Surface Characteristics that Drive Heterogeneous Ice Nucleation

化学系的环境化学科学项目资助米里亚姆·弗里德曼教授进行冰核研究。在大约零下38摄氏度（或零下36华氏度）以上的温度下，大气中的冰粒只能通过气溶胶粒子的成核形成。在这里，成核是通过液体的自组装或自组织形成固体（冰）的第一步。粒子的冰核活性差别很大。目的是测量许多材料的冰成核活性，以建立一个模型，预测颗粒的哪些表面性质对促进冰成核最重要。由于在大气中发现的颗粒种类数量有限，人们正在研究人造纳米材料、沙子和其他具有特定表面的材料。这些合成材料的性质可以调整，以探索不同的表面特征对冰成核的影响。这些研究增强了对冰核分子基础的理解，这对工业应用和大气化学非常重要，特别是研究可以减少气溶胶-云相互作用的不确定性，这是我们对天气和气候的理解中最大的不确定性。这项工作引起了物理化学界的兴趣，因为它涉及相变、多相催化和表面化学，所有这些都对工业应用至关重要。该项目为本科生和研究生提供培训，并通过以科学和科学政策为重点的外展活动向公众进行外展。目前正在研究几种材料的冰成核活性。具体建议的材料是无定形二氧化硅纳米颗粒、介孔二氧化硅、相变材料GeTe、银（Ag）和金（Au）纳米颗粒、盐（NaCl/KCl）混合物、沸石和金属有机框架。选择这些材料是因为它们具有调节表面特性的能力，如官能团、结晶度、晶体结构、孔隙度和掺杂剂。在实验室冰核室中测量了浸入式冻结和沉积式冻结。除了实验室研究外，运动学模型还用于探索非均相成核对混合相云和卷云性质的影响。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The Environmental Chemical Sciences Program in the Chemistry Division funds Professor Miriam Freedman for studies of ice nucleation. At temperatures above approximately -38 degrees Celsius (or -36 degrees Fahrenheit), ice particles in the atmosphere are only formed through nucleation on aerosol particles. Here, nucleation is the first step in the formation of solid (ice) via self-assembly or self-organization of liquid. Particles differ widely in their ice nucleation activity. The aim is to measure the ice nucleation activity of many materials to develop a model that predicts which surface properties of the particles are most important for promoting ice nucleation. Because the types of particles found in the atmosphere are limited in number, man-made nanomaterials, sand, and other materials with specific surfaces are being studied. The properties of these synthesized materials can be tuned to explore the effect of different surface characteristics on ice nucleation. These studies enhance the understanding of the molecular basis of ice nucleation, which is important for industrial applications and atmospheric chemistry, specifically the research could reduce uncertainties in aerosol-cloud interactions, which are the largest uncertainty in our understanding of weather and climate. This work is of interest to the physical chemistry community because it deals with phase transitions, heterogeneous catalysis, and surface chemistry all of which are critical to industrial applications. This project provides training for undergraduate and graduate students, as well as outreach to the public through outreach events focusing on science and science policy. The ice nucleation activity of several materials is being investigated. Specifically proposed materials are amorphous silica nanoparticles, mesoporous silica, the phase change material GeTe, silver (Ag) and gold (Au) nanoparticles, salt (NaCl/KCl) mixtures, zeolites, and metal organic frameworks. The materials are selected for their ability to tune surface characteristics such as functional groups, crystallinity, crystal structure, porosity, and dopants. Both immersion and deposition mode freezing are measured in laboratory ice nucleation chambers. In addition to laboratory studies, kinematic models are used to explore the impact of heterogeneous nucleation on the properties of mixed phase and cirrus clouds.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.