Approximating the van der Waals Interaction Potentials between Agglomerates of Nanoparticles

JOSÉ MORÁN, Jerome Yon, Christophe Henry, Mohammad Reza Kholghy, Carleton University

     Abstract Number: 636
     Working Group: Aerosol Physics

Abstract
Van der Waals (vdW) are probably one of the most important interaction forces between nanoparticles and interfaces found in many applications of aerosol technology spanning filtration, impaction, coagulation, agglomerates restructuring, and resuspension. However, the vdW interactions are currently poorly modeled especially for particles with complex geometry (e.g. raspberry-like and fractal-like agglomerates of nanoparticles).

We have adapted the code FracVAL (Morán et al., 2019) to simulate raspberry-like agglomerates and used its original version to generate representative diffusion-limited (DLCA; fractal dimension 1.78) and ballistic-limited (BLCA; fractal dimension 1.89) agglomerates representing asymptotic limits in agglomeration under diluted conditions as commonly found in aerosol science. We generate a total of 500 agglomerates for each condition to take the particle anisotropy into consideration (relevant for both DLCA and BLCA agglomerates) and generate clusters with a number of primary particles between 10 to 1000. Subsequently, we conducted a detailed morphological analysis of these agglomerates where we determine their anisotropy coefficient, packing factor, pair-correlation stretching exponent, among others. Based on this detailed morphological characterization we model the vdW interaction potential between molecule-agglomerate and agglomerate-agglomerate. For the former case we have obtained analytical equations predicting their orientationally-averaged interaction and for the latter we have introduced a semi-analytical model taking the polydispersity of agglomerates into account and thus extended the work of Babick et al. (2011) focused only on monodisperse DLCA agglomerates of micrometer-sized particles.

These new models may be used in future studies to predict vdW coagulation enhancement, particle-walls interactions, resuspension, impaction, and agglomerate filtration.

[1] Babick, F., Schießl, K., & Stintz, M. (2011). van-der-Waals interaction between two fractal aggregates. Advanced Powder Technology, 22(2), 220-225.
[2] Morán, J., Fuentes, A., Liu, F., & Yon, J. (2019). FracVAL: An improved tunable algorithm of cluster–cluster aggregation for generation of fractal structures formed by polydisperse primary particles. Computer Physics Communications, 239, 225.