Compatibility enhancement and microdomain structuring in weakly charged polyelectrolyte mixtures

Abstract

The phase structure of a mixture of weakly charged polyelectrolytes in the presence of solvent, counterions, and low molecular salt is studied theoretically. The most important contribution to the free energy of this system is connected with the presence of charges and comes from the translational entropy of counterions and ions of low molecular salt. It is shown that the presence of even a small fraction of charges on the polymers leads in many cases to an essential increase of mixture compatibility. This theoretical prediction is confirmed experimentally. Compatibility enhancement is also achieved for the mixture of stiff and flexible macromolecules if one or both components carry some fraction of charged links. On the basis of a more detailed study of this system we conclude that although the region of macrophase separation in the presence of charged links diminishes, the remaining region of the phase diagram is divided into two parts:In one part we have a true molecular compatibility, while in the other part a microdomain structure is formed which is reminiscent of microdomain structures in melts of block copolymer. The physical reason for microdomain formation originates from the translational entropy of counterions and the impossibility of the violation of the condition of total electroneutrality of the system.

A new equation of state of a flexible-chain polyelectrolyte solution: Phase equilibria and osmotic pressure in the salt-free case

“…Firstly, in a series of studies the contribution of the correlation attraction to the total Helmholtz free energy has been omitted 15,16,18 or described at the level of Debye-Hueckel approximation 17,19,25,26 , although the critical point of the electrostatic phase transition is located far from the range of applicability of a linear Debye-Hueckel theory 20 . In work 27 the contribution of the correlation attraction was described at the level of mean-spherical approximation (MSA) that allowed to obtain a good agreement with simulation results for critical temperature but underestimated the critical monomer concentration.…”

Theory of Polyelectrolyte Solutions

“…They have properties combining those of polyelectrolyte chains and of small ionic surfactants and form for example intramolecular micelles. Another system of interest is mixtures between neutral and charged polymers [119,120] which have been studied both experimentally and theoretically. The addition of a charged polymers can increase the solubility of a neutral polymer in water.…”

Charge regularization in phase separating polyelectrolyte solutions

“…All of the theories [1][2][3][4][5][6][7][8][9][10][11][12][13][14] of coexistence of polyelectrolyte phases, formulated so far, with varying levels of approximations, have the common key assumption that each polyelectrolyte chain maintains the same constant effective charge for all coexisting phases at all allowed ranges of temperature, polyelectrolyte concentration, and salt concentration. This assumption cannot be correct in view of the large body of literature, based on theoretical arguments, [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] computer simulations, [31][32][33][34][35][36][37][38] and experiments, [39][40][41][42][43][44][45][46][47]…”