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Enhanced Concentration Fluctuations in Model Polyelectrolyte Coacervate Mixtures along a Salt Isopleth Phase Diagram



Vivek Prabhu, Yuanchi Ma, Samim Ali


A temperature (T) versus polymer concentration (cp) representation leads to non-overlapping coexistence curves prepared from different initial polymer concentrations along a salt isopleth of aqueous mixtures of charge-stoichiometric, oppositely-charged polydisperse polyelectrolytes. This effect was explained by an unequal salt concentration (cs) between equilibrating phases that improves the relationship between the common cs-cp representation to T- cp along a salt isopleth in terms of a T-cs-cp phase envelope. Further quantification of the cloud points and spinodal temperatures predicts regions of metastability and instability with critical point on a salt isopleth phase diagram. As the cloud point is approached, the correlation length for concentration fluctuations far exceeds the chain dimensions with evidence of a cross-over from mean-field to fluctuation regime. The effective critical exponents for the divergence in the osmotic compressibility, via scattered intensity to zero angle, and correlation length, gamma_eff and nu_eff, respectively deviates from the 3D Ising model. These static light scattering measurements illustrate that concentration fluctuations are enhanced by polyelectrolyte chain association near the lower critical solution temperature.


polyelectrolyte, phase diagram, scattering, fluctuations


Prabhu, V. , Ma, Y. and Ali, S. (2021), Enhanced Concentration Fluctuations in Model Polyelectrolyte Coacervate Mixtures along a Salt Isopleth Phase Diagram, Macromolecules, [online],, (Accessed May 27, 2024)


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Created December 8, 2021, Updated November 29, 2022