The rheology of polymer solutions in oil

Abstract

AbstractThe flow birefringence and viscosity of solutions of two samples of polyisobutylene in 14 different solvents were measured in a wide range of rates of shear and concentrations. For a match of refractive index of solvent and polymer, the conditions could be completely described by the stress‐optical coefficient C over the whole range, the value being equal to the one measured on the 100% rubberlike polymer. For nonmatching solvents, according to the occurring form effect, the C becomes dependent on both molecular weight, concentration, and shear stress. These statements are independent of the viscosity of the solvent, but depend only on the index of refraction n of the solvent. This has been proved by measurements in low viscosity solvents and in hydrocarbon oils with a change of the viscosity of the solvent of about 100‐fold. The performed measurements on higher concentrations (up to 30 wt.‐%) give essentially the same results as those extrapolated to zero concentration. For these relations, allowance has to be made for viscosity and birefringence of the solvents. One therefore can conclude that the viscosity of the solvent as such does not affect either the viscosity or flow birefringence of polymer solutions, the conditions being fully described by the intrinsic viscosity [η]v and the index of refraction of the solvent. The main factor in the flow birefringence is the shear stress set up in the flowing solution.