title: Bimodal crystallization at polymer-fullerene interfaces.
abstract: The growth-kinetics of [6,6]-phenyl C61-butyric acid methyl ester (PCBM) crystals, on two different length-scales, is shown to be controlled by the thickness of the polymer layer within a PCBM-polymer bilayer. Using a model amorphous polymer we present evidence, from in situ optical microscopy and grazing-incidence X-ray diffraction (GIXD), that an increased growth-rate of nanoscale crystals impedes the growth of micron-sized, needle-like PCBM crystals. A combination of neutron reflectivity and GIXD measurements, also allows us to observe the establishment of a liquid-liquid equilibrium composition-profile between the PCBM layer and a polymer-rich layer, before crystallization occurs. While the interfacial composition-profile is independent of polymer-film-thickness, the growth-rate of nanoscale PCBM crystals is significantly larger for thinner polymer films. A similar thickness-dependent behavior is observed for different molecular weights of entangled polymer. We suggest that the behavior may be related to enhanced local-polymer-chain-mobility in nanocomposite thin-films.
authors.affiliation: College of Engineering, Swansea University, Singleton Park, Swansea, SA2 8PP, UK. a.m.higgins@swansea.ac.uk.
authors.forename: Dyfrig
authors.initials: D
authors.lastname: Môn
authors.forename: Anthony M
authors.initials: AM
authors.lastname: Higgins
authors.forename: David
authors.initials: D
authors.lastname: James
authors.forename: Mark
authors.initials: M
authors.lastname: Hampton
authors.forename: J Emyr
authors.initials: JE
authors.lastname: Macdonald
authors.forename: Michael B
authors.initials: MB
authors.lastname: Ward
authors.forename: Philipp
authors.initials: P
authors.lastname: Gutfreund
authors.forename: Samuele
authors.initials: S
authors.lastname: Lilliu
authors.forename: Jonathan
authors.initials: J
authors.lastname: Rawle