FLOWS OF FLEXIBLE POLYMER-SOLUTIONS IN PORES

We study the passage of flexible polymers in solution through pores (of diameter D smaller than the radius of gyration of the chains, RF) driven by hydrodynamic flows through the pore (characterized by a current of the solvent, Js). (1) For the case of slightly conical pores (first converging and then diverging) the chains are drawn in above a critical current Jc. For a dilute solution, Jc≃Jc1ε, where ε measures the angle of the cone and JC1≃T/ηs depends only on the temperature T and the solvent viscosity ηs, but is independent of D and of the molecular weight (at large molecular weights). For a semidilute solution at the entrance of the pore, one finds three regimes depending upon the bulk concentration C0, the minimal cross section, and the current's strength Js: (α) a free flowing state of the SD solution throughout the pore, (β) a partially flowing state with a dilute region extending downstream from the minimal section, (γ) a clogged state where a dilute region is present both upstream and downstream. (2) For a capillary of constant cross section passing through a flat wall, the chains are subjected to an elongational flow at the entrance. Above a critical current Js=Jc', they are sufficiently stretched to enter the pore. For dilute solutions, Jc'=Jc1 In semidilute solutions Jc' ought to vary as C-15/4. We also discuss elongational effects at the entrance of macroscopic capillaries. © 1978, American Chemical Society. All rights reserved.