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Influence of polydispersity on the micellization of triblock copolymers investigated by pulsed field gradient nuclear magnetic resonance

Nilsson, Markus LU ; Hakansson, Bjorn; Söderman, Olle LU and Topgaard, Daniel LU (2007) In Macromolecules 40(23). p.8250-8258
Abstract
The molecular motion in water of the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer with the nominal composition EO97PO68EO97 (F127) was investigated with the aid of pulsed field gradient nuclear magnetic resonance (PFG NMR). The signal decays in the PFG experiments have been recorded for 1 wt % F127 in the temperature range from 288 to 313 K and in the concentration range 0.1-35 wt % at 298 K. Below the critical micellization temperature (cmt) or the critical micellization concentration (cmc), the PFG signal decays approximately linearly when the intensities are plotted on a logarithmic scale versus the experimentally relevant parameter. At the cmt or cmc, the signal decays are curved. The NMR data were... (More)
The molecular motion in water of the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer with the nominal composition EO97PO68EO97 (F127) was investigated with the aid of pulsed field gradient nuclear magnetic resonance (PFG NMR). The signal decays in the PFG experiments have been recorded for 1 wt % F127 in the temperature range from 288 to 313 K and in the concentration range 0.1-35 wt % at 298 K. Below the critical micellization temperature (cmt) or the critical micellization concentration (cmc), the PFG signal decays approximately linearly when the intensities are plotted on a logarithmic scale versus the experimentally relevant parameter. At the cmt or cmc, the signal decays are curved. The NMR data were processed using inverse Laplace transformation to obtain the distribution of self-diffusion coefficients, P(D). At 288 K for a I wt % solution, a narrow distribution was observed, while at 362 K a bimodal distribution was observed. This observation can be explained by the polydispersity of the polymer. It implies that, at a given temperature, only the more hydrophobic compound of F127 takes part in the aggregation process, while the more hydrophilic components diffuse as free nonassociated polymer. Increasing the temperature to 313 K resulted in a monomodal distribution, suggesting that all the polymers are aggregated. It is suggested that an ideal mixing model for the Pluronic micelles can explain the self-diffusion data. The NMR self-diffusion raw data were also analyzed with the COmponent REsolved (CORE; Stilbs, P.; Paulsen, K. Rev. Sci. Instrum. 1996, 67, 43804386) algorithm, resulting in spectra for free block copolymer and micellized block copolymer. With an increase in temperature, the intensity of the peaks for free block copolymer is reduced, whereas the intensity of the peaks for aggregated block copolymer. increases. The ratios between the size of the PEO and PPO blocks (mEO/nPO) show a marked increase in free polymer compared to the ratio observed in micellized polymer when the temperature is increased. The effect of added salts to a I wt % F 127 solution at 303 K was investigated to determine how the populations of free and micellized surfactant were changed on account of the ions present. Finally, the diffusion behavior of Pluronic F68 (EO76PO29EO76) at 35 wt % has been investigated from 298 to 313 K. Both the diffusion time and the time of the gradient have been varied. The data show that the diffusion is Gaussian in the temperature range. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Macromolecules
volume
40
issue
23
pages
8250 - 8258
publisher
The American Chemical Society
external identifiers
  • wos:000250801700020
  • scopus:36349020316
ISSN
0024-9297
DOI
10.1021/ma071302p
language
English
LU publication?
yes
id
f457a687-0ec3-4758-9424-5f076851fa53 (old id 971850)
date added to LUP
2008-01-30 07:18:40
date last changed
2017-10-01 03:36:54
@article{f457a687-0ec3-4758-9424-5f076851fa53,
  abstract     = {The molecular motion in water of the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer with the nominal composition EO97PO68EO97 (F127) was investigated with the aid of pulsed field gradient nuclear magnetic resonance (PFG NMR). The signal decays in the PFG experiments have been recorded for 1 wt % F127 in the temperature range from 288 to 313 K and in the concentration range 0.1-35 wt % at 298 K. Below the critical micellization temperature (cmt) or the critical micellization concentration (cmc), the PFG signal decays approximately linearly when the intensities are plotted on a logarithmic scale versus the experimentally relevant parameter. At the cmt or cmc, the signal decays are curved. The NMR data were processed using inverse Laplace transformation to obtain the distribution of self-diffusion coefficients, P(D). At 288 K for a I wt % solution, a narrow distribution was observed, while at 362 K a bimodal distribution was observed. This observation can be explained by the polydispersity of the polymer. It implies that, at a given temperature, only the more hydrophobic compound of F127 takes part in the aggregation process, while the more hydrophilic components diffuse as free nonassociated polymer. Increasing the temperature to 313 K resulted in a monomodal distribution, suggesting that all the polymers are aggregated. It is suggested that an ideal mixing model for the Pluronic micelles can explain the self-diffusion data. The NMR self-diffusion raw data were also analyzed with the COmponent REsolved (CORE; Stilbs, P.; Paulsen, K. Rev. Sci. Instrum. 1996, 67, 43804386) algorithm, resulting in spectra for free block copolymer and micellized block copolymer. With an increase in temperature, the intensity of the peaks for free block copolymer is reduced, whereas the intensity of the peaks for aggregated block copolymer. increases. The ratios between the size of the PEO and PPO blocks (mEO/nPO) show a marked increase in free polymer compared to the ratio observed in micellized polymer when the temperature is increased. The effect of added salts to a I wt % F 127 solution at 303 K was investigated to determine how the populations of free and micellized surfactant were changed on account of the ions present. Finally, the diffusion behavior of Pluronic F68 (EO76PO29EO76) at 35 wt % has been investigated from 298 to 313 K. Both the diffusion time and the time of the gradient have been varied. The data show that the diffusion is Gaussian in the temperature range.},
  author       = {Nilsson, Markus and Hakansson, Bjorn and Söderman, Olle and Topgaard, Daniel},
  issn         = {0024-9297},
  language     = {eng},
  number       = {23},
  pages        = {8250--8258},
  publisher    = {The American Chemical Society},
  series       = {Macromolecules},
  title        = {Influence of polydispersity on the micellization of triblock copolymers investigated by pulsed field gradient nuclear magnetic resonance},
  url          = {http://dx.doi.org/10.1021/ma071302p},
  volume       = {40},
  year         = {2007},
}