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The self-assembly of nanomaterials into three-dimensional hierarchical structures is a fundamental step impacting a large number of synthetic and natural processes. These range from the scalable fabrication of nano-devices such as batteries, sensors and third generation solar cells to the uptake and accumulation of particulate pollution in the lung alveoli. Here, we show that the Dynamic behavior of ultra-fine particles (UFP < 100 nm) diverges significantly from that of sub- and micro equivalents. For freely diffusing bodies, this leads to the formation of stochastically reproducible films that approach the morphology and density of ballistically deposited ones. A novel deposition mechanism and regime are proposed that successfully capture the full spectrum of size-dependent self-assembly dynamics. These findings are a significant step toward the engineering of scalable parallel nano-fabrication approaches, and the understanding of the interaction of unbound nanostructures with their surrounding.

The assembly of nanoparticle films by flame spray pyrolysis (FSP) synthesis and deposition on temperature‐controlled substrates (323–723 K) was investigated for several application‐relevant conditions. An exemplary SnO2 nanoparticle aerosol was generated by FSP and its properties (e.g., particle size distribution), and deposition dynamics were studied in details aiming to a simple correlation between process settings and film growth rate. At high precursor concentrations (0.05–0.5·mol/L), typically used for FSP synthesis, the nanoparticles agglomerated rapidly in the aerosol leading to large (>100 nm) fractal‐like structures with low diffusivity. As a result, thermophoresis was confirmed as the dominant nanoparticle deposition mechanism down to small (≈40 K) temperature differences (ΔT) between the aerosol and the substrate surface. For moderate‐high ΔT (>120 K), thermal equilibrium was rapidly obtained yielding a constant thermophoretic flux and film growth rate. A model was developed to predict the nanoparticle deposition rates by FSP synthesis at moderate‐high ΔT that does not require detailed analysis of the aerosol composition. Comparison with previous studies having similar nozzle geometries showed that the deposition rates of FSP‐made aerosols can be reasonably well predicted for various materials and flame conditions. © 2012 American Institute of Chemical Engineers AIChE J, 2012

a b s t r a c tThe detailed three-dimensional accumulation of deposits and the build-up of pressuredrop during filtration of compressible gases laden with nanoparticles (diameter d p =50 nm) through capillaries (1-4 mm radius) was investigated by Langevin dynamics (LD) at Peclet number, Pe, 0.01-10. At low Pe, highly porous (98%) deposits were formed while at higher Pe the porosity was slightly reduced including a void cone upstream of the capillary inlet. Three distinct deposition regimes were identified: capillary deposition, clogging and cake growth. At the time of clogging (t cl ), a filter cake with constant solid volume fraction began to form, accompanied with build-up of pressuredrop which was in excellent agreement with classic cake filtration theory. An expression for the solid volume fraction of the cake (f sd,c ) was obtained as a sole function of Pe. In addition, the filtration efficiency became 1 after clogging, since the cake acts as a perfectly efficient filter. Penetration of nanoparticles takes place until the onset of cake filtration at high Pe (1-10) while for smaller ones (0.01-0.1) it is negligible at the employed capillary radii and length (10 mm). Analytical expressions for the time of capillary clogging and height of the void cone were derived and were in agreement to LD simulations. The height of the void cone is in the order of one capillary diameter at high Pe.

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