Binodal Compositions of Polyelectrolyte Complexes

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When oppositely charged polyelectrolytes are mixed below a critical salt concentration, their mixtures show macroscopic phase separation into a dilute and a dense, polyelectrolyte complex phase. Binodal compositions of the polyelectrolyte complexes have been measured experimentally using fluorescently labeled polyelectrolytes. We used fluorescein-labeled poly(acrylic acid) (PAA) of four different chain lengths (N = 20, 50, 150, and 510) to determine the binodal compositions of polyelectrolyte complexes of PAA and poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) of similar chain lengths. The water content of polyelectrolyte complexes obtained has a lower limit of about 65%, practically independent of chain length, and increases with increasing salt concentration. We interpret our results on binodal compositions, water content and critical salt concentration as a function of chain length using the mean-field model of Voorn and Overbeek and find good quantitative agreement with our experiments using only one adjustable parameter. We believe that such a model can be used to predict equilibrium concentrations also for other strongly charged flexible polyelectrolytes
Original languageEnglish
Pages (from-to)6476-6484
Issue number15
Publication statusPublished - 2010


  • oppositely charged polyelectrolytes
  • electrostatic free-energy
  • phase-behavior
  • whey-protein
  • cell model
  • coacervation
  • release
  • microencapsulation
  • approximation
  • adsorption

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