Density fluctuations in amorphous and aemicrystalline polymers

Abstract

The small-angle scattering of amorphous and semicrystalline polymers contains an intensity component related to density fluctuations (Fl) within the crystalline and amorphous domains. A quantitative study of this parameter results in information on the changes of thermal motion and disorder as a function of temperature, crystallinity and preferred orientation. Amorphous polymers show a change of slope of the Fl - T-curves at Tg. Above Tg the value of Fl corresponds to the relationship valid for a system in thermodynamic equilibrium, below Tg the Fl - T-curve tends towards a non-zero value at 0°K with decreasing slope. At very low temperatures the value of Fl can be considered a sum of the contributions from the “frozen-in” disorder and from phonons of long wave-length. Semicrystalline polymers show Fl - T-curves similar to those of amorphous polymers. At a given temperature Fl shows an approximately linear decrease with increasing crystallinity. Preferred orientation produces an anisotropy in the diffuse small-angle scattering related to the density fluctuations which can be interpreted in terms of an anisotropy of the phonon velocities. The temperature dependence of this anisotropy can be used to estimate the phonon velocities involved. © 1977, Walter de Gruyter. All rights reserved.