Chain conformation in the crystalline state by means of neutron scattering methods

Abstract

Neutron scattering experiments have been performed with n-alkane and polyethylene (PE) samples crystallized from melt and solution. Differences between different conformation models are most pronounced in the short-range order region covered by intermediate angle neutron scattering (IANS) experiments. The angular range has been extended up to k≲ 1.2 A–1 and highly concentrated mixtures of PE(H)+ PE(D) have been used. The problem of phase segregation of PE(H) and PE(D) was investigated by wide angle neutron scattering (WANS). In connection with extensive analytical and Monte Carlo calculations conformation models are proposed which explain the marked differences of the scattering curves in the IANS range between melt and solution crystallized samples. During rapid crystallization from the melt sequences of the randomly oriented molecules are apparently incorporated into the growing crystal with a minimum of chain reorganization (solidification model), whereas during crystallization from dilute solution sheets along (110) planes are formed (stacked-sheets model). IANS experiments with n-hexatriacontane reveal no short-range order tendencies between tagged alkane molecules.