Optical clearing and laser light dynamic scattering near the critical point of fluid in mesoporous materials

Abstract

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.

Second Harmonic Correlation Spectroscopy: Theory and Principles for Determining Surface Binding Kinetics

“…3 Using Pecora’s established experimental framework for photon CS, DLS has been used to obtain the translational, 22,23 rotational, 24 and intramolecular diffusion coefficients of macromolecules, 25,26 as well as provide information on equilibrium critical phenomena of fluid systems. 2,27 Since DLS is a coherent process where the signal intensity from individual photons produces stationary interferences, the spontaneous fluctuations caused by individual photon positional changes can be additive (constructive interference) or subtractive (deconstructive interference) to the measured average density distribution. 4 Experimentally, the stationary interference of the scatterers in DLS makes having a higher concentration of particles advantageous for obtaining higher S/N in the correlation data.…”