DETERMINATION OF ORIENTATIONAL ORDER PARAMETERS OF UNIAXIAL FILMS WITH A COMMERCIAL 90-ANGLE FLUORESCENCE SPECTROMETER

A method is developed to determine orientational order parameters 〈P2〉 and 〈P4〉 of films by steady state fluorescence polarization in a spectrometer with 90° angle between excitation and emission beam. This is the geometry usually found in commercial fluorescence spectrometers. The method includes the determination of the fundamental molecular anisotropy rM of the fluorescent chromophore (doped or intrinsic) in stretched and unstretched films and the determination of instrumental correction coefficients from an isotropic film. As an example, the method is applied to orientation analysis of polyethylene and polystyrene films doped with fluorescent molecules of repetitive styrene units. It is concluded that in uniaxially stretched polyethylene‐films orientation of these molecules is dominated by their molecular shape; in polystyrene films orientation is influenced by additional interactions.