Effect of Polymers on Crystallization in Glass-Forming Molecular Liquids: Equal Suppression of Nucleation and Growth and Master Curve for Prediction

Crystal nucleation plays a critical role in the stability of supercooled liquids and glasses and is often controlled through addition of polymers. A dissolved polymer alters both the thermodynamics and the kinetics of nucleation, but the current understanding of these effects is limited. The rate of crystal nucleation has been measured in two molecular liquids, D-sorbitol and D-arabitol, containing polyvinylpyrrolidone (PVP) at different concentrations (0-15 wt %) and molecular weights (224 g/mol for the dimer up to 2 Mg/mol). We observe a significant inhibitory effect of PVP on crystal nucleation. Near the peak temperature for the nucleation rate (similar to 20K above the glass transition temperature), 10 wt % PVP can slow down nucleation by approximately 1 order of magnitude, and the effect increases with polymer concentration exponentially and with molecular weight. Remarkably, the 3 polymer effect on the nucleation rate is nearly the same as that on the crystal growth rate so that the ratio of the two rates is nearly constant at a given temperature independent of polymer concentration and molecular weight. This master curve behavior can be used to predict nucleation rates in multicomponent systems from more easily measured growth rates. It argues that nucleation and growth in these viscous liquids are both mobility-limited and that a polymer solute functions mainly as a mobility modifier, suppressing nucleation and growth to a similar degree.