Laser speckle probes of relaxation dynamics in soft porous media saturated by near-critical fluids.

Speckle correlation analysis was applied to study the relaxation dynamics in soft porous media saturated by near-critical carbon dioxide. The relaxation of soft matrix deformation was caused by a stepwise change in the fluid pressure. It was found that the deformation rate in the course of relaxation and the relaxation time strongly depend on the temperature of the system. The values of relaxation time reach their maximal values in the vicinity of the critical point of saturating fluid. The contributions of hydrodynamic relaxation of the fluid density and viscoelastic relaxation of the porous matrix to its creeping are analyzed.