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Control over phase behavior and solution structure of hairy-rod polyfluorene by means of side-chain length and branching

Knaapila, Matti LU ; Stepanyan, R.; Torkkeli, M.; Garamus, V. M.; Galbrecht, F.; Nehls, B. S.; Preis, E.; Scherf, U. and Monkman, A. R. (2008) In Physical Review E (Statistical, Nonlinear, and Soft Matter Physics)2001-01-01+01:002016-01-01+01:00 77(5).
Abstract
We present guidelines on how the solution structure of pi-conjugated hairy-rod polyfluorenes is controlled by the side-chain length and branching. First, the semiquantitative mean-field theory is formulated to predict the phase behavior of the system as a function of side-chain beads (N). The phase transition at N=N* separates a lyotropic phase with solvent coexistence (N < N*) and a metastable membrane phase (N > N*). The membrane phase transforms into the isotropic phase of dissolved rodlike polymers at the temperature T-mem*(N), which decreases both with N and with the degree of side-chain branching. This picture is complemented by polymer demixing with the transition temperature T-IN*(N), which decreases with N. For N < N*,... (More)
We present guidelines on how the solution structure of pi-conjugated hairy-rod polyfluorenes is controlled by the side-chain length and branching. First, the semiquantitative mean-field theory is formulated to predict the phase behavior of the system as a function of side-chain beads (N). The phase transition at N=N* separates a lyotropic phase with solvent coexistence (N < N*) and a metastable membrane phase (N > N*). The membrane phase transforms into the isotropic phase of dissolved rodlike polymers at the temperature T-mem*(N), which decreases both with N and with the degree of side-chain branching. This picture is complemented by polymer demixing with the transition temperature T-IN*(N), which decreases with N. For N < N*, the lyotropic phase turns isotropic with increasing T at T-IN*. For N > N*, stable membranes are predicted for T-IN*< T < T-mem* and metastable membranes with nematic coexistence for T < T-IN*. Second, in experiment, samples of poly(9,9-dialkylfluorene) with N=6-10 were mixed in methylcyclohexane. For N=8 the side-chain branching was controlled by (9,9-dioctylfluorene)/(9,9-bis(2-ethylhexyl)fluorene) (F8/F2/6) random copolymers. The proportion of F8 to F2/6 repeat units was 100:0, 95:5, 90:10, 50:50, and 0:100. In accordance with the theory, lyotropic, membrane, and isotropic phases with the corresponding phase transitions were observed. For N < N*similar to 6 only the lyotropic phase is present for attainable temperatures. The membrane and isotropic phases are present for N > N*. T-mem*(N) decreases from 340 K to 280 K for N >= 8. For copolymers, the membrane phase is found when the fraction of F8 units is at least 90%, T-mem* decreasing with this fraction. The membrane phase contains three material types: loose sheets of two polymer layers, a better packed beta phase, and dissolved polymer. For N >= 7 and T < T-mem* the tendency for membrane formation becomes stronger with increasing temperature. (Less)
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organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Physical Review E (Statistical, Nonlinear, and Soft Matter Physics)2001-01-01+01:002016-01-01+01:00
volume
77
issue
5
publisher
American Physical Society
external identifiers
  • wos:000256885400085
  • scopus:43449089204
ISSN
1539-3755
DOI
10.1103/PhysRevE.77.051803
language
English
LU publication?
yes
id
dddfd6c2-562e-4228-a2a0-b19e8de76f28 (old id 1190532)
date added to LUP
2008-09-08 09:54:06
date last changed
2017-09-03 03:49:31
@article{dddfd6c2-562e-4228-a2a0-b19e8de76f28,
  abstract     = {We present guidelines on how the solution structure of pi-conjugated hairy-rod polyfluorenes is controlled by the side-chain length and branching. First, the semiquantitative mean-field theory is formulated to predict the phase behavior of the system as a function of side-chain beads (N). The phase transition at N=N* separates a lyotropic phase with solvent coexistence (N &lt; N*) and a metastable membrane phase (N &gt; N*). The membrane phase transforms into the isotropic phase of dissolved rodlike polymers at the temperature T-mem*(N), which decreases both with N and with the degree of side-chain branching. This picture is complemented by polymer demixing with the transition temperature T-IN*(N), which decreases with N. For N &lt; N*, the lyotropic phase turns isotropic with increasing T at T-IN*. For N &gt; N*, stable membranes are predicted for T-IN*&lt; T &lt; T-mem* and metastable membranes with nematic coexistence for T &lt; T-IN*. Second, in experiment, samples of poly(9,9-dialkylfluorene) with N=6-10 were mixed in methylcyclohexane. For N=8 the side-chain branching was controlled by (9,9-dioctylfluorene)/(9,9-bis(2-ethylhexyl)fluorene) (F8/F2/6) random copolymers. The proportion of F8 to F2/6 repeat units was 100:0, 95:5, 90:10, 50:50, and 0:100. In accordance with the theory, lyotropic, membrane, and isotropic phases with the corresponding phase transitions were observed. For N &lt; N*similar to 6 only the lyotropic phase is present for attainable temperatures. The membrane and isotropic phases are present for N &gt; N*. T-mem*(N) decreases from 340 K to 280 K for N &gt;= 8. For copolymers, the membrane phase is found when the fraction of F8 units is at least 90%, T-mem* decreasing with this fraction. The membrane phase contains three material types: loose sheets of two polymer layers, a better packed beta phase, and dissolved polymer. For N &gt;= 7 and T &lt; T-mem* the tendency for membrane formation becomes stronger with increasing temperature.},
  articleno    = {051803},
  author       = {Knaapila, Matti and Stepanyan, R. and Torkkeli, M. and Garamus, V. M. and Galbrecht, F. and Nehls, B. S. and Preis, E. and Scherf, U. and Monkman, A. R.},
  issn         = {1539-3755},
  language     = {eng},
  number       = {5},
  publisher    = {American Physical Society},
  series       = {Physical Review E (Statistical, Nonlinear, and Soft Matter Physics)2001-01-01+01:002016-01-01+01:00},
  title        = {Control over phase behavior and solution structure of hairy-rod polyfluorene by means of side-chain length and branching},
  url          = {http://dx.doi.org/10.1103/PhysRevE.77.051803},
  volume       = {77},
  year         = {2008},
}