Conformation of polyisobutylene in dilute solution subjected to a hydrodynamic shear field

A new light‐scattering experiment which allows a direct determination of the conformation of macromolecules deformed in flow is described. Light‐scattering relationships based on the interference function are developed, and results of an experimental study are detailed. The deformed conformation of high molecular weight polyisobutylene was determined in a Couette‐type shear field. Decalin was the solvent. Variables investigated were the shear rate (0 to 600 sec −1 ), the polymer molecular weight (1.0 × 10 7 to 1.6 × 10 7 ), and the polymer concentration (2.0 × 10 −4 to 8.0 × 10 −4 g/cc). Conformation variables determined were the orientation of the molecule in the shear field and its maximum and minimum extension ratios in the plane defined by the direction of flow and the direction of the shear rate. The deformation of the macromolecule was found to be markedly discrepant when compared to the dynamic macromolecular models which assume complete coil flexibility, and more closely in agreement with the recent theories of Cerf, developed for nonfree‐draining coils which exhibit a finite internal viscosity.