NEUTRON REFLECTIVITY STUDY OF ADSORBED DIBLOCK COPOLYMERS

In this paper, we summarize our cumulative work on neutron reflectivit y studies of polystyrene-poly(vinyl-2-pyridine) (PS-PW) and polystyren epolyethylene oxide (PS-PEO) adsorbed at a quartz-solvent interface. D euterated toluene was chosen as the solvent since it is a good solvent for PS and a poor one for either of the other two blocks. In this cas e, the polystyrene dangles into the solvent while the other block acts as an anchor. The neutron reflectivity studies reveal that the form o f the polymer density profile normal to the substrate may be varied fr om an extended <<brush>> to a condensed mushroom conformation by manip ulating the ratio of the molecular weights of the two blocks. In addit ion, we present new data on the PS-PEO system in a poor solvent, deute rated cyclohexane, under conditions of shear flow in Poiseuille geomet ry. We find that when the PS-PEO diblock is absorbed from cyclohexane and is allowed to relax, the PS chain takes on a <<mushroom>> conforma tion. However, when the shear is applied, the layer shear thickens due to the PS chains extending to nearly twice their original lengths.