CARS diagnostics of fluid adsorption and condensation in small mesopores

Abstract

Coherent anti-Stokes Raman scattering (CARS) spectroscopy is applied to diagnostics of phase behavior of a fluid in pores of nanoporous glasses. Samples with mean pore radii of 2 and 3.5 nm were filled with compressed carbon dioxide at near-room temperatures. CARS spectra of the 1388 cm −1 Q-branch were measured at isothermal compressing in a wide pressure range including the transition from gaseous to condensed state. The spectra show specific transformations caused by fluid adsorption and condensation in nanopores. We have carried out calculations of the spectral profiles based on the phase behavior of carbon dioxide in cylindrical glass nanopores. Phase behavior modeling was performed using thermodynamic concepts of surface adsorption and capillary condensation. A good agreement between experimental spectra and calculations was obtained. The potential of CARS technique for the diagnostics of fluid phase behavior in pores and for the characterization of nanoporous host structure is discussed.

CARS diagnostics of fluid phase behavior in small mesopores at near‐critical temperatures

“…a. According to earlier results, the spectral contribution of adsorbed layers is ‘red‐shifted’ (~1386.6 cm −1 ) and significantly broader (~3 cm −1 ) as compared to gas. It is even about twice broader than the spectrum of bulk liquid that is obviously caused by asymmetrical surrounding and inhomogeneity of surface adsorbed layers.…”

“…The experimental setup was described in detail in our previous papers . We used a broad‐band frequency‐domain CARS scheme.…”

“…The detailed consideration of modeling was presented previously . CARS spectrum is regarded here as the coherent sum of several contributions attributed to different phases of fluid existing simultaneously in the system.…”

“…Thermodynamic approach based on surface adsorption and capillary condensation was applied to estimate the partial amount of the adsorbed fluid and the condensed one inside pores . The theoretical considerations has been successfully approved with the spectral observations obtained for nanoporous glass samples with the pores of radii of 2 and 3.5 nm at temperatures far below the critical value . In the present paper, we develop this spectroscopic approach to analyze the fluid phase behavior in pores of radii of 2 and 3.5 nm nanometers at near‐critical (subcritical 30.5 °C and supercritical 33 °C) temperatures.…”

Development and applications of nonlinear optical spectroscopy – 9th ECONOS / 29th ECW meeting in Bremen, Germany

“…zeolite pores, is an interesting phenomenon, because molecular properties are considerably influenced by the interaction with the cage surroundings. Andreeva et al [15] present results of a CARS spectroscopic investigation of fluid adsorption and condensation in small glass mesopores. For this, CO 2 was filled under pressure into the pores having radii of 2 and 3.5 nm.…”