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Интеллектуальная Система Тематического Исследования НАукометрических данных |
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CARS detection of critical point shift of molecular matter confined in nanoporesтезисы доклада
- Авторы: Andreeva O.V., Arakcheev V.G., Morozov V.B., Valeev A.A., Bagratashvili V.N., Popov V.K.
- Сборник: 18th International Laser Physics Workshop LPHYS'09, Book of abstracts
- Тезисы
- Год издания: 2009
- Место издания: University of Barcelona Barcelona, Spain
- Первая страница: 66
- Последняя страница: 66
- Аннотация: We have applied CARS technique to study critical point shift of molecular matter confined in nanoporous glass. Two nanoporous glass samples (NGS) containing disordered interconnected network of nanopores with mean diameters of 4 and 7 nm, internal surface area ~250 and ~100 m2/g correspondingly, and porosity ~25 30% were filled with carbon dioxide in high pressure cell. CARS-spectra of high-frequency Fermi-dyad component Q-branch (1388 cm-1) were collected in large pressure range at several temperatures in the range 21oC < T < 33 oC (bulk critical value Tcr=31.1 oC) that corresponds to relative temperature range 0.965 < T/Tcr < 1.0062. CARS signal was caused both carbon dioxide from pores and from gaps between NGS and cell windows. Carbon dioxide in the gaps was under bulk conditions. In pores, significant part of carbon dioxide could be in adsorbed state due to the large internal surface area of NGS. Structure of collected CARS spectra in each realization was defined by spectral contributions of different simultaneously existing states. At temperatures 21, 24.4 and 26.4 oC at pressures below Psat CARS spectra had well defined two component structure. First component was attributed to gaseous carbon dioxide. The second one was caused by adsorbate, its spectral width and shift were defined by spectra fitting. When pressure approached Psat spectra of second component essentially narrowed from ~4 cm 1, corresponding to adsorbate, down to 1.6 cm-1 measured in bulk liquid (fig. 1, a). The narrowing was caused by carbon dioxide transition into condensed phase in pores. Pressure at which the narrowing took place was in a good agreement with capillary condensation pressure Pcc~(0.96÷0.98)·Psat calculated using Kelvin’s equation (fig. 1, a). At subcritical 30.5 oC temperature CARS spectra also had two component structure in a broad pressure range 60 atm<P<Psat (Psat=72.3 atm). Spectral width of second component was close to 1.6 cm-1 in this whole range (fig. 1, b) that corresponded to condensed state of carbon dioxide in pores. However, at 30.5 oC calculated value Pcc~72 atm was very close to Psat (fig. 1, b) owing to very small surface tension. It meant that carbon dioxide transition into condensed state cannot be caused by surface tension between gaseous and liquid phases. Similar two component structure of CARS spectra was obtained at supercritical temperature 33 oC at pressure range 65 atm<P<Pcr (fig. 1, c). At both subcritical and supercritical temperatures spectral width and shift of second component were close to ones measured in supercritical fluid (SCF) in bulk carbon dioxide. Results obtained allowed one to conclude that critical point of carbon dioxide confined in such nanoporous hosts shifts to low pressures and temperatures in comparison with bulk volume. The work is supported by Russian Foundation for Basic Research, grant #07-02-01331-а.
- Добавил в систему: Аракчеев Владимир Генрихович