Thin polymer films of block copolymers and blend/nanoparticle composites
MetadataShow full item record
In this thesis, atomic force microscopy (AFM), transmission electron microscopy (TEM) and optical microscopy techniques were used to investigate systematically the self-assembled nanostructure behaviour of two different types of spin-cast polymer thin films: poly(isoprene-b-ethylene oxide), PI-b-PEO diblock copolymers and [poly(9,9-dioctylfluorene-co-benzothiadiazole)]:poly[9,9- dioctyfluorene-co-N-(4-butylphenyl)-diphenylamine], F8BT:TFB conjugated polymer blends. In the particular case of the polymer blend thin films, the morphology of their composites with cadmium selenide (CdSe) quantum dot (QD) nanoparticles was also investigated. For the diblock copolymer thin films, the behaviour of the nanostructures formed and the wetting behaviour on mica, varying the volume fraction of the PEO block (fPEO) and the average film thickness was explored. For the polymer blend films, the effect of the F8BT/TFB blend ratio (per weight), spin-coating parameters and solution concentration on the phase-separated nanodomains was investigated. The influence of the quantum dots on the phase separation when these were embedded in the F8BT:TFB thin films was also examined. It was found that in the case of PI-b-PEO copolymer thin films, robust nanostructures, which remained unchanged after heating/annealing and/or ageing, were obtained immediately after spin coating on hydrophilic mica substrates from aqueous solutions. The competition and coupling of the PEO crystallisation and the phase separation between the PEO and PI blocks determined the ultimate morphology of the thin films. Due to the great biocompatible properties of the PEO block (protein resistance), robust PEO-based nanostructures find important applications in the development of micro/nano patterns for biological and biomedical applications. It was also found that sub-micrometre length-scale phase-separated domains were formed in F8BT:TFB spin cast thin films. The nanophase-separated domains of F8BT-rich and TFB-rich areas were close to one order of magnitude smaller (in the lateral direction) than those reported in the literature. When the quantum dot nanoparticles were added to the blend thin films, it was found that the QDs prefer to lie in the F8BT areas alone. Furthermore, adding quantum dots to the system, purer F8BT and TFB nano-phase separated domains were obtained. Conjugated polymer blend thin films are excellent candidates for alternatives to the inorganic semiconductor materials for use in applications such as light emitting diodes and photovoltaic cells, mainly due to the ease of processing, low-cost fabrication and mechanical flexibility. The rather limited optoelectronic efficiency of the organic thin films can be significantly improved by adding inorganic semiconducting nanoparticles.