CARS diagnostics of molecular media under nanoporous confinement

Morozov

2014

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Coherent anti‐Stokes Raman scattering (CARS) spectroscopy is applied to probe the microstructure of CO2 adsorbed in nanoporous glass Vycor with a mean pore radius of 2 nm. CARS spectra of the Q‐branch (1388 cm‐1) were measured at 22 °C at pressures decreasing in a range providing the transition from the condensed phase in the whole volume of the pores to submonolayer coverage on their walls. The spectral behavior demonstrates sequential changes in the fluid state inside the nanopores. The analysis of the experimental results allowed us to characterize and compare the spectral properties of gas‐like, liquid‐like, and surface adsorbed carbon dioxide. The results provide clear evidence that as the surface coverage is decreased, the vibrational frequency shifts down. Copyright © 2014 John Wiley & Sons, Ltd.

Section: Introductionsupporting

confidence: 66%

Vibrational spectra of carbon dioxide adsorbed on nanopore walls at supermonolayer and submonolayer coverage

Morozov

2014

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“…For the multilayer adsorbate spectral contribution, we used values of 3.0 cm −1 for the line width and 1386.6 cm −1 for the Raman shift on the basis of the experimental results. [7,8] The normalized spectral contributions of all the three phases at 20.5 • C at 53 atm are shown in Fig. 5.…”

Section: Results and Analysismentioning

confidence: 99%

“…The simplest way to interpret the experimental data is to fit the spectra by the two-component model. [7,8] This approach allows us to identify the spectral characteristics of both the multilayer adsorbate and the fluid condensed in the volume of the pores. A specific case appears in the pressure range where all three different phases coexist.…”

Section: Discussionmentioning

confidence: 99%

CARS diagnostics of fluid adsorption and condensation in small mesopores

Andreeva

Баграташвили

et al. 2011

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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.

“…The spectra of adsorbed layers were several times wider and shifted to lower (‘red’) wavenumbers. The presence of admixtures inside nanopores caused a noticeable transformation of the spectrum profile . 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 .…”

Section: Introductionmentioning

confidence: 99%

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

Morozov

2013

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Coherent anti-Stokes Raman scattering (CARS) spectroscopy is applied to investigate the fluid phase behavior in small mesopores at bulk sub-and supercritical temperatures. CARS spectra of the Q-branch (1388 cm À1 ) of carbon dioxide were measured at isothermal compression in pores of two nanoporous glass samples with pore radii of 2 and 3.5 nm. The spectral transformations with pressure of the fluid indicate the formation of a condensed phase in the volume of pores that clearly demonstrates the shift of the critical point. The spectrum of carbon dioxide condensed in the wider pores corresponds approximately to the critical density in bulk. In the narrower pores, the spectrum is noticeably shifted towards the lower wavenumbers that correspond to higher density of condensed fluid.