Breakup of an Oldroyd liquid bridge as a method for testing the rheological properties of polymer solutions

The rheological properties of polymer solutions were studied by monitoring the breakup of the liquid bridge (thinning filament). The behavior of the l iquid subjected to a deformation in a bridge (filament) was modeled by the Oldroyd general equation of state, which takes into account nonlinear effec ts, finite extension limit, and a spectrum of relaxation times. A procedure and a corresponding algorithm were developed for determining rheological c onstants from experimental data on the time dependence of the filament diam eter. The thinning of filaments of polymer solutions with various viscositi es of the solvent were experimentally studied. Solutions of poly(acrylamide ) with M = 1.1 x 10(7) were studied in the concentration range from 0.5 to 30000 ppm. The solvents were water and water-glycerin mixtures. It was esta blished that the rheological behavior of the liquids under study is closely described by the Oldroyd model with a single relaxation time. The dependen ces of the relaxation time and modulus of elasticity on the concentration o f polymer and on the solvent viscosity were obtained. The experimental data were found to contradict the predictions of the molecular-kinetic theory o f polymer solutions.