Polyfluorene nano-rings and nano-dots on mica surfaces: evaporation-induced polymer self-assembly and photoluminescence properties of the assemblies

A facile formation of nano-ring architectures of poly(9,9-di-n-decylfluorene) (PF10) on mica surfaces in a room temperature atmosphere was accomplished by evaporation-induced self-assembly from a dilute chloroform solution saturated with water (∼0.1%). AFM investigation verified that isolated rings having diameters within a narrow distribution of around 150 nm are reproducibly formed on mica by simple drop-cast and evaporation procedures. Wormlike assemblies and/or irregular dots were predominantly observed when untreated and dehydrated chloroform solutions of PF10 were subjected to the same conditions, respectively. Water droplets generated from dissolved water during evaporation were assumed to act as a dynamic template for the ring formation. Photoluminescence (PL) measurements at 77 K indicated that the PL properties of the PF10 rings were very different from those of the PF10 dots. Very narrow PL bands from the rings implied that the PF10 molecules exist in a planar conformation and have well-ordered interchain packing. Broader PL bands from the dots suggested a disordered glassy phase. Further investigation of a series of PFs containing shorter and longer alkyl side-groups, varying from n-hexyl to n-octadecyl, suggested a marked side-chain dependency for the ring assembly formation ability.