Composition profiling in a binary polymer blend thin film using polarized neutron reflectivity

The concentration profile in an ultra-thin film (film thickness d = 435 Å) of a high molecular mass poly(isoprene)/deuterated poly(butadiene) blend is measured in the bulk system's miscible region with a new polarized neutron reflectivity method. By using a buried ferromagnetic layer inside the wafer and a polarized neutron beam, it is possible to obtain the neutron specular reflection amplitude A including its phase angle φ. Conventional reflectivity measurements only determine the reflected intensity I = A 2 which does not contain information on the phase angle. Only the knowledge of the phase angle allows an unambiguous determination of the neutron scattering length density profile of the film. The scattering length density profile thus obtained reveals poly(isoprene) segregating symmetrically to the polymer/air and polymer/Si interfaces. The adsorption profile at both interfaces can be approximately described using an exponential- or tanh-function with a decay constant smaller than the bulk correlation length.