EXTENSION AND COMPRESSION OF GRAFTED POLYMER LAYERS IN STRONG NORMAL FLOWS

We study the deformation of polymer brushes grafted to porous substrat es in strong permeation flows normal to the grafting surface. Our mode l predicts a strong deformation regime for both compressive and extens ive permeation flows of sufficiently high solvent how rates. These reg imes are characterized by non-linear scaling of brush thickness L with molecular weight N and solvent velocity V and by non-linear scaling o f solvent velocity V with the pressure drop Delta P across the brush. For the case of strong brush extension, L similar to (NV2)-V-3, as in the case of isolated chains in uniform solvent flows, and V similar to Delta P-1/3; while for strong brush compression, L similar to (NV-4/1 3)-V-9/13 and V similar to Delta P-13/15.