Fully atomistic modeling of an electric field poled guest-host nonlinear optical polymer

Abstract

Fully atomistic molecular modeling is performed on an electric field poled guest-host nonlinear optical polymer system at two different densities. The higher density (HD) represents a sub-Tg system, while the lower density (LD) corresponds to a system above Tg. The electric field alignment of dopants was studied by calculating 〈cos θ〉 and 〈cos3 θ〉 and comparing with the theoretically predicted order parameters. For the LD system, the dipole orientational order achieved during 1.5 ns of NVT dynamics at 500 K was similar to the theoretical prediction. The applied field was also found to constrain the side group of the host, poly(methyl methacrylate) (PMMA). The shape of the volume swept by the dopants was found to be less cylindrical as the field was increased. The partial radial distribution functions indicated that the dopants were likely to be located near the host side group. No significant differences in the static conformational properties of the host were observed between poled and unpoled structures. In the HD system, the COOCH3 side group motion was found to be more correlated with dopant orientation than the atoms in the backbone units. In the LD system, nearly equal side group and backbone contributions were involved in dopant orientation.