一种新方法。在测试的方法中，安东诺夫规则最符合高度不混溶混合物中观察到的液-液界面张力，而修改后的巴特勒方程则非常适合更易混溶的系统。我们发现两种方法大大降低了所研究系统的 LLPS 起始相对湿度。