Môn Dyfrig, Higgins Anthony M, James David, Hampton Mark, Macdonald J Emyr, Ward Michael B, Gutfreund Philipp, Lilliu Samuele, Rawle Jonathan
College of Engineering, Swansea University, Singleton Park, Swansea, SA2 8PP, UK.
Phys Chem Chem Phys. 2015 Jan 21;17(3):2216-27. doi: 10.1039/c4cp04253k. Epub 2014 Dec 8.
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.
