The formation rates and structure of nanodroplets

俄亥俄州立大学的Barbara Wyslouzil在实验物理化学项目的支持下，测量了超音速喷嘴膨胀过程中形成的纳米液滴的成核速率和结构。具体目标是：(1)在远离平衡的条件下测量一元和二元成核速率J作为过饱和S和温度T的函数；(2)将成核定理应用于等温二元成核速率数据并确定临界团簇的组成；(3)利用小角中子散射（SANS）实验探索多组分纳米液滴的内部结构作为组成的函数。这些目标是高度耦合的，因为为了测量成核率，在喷嘴中形成的气溶胶的数量密度N是用SANS确定的。在二元情况下，确定N与确定组成气溶胶的液滴的内部结构密切相关。这些生成的数据很重要，因为喷嘴中的成核速率比其他现有实验技术高4到6个数量级。将来自喷嘴的数据与其他实验设备相结合，产生的数据集涵盖了近20个数量级，为预测成核理论和标度定律提供了严格的测试。最后，确定半径约为10纳米的多组分液滴的结构可能会为非均匀液体状态下物质的行为提供更好的模型。多组分纳米级液滴在自然和工业环境中都能形成。准确预测相变发生的速率和最终液滴的结构对于建立可靠的工业过程、气候和大气化学模型至关重要。成核速率直接影响气溶胶的大小分布，从而影响非均相化学反应的表面积。另一方面，表面和内部的差异会影响非均相化学、生长和蒸发的速率，甚至液滴本身形成的速率。

Barbara Wyslouzil of the Ohio State University is supported by the Experimental Physical Chemistry Program to measure the nucleation rates and the structure of nanodroplets formed in supersonic nozzle expansions. The specific objectives are: (1) to measure unary and binary nucleation rates J as a function of supersaturation S and temperature T under conditions that are far from equilibrium, (2) to apply the nucleation theorem to isothermal binary nucleation rates data and determine the composition of critical clusters, and (3) to explore the internal structure of multicomponent nanodroplets as a function of composition using small angle neutron scattering (SANS) experiments. These goals are highly coupled because to measure nucleation rates the number density N of the aerosol formed in the nozzles is determined using SANS. In the binary case, determining N goes hand in hand with determining the internal structure of the droplets comprising the aerosol. These data to be generated are important because nucleation rates in nozzles are four to six orders of magnitude higher than other existing experimental techniques. Combining data from nozzles with other experimental devices yields data sets covering almost 20 orders of magnitude, posing a stringent test for predictive nucleation theories and scaling laws. Finally, determining the structure of multicomponent droplets with approximately 10 nanometer radii may lead to better models for the behavior of matter in inhomogeneous liquid states.Multicomponent nanometer-sized droplets form in both natural and industrial environments. Accurate predictions of the rate at which phase transitions occur and the structure of the final droplets are critical for developing reliable models of industrial processes, climate, and atmospheric chemistry. The nucleation rate directly affects the aerosol size distribution and thus, the surface area available for heterogeneous chemical reactions. Differences between the surface and the interior, on the other hand, will affect heterogeneous chemistry, the rates of growth and evaporation, and even the rate at which the droplets themselves are formed.