Molecular orientation of polydimethylsiloxane induced by elongational and shearing strains

Abstract

AbstractA study examining the molecular orientation of poly(dimethylsiloxane) for different combinations of elongational and shear strains is presented. Three different cases were studied: (1) pure elongational strain; (2) increasing shear and decreasing elongational strains; (3) increasing shear and increasing elongational strains. The experiments were performed in a converging flow cell (at room temperature), where elongational and shearing strain rates achieved values of 370 s−1 and 640 s−1 respectively. Values of the Hermans orientation function were obtained from measurements of birefringence and polarization angles while strain rates were estimated from laser Doppler anemometry velocity measurements. Prospects for predicting molecular orientation from the stress‐optical laws and rheological flow models are outlined and commented on.