INFLUENCE OF POLING METHODS ON THE ORIENTATIONAL DYNAMICS OF 2-METHYL-4-NITRO-ANILINE IN POLY(METHYL METHACRYLATE) STUDIED BY SECOND-HARMONIC GENERATION

The magnitude and stability of the induced dipolar orientation of 2-me thyl-4-nitroaniline (MNA)/poly(methyl methacrylate) (PMMA) guest/host system is investigated. The chromophores are aligned using both the co rona discharge and contact electrode poling techniques. The magnitude of order parameter (also an indicator for the second order nonlinear s usceptibility) is measured by recording absorbances of the poled (by t he two different techniques) and unpoled PMMA films at different conce ntrations of MNA. Under the same conditions the corona poling techniqu e creates a higher alignment of molecules along the field direction. T he time dependence of the second harmonic intensity of the MNA/PMMA fi lm prepared by the two techniques can be described by a Kohlrausch-Wil liams-Watts stretched exponential. The temperature dependence of the d ecay time constant is found to generally follow a modified Williams-La ndel-Ferry (WLF) or Vogel-Tamann-Fulcher (VTF) equation. The glass tra nsition temperature seems to be the single most important parameter fo r determining the relaxation time tau(T).