Self-assembling into interconnected nanoribbons in thin films of hairy rod poly(9,9-di(2-ethylhexyl)fluorene): Effects of concentration, substrate and solvent

This study utilizes atomic force microscopy to investigate the self-assembling behaviors from dilute solution into thin film of a well-known conjugated polymer, poly(9,9-di(2-ethylhexyl)fluorene) (PF2/6). We have found that the structures of nanoscale aggregates depend on various experimental parameters including concentration, substrate and solvent. The self-assembling of PF2/6 from 0.05 mg/mL solution in toluene onto SiOx/Si substrate results in the formation of interconnected nanoribbons with thickness and width of about 20 and 150 nm, respectively. Varying polymer concentration and type of substrate (SiOx/Si or mica) significantly affects the nanoscale structures. The change of solvent to chlorobenzene, a slightly more polar solvent with slower evaporation rate, causes the growth of ribbon width to micron size with slight increase of the thickness. When the solvents with higher evaporation rate (i.e. chloroform and dichloromethane) are used, densely packed nanoribbons are obtained. Its width also grows to micron size. The measurements of UV/vis absorption and photoluminescence spectra detect some discrepancies in pattern, reflecting the variation of local chain organization within thin films prepared by using different solvents.