Laboratory Studies Investigating the Influence of Particle Diameter on Viscosity

小于100纳米的悬浮颗粒会影响能见度、云的形成、气候和人体健康，然而，许多关键的颗粒特性仍然不明确。在这个项目中，新的实验技术被用来增加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有影响的大气化学过程，并适用于存在纳米颗粒的广泛领域。研究生和本科生将是这项工作不可或缺的一部分，并计划为高中生开展外联活动。随着颗粒尺寸的减小，颗粒-空气界面的强曲率导致物理性质与在散体材料中观察到的偏离。粘度就是这样一种性质，人们对它与颗粒大小的依赖关系知之甚少，然而，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。为了阐明颗粒大小-粘度的关系，本研究试图量化颗粒直径在10到100 nm之间对固-液相转变的影响。特别关注的是50纳米颗粒，由一系列官能化有机化合物的纯或多组分混合物组成，用作氧化大气有机气溶胶(OA)的模型。形状松弛方法的使用依赖于实验室产生的哑铃形二聚体颗粒凝聚到单个球体上。这种转变发生在代表固-液相变的温度和粘度。颗粒形态的变化是在差示迁移率分析仪中测量的。除了影响气候和人类健康，研究结果还将被转移到大气科学领域之外，在大气科学领域对纳米粒子进行研究。通过这个项目，研究生和本科生将接受关于尖端仪器的实践培训。高中生将通过参加在大学校园组织的国际象棋比赛来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优势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.