Ultra-high resolution small-angle neutron scattering investigations of liquid-liquid phase separation in linear low-density polyethylene

Previous small-angle neutron scattering (SANS) studies [1] of heterogeneous ethylenehexene linear low-density polyethylene (LLDPE) copolymers have confirmed the existence of a dispersed minority phase (volume fraction phi similar to 10(-2)) consisting of highly branched, amorphous material. However, these experiments were conducted via a pinhole SANS spectrometer with an upper resolution limit similar to 10(3) Angstrom, whereas microscopy indicates that the dimensions of the disperse phase extend to the mu m-range. We have therefore complemented these investigations via a Bonse-Hart ultra-small angle neutron scattering (USANS) instrument which increases the instrumental resolution in reciprocal space by a factor similar to 100, and thus particle size up to 30 mu m can be resolved. The sensitivity of the USANS camera has recently been increased by two orders of magnitude by using the modified channel cut crystals [2], and the performance is therefore comparable to the best x-ray Bonse-Hart cameras. Xylene extraction removes the highly branched molecules and hence the volume fraction of the disperse phase is higher (phi similar to 0.3) in the extracted material.