Polyelectrolyte Gel Swelling and Conductivity vs Counterion Type, Cross-Linking Density, and Solvent Polarity

Abstract

A joint theoretical and experimental study is devoted to the swelling and electrical conductivity of highly charged polyelectrolyte (PE) gels in media of different polarity. Deprotected poly­(tert-butyl carbamate l-alanine) gels provided with fluorine, bromine, chlorine, sulfate, and trifluoroacetic counteranions demonstrated different conductivity in aqueous medium as well as solvent uptake in water/methanol mixtures. Counterion specificity in PE gel properties was theoretically explained in the framework of the model which treats ion association within the network as a two-stage process. Manning-type condensation, being the first condensation stage not affected by counterion type, provides understanding of a gel maximal swelling at intermediate degrees of gel ionization f and a slight gel contraction at f tending to unity, which were earlier observed in experimental investigations. The second ion association stage is an ion pairing influenced by the kind of counterion. Since a considerable fraction of ions form pairs even in a swollen hydrogel, its properties are largely influenced by counterion type. Conductivity of the gel was calculated theoretically owing to the known fraction of free and condensed counterions. Developed theory containing no adjusting parameters allows for the first time to reach semiquantitative matching of experimental results on highly charged gel swelling and conductivity.

Two regions of microphase separation in ion-containing polymer solutions

“…Thus, eqn (33) defining Lifshitz points has the only root corresponding to the plus sign in the righthand side of it. This root F L + and the corresponding ion pair and multiplet fractions p L + and q L + are given by the system of three equations, namely, eqn (19), (20) and equation…”

“…15,16 The mixed polyelectrolyte/ ionomer behavior of polymer gels in organic solvents (e.g. methanol) under ionization [17][18][19] as well as counterion specificity in polyelectrolyte gel swelling and solution behavior 16,[19][20][21][22] are striking manifestations of ion association processes. The formation of ion pairs and multiplets was observed in computer simulations 23,24 and confirmed experimentally in luminescence 25,26 and conductivity 17,27,28 studies.…”

“…Finally, theoretical approaches show that a considerable fraction of counterions binds with charges in chains even in semidilute solutions and swollen gels. 20,[29][30][31] For polyelectrolyte solutions, theoretical binodals and spinodals towards macrophase separation that account for ion condensation were constructed in ref. 29, 30 and 32. The theoretical comprehension of the experimental results on polyelectrolyte gels and solutions revealed that the effect of dielectric mismatch between the solvent and polymer resulting in the dependence of the local medium dielectric constant on the polymer volume fraction plays a crucial role in ion association processes and, hence, the resulting system behavior.…”

Ultrastretchable, Tough, and Notch‐Insensitive Hydrogels Formed with Spherical Polymer Brush Crosslinker

“…Yielding appeared at a critical strain, followed by necking, elongation, and strain hardening until fracture. Other hydrogels also showed yielding behaviors . The yielding strength increased with the PAA content because of more hydrogen bonding and entanglement in hydrogels.…”

Influence of weak groups on polyelectrolyte mobilities

“…In contrast to strong electrolytes whose groups are always dissociated, the dissociation of weak electrolytes is sensitive to changes in the local conditions like temperature or pH . Polyelectrolytes (PE) with weakly dissociable groups can thus be used in novel materials like nano/microgels that react to externally imposed stimuli .…”