The European Physical Journal E

, Volume 7, Issue 2, pp 141–151 | Cite as

Microphase separation in weakly charged hydrophobic polyelectrolytes

  • O. Braun
  • F. Boué
  • F. Candau
  • 94 Downloads

Abstract:

Aqueous solutions of a well-defined poly(N-isopropylacrylamide-co-sodium 2-acrylamido-methylpropanesulfonate) (NIPAM/NaAMPS in a 95/5 molar ratio) have been investigated by means of small-angle neutron scattering (SANS) and rheological experiments as a function of temperature ( 25°C\(\)T\(\) 60°C) and polymer concentration ( 0.5wt% \(\)C\(\) 12wt%). The solutions remain optically transparent and isotropic over the whole temperature range, in contrast with the homopolyNIPAM which precipitates above its lower critical solution temperature (LCST = 32°C). Upon addition of salt, the systems undergo a micro-macrophase separation. At temperatures above 45°C, the SANS spectra exhibit a sharp peak at a scattering wave vector, qmax, which increases slightly with temperature. At high temperature ( T∼ 60°C), the scattered intensity follows a power law I(q) ∼q-4 in the asymptotic regime, characteristic of two-density media with sharp interfaces, and qmax is found to vary with polymer concentration as qmaxC0.22. Estimates of the typical sizes give values between 40 Å and 200 Å. These results provide a strong evidence of a thermally induced microphase separation, which is corroborated by the very sharp increases of the viscosity (over 2 decades) and of the stress relaxation time of the solutions, occurring in the temperature range where the scattering peak is observed. The results are discussed and compared with the theoretical models proposed for weakly charged polyelectrolytes in a poor solvent.

PACS. 82.35.Jk Copolymers, phase transitions, structure – 82.35.Rs Polyelectrolytes – 83.85.Cg Rheological measurements - rheometry – 61.12.Ex Neutron scattering techniques (including small-angle scattering) 

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Copyright information

© EDP Sciences, Springer-Verlag, Società Italiana di Fisica 2002

Authors and Affiliations

  • O. Braun
    • 1
  • F. Boué
    • 2
  • F. Candau
    • 1
  1. 1.Institut Charles Sadron (UPR 22 du CNRS), 6 rue Boussingault, F-67083 Strasbourg Cedex, FranceFR
  2. 2.Laboratoire Léon Brillouin (UMR 12 du CNRS et du CEA), CEA-Saclay, F-91191 Gif-sur-Yvette, FranceFR

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