title: An interfacial instability in a transient wetting layer leads to lateral phase separation in thin spin-cast polymer-blend films.
abstract: Spin-coating is a very widely used technique for making uniform thin polymer films. For example, the active layers in most experimental semiconducting polymer-based devices, such as light-emitting diodes and photovoltaics, are made this way. The efficiency of such devices can be improved by using blends of polymers; these phase separate during the spin-coating process, creating the complex morphology that leads to performance improvements. We have used time-resolved small-angle light scattering and light reflectivity during the spin-coating process to study the development of structure directly. Our results provide evidence that a blend of two polymers first undergoes vertical stratification; the interface between the stratified layers then becomes unstable, leading to the final phase-separated thin film. This has given us the basis for establishing a full mechanistic understanding of the development of morphology in thin mixed polymer films, allowing a route to the rational design of processing conditions so as to achieve desirable morphologies by self-assembly.
authors.affiliation: Department of Physics and Astronomy, University of Sheffield, UK. s.heriot@sheffield.ac.uk
authors.forename: Sasha Y
authors.initials: SY
authors.lastname: Heriot
authors.forename: Richard A L
authors.initials: RA
authors.lastname: Jones
mesh_terms: D020099:Coated Materials, Biocompatible / Q000032:analysis / Q000737:chemistry*; D045424:Complex Mixtures / Q000032:analysis / Q000737:chemistry; D003460:Crystallization / Q000379:methods*; D008567:Membranes, Artificial; D049329:Nanostructures / Q000032:analysis / Q000737:chemistry* / Q000648:ultrastructure*; D044367:Phase Transition; D011108:Polymers / Q000032:analysis / Q000737:chemistry; D019904:Polymethyl Methacrylate / Q000032:analysis / Q000737:chemistry*; D011137:Polystyrenes / Q000032:analysis / Q000737:chemistry*; D012399:Rotation; D017155:Wettability
chemical_list: D020099:Coated Materials, Biocompatible; D045424:Complex Mixtures; D008567:Membranes, Artificial; D011108:Polymers; D011137:Polystyrenes; D019904:Polymethyl Methacrylate