Control over phase behavior and solution structure of hairyrod polyfluorene by means of sidechain length and branching
(2008) In Physical Review E (Statistical, Nonlinear, and Soft Matter Physics) 77(5). Abstract
 We present guidelines on how the solution structure of piconjugated hairyrod polyfluorenes is controlled by the sidechain length and branching. First, the semiquantitative meanfield theory is formulated to predict the phase behavior of the system as a function of sidechain 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 Tmem*(N), which decreases both with N and with the degree of sidechain branching. This picture is complemented by polymer demixing with the transition temperature TIN*(N), which decreases with N. For N < N*,... (More)
 We present guidelines on how the solution structure of piconjugated hairyrod polyfluorenes is controlled by the sidechain length and branching. First, the semiquantitative meanfield theory is formulated to predict the phase behavior of the system as a function of sidechain 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 Tmem*(N), which decreases both with N and with the degree of sidechain branching. This picture is complemented by polymer demixing with the transition temperature TIN*(N), which decreases with N. For N < N*, the lyotropic phase turns isotropic with increasing T at TIN*. For N > N*, stable membranes are predicted for TIN*< T < Tmem* and metastable membranes with nematic coexistence for T < TIN*. Second, in experiment, samples of poly(9,9dialkylfluorene) with N=610 were mixed in methylcyclohexane. For N=8 the sidechain branching was controlled by (9,9dioctylfluorene)/(9,9bis(2ethylhexyl)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*. Tmem*(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%, Tmem* 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 < Tmem* the tendency for membrane formation becomes stronger with increasing temperature. (Less)
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http://lup.lub.lu.se/record/1190532
 author
 Knaapila, Matti ^{LU} ; Stepanyan, R. ; Torkkeli, M. ; Garamus, V. M. ; Galbrecht, F. ; Nehls, B. S. ; Preis, E. ; Scherf, U. and Monkman, A. R.
 organization
 publishing date
 2008
 type
 Contribution to journal
 publication status
 published
 subject
 in
 Physical Review E (Statistical, Nonlinear, and Soft Matter Physics)
 volume
 77
 issue
 5
 article number
 051803
 publisher
 American Physical Society
 external identifiers

 wos:000256885400085
 scopus:43449089204
 pmid:18643093
 ISSN
 15393755
 DOI
 10.1103/PhysRevE.77.051803
 language
 English
 LU publication?
 yes
 id
 dddfd6c2562e4228a2a0b19e8de76f28 (old id 1190532)
 date added to LUP
 20160401 12:13:37
 date last changed
 20200112 09:26:50
@article{dddfd6c2562e4228a2a0b19e8de76f28, abstract = {We present guidelines on how the solution structure of piconjugated hairyrod polyfluorenes is controlled by the sidechain length and branching. First, the semiquantitative meanfield theory is formulated to predict the phase behavior of the system as a function of sidechain 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 Tmem*(N), which decreases both with N and with the degree of sidechain branching. This picture is complemented by polymer demixing with the transition temperature TIN*(N), which decreases with N. For N < N*, the lyotropic phase turns isotropic with increasing T at TIN*. For N > N*, stable membranes are predicted for TIN*< T < Tmem* and metastable membranes with nematic coexistence for T < TIN*. Second, in experiment, samples of poly(9,9dialkylfluorene) with N=610 were mixed in methylcyclohexane. For N=8 the sidechain branching was controlled by (9,9dioctylfluorene)/(9,9bis(2ethylhexyl)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*. Tmem*(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%, Tmem* 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 < Tmem* the tendency for membrane formation becomes stronger with increasing temperature.}, 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 = {15393755}, language = {eng}, number = {5}, publisher = {American Physical Society}, series = {Physical Review E (Statistical, Nonlinear, and Soft Matter Physics)}, title = {Control over phase behavior and solution structure of hairyrod polyfluorene by means of sidechain length and branching}, url = {http://dx.doi.org/10.1103/PhysRevE.77.051803}, doi = {10.1103/PhysRevE.77.051803}, volume = {77}, year = {2008}, }