Recirculation cell for the small-angle neutron scattering investigation of polymer melts in flow

Abstract

A small-scale flow cell has been developed and used for small-angle neutron scattering (SANS) investigations of polymer melts in Poiseuille flow through a 4:1 contraction. The cell enables the investigation of polymer melt flow subject to a volumetric flow rate of up to 6 cm3 s−1, at pressures up to 10 MPa, temperatures up to 230 °C, and a melt viscosity up to 65 000 Pa s. The cell has recirculating flow path and a relatively small capacity (circa 200 g of polymer) so that polymers with novel and well-defined molecular architectures may be investigated. The details of its construction and operation are described. When two walls of the cell are composed of zero order birefringent sapphire, both small-angle neutron scattering and birefringence studies can be undertaken in the same cell providing a link between macroscopic and molecular level descriptions of the influence of melt flow. Both birefringence and the first melt flow SANS data for a monodisperse, linear polystyrene are presented. These demonstrate the capability and potential of the apparatus to provide data which provide a crucial test for molecular theories of the rheology of entangled polymer melts. However, the use of sapphire windows limits the maximum flow rate that can be used and higher flows necessitated an all aluminum flow cell to cope with the higher pressures developed in flow. Clear evidence of a stretching of the molecule in the direction of the melt flow and a contraction perpendicular to the flow direction has been provided.