Chain conformation in elongational and shear flow as seen by SANS

Abstract

The reliability of the experimental procedure (deformation in the melt, quenching, and characterization of orientation at room temperature) could be verified in elongation (specimens quenched for different macroscopic extensions in steady elongational flow) and in simple shear (good correlation of the chain dimensions measured in all principal shear directions). In the uniaxial elongational flow geometry, the proposed model of a temporary network leads to a satisfactory description of the SANS data both in the intermediate scattering vector range and in the Guinier range. The number of elastic strands per chain determined from both stress and SANS data is approximately the same. The agreement also holds for high molecular weight chains and binary blends. For these systems, SANS proves to be a powerful technique because selective deuteration allows one to characterize the orientation of the various components of the blends. For the characterization of chain orientation in shear, specific experimental problems are solved. An apparatus is specifically designed for quenching thick specimens oriented in simple shear with good homogeneity of orientation throughout the thickness.