Microscopic calculation of the energetics of charged states in amorphous polyethylene.

Abstract

Polarization energies are calculated for a single excess charge on a polyethylene chain in amorphous polyethylene using (i) local segment and nonlocal distributed molecular polarizabilities, (ii) material structures simulated by both general-purpose and specialist Monte Carlo software, and (iii) uniform and Gaussian distributions of charge with different extents of charge delocalization. Local and distributed response lead to results that are essentially the same except that they correspond to different mean polarizabilities. With increasing delocalization of the charge along the chain, the polarization energies shift to higher values and the width of their distribution decreases, the differences being more pronounced for the uniform distribution. The polarization energies for charges delocalized over 10-20 methylene units form a distribution some 14 eV wide centered around 1 eV, narrowing significantly for more homogeneous polymer melts. The calculations are relevant to trapping of charge in polyethylene. They also yield the microscopic variation in the potential along the polymer chain caused by the polarization energy difference, and so may provide useful inputs to theories of electronic conduction in polymer materials.