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.
Analysis of the structure functions of intensity fluctuations of scattered laser light was applied to monitor the phase separation in probed disperse media. UV-cured mixtures of a liquid crystal and prepolymer were studied during the formation of the structure of dispersive polymer-liquid crystal (DPLC) composites. The experimentally observed features of light beating induced by dynamic light scattering in DPLC systems (the scaling properties of the structure functions, the narrowing of the beating spectrum for certain weight fractions of the liquid-crystalline component) were interpreted in terms of the discrete scattering model using the results of statistical modeling.
The effects of dynamic scattering of laser light and optical clearing of a mesoporous system impregnated by near-critical fluid (carbon dioxide) were studied for the case of quasi-equilibrium isothermal transitions between the phase states of the fluid (CO 2 ) in the vicinity of the critical point. The rate of optical clearing with increasing pressure near the saturation vapor point of the filling subcritical substance was found to be controlled by the co-existence of the liquid and gaseous phases in mesopores and decayed with an increase in detuning from the critical temperature. It was shown that the decorrelation of speckle-modulated scattered light during slow variations of the pressure can be described in terms of the Fourier transform of the pathlength probability density of the scattered light. The transform parameter is defined by the pressure derivative of the effective refractive index of the system. The results obtained can be used as a physical basis for laser probing of near-critical disperse systems.
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