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

M. Knaapila, R. Stepanyan, M. Torkkeli, D. Haase, N. Fröhlich, A. Helfer, M. Forster, and U. Scherf
Phys. Rev. E 93, 042504 – Published 28 April 2016

Abstract

We study relations among the side-chain asymmetry, structure, and order-disorder transition (ODT) in hairy-rod-type poly(9,9-dihexylfluorene) (PF6) with two identical side chains and atactic poly(9-octyl-9-methyl-fluorene) (PF1-8) with two different side chains per repeat. PF6 and PF1-8 organize into alternating side-chain and backbone layers that transform into an isotropic phase at TODT(PF6) and TbiODT(PF18). We interpret polymers in terms of monodisperse and bidisperse brushes and predict scenarios TODT<TbiODT and TODTTbiODT for high and low grafting densities (the side-chain length above or below the average grafting distance). Calorimetry and x-ray scattering indicate the condition TODT(PF6)TbiODT(PF18) following the low grafting prediction. PF6 side chains coming from the alternating backbone layers appear as two separate layers with thickness H(PF6), whereas PF1-8 side chains appear as an indistinguishable bilayer with a half thickness Hbilayer(PF18)/2H(PF6). The low grafting density region is structurally possible but not certain for PF6 and confirmed for PF1-8.

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  • Received 21 December 2015

DOI:https://doi.org/10.1103/PhysRevE.93.042504

©2016 American Physical Society

Physics Subject Headings (PhySH)

  1. Research Areas
  1. Physical Systems
Polymers & Soft Matter

Authors & Affiliations

M. Knaapila1,*, R. Stepanyan2, M. Torkkeli3, D. Haase4, N. Fröhlich5, A. Helfer5, M. Forster5, and U. Scherf5

  • 1Department of Physics, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
  • 2Materials Science Centre, DSM Research, 6160 MD Geleen, The Netherlands
  • 3Department of Physics, University of Helsinki, 00014 Helsinki, Finland
  • 4MAX IV Laboratory, Lund University, 22100 Lund, Sweden
  • 5Macromolecular Chemistry Group (buwmakro), Bergische Universität Wuppertal, 42119 Wuppertal, Germany

  • *matti.knaapila@fysik.dtu.dk

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Vol. 93, Iss. 4 — April 2016

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