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尺寸小于100纳米的悬浮颗粒的影响，然而，许多关键颗粒的性质仍然不明确。在这个项目中，使用了新的实验技术来增加对颗粒粘度随尺寸变化的理解。研究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，并适用于纳米粒子存在的广泛领域。研究生和本科生将是工作的组成部分，并计划为高中生开展拓展活动。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块状材料中观察到的偏差。粘度就是其中一种性质，人们对其与粒径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。为了阐明粒径与粘度的关系，本研究试图量化10到100纳米之间的粒径对固液相变的影响。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纳米颗粒，这些颗粒可作为氧化大气有机气溶胶（OA）的模型。使用了一种形状松弛方法，该方法依赖于实验室生成的哑铃形状二聚体粒子到单个球体的凝固。这种转变发生在一个温度和粘度，是代表固-液相变。颗粒形态的变化是用微分迁移率分析仪测量的。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粒子的大气科学领域之外。通过这个项目，研究生和本科生将接受最前沿仪器的实践培训。高中学生将通过参加在大学校园举办的国际象棋比赛，来吸引他们参观大学科学实验室。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。

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.