ANALYSIS OF POLARIZED FLUORESCENCE INTENSITY IN AN ANISOTROPIC POLYMER MEDIUM AND ITS APPLICATION TO THE ORIENTATION MEASUREMENTS FOR NYLON-6 FIBERS

Polarized components of the fluorescence emitted from rod-like molecul es (probes) oriented in a polymer medium are analysed theoretically. A n 'envelope curve' of the polarized fluorescence intensity obtained in a rotating frame of two polaroids in the measuring system, is useful for characterizing the molecular orientation distribution. The model c alculations are carried out in terms of three basic molecular orientat ion modes, i.e. uniaxial, random, and planar orientation modes. Genera lly, the envelope curve is affected by the birefringence due to the op tical anisotropy of the polymer medium. In the highly uniaxial orienta tion mode, however, the shapes of the envelopes are scarcely distorted by the effect of birefringence. The fluorescence technique to measure envelope curves is employed to investigate the structural change of n ylon 6 fibres upon drawing. The transformation of molecular orientatio n pattern in the non-crystalline phase of the drawn fibres is describe d satisfactorily by using a combination model composed of the three ba sic modes mentioned above, with their fractional parameters. A conside rable portion of molecules in the amorphous regions may orient perpend icular to the draw direction, before the uniaxial orientation mode bec omes predominant above ca 100% elongation. (C) 1997 Elsevier Science L td.