Laboratory Studies Investigating the Influence of Particle Diameter on Viscosity

能见度、云的形成、气候和人类健康都受到小于 100 nm 的悬浮颗粒的影响，但许多关键颗粒特性仍然不明确。在该项目中，采用新颖的实验技术来加深对颗粒粘度如何随尺寸变化的理解。结果将有助于解释和预测对气候和人类健康产生影响的大气化学过程，并适用于存在纳米粒子的广泛领域。研究生和本科生将成为工作中不可或缺的一部分，并计划针对高中生开展外展活动。随着颗粒尺寸减小，颗粒-空气界面的强烈弯曲导致物理性质与散装材料中观察到的物理性质发生偏差。粘度就是这样一种性质，人们对其对颗粒尺寸的依赖性知之甚少，但粘度在影响大气化学、全球气候和人类健康的扩散和反应速率中起着关键作用。为了阐明颗粒尺寸与粘度的关系，本研究试图量化 10 至 100 nm 颗粒直径如何影响固液相变。特别关注的是由一系列功能化有机化合物的纯或多组分混合物组成的 50 nm 颗粒，这些颗粒可用作氧化大气有机气溶胶 (OA) 的模型。使用形状松弛方法，该方法依赖于实验室生成的哑铃形二聚体颗粒凝结成单个球体。这种转变发生在代表固-液相变的温度和粘度下。在微分迁移率分析仪中测量颗粒形态的变化。除了影响气候和人类健康之外，研究结果还可以转移到研究纳米颗粒的大气科学领域之外。通过该项目，研究生和本科生将接受尖端仪器的实践培训。高中生将通过参加大学校园内组织的国际象棋锦标赛来吸引参观大学科学实验室。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

Visibility, cloud formation, climate and human health are affected by suspended particles that are smaller than 100 nm in size, yet, many key particle properties remain ill-defined. In this project, novel experimental techniques are used to increase understanding of how particle viscosity changes with size. Results will help explain and predict atmospheric chemical processes with implications on climate and human health, as well as apply to a wide range of fields where nanoparticles are present. Graduate and undergraduate students will be an integral part of the work, and outreach activities are planned for high school students. As particle size decreases, strong curvature of the particle-air interface leads to deviations in physical properties from those observed in bulk materials. Viscosity is one such property, which dependence on particle size is poorly understood, yet, viscosity plays key roles in diffusion and reaction rates affecting atmospheric chemistry, global climate and human health. To shed light on the particle size-viscosity relationship, the present study seeks to quantify how solid-liquid phase transitions are influenced by particle diameter between 10 and 100 nm. Particular focus is on 50 nm particles composed of pure or multicomponent blends of a series of functionalized organic compounds that serve as models for oxidized atmospheric organic aerosol (OA). A shape-relaxation method is used that relies on the coagulation of laboratory-generated dumbbell-shaped dimer particles to single spheres. This transformation occurs at a temperature and viscosity that is representative of the solid-liquid phase transition. The change in particle morphology is measured in a differential mobility analyzer. Besides impacting climate and human health, findings will be transferable beyond the field of atmospheric sciences where nanoparticles are investigated. Through this project, graduate and undergraduate students will receive hands-on training on cutting edge instrumentation. High school students will be enticed to visit university sciences laboratories by participating in chess tournaments organized on the university campus.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.