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Recently, Pantina and Furst [Phys. Rev. Lett. 94, 138301 (2005)] experimentally demonstrated the existence of tangential forces between bonded colloidal particles and the capability of these bonds to supporting bending moments. We introduce a model to be used in computer simulations that describes these tangential interactions. We show how the model parameters can be determined from experimental data. Simulations using the model are in agreement to the measurement by Pantina and Furst. Application of the model to an aggregate with fractal structure leads to more realistic behavior than using classical approaches only.

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In this work, the possibility of predicting absolute crystal dissolution rates for active pharmaceutical ingredients on the basis of only their corresponding molecular structures is presented. Toward this end, a combination of molecular dynamics (MD) and kinetic Monte Carlo (kMC) approaches is used. The dissolution processes are first investigated within a MD framework. Thereby, the benefit of applying a three-dimensional crystal representation is demonstrated. MD simulations are used to parametrize kMC simulations. A simple and universal way to define Markovian states and calculate rate constants for kMC simulations is proposed. Given the set of states and rate constants, a kMC approach provides a stochastic procedure to produce a state-to-state trajectory, representing a valid realization of the state-to-state dynamics, while at the same time significantly extending the range of length and time scales accessible to simulation. The results of combined MD and kMC simulations are presented for the dissolution of an aspirin crystal. A comparison with experimental data demonstrates the success of the approach.

The formation and growth of gas-made silica particles by coagulation and sintering is investigated theoretically. A model for the characteristic time for silica sintering is proposed de ning a minimum primary particle diameter above which macroscopic expressions are applied. The value of the minimum primary particle diameter is selected consistently with molecular dynamics simulations. The proposed characteristic sintering time is tested using a monodisperse model for aggregate dynamics by coagulation and sintering. The model predictions are compared with experimental data for silica formation and growth in premixed ames and hot wall aerosol ow reactors by oxidation of hexamethyl-disiloxane (HMDSO) and silicon-tetrachloride (SiCl 4 ).