Место издания:University of Bremen Bremen, Germany
Первая страница:C22
Последняя страница:C22
Аннотация:Nowadays there is an extensive growth of Raman spectroscopy applications for diagnostics, and characterization of nanostructured and nanocomposite materials and effects taking place in nanoworld [1-2]. Here we introduce the application of CARS technique for diagnostics of phase behavior of molecular media confined in nanopores. The topicality of the subject is defined by the permanently growing interest in applications of nanoporous structures in modern and future technologies of pharmacological, biomedical, food, chemical and other industries and in science [3 4]. The media phase behavior under conditions of nanoconfinement is naturally connected with its physico-chemical properties playing the key role in the great part of developed and prospective applications. The preference of CARS spectroscopy over the most of other commonly used methods is connected with its universality regarding the topology and morphology of nanoporous structure and sizes of pores. Another positive moment is that high time and spacial resolutions peculiar to CARS technique allow to characterize the dynamics of process of equilibrium achievement in the volume of essentially 3-dimentinal nanoporous materials. The main requirement is the transparency of host material, therefore nanoporous glasses, aerogels, zeolites and some other can be used.
The fundamental basis of the presented approach is based on the difference of molecular vibrations in different phase states of media. Each phase causes corresponding resonant spectral contribution, the total resonant spectra presents the interference between these contributions. The phase behavior of media in nanopores by changing thermodynamical conditions is reflected in the behavior of resonant contributions of CARS spectra. In the context of this work the behavior of vibrational spectra of carbon dioxide in glass nanopores with diameter of several nanometers were analyzed by varying pressure along several isotherms including subcritical and supercritical ones. It was shown that spectral properties of gaseous and condensed phases as well as surface-adsorbed state differ from each other enough to identify each state including the case of simultaneous presence. The phase transitions were diagnosed by transformations of spectra structure. The results are in good agreement with calculations based on thermodynamical conceptions of adsorption and capillary condensation.
The promising idea is to apply the presented approach for characterization of nanoporous structures. The phase behavior of a media confined in nanopores that can be described using presented approach is naturally defined by morphology and dimensions of pores as well as by internal surface area. The level of nonresonant background in CARS signal caused by the host material is defined by the void space. Therefore, the analysis of spectroscopic data based on thermodynamical conceptions should give an opportunity to characterize the structure of the transparent nanoporous materials.
References:
1. D. Mehtani, N. Lee, R. D. Hartschuh, A. Kisliuk, M. D. Foster, A. P. Sokolov and J. F. Maguire, J. Raman Spectrosc, 36, 1068–1075 (2005).
2. A.M. Zheltikov, Laser Physics Letters, 1 (9), pp. 468–472 (2004).
3. T.A. Desai, S. Sharma, R. J. Walczak, A. Boiarski, M. Cohen, J. Shapiro, T. West, K. Melnik, C. Cosentino, P. M. Sinha and M. Ferrari, BioMEMS and Biomedical Nanotechnology 3 (Therapeutic Micro/Nanotechnology), pp. 263-286 (2007)
4. T. Lebold, C. Jung, J. Michaelis and C. Brauchle, Nano Lett., 9 (8), pp. 2877–2883 (2009)