(361d) Factors Affecting Strength of Porous Films Made by Gas to Particle Conversion/ Thermophoretic Deposition of Nanoparticle Agglomerates

High surface area porous films are of interest for applications ranging from catalysts to solar light harvesting for photovoltaic energy conversion. In this work, porous films of titania were synthesized via a hybrid process based upon gas-to-particle conversion and thermophoretic deposition. In the final product of this process, agglomerates of titania nanoparticles made at high temperature are held together by van der Waals forces to form the nanoporous film with a porosity of greater than 95%. These films can be grown rapidly, greater than a micron per minute, but the films are fragile as prepared, with a modulus on the order of 0.50 Mpa as measured using atomic force microscopy. Using this AFM technique, the effects of primary particle size as well as the effects of infiltration and capillary condensation and low temperature reaction of a second species on the Young's modulus of the porous films were explored. The goal of the capillary condensation step was to strengthen the films by condensing material at the neck between particles, increasing the interconnectivity of the film by replacing van der Waals bonds by chemical bonds. Condensation of a second species into the structure increased the Young's modulus of the films, although this increase did not correspond to the saturation ratio of the condensing species as expected. Additional results for effects of primary particle size will be presented and discussed in the context of simulation results for this system.