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Polarized optical absorption spectroscopy, NEXAFS, and GIXRD measurements of chain alignment in polyfluorene thin films

Cheun, H.; Liu, X.; Himpsel, F. J.; Knaapila, Matti LU ; Scherf, U.; Torkkeli, M. and Winokur, A. J. (2008) In Macromolecules 41(17). p.6463-6472
Abstract
The uniaxial chain alignment of low molecular weight poly(9,9-bis(ethylhexyl)fluorene-2,7-diyl) (PF2/6) in thin films cast atop rubbed polyimide templates is characterized by polarized optical absorption spectroscopy, carbon K near-edge X-ray absorption fine structure spectroscopy (NEXAFS), and grazing incidence X-ray diffraction (GIXRD) in response to thermal annealing and increasing film thickness (ca. 15-150 nm). The highest overall levels of uniaxial alignment are obtained in the thinnest PF2/6 films. However, the orientation of chains at the top surface after thermal annealing is nearly thickness independent despite a large drop in the maximum optical dichroic ratio as the film thickness increases. The kinetics of chain alignment on... (More)
The uniaxial chain alignment of low molecular weight poly(9,9-bis(ethylhexyl)fluorene-2,7-diyl) (PF2/6) in thin films cast atop rubbed polyimide templates is characterized by polarized optical absorption spectroscopy, carbon K near-edge X-ray absorption fine structure spectroscopy (NEXAFS), and grazing incidence X-ray diffraction (GIXRD) in response to thermal annealing and increasing film thickness (ca. 15-150 nm). The highest overall levels of uniaxial alignment are obtained in the thinnest PF2/6 films. However, the orientation of chains at the top surface after thermal annealing is nearly thickness independent despite a large drop in the maximum optical dichroic ratio as the film thickness increases. The kinetics of chain alignment on heating are strongly film thickness dependent and only weakly correlated with a crossover to a nematic liquid crystal state. All told these data support a structural model in which there is a graded morphology such that the top and bottom surfaces exhibit appreciable planar, uniaxial alignment while the film interior includes a greater proportion of nomplanar (i.e., tilted) chains after thermal cycling. These inhomogeneities are likely to influence technologically important optical and transport properties. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Macromolecules
volume
41
issue
17
pages
6463 - 6472
publisher
The American Chemical Society
external identifiers
  • wos:000258909000029
  • scopus:52449104616
ISSN
0024-9297
DOI
10.1021/ma702579r
language
English
LU publication?
yes
id
8602cc70-982d-4ae0-ad07-4e698916bdae (old id 1247709)
date added to LUP
2008-11-21 09:44:44
date last changed
2017-01-01 04:22:37
@article{8602cc70-982d-4ae0-ad07-4e698916bdae,
  abstract     = {The uniaxial chain alignment of low molecular weight poly(9,9-bis(ethylhexyl)fluorene-2,7-diyl) (PF2/6) in thin films cast atop rubbed polyimide templates is characterized by polarized optical absorption spectroscopy, carbon K near-edge X-ray absorption fine structure spectroscopy (NEXAFS), and grazing incidence X-ray diffraction (GIXRD) in response to thermal annealing and increasing film thickness (ca. 15-150 nm). The highest overall levels of uniaxial alignment are obtained in the thinnest PF2/6 films. However, the orientation of chains at the top surface after thermal annealing is nearly thickness independent despite a large drop in the maximum optical dichroic ratio as the film thickness increases. The kinetics of chain alignment on heating are strongly film thickness dependent and only weakly correlated with a crossover to a nematic liquid crystal state. All told these data support a structural model in which there is a graded morphology such that the top and bottom surfaces exhibit appreciable planar, uniaxial alignment while the film interior includes a greater proportion of nomplanar (i.e., tilted) chains after thermal cycling. These inhomogeneities are likely to influence technologically important optical and transport properties.},
  author       = {Cheun, H. and Liu, X. and Himpsel, F. J. and Knaapila, Matti and Scherf, U. and Torkkeli, M. and Winokur, A. J.},
  issn         = {0024-9297},
  language     = {eng},
  number       = {17},
  pages        = {6463--6472},
  publisher    = {The American Chemical Society},
  series       = {Macromolecules},
  title        = {Polarized optical absorption spectroscopy, NEXAFS, and GIXRD measurements of chain alignment in polyfluorene thin films},
  url          = {http://dx.doi.org/10.1021/ma702579r},
  volume       = {41},
  year         = {2008},
}