Network structure of polyfluorene sheets as a function of alkyl side chain length

Abstract

The formation of self-organized structures in poly(9,9-di-n-alkylfluorene)s ∼1 vol % methylcyclohexane (MCH) and deuterated MCH solutions was studied at room temperature using neutron and x-ray scattering (with the overall q range of 0.000 58-4.29Å−1 ) and optical spectroscopy. The number of side chain carbons (N ) ranged from 6 to 10. The phase behavior was rationalized in terms of polymer overlap, cross-link density, and blending rules. For N = 6−9, the system contains isotropic areas and lyotropic areas where sheetlike assemblies (lateral size of >400Å) and free polymer chains form ribbonlike agglomerates (characteristic dimension of >1500Å) leading to a gel-like appearance of the solutions. The ribbons are largely packed together with surface fractal characteristics for N = 6−7 but become open networklike structures with mass fractal characteristics for N = 8−9, until the system goes through a transition to an isotropic phase of overlapping rodlike polymers for N = 10. The polymer order within sheets varies allowing classification for loose membranes and ordered sheets, including the so-called β phase. The polymers within the ordered sheets have restricted motion for N = 6−7 but more freedom to vibrate for N = 8−9. The nodes in the ribbon network are suggested to contain ordered sheets cross-linking the ribbons together, while the nodes in the isotropic phase appear as weak density fluctuations cross-linking individual chains together. The tendencies for macrophase separation and the formation of non beta sheets decrease while the proportion of free chains increases with increasing N. The fraction of β phase varies nonlinearly, reaching its maximum at N = 8.

Topological Transformation of π‐Conjugated Molecules Reduces Resistance to Crystallization

“…[18] Changes in TT film absorption suggest ar eorganization that reduces the internal dihedral angle between the two thiophenes [19] and thereby increases electron delocalization. [21] TT films were probed by X-ray diffraction (XRD,F igure 5a). Upon heating of the film to above 124 8 8C, the color changes back to red.…”

Effect of side-chain asymmetry on the intermolecular structure and order-disorder transition in alkyl-substituted polyfluorenes

“…PF6 side chains coming from opposite backbone layers were found segregated with the layer thickness of H (PF6) ≈ 5.6Å whereas the PF1- . Forthcoming studies should expand these ideas to isotactic PF1-8 and from the solid state layers to sheetlike solution assemblies known for polyfluorenes [36] and other conjugated polymers, such as polyphenylenevinylenes [37].…”

Precipitation and sol formation from poly(p-phenylene)s solutions by spectroscopic study

“…The addition of alcohol results the blue-shifts of the UV-Vis absorption band, suggesting the twisted conformation of PP8P with the decreasing of the effective conjugation length. The increasing content of alcohol can further push the polymer molecules together to form aggregates [12,44], which can grow into colloidal particles to minimize the free energy. Afterwards, further agglomeration of polymeric particles leads to the precipitation of PP8P.…”