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Интеллектуальная Система Тематического Исследования НАукометрических данных |
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CARS Diagnostics of Phase Transitions of Molecular Media Confined in Nanoporesтезисы доклада
- Авторы: Arakcheev V.G., Morozov V.B., Valeev A.A.
- Сборник: CLEO/Europe-EQEC’2009, June 14-19, 2009, Munich, Germany, Book of abstracts
- Тезисы
- Год издания: 2009
- Место издания: Technical University Munich Munich, Germany,
- Первая страница: 88
- Последняя страница: 88
- Аннотация: Coherent anti-Stokes Raman Scattering (CARS) spectroscopy proved to be an powerful tool for diagnostics of states (including more than one simultaneously existing) and phase transitions of molecular media confined in nanopores [1, 2]. Contributions of gas phase, molecular layers adsorbed on the pores surface and liquid-like phase condensed inside pores can be recognized using the analysis of measured CARS spectra. Phase transitions can be revealed by appearing or disappearing of corresponding contributions in measured CARS spectra. In present investigation we apply CARS approach for studying following topics: i) the influence of nanopores diameter on condensation conditions; ii) features of condensation conditions in nanopores at subcritical and supercritical temperatures. Nanoporous glass sample (NGS) was placed inside high-pressure cell between its windows and filled with carbon dioxide. CARS spectra of high-frequency (“blue”) Fermi-dyad component 1 Q branch were collected. Spectra shape was defined by interference of two main spectral contributions (fig. 1). High-frequency peak was caused by gaseous carbon dioxide in pores core area as well as from gaps between NGS and cell windows. Low frequency peak was caused by carbon dioxide adsorbed on pores surface or condensed inside pores depending on pressure and temperature. Carbon dioxide transition into condensed phase inside pores is recognized by substantial narrowing of low-frequency peak from 4 cm-1 (corresponding to adsorbate) to 1.6 cm-1 as in liquid in unconfined volume (fig. 2). As to (i), we use two analogous nanoporous glass samples (NGS) with pore diameter of 4 and 7 nm and porosity 26 and 28% correspondingly. Measurements were conducted at far-from-critical temperatures in the range 20 ÷26.5 oC (critical value Tcr=31.1 oC). It was obtained that carbon dioxide turns into condensed state inside pores at normalized pressure values p/psat ~0.95 and ~0.96 in the case of pores diameter of 4 and 7 nm correspondingly. Thus, the decrease of pores diameter leads to decrease of pressure of condensation inside pores. This is in a good agreement with values (0.97 and 0.98 correspondingly) calculated using Kelvin’s equation for condensation in macroscopic capillaries. As to (ii), measurement were fulfilled at subcritical 30.5 oC and supercritical 33 oC temperatures using NGS with pores diameter of 4 nm. Results showed that carbon dioxide turns from gas phase to condensed state inside nanopores at abnormally (from macroscopic point of view) small pressures. In both cases it cannot be explained by transition of gas to liquid (at 30.5 oC) or to super critical fluid (at 33 oC) in terms of macroscopic thermodinamics. Thus, one can conclude that observed transition from gas phase to condensed state in nanopores is connected with critical point shift to lower values of temperature and pressure in confined geometry. The work is supported by Russian Foundation for Basic Research, grant #07-02-01331-а
- Добавил в систему: Аракчеев Владимир Генрихович