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

M. Knaapila, D. W. Bright, R. Stepanyan, M. Torkkeli, L. Almásy, R. Schweins, U. Vainio, E. Preis, F. Galbrecht, U. Scherf, A. P. Monkman

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The formation of self-organized structures in poly(9,9-di-n-alkylfluorene)s ∼1 vol % methylcyclohexane (MCH) and deuterated MCH (MCH-d14) solutions was studied at room temperature using neutron and x-ray scattering (with the overall q range of 0.00058-4.29 -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 >400) and free polymer chains form ribbonlike agglomerates (characteristic dimension of >1500) 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.

Original languageEnglish
Article number051803
JournalPhysical Review E - Statistical, Nonlinear, and Soft Matter Physics
Issue number5
Publication statusPublished - May 19 2011


ASJC Scopus subject areas

  • Statistical and Nonlinear Physics
  • Statistics and Probability
  • Condensed Matter Physics

Cite this

Knaapila, M., Bright, D. W., Stepanyan, R., Torkkeli, M., Almásy, L., Schweins, R., Vainio, U., Preis, E., Galbrecht, F., Scherf, U., & Monkman, A. P. (2011). Network structure of polyfluorene sheets as a function of alkyl side chain length. Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 83(5), [051803].