Ambiguities in the interpretation of small-angle neutron scattering from blends of linear and branched polyethylene

This paper describes the difficulties of interpretation of small-angle neutron scattering data from blends of linear with lightly branched polyethylenes. The expected 'phase diagram' for the blend system was determined using indirect techniques, i.e. differential scanning calorimetry and transmission electron microscopy. Two different blends have been examined by neutron scattering at temperatures well above the melting point of both components. The neutron scattering data from one blend (mixed according to the 'phase diagram'), containing 50% linear deuterated material and 50% branched polymer, showed it to be demixed. The phase sizes stayed constant at around 23 nm over 36h. The scattering from the other blend (demixed according to the 'phase diagram'), containing 10% linear deuterated material and 90% branched polymer, could be interpreted in two different ways. The data are consistent with a homogeneously mixed blend, but can equally well be interpreted as coming from a system which is phase-separated with a large domain size, as seen in the electron micrographs. Crown (C) 1996 Published by Elsevier Science Ltd.