title: Measurement of molecular mixing at a conjugated polymer interface by specular and off-specular neutron scattering.
abstract: Measurements have been performed on thermally equilibrated conjugated-polymer/insulating-polymer bilayers, using specular and off-specular neutron reflectivity. While specular reflectivity is only sensitive to the structure normal to the sample, off-specular measurements can probe the structure of the buried polymer/polymer interface in the plane of the sample. Systematic analysis of the scattering from a set of samples with varying insulating-polymer-thickness, using the distorted-wave Born approximation (DWBA), has allowed a robust determination of the intrinsic width at the buried polymer/polymer interface. The quantification of this width (12 Å ± 4 Å) allows us to examine aspects of the conjugated polymer conformation at the interface, by appealing to self-consistent field theory (SCFT) predictions for equilibrium polymer/polymer interfaces in the cases of flexible and semi-flexible chains. This analysis enables us to infer that mixing at this particular interface cannot be described in terms of polymer chain segments that adopt conformations similar to a random walk. Instead, a more plausible explanation is that the conjugated polymer chain segments become significantly oriented in the plane of the interface. It is important to point out that we are only able to reach this conclusion following the extensive analysis of reflectivity data, followed by comparison with SCFT predictions. It is not simply the case that conjugated polymers would be expected to adopt this kind of oriented conformation at the interface, because of their relatively high chain stiffness. It is the combination of a high stiffness and a relatively narrow intrinsic interfacial width that results in a deviation from flexible chain behaviour.
authors.affiliation: College of Engineering, Swansea University, Fabian Way, Crymlyn Burrows, Swansea, SA1 8EN, Wales, UK. a.m.higgins@swansea.ac.uk.
authors.forename: David
authors.initials: D
authors.lastname: James
authors.affiliation: College of Engineering, Swansea University, Fabian Way, Crymlyn Burrows, Swansea, SA1 8EN, Wales, UK. a.m.higgins@swansea.ac.uk.
authors.forename: Anthony M
authors.initials: AM
authors.lastname: Higgins
authors.affiliation: College of Engineering, Swansea University, Fabian Way, Crymlyn Burrows, Swansea, SA1 8EN, Wales, UK. a.m.higgins@swansea.ac.uk.
authors.forename: Paul
authors.initials: P
authors.lastname: Rees
authors.affiliation: Department of Physics and Astronomy, University of Sheffield, Hounsfield Road, Sheffield, S3 7RH, UK.
authors.forename: Mark
authors.initials: M
authors.lastname: Geoghegan
authors.affiliation: College of Engineering, Swansea University, Fabian Way, Crymlyn Burrows, Swansea, SA1 8EN, Wales, UK. a.m.higgins@swansea.ac.uk.
authors.forename: M Rowan
authors.initials: MR
authors.lastname: Brown
authors.affiliation: College of Engineering, Swansea University, Fabian Way, Crymlyn Burrows, Swansea, SA1 8EN, Wales, UK. a.m.higgins@swansea.ac.uk.
authors.forename: Shion-Seng
authors.initials: SS
authors.lastname: Chang
authors.affiliation: College of Engineering, Swansea University, Fabian Way, Crymlyn Burrows, Swansea, SA1 8EN, Wales, UK. a.m.higgins@swansea.ac.uk.
authors.forename: Dyfrig
authors.initials: D
authors.lastname: Môn
authors.affiliation: Institut Laue-Langevin, 71 Avenue des Martyrs, 38000 Grenoble, France.
authors.forename: Robert
authors.initials: R
authors.lastname: Cubitt
authors.affiliation: ISIS, Rutherford Appleton Laboratory, Harwell Oxford, Didcot, OX11 OQX, UK.
authors.forename: Robert
authors.initials: R
authors.lastname: Dalgliesh
authors.affiliation: Institut Laue-Langevin, 71 Avenue des Martyrs, 38000 Grenoble, France.
authors.forename: Philipp
authors.initials: P
authors.lastname: Gutfreund