Effect of Monovalent−Divalent Cation Exchange on the Swelling of Polyacrylate Hydrogels in Physiological Salt Solutions

Abstract

The volume transition induced by monovalent-divalent cation exchange of fully neutralized polyacrylate hydrogels was investigated in aqueous NaCl solutions. The variation of the osmotic swelling pressure, shear modulus, and mixing pressure was measured when Na(+) ions were substituted by divalent or trivalent cations. Alkali metal salts move freely throughout the entirely network, and alkaline earth metal salts (CaCl(2), SrCl(2)) promote aggregation of polyacrylate chains, but these aggregates are relatively weak. Transition metal salts (CoCl(2), NiCl(2)) form stronger interchain associates. Rare earth cations (La(3+) and Ce(3+)) bind practically irreversibly to the polymer. Experimental data indicate that transition metal cations modify both the elastic and mixing components of the free energy, while alkaline earth metal cations affect primarily the mixing term. The behavior of freely swollen gels was compared with similar gels subjected to uniaxial compression. In uniaxially compressed gels, volume transition occurs at lower cation concentrations than in the corresponding undeformed gels. The shift of the transition point increases with the deformation ratio and is larger for Co(2+) than for Ca(2+).

Molecular thermodynamics for swelling of a mesoscopic ionomer gel in 1 : 1 salt solutions

“…Divalent 7,13 and trivalent 11 cations have a stronger effect on swelling of a gel than the monovalent cations. An important factor is the nature of a multivalent ion 11 . For weak polyelectrolyte gels, the ionization degree may depend substantially on pH and salinity of the surrounding solution.…”

“…1 to ca. 100 mM [3][4][5][6][7][8][9][10][11][12][13][14] . At sufficiently large ionic strength, swelling is no longer sensitive to the polymer's degree of ionization or to ionic strength.…”

Theory of volume transition in polyelectrolyte gels with charge regularization

“…49 Thus it is necessary for theoretical formulations of charged polymer systems to take into effect this property of self-regularization of the effective charge, where the effective charge of the polymer, and hence the counterion concentration is determined by a balance between the electrostatic attraction between the counterions and the ionized polymer backbone, and the translational entropy of the counterions in the solution. 46,[50][51][52] There have been extensive experiments 4,[53][54][55][56][57][58][59][60][61][62][63] and simulations [64][65][66][67][68][69][70][71][72][73][74][75][76] that have studied the volume transition in ionic gels. In particular, Tanaka and co-workers have investigated the effect of added salt concentrations in the volume collapse both for monovalent and divalent salts.…”

“…There have also been studies which looked at the specific response of a polyelectrolyte gel in the presence of differing species of salt ions, both in the case of monovalent 56 and divalent salts. 54 It was found that the response of the system depends on the specific type of ion that is added, implying that other physical characteristics such as ionic size play a significant role in addition to the charge of the ion species. In general, it has proved difficult to address the role of multivalent ions in charged polymer systems.…”

Improved Concrete Materials with Hydrogel-Based Internal Curing Agents

“…HPC can easily achieve compressive strengths as high as 110 MPa, in contrast to the more common compressive strengths of (30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40) MPa [4]. The decreased porosity as well as disconnected pore network makes HPC quite resistant to corrosive fluid ingress and therefore extremely durable even in harsh environments [5].…”