6533b86cfe1ef96bd12c892b

RESEARCH PRODUCT

A raman spectroscopic determination of the interlamellar forces in crystalline n-alkanes and of the limiting elastic modulus Ec of polyethylene

subject

description

A simple treatment based on continuum mechanics shows that weak interlamellar forces in crystalline n-alkanes should result in a characteristic upward shift of the frequencies of the longitudinal acoustical (LA) modes, which is independent of the chain length and decreases inversely with the mode order. A raman spectroscopic determination of the LA mode frequencies of a series of different n-alkanes confirms the theoretical conclusion and permits a derivation of a force constant characteristic of the interlamellar forces. The discussion results in a new formula valid for the LA mode frequencies of the orthorhombic n-alkanes in the acoustical limit and yields a new determination of the limiting elastic modulus Ec of crystalline polyethylene. The value obtained, Ec = 2.9 × 1012 dyne/cm2, is markedly smaller than the value derived by Schaufele and Shimanouchi neglecting the influence of the interlamellar forces on the LA mode frequencies.