Characterisation of the Properties and Dynamics of Single Microparticles

气雾剂在广泛的科学学科中都很重要，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，再到它们在运送燃烧燃料方面的应用，以及它们在等离子体中的加工以制备功能性材料。气溶胶定义为固体或液体颗粒在气相中的分散，气溶胶的性质由单个颗粒的化学成分和大小决定。人们还广泛认识到，颗粒表面的化学成分可以在控制气溶胶的性质方面发挥关键作用。这主要是因为气溶胶会给周围的气相带来很大的表面积。发生的任何化学作用都必须通过分子从气相转移到表面的颗粒主体中来实现。表面的化学组成可以显著影响这种转移。此外，人们认识到，在整个体积中，颗粒的组成通常不是均匀的。例如，单个颗粒可能由有机相和水相组成，它们不是混合的，而是相分离的。与均匀混合粒子的预期性质相比，这将对粒子的性质产生深远的影响。在这项研究中，我们将研究气溶胶粒子的化学、物理和光学性质与它们的化学成分和组成的均匀性之间的关系。我们将开发新的技术来检查单个颗粒的内部结构，探索不同的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被吸收的容易程度。此外，我们将开发一种新的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，抵消温室气体的热量捕获特性。然而，一些污染物颗粒，如燃烧过程中产生的黑碳，会强烈吸收阳光，加剧大气变暖。气溶胶的影响仍然很难量化，需要新的技术来研究它们的光吸收特性。上述新颖的实验是基于两项新的强大的技术。使用紧聚焦的激光光束，我们可以无限期地抓住单个粒子。这种被称为光学镊子的方法已被广泛用于在液体中保持颗粒。然而，我们已经证明，同样的方法也可以用来保持气溶胶颗粒。此外，光可以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。在逃逸之前，光可以绕着液滴边缘传播一米远。通过测量光的波长，我们可以确定光必须传播多远才能形成一个完整的液滴周长。这不仅可以提供一种非常准确的确定液滴大小的方法，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有关气雾剂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.