Development of modern methods of theoretical research and prediction of the properties of nanoscale powder media in the framework of the original methods of computer modeling (granular dynamics, stochastic dynamics, etc.) taking into account the contact forces of elastic interparticle interaction, tangential forces of "friction", the dispersion forces of attraction, electrostatic repulsion forces due to the formation of surface double electric layers, etc.
The original method of Brownian dynamics for the numerical analysis of the processes of coagulation of nanoscale suspensions is developed. The rate of coagulation is analyzed theoretically and in the framework of computer modeling. Analytical expressions that determine the rate of stationary coagulation of nanoparticles suspended in a solvent (dna /dt where na is the particle concentration) and the characteristic coagulation time θ = -na/(dna /dt) are proposed. In contrast to the traditionally used ratios, the obtained expressions allow us to describe with high accuracy the rate of stationary coagulation not only of weak solutions, when the volume content of nanoparticles ρ ≪1%, but also of sufficiently highly concentrated suspensions, at ρ ≈1% and above (ρ=nava where va is the volume of one particle). Analytical expressions are written for cases of three-dimensional geometry, which is relevant for working with real solutions, and two-dimensional geometry, which is convenient for comparison with the corresponding results of numerical modeling. Computer experiments were performed using the two-dimensional stochastic dynamics method. A satisfactory agreement of the obtained theoretical expressions with the results of numerical calculations is demonstrated. The dependence of the coagulation time on the height of the interparticle energy barrier and on the concentration of the solution is analyzed. It is shown that, in contrast to the theoretical expressions obtained, the traditionally used ratios for highly concentrated suspensions (ρ ≈1%) overestimate the characteristic coagulation times by more than an order of magnitude.
