A Study of Chemical and Photo-Chemical Reactions in Microdroplets

摘要-射线/9309055定制粒子在制造先进陶瓷材料、电子和光子器件、催化剂、用于控制释放的微胶囊聚合物粒子和薄膜涂层方面得到了越来越多的应用。其中一些工艺需要特定尺寸和组成的单分散颗粒或复合颗粒(例如层状颗粒)，而最近基于量子点的电子设备需要纳米尺寸的颗粒。在目前生产小颗粒的技术中，气雾剂反应是生产所需尺寸的高纯度颗粒的最简单的技术之一。通过这样的技术可以产生所需尺寸的均匀、复合、中空和分层的颗粒，其中组成和结构(以及尺寸)决定了颗粒的可能应用。这项研究的目的是了解小颗粒中的化学和光化学反应所涉及的物理和化学过程，控制最终颗粒的形态和机械强度的因素，并开发产生定制颗粒的技术。实验将在电动天平中悬浮的单个液滴和由振动孔板气溶胶发生器产生的高度单分散的液滴上进行。基于光学共振的弹性散射技术将被应用于精确确定均匀或分层液滴在与周围蒸汽反应期间的大小和折射率。这项技术与拉曼散射和重力测量技术相结合，将提供有关粒子的质量、组成和孔隙率的信息。最终固体颗粒中的孔径分布将通过对蒸汽的吸附和解吸来分析。为了估计覆盖由反应产生的核心液滴的无机或聚合物外壳的机械强度，将使用一种技术，该技术基于外壳的应力和应变之间的关系以及可溶于核心的周围蒸汽的渗透压力和核心成分之间的关系。光与小液滴的相互作用理论为利用微滴作为光化学反应介质提供了一条有效的途径。需要高功率光源的光化学反应将在低功率光源的微滴中进行检测。还将测试光化学反应是否可以限制在区域内，以形成所需厚度的壳层。此外，还将研究微滴中无表面活性剂乳液的形成及其在纳米颗粒生成中的应用。///

Abstract - Ray/9309055 Tailored particles are finding increasing applications in the manufacturing of advanced ceramic materials, electronic and photonic devices, catalysts, microencapsulated polymer particles for control release and thin film coating. Some of these processes require monodisperse particles of specific size and composition or composite particles (for example layered particles), and recent electronic devices based on quantum dots require nano-size particles. Of the current techniques for the production of small particles, reactions with aerosols is one of the simplest for the production of high purity particles of a desired size. Homogeneous, composite, hollow and layered particles of desired size can be generated by such techniques where composition and structure (along with the size) dictate the possible applications of the particles. The objectives of this research are to understand the physical and chemical processes involved in the chemical and photochemical reactions in small particles, factors that control the morphology and mechanical strength of the final particles, and to develop techniques for the generation of tailored particles. Experiments will be conducted on single droplets suspended in an electrodynamic balance and on highly monodisperse droplets generated by a vibrating orifice aerosol generator. An elastic scattering technique, based on optical resonance, will be applied for the precise determination of the size and the refractive index of a homogeneous or a layered droplet during a reaction with the surrounding vapor. This technique, in conjunction with Raman scattering a nd graviometric techniques, will provide information on the mass, composition, and porosity of a particle. The pore size distribution in a final solid particle will be analyzed by adsorption and desorption of vapors. To estimate the mechanical strength of an inorganic or a polymeric shell covering a core droplet generated by a reaction, a technique, based on the relations between the stress and strain for the shell and between the osmotic pressure and core composition for a surrounding vapor soluble in the core, will be used. The theory of interaction of light with small droplets suggests an efficient way for the utilization of microdroplets as photochemical reaction media. Photochemical reactions requiring high power light sources will be examined in microdroplets with low power sources. Whether a photochemical reaction can be limited to region to form a shell of desired thickness will also be tested. The formation of surfactant-free emulsions in microdroplets and their use for the generation of nano-size particles will also be examined. / / / / / / / / / / / / / / / / / / /!/"/#/$/%/&/'/(/