Lattice Defects in Plastic Organic Crystals: Part 7.—Isotope Mass Effects in Self-diffusion in Cyclohexane

Abstract

A study has been made of the diffusion of the species 12C514C11H12 and 12C62H113H1 in single crystals of cyclohexane at 242 K. The measured diffusion coefficients are in good agreement with previously published values. An estimate of the isotope mass effect yields a value of the mass factor Eab= 0.003 ± 0.004. This virtually-zero value indicates that self-diffusion in cyclohexane proceeds by a complicated mechanism in which many molecules are involved ( >12). This discovery confirms previous speculations on the defect structure of the low entropy of fusion plastic solids.