(744a) A Theoretical Model for Accelerated Nucleation Due to Adsorbing Additives

Additives are used to control nucleation in many natural and industrial environments. However, the mechanisms by which additives inhibit or accelerate solute precipitate nucleation are not well understood. We modify classical nucleation theory (CNT) to predict reductions in surface tension and therefore nucleation barriers due to the adsorption of trace additives. Our model shows that nucleant efficacy depends primarily on additive concentration and adsorption equilibrium constant, suggesting that assays that screen for large equilibrium constants might facilitate nucleant design. We confirm this trend using a Potts-lattice gas model with surfactant-like additives in addition to solutes and solvents. We also show that the reaction coordinate is no longer nucleus size but is tilted toward the number of adsorbed additives coordinate. However, we show that rate corrections decay algebraically to zero as additive coverage approaches zero. Therefore, CNT can be simply modified by using a reduced surface tension due to quasi-equilibrated additive adsorption but only for weakly adsorbing and/or low concentration additives.