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 dichroism. Precise determination of the dichroic effects, In the mid- as well as in the near-infrared range, is obtained by polarization modulation of the incident electromagnetic field. Near-infrared spectroscopy gives the possibility of analyzing samples of several millimeters in thickness because of the reduced intensity of the absorptions. Dichroic effects measured in the near-infrared region are higher than those obtained in the mid-infrared range, thus suggesting that the vibrations are less coupled at high energies. Introduction 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.