Low-Concentration Polymers Inhibit and Accelerate Crystal Growth in Organic Glasses in Correlation with Segmental Mobility

Crystal growth in organic glasses has been studied in the presence of low-concentration polymers. Doping the organic glass nifedipine (NIF) with 1 wt % polymer has no measurable effect on the glass: transition temperature T-g of host molecules, but substantially alters. the rate: of crystal growth; from a 10-fold reduction to a 30% increase at 12 degrees C below the host T-g. Among the polymers tested, all but polyethylene oxide (PEO) inhibit growth. The inhibitory effects greatly diminish in the liquid state (at T-g + 38 degrees C), but PEO persists to speed crystal growth. The crystal growth rate varies exponentially with polymer concentration, in analogy with the polymer effect on solvent mobility, though the effect on crystal growth can be much stronger. The ability, to inhibit crystal growth is not well. ordered by the strength of host polymer hydrogen bonds, but correlates. remarkably well with the neat polymer's T-g, suggesting that the mobility of polymer chains is an important factor in inhibiting crystal growth in organic glasses. The polymer dopants also affect crystal growth at the free surface Of NIF glasses, but the effect is attenuated according to the power law u(s) proportional to u(b)(0.35), where u(s) and u(b) are the surface and bulk growth rates.