Microscopic morphology of polyfluorene-poly(ethylene oxide) block copolymers:: Influence of the block ratio

In this paper, we describe the synthesis and characterization of poly(9,9'-dioctylfluorene)-poly(ethylene oxide) (PF-PEO) block copolymers with different block ratio and molecular architectures (diblock or triblock copolymers). Tapping-mode atomic force microscopy is used to investigate the relationship between the molecular structure and the microscopic morphology of thin deposits. Copolymers with a low average volume ratio of PEO (f(EO) from 0.1 to 0.3) exhibit a well-defined organization into nanoribbons. A model of chain packing is proposed; these structures arise from the interplay of pi-pi interactions between conjugated PF segments and the interactions of PEO with the mica substrate surface. For copolymers with higher average volume ratio of PEO (f(EO) > 0.4), the organized structures disappear and lead to untextured aggregates, probably because long-range, regular pi-pi stacking of the segments can no longer take place. We also observe that the nature of the solvent from which deposits are grown and the substrate polarity have a strong impact on the microscopic morphology.