CHAIN OVERLAP AND ENTANGLEMENTS IN DILUTE POLYMER-SOLUTIONS - BROWNIAN DYNAMICS SIMULATION

We have analyzed chain conformations and the existence - or otherwise - of chain overlaps and entanglements in dilute polymer solutions (at concentrations c < c c* = critical concentration). The fundamental pr oblem of existence of chain overlaps in dilute solutions is also relat ed to the drag reduction phenomenon (DR). Some experimental results pe rtinent to DR are explained in terms of entanglements even for solutio ns at concentrations defined in ppm. We report results of Brownian dyn amics simulations of polymer solutions in which the equations of motio n of the chains are solved by using the Langevin equation. Chains move according to actions of a systematic frictional force and a randomly fluctuating force w(t), where t is time. In addition, a shear flow fie ld can be introduced into the model. To evaluate the structure of poly mer chains in solution we have devised a measure of interchain contact s and two different measures of entanglements. The results for c = 0.3 c demonstrate that both chain entanglements and overlaps take place even in dilute solution. They also confirm predictions from an earlier combinatorial model.