NSF-DFG: Nonequilibrium Thermal Processing of Nanoparticles via Laser Melting and Fragmentation in Liquid

University Of Virginia Main Campus, Charlottesville VA

Investigators

Abstract

The widespread and rapidly expanding use of nanoparticles in the manufacturing of advanced nanomaterials for applications in catalysis and biomedicine calls for the development of nanoparticle manufacturing techniques capable of meeting the sharp rise in global demand. Laser processing of colloidal solutions of nanoparticles is a unique green chemistry technique, working at room temperature and ambient pressure without the need for any chemical additives or reactants, saving resources and minimizing waste. To fully unleash the potential of this scalable nanomanufacturing technique, this award supports fundamental research to reveal, through tightly integrated computer modeling and experiments, the fundamental mechanisms of the laser-induced modification of nanoparticles in a liquid environment. These insights into mechanisms of nanoparticle formation foster the advancement of manufacturing techniques for environment-friendly and energy-efficient generation of nanoparticles with sizes and structural characteristics that meet the high demand of future developments in catalysis and biomedicine. The multidisciplinary nature of the research and the international collaboration with the University of Duisburg Essen, Germany facilitate the professional preparation of a new generation of researchers ready for work at the forefront of the rapidly expanding fields of laser-based advanced manufacturing and scientific computing. The impact of the project is augmented by bringing an established International Conference on Advanced Nanoparticle Generation and Excitation by Lasers in Liquids to the US for the first time and broadening participation of US students in the Venice International School on Lasers in Materials Science. Laser fragmentation in liquids and laser melting in liquids are two nonequilibrium thermal processing techniques to fabricate chemically clean nanoparticles for catalysis and biomedicine. However, the underlying nanoparticle formation mechanisms are poorly understood. This project tackles the challenge of probing the rapid highly nonequilibrium processes triggered by short pulse laser irradiation by combining multiscale and multiphysics modeling, time-resolved optical probing, and ex situ characterization of nanoparticle phase composition and defect density. An advanced computational model for investigation of the nanoparticle fragmentation and melting dynamics is developed and verified in experiments using a continuous-flow flat jet laser processing setup that ensures precise control over the pulse number and laser fluence exposure of dispersed nanoparticles. Transient optical properties are calculated for nanoparticles undergoing laser-induced melting and disintegration to facilitate the connections to the results of time-resolved experimental optical probing (pump-probe) and to reveal optimum conditions for the energy-efficient nanoparticle processing in a novel double-pulse irradiation strategy. These optimum conditions are key for better nanoparticle size, shape, and structure control, as well as for further upscaling. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.