A Study of Chemical and Photo-Chemical Reactions in Microdroplets

摘要- Ray/9309055 定制颗粒在先进陶瓷材料、电子和光子器件、催化剂、用于控制释放的微胶囊化聚合物颗粒和薄膜涂层的制造中的应用越来越多。 这些方法中的一些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），并且最近基于量子点的电子器件需要纳米尺寸的颗粒。 在目前生产小颗粒的技术中，与气溶胶的反应是生产所需尺寸的高纯度颗粒的最简单的技术之一。 具有所需尺寸的均匀、复合、中空和层状颗粒可以通过这样的技术产生，其中组成和结构（沿着尺寸）决定颗粒的可能应用。 本研究的目的是了解小颗粒中化学和光化学反应所涉及的物理和化学过程，控制最终颗粒形态和机械强度的因素，并开发生成定制颗粒的技术。 实验将进行单液滴悬浮在电动平衡和高度单分散液滴产生的振动孔气雾剂发生器。 基于光学共振的弹性散射技术将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。 该技术与拉曼散射和重量分析技术相结合，将提供关于颗粒的质量、组成和孔隙度的信息。 最终固体颗粒中的孔径分布将通过蒸气的吸附和解吸来分析。 为了估计覆盖由反应产生的芯液滴的无机或聚合物壳的机械强度，将使用基于壳的应力和应变之间的关系以及渗透压和芯中可溶的周围蒸气的芯组成之间的关系的技术。 光与小液滴相互作用理论为利用微液滴作为光化学反应介质提供了一条有效途径。 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查。 还将测试光化学反应是否可以被限制在区域内以形成所需厚度的壳。 在微滴中形成无表面活性剂的乳液及其用于产生纳米尺寸颗粒的用途也将被检查。 / / / / / / / / / / / / / / / / / / /!/ "/#/$/%//'/(/

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. / / / / / / / / / / / / / / / / / / /!/"/#/$/%/&/'/(/