Forces of inertia acting on the aqueous pore fluid of anionic polyelectrolyte gels

Abstract

Pulses of an inertia electromotive force are generated during deceleration of stiff rods of polyelectrolyte gels with negatively charged ionic groups covalently bound to the matrix of the gel. The gels are loaded with Li⁺, Cs⁺, Ag⁺, H⁺ and Ba²⁺, respectively, and are in swelling equilibrium with water. The values of (m/q)_exp, (m, mass and q, charge of one counterion in the pore field) calculated from the recorded voltage pulse ∫U dt(U, inertia electromotive force and t, time) during deceleration (time constant τ≈ 1 ms) are larger by a factor of at least five than that calculated from the mass and charge of a ‘naked’ single counterion. This is attributed to an effective mass of the counterions in the pore fluid of the gels which has a larger value than the mass of naked single counterion. During deceleration the hydrated counterions, together with the mobile water molecules in the pore fluid, are shifted relative to the ionic groups fixed to the stiff matrix of the gels. This generates an electric field causing the observed voltage pulse. The value of (m/q)_exp of the H⁺ counterion is smaller by a factor of about five than that of the other counterion species (Li⁺, Cs⁺, Ag⁺). It is assumed that this is caused by the chain mechanism of proton migration found in aqueous solutions. Measurements of the electrical conductivity of gels loaded with different counterion species, including H⁺ ions, reveal that the ratios of the counterion conductivity in the gel phase to that in free solution at infinite dilution have approximately the same value. The inertia electromotive force and the electrical conductivity measurements indicate that the mechanism of H⁺ ion transport in the pore fluid is not modified considerably by the matrix of the gel.