Thin film morphologies of π-conjugated rod-coil block copolymers with thermoresponsive property: A combined experimental and molecular simulation study

Abstract

A combined experimental and simulational investigation is performed to study the surface morphologies of polymer films formed by poly[2,7-(9,9-dihexylfluorene)]-b-poly[N-isopropylacrylamide] (PF-b-PNIPAAm) rod-coil block copolymers, where PF possesses pi-pi interactions and PNIPAAm is known to exhibit a coil-to-globule phase transition at T=32 degrees C. Two (PF-b-PNIPAAm) rod-coil block copolymers with different block ratios are synthesized and used to prepare thin films on the quartz glass by physisorption. The surface structures of the thermoresponsive polymer films are found to alter significantly in response to thermostimuli. Small, hemispherical domains of the aggregations of rod-blocks are formed at low temperatures. As the temperature increases, the conformations transform to isolated islands, wormlike structures, or even networklike morphologies depending on the grafting density. These morphological transformations due to temperature variation are consistent with simulation findings. The photophysical properties of PF-b-PNIPAAm films are also found to vary with thermostimuli. The PL spectra reveals that the emission originates from the aggregation of PF blocks and the intensity changes as temperature varies. Our study demonstrates that the surface morphologies and the corresponding photophysical properties of the PF-b-PNIPAAm polymer films can be tuned by thermostimuli.