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Rheological Study of the Shape Transition of Block Copolymer-Nonionic Surfactant Mixed Micelles

Löf, David LU ; Schillén, Karin LU ; Torres, Miguel F. and Müller, Alejandro J. (2007) In Langmuir 23. p.11000-11006
Abstract
A rheological study of mixed micelles formed by PEO-PPO-PEO triblock copolymer P123 and nonionic surfactant C12EO6 in aqueous solutions has been carried out with the purpose of investigating the time dependence of a shape transition of the mixed micelles and characterizing the shape before and after the transition. The rheology results presented in this report give clear evidence that the P123-C12EO6 mixed micelle grows and changes gradually in shape from spherical to elongated (rodlike) geometry with increasing temperature. These results are in accordance with the results found in the parallel dynamic and static light scattering and calorimetrical investigation.(1,2) By using steady-state rheology, the time dependence of the sphere-to-rod... (More)
A rheological study of mixed micelles formed by PEO-PPO-PEO triblock copolymer P123 and nonionic surfactant C12EO6 in aqueous solutions has been carried out with the purpose of investigating the time dependence of a shape transition of the mixed micelles and characterizing the shape before and after the transition. The rheology results presented in this report give clear evidence that the P123-C12EO6 mixed micelle grows and changes gradually in shape from spherical to elongated (rodlike) geometry with increasing temperature. These results are in accordance with the results found in the parallel dynamic and static light scattering and calorimetrical investigation.(1,2) By using steady-state rheology, the time dependence of the sphere-to-rod transition of the mixed micelle system was carefully followed with time and temperature as simultaneously recorded variables in the experiments. This was performed by a designed novel experimental procedure. A temperature ramp was applied at a rate of 2.6 degrees C/min from a temperature below to a temperature above the shape transition at a constant shear rate while the viscosity of the solution was measured. The investigation was limited to two different compositions, surfactant-to-copolymer molar ratios (MR = n(C12EO6)/n(P123)) of 2.2 and 6.0 with varying total concentration from 1.5 to 21 wt % in comparison with the neat component. At low concentration, a slow transition was observed, which indicated that the mixed micelles are still growing into rods for several minutes after reaching the final temperature. At a total concentration of 4.0 wt % and above, the system reached equilibrium quickly. A concentration-dependent kinetic process is therefore anticipated, which was also found in the time-resolved static light scattering experiments previously performed (Lof, D.; Schillen, K.; Olofsson, G.; Niemiec, A.; Loh. W. J. Phys. Chem. B 2007, 111, 5911). At concentrations above 10 wt %, shear-thinning behavior was observed for the mixed solutions, which strongly suggests the extended shape of the mixed micelles after the shape transition. The obtained zero-shear viscosity at the investigated molar ratios was found to be lower with higher molar ratios, which indicates that the mixed micelles both in the spherical and in the rodlike state becomes smaller with higher content Of C12EO6. These results correlate well with the obtained results from the previous dynamic light scattering measurements on the same system. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Langmuir
volume
23
pages
11000 - 11006
publisher
The American Chemical Society
external identifiers
  • wos:000250228100025
  • scopus:35949001679
ISSN
0743-7463
DOI
10.1021/la701818y
language
English
LU publication?
yes
id
b05521e6-d6d7-4adf-8595-1d35cc0ab4b0 (old id 697235)
date added to LUP
2007-12-14 09:37:19
date last changed
2017-01-01 04:30:23
@article{b05521e6-d6d7-4adf-8595-1d35cc0ab4b0,
  abstract     = {A rheological study of mixed micelles formed by PEO-PPO-PEO triblock copolymer P123 and nonionic surfactant C12EO6 in aqueous solutions has been carried out with the purpose of investigating the time dependence of a shape transition of the mixed micelles and characterizing the shape before and after the transition. The rheology results presented in this report give clear evidence that the P123-C12EO6 mixed micelle grows and changes gradually in shape from spherical to elongated (rodlike) geometry with increasing temperature. These results are in accordance with the results found in the parallel dynamic and static light scattering and calorimetrical investigation.(1,2) By using steady-state rheology, the time dependence of the sphere-to-rod transition of the mixed micelle system was carefully followed with time and temperature as simultaneously recorded variables in the experiments. This was performed by a designed novel experimental procedure. A temperature ramp was applied at a rate of 2.6 degrees C/min from a temperature below to a temperature above the shape transition at a constant shear rate while the viscosity of the solution was measured. The investigation was limited to two different compositions, surfactant-to-copolymer molar ratios (MR = n(C12EO6)/n(P123)) of 2.2 and 6.0 with varying total concentration from 1.5 to 21 wt % in comparison with the neat component. At low concentration, a slow transition was observed, which indicated that the mixed micelles are still growing into rods for several minutes after reaching the final temperature. At a total concentration of 4.0 wt % and above, the system reached equilibrium quickly. A concentration-dependent kinetic process is therefore anticipated, which was also found in the time-resolved static light scattering experiments previously performed (Lof, D.; Schillen, K.; Olofsson, G.; Niemiec, A.; Loh. W. J. Phys. Chem. B 2007, 111, 5911). At concentrations above 10 wt %, shear-thinning behavior was observed for the mixed solutions, which strongly suggests the extended shape of the mixed micelles after the shape transition. The obtained zero-shear viscosity at the investigated molar ratios was found to be lower with higher molar ratios, which indicates that the mixed micelles both in the spherical and in the rodlike state becomes smaller with higher content Of C12EO6. These results correlate well with the obtained results from the previous dynamic light scattering measurements on the same system.},
  author       = {Löf, David and Schillén, Karin and Torres, Miguel F. and Müller, Alejandro J.},
  issn         = {0743-7463},
  language     = {eng},
  pages        = {11000--11006},
  publisher    = {The American Chemical Society},
  series       = {Langmuir},
  title        = {Rheological Study of the Shape Transition of Block Copolymer-Nonionic Surfactant Mixed Micelles},
  url          = {http://dx.doi.org/10.1021/la701818y},
  volume       = {23},
  year         = {2007},
}