Kinetics of Crystal Nucleation in Some Normal Alkane Liquids

Abstract

The crystal nucleation behavior of some normal alkane liquids—C₁₆H₃₄, C₁₇H₃₆, C₁₈H₃₈, C₂₄H₅₀, and C₃₂H₆₆—was investigated by the droplet technique. The relative undercoolings, 1—λ, (i.e., the actual undercooling in units of the absolute melting temperature) at which the crystal nucleation frequency in these liquids becomes 10⁷ cm^—3 sec^—1 are 0.037 to 0.043, and almost an order of magnitude smaller than those for simple molecular substances. Crystal nucleation frequencies in droplets of C₁₇H₃₆ and C₁₈H₃₈ samples of very high purity were determined quantitatively. The frequencies were proportional to droplet volume and increased by a factor of 5000 to 8000 per 1° decrease in temperature. The results are satisfactorily described by the classical nucleation theory with values of the crystal nucleus ‐ liquid interfacial tension σ, 7.2 erg‐cm^—2 for C₁₇H₃₆ and 9.6 erg‐cm^—2 for C₁₈H₃₈. The experimental pre‐exponential factors in the nucleation expression agree with the theoretical values to well within the experimental uncertainty. The small relative undercooling and the weak glass‐forming tendency in the high‐molecular weight n‐alkane liquids is satisfactorily explained by the hypothesis of nucleation of small segments of molecules.