Relaxation of strains in fibrillar porous carbon dioxide saturated media near their critical point

The isothermal relaxation of strains in deformed fibrillar porous layers saturated with subcritical or supercritical carbon dioxide has been studied at different temperatures by full-field speckle correlometry. The relaxation of strains is produced by the porous layer—fluid transition of a system from one equilibrium thermodynamic state to another due to a jump-like change in pressure. It has been established that the relaxation time attains a maximum near a critical point and rapidly decreases with increasing deviation of the system temperature from its critical value. The mechanisms of hydrodynamic relaxation in the density of a fluid layer and viscoelastic relaxation in a porous matrix are discussed. It is shown that the experimentally observed slow relaxation of a system is due to the viscoelastic relaxation of a porous fluid saturated layer at equal fluid densities inside and outside the layer.