(369a) Modeling Aggregation and Size Distribution of Nanoparticles In Aqueous Suspensions

The size distribution of the engineered nanoparticles (eNMs) and their aggregates in aqueous suspensions is crucial for predictions of the fate and transport of nanoparticles in the environment. Diffusion, sedimentation and interaction of nanoparticles with solid surfaces (including sedimentation), as well as living organisms are all affected by the size distribution of eNMs. In order to obtain the nanoparticle size distribution over the expected ranges of water chemistry and nanoparticle properties, predictive models are needed to assess the aggregation tendency of eNMs. In the present work, a constant-number kinetic Monte Carlo based model was developed to predict the aggregation rate and size distribution of nanoparticles. The modeling approach followed the "particles in a box" simulation method while allowing for particle sedimentation. The likelihood of nanoparticle aggregation was determined, based on the classical DLVO theory, via calculation of the aggregation probability of nanoparticle pairs. In developing the model, the reasonable minimum number of simulation particles and simulations instances were first evaluated to ensure convergence of the stationary statistics, demonstrating the ability to use parallel computing to dramatically decreasing simulation time. Model performance with respect to the predicted size distribution of eNMs was evaluated via comparison with experimental dynamic light scattering (DLS) measurements and with available literature data under varying conditions (e.g., pH, ionic strength, size distribution of the primary nanoparticles and nanoparticle surface charge). Model performance compared favorably with experimental DLS data demonstrating the potential of the present modeling approach for environmental analysis of the transport and fate of nanoparticles