Simulations of color development in tinted paints

Monte Carlo simulations have been used to investigate how several thermodynamic and kinetic factors affect the distribution of pigments, when a water-based pigment dispersion is added to a solvent-borne paint. Our model contains three types of lattice particles: water, pigment and organic solvent, with short-ranged interactions. These particles move through biased diffusion, with a species-dependent mobility. Moreover, to mimic the crosslinking of the resin, the mobility of the solvent particles decreases in time. Also, the water of the pigment dispersion evaporates slowly. First, we study which conditions yield the desired equilibrium phase behavior, with homogeneously distributed pigment. Next, we study how kinetics can prevent the system to reach equilibrium. We present examples in which these kinetic processes prevent dispersion in spite of favorable equilibrium conditions, as well as examples in which a homogeneous distribution is reached against unfavorable equilibrium conditions.