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Block-copolymer micro-emulsion with solvent-induced segregation

Arleth, Lise; Svensson, Birgitta; Mortensen, Kell; Pedersen, Jan Skov and Olsson, Ulf LU (2007) In Langmuir 23(4). p.2117-2125
Abstract
Reverse micelle formation of the poly(ethylene oxide)/poly(propylene oxide) block-copolymer (EO)(13)(PO)(30)(EO)(13) (L64) in p-xylene was investigated as a function of water content and copolymer content, using small-angle neutron scattering (SANS). PEO/PPO block-copolymers are generally soluble in xylene but without forming aggregates. However, the effective block segregation increases dramatically upon addition of small amounts of water, and micelles form. The SANS data were analyzed using an absolute scale model fitting approach. This way, a detailed quantitative description of the system in terms of unimer concentration, micelle structure, and aggregation number as well as particle-particle interactions can be obtained. This approach... (More)
Reverse micelle formation of the poly(ethylene oxide)/poly(propylene oxide) block-copolymer (EO)(13)(PO)(30)(EO)(13) (L64) in p-xylene was investigated as a function of water content and copolymer content, using small-angle neutron scattering (SANS). PEO/PPO block-copolymers are generally soluble in xylene but without forming aggregates. However, the effective block segregation increases dramatically upon addition of small amounts of water, and micelles form. The SANS data were analyzed using an absolute scale model fitting approach. This way, a detailed quantitative description of the system in terms of unimer concentration, micelle structure, and aggregation number as well as particle-particle interactions can be obtained. This approach throws light on very atypical features of the system as compared to standard amphiphilic systems. Data from samples measured along water-swelling lines with fixed EO/p-xylene-d(10) molar ratios show that reverse micelles are formed at the water/EO molar ratio, W-0 congruent to 0.2, independent of copolymer concentration. The majority of the block-copolymers are on a free monomer state (unimer state) at this W-0. Increasing W-0 above 0.2 only has a small effect on the micelle size. However, it does induce a strong increase of the total number of micelles and induce a corresponding decrease of the unimer concentration. On the other hand, increasing the overall copolymer concentration at fixed W-0 gives rise to a significant decrease of the micelle size in terms of the micellar aggregation number. This observed behavior is totally different from what is normally observed for binary surfactant-solvent systems and droplet micro-emulsion systems, respectively. We believe that the atypical behavior is a result of the unusually weak segregation in the system, and we are not aware of previous discussions of the phenomenon for reverse micellar systems. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Langmuir
volume
23
issue
4
pages
2117 - 2125
publisher
The American Chemical Society
external identifiers
  • wos:000243990200075
  • scopus:33947181474
ISSN
0743-7463
DOI
10.1021/la0625704
language
English
LU publication?
yes
id
d0912b34-5111-4c55-9eb4-f1e7fa9743ac (old id 675124)
date added to LUP
2007-12-04 15:33:02
date last changed
2017-05-07 03:38:31
@article{d0912b34-5111-4c55-9eb4-f1e7fa9743ac,
  abstract     = {Reverse micelle formation of the poly(ethylene oxide)/poly(propylene oxide) block-copolymer (EO)(13)(PO)(30)(EO)(13) (L64) in p-xylene was investigated as a function of water content and copolymer content, using small-angle neutron scattering (SANS). PEO/PPO block-copolymers are generally soluble in xylene but without forming aggregates. However, the effective block segregation increases dramatically upon addition of small amounts of water, and micelles form. The SANS data were analyzed using an absolute scale model fitting approach. This way, a detailed quantitative description of the system in terms of unimer concentration, micelle structure, and aggregation number as well as particle-particle interactions can be obtained. This approach throws light on very atypical features of the system as compared to standard amphiphilic systems. Data from samples measured along water-swelling lines with fixed EO/p-xylene-d(10) molar ratios show that reverse micelles are formed at the water/EO molar ratio, W-0 congruent to 0.2, independent of copolymer concentration. The majority of the block-copolymers are on a free monomer state (unimer state) at this W-0. Increasing W-0 above 0.2 only has a small effect on the micelle size. However, it does induce a strong increase of the total number of micelles and induce a corresponding decrease of the unimer concentration. On the other hand, increasing the overall copolymer concentration at fixed W-0 gives rise to a significant decrease of the micelle size in terms of the micellar aggregation number. This observed behavior is totally different from what is normally observed for binary surfactant-solvent systems and droplet micro-emulsion systems, respectively. We believe that the atypical behavior is a result of the unusually weak segregation in the system, and we are not aware of previous discussions of the phenomenon for reverse micellar systems.},
  author       = {Arleth, Lise and Svensson, Birgitta and Mortensen, Kell and Pedersen, Jan Skov and Olsson, Ulf},
  issn         = {0743-7463},
  language     = {eng},
  number       = {4},
  pages        = {2117--2125},
  publisher    = {The American Chemical Society},
  series       = {Langmuir},
  title        = {Block-copolymer micro-emulsion with solvent-induced segregation},
  url          = {http://dx.doi.org/10.1021/la0625704},
  volume       = {23},
  year         = {2007},
}