Computer simulation of dilute polymer solutions in transient elongational flows

The behaviour of polymer molecules in solution flowing through a succession of contraction-expansion zones was simulated using the Brownian dynamics m ethod. The velocity profile of the flow field calculated previously, assumi ng that the flow modification in dilute polymer solution is negligible, was used. In the vicinity of the cell symmetry axis the flow can be described as an oscillatory elongational planar flow. The dumbbell with conformation- dependent friction and elastic coefficients was chosen as a model for the p olymer chain. When the initial state of the polymer chain entering the firs t contraction zone had corresponded to a gaussian coil the initial increase in the polymer deformation along the now direction was observed. After som e time independent of the flow rate, the amplitude of deformation gradually decreased to the stationary value further in the cell where the polymer de formation followed the flow oscillations. The amplitude of the deformation oscillations showed the critical behaviour: they increased for flow rates l ess than a critical value and did not change with further increase in the f low rate.