| Abstract
| - Small-angle neutron scattering (SANS) experiments have indicated that mixtures of linear(high density) and long chain branched (low density) polyethylenes (HDPE/LDPE) form a one-phasemixture in the melt. However, the maximum spatial resolution of pinhole SANS cameras is ∼103 Å, andit has been suggested that such experiments do not provide unambiguous evidence for a homogeneousmelt. Thus, the SANS data might also be interpreted as arising from a biphasic melt with a very largeparticle size (∼3 μm), because most of the scattering from the different phases would not be resolved. Wehave addressed this hypothesis by means of ultra-small-angle neutron scattering (USANS) experiments,using a newly developed Bonse-Hart USANS facility, which can resolve particle dimensions up to 30 μm.The experiments confirm that HDPE/LDPE blends are homogeneous in the melt on length scales probedby pinhole SANS and also by USANS. We have also studied blends of linear and short-chain branchedpolyethylenes, which phase separate when the branch content is sufficiently high. It is shown that USANScan directly resolve both the size of the dispersed phase (∼4 μm) and the forward cross section [dΣ/dΩ(0)∼ 108 cm-1], which is 6 orders of magnitude higher than for homogeneous blends.
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