Two regions of microphase separation in ion-containing polymer solutions

Abstract

The phenomenon of spinodal decomposition in weakly charged polyelectrolyte solutions is studied theoretically within the random phase approximation. A novel feature of the theoretical approach is that it accounts for the effects of ionic association, i.e. ion pair and multiplet formation between counterions and ions in polymer chains, as well as the dependence of local dielectric permittivity on the polymer volume fraction Φ. The main focus is on the spinodal instability of polyelectrolyte solutions towards microscopic phase separation. It has been shown that increasing the binding energy of ions decreases the classical microphase separation region (possible at low polymer concentrations) due to the effective neutralization of the chains. A qualitatively new type of microphase separation is found in the presence of a dielectric mismatch between polymer and solvent. This new branch of microphase separation is realized at high polymer concentrations where ion association processes are the most pronounced. Typical microstructures are shown to have a period of a few nanometers like in ionomers. The driving force for the microphase formation of a new type is more favourable ion association in polymer-rich domains where ionomer-type behavior takes place. Effective attraction due to ion association promotes microscopic as well as macroscopic phase separation, even under good solvent conditions for uncharged monomer units of polymer chains. Polyelectrolyte-type behavior at low Φ and ionomer-type behavior at high Φ result in the presence of two critical points on the phase diagrams of polyelectrolyte solutions as well as two separate regions of possible microscopic structuring. Our predictions on the new type of microphase separation are supported by experimental data on polymer solutions, membranes and gels.

Explicit description of complexation between oppositely charged polyelectrolytes as an advantage of the random phase approximation over the scaling approach

“…Possibility of microphase separation in semidilute PE solutions and mixtures of oppositely charged polyions was predicted within the framework of this approach. 24,[26][27][28] Later on, similar theory was applied for the description of PE multilayers, 29 polyampholytes 30 and overcharged interpolyelectrolyte complexes. 31,32 Further development of the RPA included consideration of ion pairing, 28,33,34 short wavelength integration cutoff, 33,35 hard-core and finite-size ion effects.…”

“…24,[26][27][28] Later on, similar theory was applied for the description of PE multilayers, 29 polyampholytes 30 and overcharged interpolyelectrolyte complexes. 31,32 Further development of the RPA included consideration of ion pairing, 28,33,34 short wavelength integration cutoff, 33,35 hard-core and finite-size ion effects. 33,34,36,37 In our group, fluctuations of polymer and charge densities were examined independently (discrete charge distribution), which allowed getting a general expression for the free energy unifying different limiting cases.…”

Dissipative particle dynamics for systems with polar species: Interactions in dielectric media

“…Having studied the bulk properties of the polar liquids, let us now investigate the interaction of charges in such liquids. The resulting Coulomb force between two charges in a medium with the dielectric permittivity of ε is equal to 12 3 0 4 ij ij ij qq r  r F  , i.e. it is ε times smaller than the corresponding force in vacuum.…”

Complexes of end-functionalized polystyrenes carrying amine end-group with transition metals: association effects in organic solvents

“…where k is the Boltzmann's constant, T the absolute temperature and η s the viscosity of the solvent. Viscometric data were analyzed using the Huggins equation 4: (4) and the Kraemer equation 5:…”

“…This is the basis of understanding the correlation between structure and dynamics in soft matter physics [1][2]. These studies include various fields of research, such as macrophase and microphase separation [3][4][5], gelation [6][7][8], crystallization [9,10] and association phenomena [11][12][13]. The progress in this area is closely related to the advances in the synthesis of well-defined macromolecular structures having the maximum control over the molecular characteristics and the architecture [14][15][16][17][18][19][20][21][22].…”