Self-assembling structures and thin-film microscopic morphologies of amphiphilic rod-coil block oligomers

This paper examines the influences of solvent evaporation and atmosphere humidity on self-assembling structures and thin-film microscopic morphologies of amphiphilic rod-coil block oligomers (EO_nOPV) containing conjugated oligo(phenylene vinylene) dimer (OPV) coupled to poly(ethylene oxide) (PEO; n, the average number of ethylene oxides, is 16, 12, 7, and 3, respectively) on hydrophilic substrates. Atomic force microscopy (AFM), UV-vis absorption, and small angle X-ray diffraction are employed to investigate the thin-film morphology and structure. Solvent evaporation and atmosphere humidity are found to exert a strong influence on thin-film morphology and structure. Under the condition of quick evaporation and dry atmosphere, all EO_nOPV oligomers form the monolayer islands. Increasing the solute volume, both EO ₁₆OPV and EO₁₂OPV oligomers can form the polar lamellas with a head-to-tail packing arrangement. Under the condition of slow evaporation and humid atmosphere, EO₁₆OPV and EO₁₂OPV may self-assembly into curvy nanoribbons with well-defined width and curvature radii on mica, while EO₇OPV and EO₃OPV with the shorter PEO coils do not form. A symmetric bilayer structure for the ribbons is proposed. Plausible reasons for the variation in thin-film morphology are discussed, based on the results obtained from investigation of PEO coil length, solvent evaporation, and atmosphere humidity effects.