Characterisation of the Properties and Dynamics of Single Microparticles

气溶胶在广泛的科学学科中发挥着重要作用，从向肺部输送药物，到它们对地球气候的影响及其在气候变化中的作用，再到它们在输送燃烧燃料中的应用，以及在等离子体中加工以制备功能化材料。气溶胶定义为气相中固体或液体颗粒的分散体，其特性由单个颗粒的化学成分和尺寸决定。人们还广泛认识到，颗粒表面的化学成分在控制气溶胶的特性方面可以发挥关键作用。这主要是因为气溶胶可以为周围的气相提供很大的表面积。发生的任何化学反应都必须通过分子从气相转移到表面的颗粒主体来介导。表面的化学组成可以显着影响这种转移。此外，人们认识到颗粒在其整个体积内的组成通常不均匀。例如，单个颗粒可能由不混合而是相分离的有机相和水相组成。与均匀混合的颗粒的预期特性相比，这会对颗粒的特性产生深远的影响。在这项研究中，我们将研究气溶胶颗粒的化学、物理和光学特性与其化学成分和成分均匀性之间的关系。我们将开发新技术来检查单个颗粒内的内部结构，探索不同化学物质如何在单个颗粒中混合或分离，并研究分子在颗粒表面吸收的难易程度。此外，我们将开发一种新仪器来测量粒子吸收光的效率。在大气中，气溶胶颗粒可以将阳光散射回太空，抵消温室气体的吸热特性。然而，一些污染物颗粒，例如燃烧产生的黑碳，会强烈吸收阳光，从而加剧大气变暖。气溶胶的影响仍然很难量化，需要新技术来研究它们的光吸收特性。上述新颖的实验基于两种强大的新技术。使用紧密聚焦的激光束，我们可以无限期地抓住单个粒子。这种方法被称为光镊，已广泛用于固定液体中的颗粒。然而，我们已经证明，可以使用相同的方法来保留气溶胶颗粒。此外，光会被困在球形气溶胶液滴中，就像光在形成彩虹时经历全内反射一样。光在逸出之前可以围绕液滴边缘传播数米的距离。通过测量光的波长，我们可以确定光必须传播多远才能绕完液滴圆周一圈。这不仅可以提供一种非常准确的方法来确定液滴的尺寸，而且可以使我们能够对液滴表面附近的液滴成分进行灵敏的测量。预计这些新技术的开发和应用将产生关于气溶胶特性及其在上述许多复杂科学问题中的行为的重要新信息。

Aerosols are important in a wide range of scientific disciplines, from the delivery of drugs to the lungs, to their impact on the earth's climate and their role in climate change, through to their application in the delivery of fuels for combustion, and their processing in plasmas to prepare functionalised materials. Defined as a dispersion of solid or liquid particles within the gas phase, aerosol properties are governed by the chemical composition and size of the individual particles. It is also widely recognised that the chemical composition of the surface of a particle can play a critical role in governing the properties of the aerosol. This is primarily because aerosols can present a large surface area to the surrounding gas phase. Any chemistry that occurs must be mediated through transfer of molecules from the gas phase into the bulk of the particle across the surface. The chemical make-up of the surface can significantly influence this transfer. Further, it is recognised that particles are generally not uniform in composition throughout their volume. For example, a single particle may consist of organic and water phases that are not mixed, but are phase separated. This can have a profound influence on the properties of a particle when compared with the properties expected for a particle characterised by uniform mixing.In this research we will investigate the relationship between the chemical, physical and optical properties of aerosol particles and their chemical composition and uniformity in composition. We will develop new techniques to examine the internal structure within a single particle, to explore how different chemicals mix or separate in a single particle, and to investigate the ease with which molecules are taken up at the surface of the particle. In addition, we will develop a new instrument to measure how efficiently a particle absorbs light. In the atmosphere, aerosol particles can scatter sunlight back into space, counteracting the heat trapping properties of the greenhouse gases. However, some pollutant particles, such as black carbon produced in combustion, strongly absorb sunlight enhancing the warming of the atmosphere. The impact of aerosols remains poorly quantified and new techniques are required to study their light absorption properties.The novel experiments described above are based around two new powerful techniques. Using a tightly focussed laser beam, we can hold onto a single particle indefinitely. Known as optical tweezers, this approach has been widely used for holding particles in liquids. However, we have shown that the same approach can be used to hold onto aerosol particles. Further, light can become trapped in spherical aerosol droplets in much the same way as light undergoes total internal reflection in the formation of a rainbow. The light can travel a distance of metres around the edge of the droplet before escaping. By measuring the wavelength of the light, we can determine how far the light must travel to make one complete circuit of the droplet circumference. Not only can this provide a very accurate way of determining the size of the droplet, but it can enable us to make sensitive measurements of the composition of the droplet near the droplet surface. It is anticipated that the development and application of these new techniques will yield important new information on the properties of aerosols and their behaviour in many of the complex scientific problems highlighted above.