Determination of mechanical parameters related to the kinetics of swelling in an electrically activated contractile gel
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We report on an analytical model and related experiments to determine the mechanical parameters governing the kinetics of mechanical readjustment of a thermally crosslinked polyacrylic acid (20% by weight) and polyvinylalcohol (80% by weight) (PAA-PVA) gel.
Either thin films on spherical samples have been used in the experiments. The characteristic time of swelling in the case of a thin film has been found to be proportional to the square of a linear dimension of the sample divided by a diffusion coefficient D, defined as D = μ/f, where μ is the shear modulus of the gel network and f is the friction coefficient between the network and fluid.
This constitutes and essential difference between the swelling of spherical samples reported in literature in which the diffusion coefficient is D* = (k + 4/3)/f, where k is the bulk modulus of the gel network.
We have derived the value of the bulk modulus k, the shear modulus μ and the friction coefficient f by free swelling experiments performed on spherical and planar thin samples, and by direct measurement of water permeability across the gel.
Mechanical readjustment time constant and diffusion-reaction time constant, which has been previously determined, are then compared to evaluate the limiting rate phenommena which govern the kinetics of gel deswelling under electrochemical stimuli in different pH ranges.
Key wordsPolyelectrolyte gels polyacrylic acid + polyvinylalcohol thermally cross-linked swelling kinetics electromechanochemistry
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