title: In situ imaging and height reconstruction of phase separation processes in polymer blends during spin coating.
abstract: Spin coating polymer blend thin films provides a method to produce multiphase functional layers of high uniformity covering large surface areas. Applications for such layers include photovoltaics and light-emitting diodes where performance relies upon the nanoscale phase separation morphology of the spun film. Furthermore, at micrometer scales, phase separation provides a route to produce self-organized structures for templating applications. Understanding the factors that determine the final phase-separated morphology in these systems is consequently an important goal. However, it has to date proved problematic to fully test theoretical models for phase separation during spin coating, due to the high spin speeds, which has limited the spatial resolution of experimental data obtained during the coating process. Without this fundamental understanding, production of optimized micro- and nanoscale structures is hampered. Here, we have employed synchronized stroboscopic illumination together with the high light gathering sensitivity of an electron-multiplying charge-coupled device camera to optically observe structure evolution in such blends during spin coating. Furthermore the use of monochromatic illumination has allowed interference reconstruction of three-dimensional topographies of the spin-coated film as it dries and phase separates with nanometer precision. We have used this new method to directly observe the phase separation process during spinning for a polymer blend (PS-PI) for the first time, providing new insights into the spin-coating process and opening up a route to understand and control phase separation structures.
authors.affiliation: Department of Chemical and Biological Engineering, The University of Sheffield, Sheffield. S1 3JD. U.K.
authors.forename: Stephen
authors.initials: S
authors.lastname: Ebbens
authors.forename: Richard
authors.initials: R
authors.lastname: Hodgkinson
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Parnell
authors.forename: Alan
authors.initials: A
authors.lastname: Dunbar
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Martin
authors.forename: Paul D
authors.initials: PD
authors.lastname: Topham
authors.forename: Nigel
authors.initials: N
authors.lastname: Clarke
authors.forename: Jonathan R
authors.initials: JR
authors.lastname: Howse
mesh_terms: D005583:Fourier Analysis; D008027:Light; D008422:Materials Testing; D008567:Membranes, Artificial; D018625:Microscopy, Atomic Force / Q000379:methods; D049329:Nanostructures / Q000737:chemistry; D036103:Nanotechnology / Q000379:methods*; D011108:Polymers / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry; D013499:Surface Properties
chemical_list: D008567:Membranes, Artificial; D011108:Polymers; D012997:Solvents