Stress-relaxation behavior of a physical gel: Evidence of co-occurrence of structural relaxation and water diffusion in ionic alginate gels

• Stress relaxation in alginate gels at different calcium concentrations was measured.
• A double step relaxation at all concentrations was found.
• Co-occurrence of detaching/re-bonding and diffusive mechanisms was proved.
• A two-fluid model was proposed to interpret the observed behavior.

Stress relaxation measurements on ionically cross-linked alginate gels in an unconfined uniaxial compression are reported. Data are obtained as a function of ionic (divalent calcium) concentration and for various sample radii. Analysis of the results shows that such gels, at all investigated concentrations, relax the stress by two different concurring mechanisms: (a) an internal relaxation, most probably due to detachment and re-bonding of the cations along the alginate chains, and (b) the diffusion of water out of the gel.

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