Determination of elastic shear constants of polyethylene at room temperature by inelastic neutron scattering

Abstract

AbstractThe elastic shear constants of both the amorphous and crystalline regions of polyethylene have been measured at room temperature. A newly developed method is used which allows the determination of elastic constants from the coherent inelastic neutron scattering of polycrystals. A deuterated and partially oriented sample is investigated on a triple‐axis spectrometer and a time‐of‐flight instrument. The elastic constants of the crystalline regions of polyethylene are c44 = 2.1 ± 0.3, c55 = 2.2 ± 0.3, c66 = 1.8 ± 0.2, and c′ = 1/4(c11 + c22 − 2c12) = 0.92 GPa. The shear modulus of the amorphous regions is obtained as G = 0.55 ± 0.03 GPa. In connection with other experimental results the elastic constant matrix is given and compared with theoretical estimates. With simple models, macroscopic moduli are calculated which are in good agreement with published experimental data.