Studies on the transport and deposition of charged nanoparticles

Nanoparticle transport and deposition at the interface between gas-solid or liquid-solid is of principal importance in many technological applications including fluid-article separation processes and deposition of nanoparticle films. Due to small length scales associated with nanoparticle systems, interparticle interactions assume relatively greater importance. Particle-particle and particle-surface interactions may significantly influence the morphology and/or deposition dynamics in the interfacial region. On the other hand, the morphology of the particle deposit may influence the transport dynamics, which, in turn, is affected by the transport mechanism itself. The main focus of this dissertation is to investigate the link between interparticle interactions, deposit morphology, and deposition dynamics in nanoparticle systems.; The dissertation is broadly divided into three parts. In the first part, computer simulations are used to investigate monolayer and multilayer deposition in liquids. A mesoscale simulation incorporating interparticle interactions, which is also consistent with the continuum level mass conservation at the same time, is used. Variation of surface coverage in different layers above the deposition surface, as a function of range and magnitude of electrostatic interactions are reported for the first time. The microstructural information on the nanoparticle deposit obtained at the mesoscale is then used to understand the macroscopic deposition dynamics. A computational approach for evaluating ‘available surface function’, a function that characterizes transient features of deposition kinetics, for multilayer deposition is proposed.; The main focus of the second part of the dissertation is to predict morphology of nanoparticle films resulting from different phoretic transport mechanisms in the gas phase. Sequential Brownian dynamic simulation of nanoparticle deposition, accounting for the interparticle van der Waals and Coulomb interactions is carried out. Influence of gas temperature, thermophoretic, and electrophoretic interactions on morphology of nanoparticle film is investigated. Fractal dimension, packing density, coordination number and contact angle distributions for the nanoparticle films are reported for the first time. A new computational approach has also been developed to account for influence of coalescence or sintering on morphology of films at high temperatures. These simulations can be used as tools to obtain optimum window of process conditions required to fabricate tailored nanoparticle films for environmentally benign photocatalytic applications.; In the last part of the dissertation, experimental studies on the deposition and capture of particles in an external electrical field are presented. An innovative method, using a soft X-ray radiation, is developed to electrically charge the nanoparticles in electrostatic precipitators. The method has been demonstrated to be very effective and has potential applications in nanoparticle capture in industrial systems, bioaerosol capture and inactivation, and electrical charging in aerosol instrumentation.