ISOTHERMAL THICKENING OF CRYSTALS OF HIGH-MOLECULAR-WEIGHT N-ALKANES

The kinetics of the isothermal thickening of folded high molecular wei ght n-alkane crystallites have been studied for C168H338 Crystallized from solution and C240H482 Crystallized from both the pure melt and so lution. The effect of concentration on the isothermal thickening rate was also analyzed for the n-alkane with 168 carbons. Depending on the length of the n-alkane and the mode of crystallization, the isothermal thickening may proceed from initially a close to once folded crystal to an extended one or may also proceed through multiple refolding stag es. The characteristics of the curves describing the relation between thickening rate and crystallization temperature are common for both of the n-alkanes and are independent of the mode of crystallization. The rate of thickening increases with crystallization temperature and the process is autocatalytic. Undercooling normalizes the rates obtained at different concentrations. The experimental facts and theoretical co nsiderations favor the mechanism of the isothermal thickening being a melting and recrystallization process as opposed to solid-state diffus ion.