Effect of solvent transfer in agar gels on stress relaxation under large deformation

• Water exudation from gel surface by compression induced special stress inhomogeneity.
• Water exudation was responsible for stress relaxation which has gel size dependence.
• Water exudation and stress relaxation by it was increased with storage time of gel.
• Gels with lower concentration exuded more water and showed larger stress relaxation.

We measured stress relaxation, volume of exuded water, and spatial distribution of stress in agar gels under large deformation. Gels with smaller sample size and lower concentration exuded water faster and had shorter stress relaxation time. Gels with the storage time of 3 days exuded more water and had shorter stress relaxation time than gels with the storage time of 1 day, and this tendency was remarkable for low-concentration gels. Examination of the spatial distribution of stress in a cylindrical gel under large deformation showed that the outer part of the gel had smaller stress than the inner part at an early stage, and the area with small stress gradually extended into the inner part. This result indicates that the inhomogeneity of water content caused by water exudation from the gel surface induces the stress distribution in the gel.