Philippe Sergot

Orientation of polystyrene chains stretched above Tg as studied by fluorescence polarization

Abstract Fluorescence polarization has been used to measure the orientation of polystyrene chains labelled by an anthracene group covalently bound in the middle of the chains and dispersed in atactic uncrosslinked polystyreme. Stretching is performed at constant strain rate and various temperatures above T g using equipment which is described. The influence of strain rate and temperature on chain orientation is reported and leads to the conclusion that the orientation of the central part of the labelled chains is not related to the complete stress but is governed by the rubbery deformation. The occurrence of relaxation phenomena during stretching is demonstrated.

Fluorescence polarization characterization of biaxial orientation

Abstract A mathematical treatment is proposed to calculate five orientation averages in a biaxially oriented sample from six convenient polarized fluorescence intensities. An experimental method allowing intensity measurements is accurately described and applied to isotropic, uni- and biaxially oriented poly(ethylene terephthalate glycol) films doped with a fluorescent probe.

Amorphous phase orientation in biaxially drawn poly(ethylene terephthalate) films

An experimental study of the development of molecular orientation in the amorphous phase during the transverse drawing of one-way drawn poly(ethylene terephthalate) films has been carried out. Both the behaviours of phenyl ring normals or chain axes and of fluorescent rigid probes have been considered. The influence of the size of the crystallites in the one-way drawn films has been studied. It is first shown that the phenyl ring normals in the amorphous phase tend to become more perpendicular to the draw direction, as expected. However, there is no marked tendency for the rings to lie in the plane of the film, on the contrary with the crystalline phase. The chain axes, as well as the fluorescent probes, tend to align along the second draw direction. In films possessing initially long crystals, this reorientation appears less efficient at equivalent draw ratios. A memory of the state of the amorphous orientation in the one-way drawn films is observed in the sense that more relaxed one-way drawn films will lead to broader distributions in the final biaxially stretched films.

Investigation of polymer dynamics through the pressure effect on intramolecular excimer formation of a small probe

Abstract The pressure effect on intramolecular excimer formation of meso-bis[1-(2-pyrenyl)ethyl]ether dissolved in polyisoprene and in polyisobutylene has been investigated. The rate of conformational change of the probe is free-volume dependent. The results show that, at a given fractional free volume, obtained by changing either temperature or pressure, the probe has the same mobility.

Using the emission properties of an intramolecular excimer-forming probe molecule to determine the effect of hydrostatic pressure on local polymer dynamics

Abstract The fluorescence lifetime of the intramolecular excimer-forming probe molecule meso-2,4-di(N-carbazolyl) pentane dissolved in cis-polyisoprene and poly(propylene oxide) has been determined as a function of hydrostatic pressure. The rate of the local scale motion of the probe required to form the intramolecular excimer conformation is shown to be controlled by polymer segmental motions connected with the glass-rubber transition phenomenon. The experimental data are compared with the predictions of several free volume-based models of polymer dynamics.