Effect of solvent flow on a polymer brush: A neutron reflectivity study ofthe brush height and chain density profile

We present here the results of neutron and X-ray reflectivity studies on th e effects of solvent flow on the height and density profile of polymer chai ns chemically end-tethered to a surface. Our system consists of perdeuterat ed polystyrene chains, molar mass 80 000, that were chemically tethered to a silicon oxide surface via trichlorosilane (SiCl3) terminal groups. The br ush was exposed to a range of flow rates in both toluene and cyclohexane to a maximum shear rate of 130 000 s(-l). We observe that both the polymer br ush profile and height remain unchanged even at the highest flow rates and that no loss of polymer occurred. These results are discussed in the contex t of the various theoretical, simulation, and experimental results presente d in the literature.