Hershel Markovitz

Lateral Surface Energy of Polyethylene Crystals

Based on the theory originally devised by Born and Stern for crystals of the rare gases and alkali halides, lateral specific surface energies have been calculated for polyethylene from interatomic potentials. The specific surface energy of the {110} face was found to be about 100 to 140 ergs/cm2; of the {100} face, about 6% greater and of the {010} face, about 14% greater. The broad range of values is due to the wide variety of interatomic potentials found in the literature. For infinitely long crystals of rhomboidal cross section the average edge energy is about 3 × 10−6 erg/cm. In a crystal of this type containing nine chains, the edge energy constitutes about 30% of the surface energy.

New Interpretations: Molecular Weight Averages for a Polymer

Abstract The statement is often made in the polymer literature, without proof, that M z ≤ M w ≤ M n, where M z, M w, and M n are the z-, z weight-, and number-average molecular weights respectively. Four proofs of a generalization of these inequalities are given. It is shown that a higher-order molecular weight average is larger than a lower-order one, regardless of the form of the molecular weight distributions, except for the case when all the molecules have the same molecular weight. A brief discussion of the viscosity-average molecular weight is also included.