One-step aerosol synthesis of nanoparticle agglomerate films: simulation of film porosity and thickness

Abstract

A method is described for designing nanoparticle agglomerate films with desired film porosity and film thickness. Nanoparticle agglomerates generated in aerosol reactors can be directly deposited on substrates to form uniform porous films in one step, a significant advance over existing technologies. The effect of agglomerate morphology and deposition mechanism on film porosity and thickness are discussed. Film porosity was calculated for a given number and size of primary particles that compose the agglomerates, and fractal dimension. Agglomerate transport was described by the Langevin equation of motion. Deposition enhancing forces such as thermophoresis are incorporated in the model. The method was validated for single spherical particles using previous theoretical studies. An S-shape film porosity dependence on the particle Peclet number typical for spherical particles was also observed for agglomerates, but films formed from agglomerates had much higher porosities than films from spherical particles. Predicted film porosities compared well with measurements reported in the literature. Film porosities increased with the number of primary particles that compose an agglomerate and higher fractal dimension agglomerates resulted in denser films. Film thickness as a function of agglomerate deposition time was calculated from the agglomerate deposition flux in the presence of thermophoresis. The calculated film thickness was in good agreement with measured literature values. Thermophoresis can be used to reduce deposition time without affecting the film porosity.

Determination of the Transition Regime Collision Kernel from Mean First Passage Times

“…Nonetheless, there are several reasons for further examination of the transition regime collision kernel. First, collision kernel expressions have been sparingly compared with results of Brownian dynamics simulations (Trzeciak et al 2004;Madler et al 2006;Heine and Pratsinis 2007), and when comparison has been performed (Nowakowski and Sitarski 1981;Narsimhan and Ruckenstein 1985), it has been limited to collisions between identical-sized particles or led to poor agreement with the unambiguous free molecular and continuum limiting expressions (Gutsch et al 1995). With recent advances in computational capabilities, Brownian dynamics simulations can accurately predict thermally driven particle-particle collision rates (the Z → ∞ limit); hence, they should be able to provide a means for more detailed examination of collision kernel expressions than is possible with currently available experimental approaches.…”

“…First, we develop an expression for the collision kernel in the Z → ∞ limit, which converges to the correct continuum and free molecular expressions and, with an appropriate definition of Kn D , can correctly predict collision kernels in the transition regime. For this purpose, we make use of mean first passage time calculations (Klein 1952;Narsimhan and Ruckenstein 1985), with the assumptions that the colliding entities are dilute in concentration and that the motion of colliding entities is accurately described by Langevin dynamics (Chandrasekhar 1943;Sitarski and Seinfeld 1977;Ermak and Buckholz 1980;Madler et al 2006;Isella and Drossinos 2010). We further show that the transition regime collision kernel is best represented in a nondimensionalized form that can be predicted with Buckingham theorem (Buckingham 1914(Buckingham , 1915.…”

Achieving a slippery, liquid-infused porous surface with anti-icing properties by direct deposition of flame synthesized aerosol nanoparticles on a thermally fragile substrate

“…5 This repeated coating process produces a 0.5-1 lm thick coating with excess of 90% porosity. 8 This porous structure was then pipetted full with silicone oil with a viscosity of 50 cSt (25 C, Sigma Aldrich). A great deal of care was taken not to overfill the samples with the oil, by letting the oil infiltrate into the structure on its own, as not to only test the oil surface in the following tests.…”

Liquid Flame Spray—A Hydrogen-Oxygen Flame Based Method for Nanoparticle Synthesis and Functional Nanocoatings

“…Comparison of the cross-sectional SEM image of LFSmade TiO 2 layer by Stepien et al (2013c) and simulations made by Mädler et al (2006b) indicates that the LFSmade porous TiO 2 -nanoparticle layer consists of deposits of multiple agglomerates produced by flame process. Deposited agglomerates consist of several primary nanoparticles, forming thick layer of nanoparticles with high porosity.…”

“…(Mädler et al 2006;Nasiri et al, 2015) The layer thickness and porosity can be individually controlled as shown by e.g. Mädler et al (2006b). Ballistic deposition of individual particles produces denser layers than those produced by letting agglomerates with low fractal dimension diffuse to the surface.…”