Self-organization of graft copolymers at surfaces, interfaces and in bulk

Abstract

The morphology in bulk and thin film of high-integrity graft copolymers has been investigated by small-angle neutron and light scattering, neutron reflectity and transmission electron microscopy. The model graft copolymers are based on two chemically incompatible blocks composed of an elastomeric poly(ethyl acrylate)(PEA) backbone onto which pendant monodisperse thermoplastic polystyrene (PS) are statistically placed. Two different levels of graft corresponding to an average of one and three per chain were investigated. In the bulk phase, the low graft-level shows irregular fractal-like structures while the high graft-level exhibits lamellar microdomains. In thin film, ordered structures were observed also in both compositions. The interphase adhesion between the PS and the PEA microdomain was investigated by elongating the copolymer films uniaxially. The low graft-level material exhibits normal behaviour characteristic of filler-reinforced rubber: the isotropic scattering pattern deforms in an anisotropic manner, i.e. ellipsoid-shaped with the long axis perpendicular to the stretching direction. An ‘abnormal butterfly’ pattern was observed with the high graft-level. The butterfly pattern is attributed to the deformation of the lamellar morphology of the copolymer.