EQUILIBRIUM PROPERTIES AND RELAXATION-TIM E SPECTRUM OF A POLYMER-CHAIN IN A QUADRUPOLE FIELD - COMPUTER-SIMULATION

Brownian dynamics simulations were conducted to study the statistical properties, local orientational mobility of segments, and relaxation-t ime spectra of a model polymer chain with hindered internal rotation i n a strong external field of quadrupole symmetry. With the amplitude o f the external field increasing, reorientation of segments occurs with the order parameter being slightly smaller than that for a freely joi nted chain in a quadrupole field of the same amplitude. A change in th e orientational mobility of segments with the increasing external fiel d (and, therefore, the increasing order parameter) favors an increase in the characteristic relaxation times for the projections parallel to the direction of the field (''longitudinal'' relaxation) and a decrea se in the relaxation times, for the projections perpendicular to the f ield (''transverse'' relaxation). When the quadrupole field is applied , the spectrum of the Rouse normal modes splits to the longitudinal an d transverse component spectra. The relaxation times of the transverse normal modes decrease, and those of the longitudinal normal modes inc rease, with the increasing orientational order. This is associated wit h the presence of two different mechanisms of orientational mobility i n a quadrupole field: small-amplitude motion near the potential minimu m and passing over the barrier of the external quadrupole field.