Heterogeneous ice nucleation in aqueous solutions: the role of water activity.
Heterogeneous ice nucleation in aqueous solutions: the role of water activity.
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DOI：
10.1021/jp7112208
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发表时间：
2008-03
期刊：
影响因子：
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通讯作者：
B. Zobrist;C. Marcolli;Thomas Peter;T. Koop
中科院分区：
文献类型：
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作者：
B. Zobrist;C. Marcolli;Thomas Peter;T. Koop
非均质冰核实验已经进行了四个不同的冰核（IN），即十九烷醇，二氧化硅，碘化银和亚利桑那州的测试灰尘。所有的IN要么浸没在液滴中，要么位于液滴表面。将IN暴露于各种水溶液，其由（NH 4）2SO 4、H2SO 4、MgCl 2、NaCl、LiCl、Ca（NO3）2、K2 CO 3、CH 3COONa、乙二醇、甘油、丙二酸、PEG 300或NaCl/丙二酸混合物组成。使用差示扫描量热仪和冷指细胞研究冷冻。结果表明，非均质冰的冻结温度随溶质浓度的增加而降低，但这种影响的大小与溶质有关。与此相反，当分析的结果中的溶解水活性的一个非常一致的行为出现：非均质冰成核温度为所有四个IN收敛到一个单一的线，无论溶质的性质。我们发现，一个恒定的偏移量相对于冰的熔点曲线，Δ aw，het，可以描述所观察到的冻结温度为每个IN。这种行为对于来自过冷液滴的均匀冰成核是众所周知的，并且已经导致了基于水活度的冰成核理论的发展。各种各样的研究溶质与不同的一般类型的冰核研究（单层，离子晶体，共价键结合的网络形成的化合物，和化学上不同的微晶的混合物）一起强调了水活性为基础的冰成核理论的普遍适用性，也为非均质冰成核在浸没模式。最后，冰成核效率的各种IN，以及大气的影响，发达国家的参数化进行了讨论。
Heterogeneous ice nucleation experiments have been performed with four different ice nuclei (IN), namely nonadecanol, silica, silver iodide and Arizona test dust. All IN are either immersed in the droplets or located at the droplets surface. The IN were exposed to various aqueous solutions, which consist of (NH4)2SO4, H2SO4, MgCl2, NaCl, LiCl, Ca(NO3)2, K2CO3, CH3COONa, ethylene glycol, glycerol, malonic acid, PEG300 or a NaCl/malonic acid mixture. Freezing was studied using a differential scanning calorimeter and a cold finger cell. The results show that the heterogeneous ice freezing temperatures decrease with increasing solute concentration; however, the magnitude of this effect is solute dependent. In contrast, when the results are analyzed in terms of the solution water activity a very consistent behavior emerges: heterogeneous ice nucleation temperatures for all four IN converge each onto a single line, irrespective of the nature of the solute. We find that a constant offset with respect to the ice melting point curve, Deltaaw,het, can describe the observed freezing temperatures for each IN. Such a behavior is well-known for homogeneous ice nucleation from supercooled liquid droplets and has led to the development of water-activity-based ice nucleation theory. The large variety of investigated solutes together with different general types of ice nuclei studied (monolayers, ionic crystals, covalently bound network-forming compounds, and a mixture of chemically different crystallites) underlines the general applicability of water-activity-based ice nucleation theory also for heterogeneous ice nucleation in the immersion mode. Finally, the ice nucleation efficiencies of the various IN, as well as the atmospheric implication of the developed parametrization are discussed.