Collaborative Research: ISS: Colloidal Microflyers: Observation and Characterization of (Self-)Thermophoresis through Air in Microgravity

合作研究：ISS：胶体微飞行器：微重力下空气（自）热泳的观察和表征

• 批准号: 2323010
• 负责人: Jeffrey Moran
• 金额: $ 30.35万
• 依托单位: George Mason University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-08-01 至 2027-07-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2323010&HistoricalAwards=false
• 关键词: Collaborative; Research; ISS; Colloidal; Microflyers

Thermophoresis, the motion of small particles in response to temperature gradients, is challenging to study in air on Earth because of the influence of air currents and gravity. Temperature gradients abound in the atmosphere, and accordingly thermophoresis affects the migration of atmospheric aerosols, which influence Earth’s climate by reflecting or absorbing sunlight and effecting cloud formation. However, the contributions of thermophoresis to these processes are difficult to disentangle from other factors, including air currents, gravity, evaporation, and electrical charge, exacerbating uncertainty surrounding the role aerosols play in both driving and remediating climate change. The objective of this work is to characterize thermophoresis of small particles in microgravity, where these confounding factors are absent. Microparticles will be packaged into specially-designed cuvettes on the ground and launched to the International Space Station (ISS), where their motion will be characterized visually. The temperature gradient may be externally imposed via heating one face of the cuvette, or it could be self-generated by particles that absorb light unevenly, a phenomenon known as “self-thermophoresis.” Self-thermophoresis has been observed in water but never in air; this work will reveal the extent to which asymmetric aerosols can undergo this same phenomenon. By providing data for a range of relevant materials, this work will inform climate models and be useful for other applications such as the use of thermophoresis to collect aerosols from air, including bioaerosols that transmit infectious diseases.The research objective of this work is to observe and quantify thermophoresis and self-thermophoresis through air in microgravity. The thermophoretic speeds will be measured visually (via the KERMIT microscope on the ISS) using airtight cuvettes designed, fabricated, and packaged on the ground. The particles characterized will be silica, alumina, and kaolinite, all of which are found in the atmosphere but whose thermophoretic properties have been incompletely characterized. After launch, the ISS-based experiments will proceed in two phases. First, in the thermophoresis experiments, the velocities of various microparticles will be characterized as a function of size, shape, and air pressure inside the cuvette (to simulate high altitudes). Second, the self-thermophoresis experiments will expose silica microspheres half-coated in gold to infrared and visible light, allowing the first-ever observation of self-thermophoretic motion by particle-generated temperature gradients. This work will provide the first-ever experimental demonstration of colloidal self-propulsion through a gas. In addition, this research could inform geoengineering proposals to release planet-cooling aerosols into the atmosphere, for which there is ongoing investigation into both their benefits and side effects. Finally, this work also provides a platform for future innovations in the engineering of three-dimensional “microflyers” for defense, environmental, or space applications.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.

热粒子是响应温度梯度的小颗粒的运动，由于气流和重力的影响，在地球上的空气中挑战。温度梯度在大气中比比皆是，因此热疗法会影响大气气溶胶的迁移，这通过反射或吸收阳光并影响云形成来影响地球的气候。但是，嗜热疗法对这些过程的贡献很难与其他因素（包括气流，重力，经济和电荷）脱离，加剧了气雾剂在驾驶和修复气候变化中扮演角色的不确定性。这项工作的目的是表征微重力中小颗粒的嗜热，其中这些混杂因素不存在。微粒将在地面上包装到专门设计的库中，并发射到国际空间站（ISS），在那里他们的运动将在视觉上进行特征。温度梯度可以通过加热比色杯的一张脸来外部施加，也可以通过吸收光线不均匀的颗粒来自我生成，这种现象称为“自我疗法”。在水中已经观察到自疗法，但从未在空气中观察到。这项工作将揭示不对称气溶胶可以在多大程度上经历同样的现象。通过为一系列相关材料提供数据，这项工作将为气候模型提供信息，并对其他应用程序有用，例如使用热脚体从空气中收集气溶胶，包括传播感染性疾病的生物溶质溶质。这项工作的研究目标是通过微电场中的空气观察并量化热疗法和自我热层。嗜热速度将使用在地面上设计，制造和包装的气密比色调板以视觉量（通过ISS上的Kermit显微镜）进行测量。表征的颗粒将是二氧化硅，氧化铝和高岭石，所有这些都在大气中发现，但其嗜热特性未完全表征。发布后，基于ISS的实验将分为两个阶段。首先，在热疗实验中，各种微粒的速度将以尺寸，形状和气压内部的函数（模拟高度）来表征。其次，自我疗法实验将使一半涂层的二氧化硅微球暴露于红外和可见光，从而使颗粒生成的温度梯度对自感觉运动进行了首次观察。这项工作将通过气体提供有史以来的胶体自我推测的第一个实验证明。此外，这项研究可以告知地球工程提案，以将行星冷却的气溶胶释放到大气中，为此，对其益处和副作用进行了持续的调查。最后，这项工作还为未来的创新提供了一个平台，以在国防，环境或空间应用的三维“小翼板”的工程中进行工程。该奖项反映了NSF的法定任务，并被认为是通过基金会的知识分子优点和更广泛的影响审查标准通过评估来获得的支持。