Rotational Diffusion of Chromophores Inside a Glassy Polymeric Film Studied By Electrooptical Interferometry
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ROTATIONNAL DIFFUSION OF CHROMOPHORES INSIDE A GLASSY POLYMERIC FILM STUDIED BY ELECTROOPTICAL INTERFEROMETRY
MEYRUEIX R. AND MIGNANI G. Rh6ne-Poulenc Recherches, 85 avenue des Fr~res Perret, B.P. 62, 69192 SAINT FONS CEDEX - France
ABSTBACT Perot Fabry interferometry under oblique incidence provides a powerful tool for the determination of the complex values of the independant components of the tensors X2 (-w;w,o) and X3 (-w;w,o,o) of poled films. Deorientation of Disperse Red One chromophore in a poled film can be followed by the decrease with time of two order parameters. In the short term regime, the relaxation times of this process are spread over a broad spectrum. By comparing the chromophore dynamics in PMMA, PS and SAN at different temperatures, it appears that free volume and secondary transition concepts cannot fully explain the chromophore behavior. Chromophore dipole/Polymer dipole interactions are invoked in order to explain the slow deorientation rate in SAN.
Introduction Poled polymers films containing conjugated charge transfert chromophores appear to be very promising for application in emerging guided wave integrated technologies (1]. The additive acentric order required for second order non linear optical (NLO) processes is usually achieved by poling the film above the glassy temperature Tg and freezing the induced polar order of the chromophores at T < Tg (2,31. It is now well established that deorientation occurs in the glassy state over periods of months [4-6]. This residual mobility is usually interpreted as a consequence of the dynamics processes by which glassy polymers undergo physical aging (6,7]. In the first part of this paper, we present an electrooptical (E/O) method for the measurement of the complex components of the tensors 2 X (-w;w,o) and X3 (-w;w,o,o) of a poled film. Two order parameters of the chromophores can be measured. A simplified version of this method is used in the second part to compare the dynamics of the Disperse Red One (DR1) azodye in PMMA, PS and Poly(Styrene Acrylonitrile) (SAN). E/O Measurement of order parameters of NLO chromophores in a poled polymeric film In the case of monodimensional CT chromophores, the quadratic 2 susceptibility X is related to the microscopic static value of the hyperpolarisability 9uu m 0 by the relation [3] : (' V i ik (•h
()
= 13.tatQ(%•,
(k) (1)
Mat. Res. Soc. Symp. Proc. Vol. 173. ©1990 Materials Research Society
620
Where Q (w1 , uk) describes the wavelenght dependance of 0. Eq.(l) shows that NLO effects provide a powerful method of measurement of the order parameters 0 ijk = of the dopant. In one of the earliest work, Blumenfeld et al. [4] have studied the deorientation of NLO azodyes in PMMN by linear electrochromism. Other have used second harmonic generation (5,6,8,15], Mach Zender interferometry [3,9,13], polarimetry [7,10], attenuated total reflection [11] or Perot Fabry interferometry with continuously varying wavelength (12]. In our Perot Fabry under oblique incidence method (PFOI), the sample is a plane 4-layer
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