The study of aerosol particles composed of mixtures of organic and inorganic compounds provides insights for understanding chemistry in the atmosphere as well as information about phase transitions of systems under confinement. In the submicron size regime, we have previously found that liquid–liquid phase separation can be inhibited at sufficiently small particle diameters leading to phase separated particles at larger sizes and homogeneous particles below a threshold diameter. In this paper, we have investigated the influence of cations and anions in the inorganic compound (NH₄⁺, Na⁺, SO₄^2–, HSO₄^–, and Cl^–) on the phase separation of submicron aerosol particles. Each of five salts were studied with two different organic compounds. Surprisingly, a strong dependence on the identity of the cation is evident in the size dependence of the particle morphology, and no dependence on the anion was found. Sodium containing samples exhibit phase separation in particles below 20 nm in diameter, whereas ammonium containing samples cease to undergo phase separation in particles between 45 and 65 nm in diameter. The separation relative humidity for supermicron droplets also depends on the identity of the cation in the inorganic component if the anion is the same across the salts compared. In addition, the correlation between the separation relative humidity and size dependence was investigated and displays a trend but is not a dominant feature of the data. We explain the results in terms of hard and soft ions, where the harder cation (Na⁺) leads to phase separation down to smaller sizes while the softer cation (NH₄⁺) prevents phase separation and causes particles up to a larger diameter to remain homogeneous. This study has implications for atmospheric chemistry in regions dominated by sea spray aerosol, which contains sodium as the primary cation, when compared to continental aerosol, where ammonium is an abundant cation. Additionally, these findings can be used to understand the influence of cations on the phase transitions of confined materials.

中文翻译：

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离子对气溶胶粒子尺寸相关形态的影响

对由有机和无机化合物混合物组成的气溶胶粒子的研究为理解大气中的化学以及有关受限系统相变的信息提供了见解。在亚微米尺寸范围内，我们之前已经发现，在足够小的粒径下可以抑制液-液相分离，导致相分离的颗粒尺寸较大，而均匀颗粒低于阈值直径。在本文中，我们研究了无机化合物（NH ₄ ⁺、Na ⁺、SO ₄ ^2–、HSO ₄ ^–和 Cl ^–）中阳离子和阴离子的影响。) 关于亚微米气溶胶颗粒的相分离。用两种不同的有机化合物研究了五种盐中的每一种。令人惊讶的是，在粒子形态的大小依赖性中，对阳离子身份的强烈依赖性是明显的，并且没有发现对阴离子的依赖性。含钠样品在直径小于 20 nm 的颗粒中表现出相分离，而含铵样品在直径在 45 和 65 nm 之间的颗粒中不再发生相分离。如果所比较的盐中的阴离子相同，超微米液滴的分离相对湿度还取决于无机组分中阳离子的特性。此外，研究了分离相对湿度和尺寸依赖性之间的相关性，并显示了一种趋势，但不是数据的主要特征。⁺ ) 导致较小尺寸的相分离，而较软的阳离子 (NH ₄ ⁺ ) 会阻止相分离并导致较大直径的颗粒保持均匀。与铵是丰富阳离子的大陆气溶胶相比，这项研究对以钠为主要阳离子的海喷雾气溶胶为主的地区的大气化学具有影响。此外，这些发现可用于了解阳离子对受限材料相变的影响。