Mid- and near-infrared investigation of molecular orientation in elastomeric networks

Segmental orientation in uniaxially stretched poly(dimethylsiloxane) (PDMS) elastomeric networks is investigated by Fourier transform infrared dichroi sm. Precise determination of the dichroic effects, In the mid- as well as i n the near-infrared range, is obtained by polarization modulation of the in cident electromagnetic field. Near-infrared spectroscopy gives the possibil ity of analyzing samples of several millimeters in thickness because of the reduced intensity of the absorptions. Dichroic effects measured in the nea r-infrared region are higher than those obtained in the mid-infrared range, thus suggesting that the vibrations are less coupled at high energies. Int roduction of reinforcing filler such as silica in PDMS networks leads to an increase in orientation, attributed to the additional cross-links produced by the filler.