Аннотация:The characterization of nanostructured and nanocomposite materials as well as the diagnostics of the nanoworld processes are among the most attractive trends of modern science. Methods of coherent nonlinear spectroscopy give a wide range of opportunities in this area [1-2]. Here we introduce the application of the coherent anti-Stokes Raman spectroscopy (CARS) technique for diagnostics of the composite materials constituted of the transparent nanoporous host and the medium filling pores. The presented approach partly described in the recent works [3-4] allows to carry out the spectroscopic diagnostics of the phase behavior of a medium confined in pores of 3-dimentional nanoporous host. It is based on the fundamental difference between molecular vibrations in different phase states of medium. In the present work the behavior of the vibrational spectra of carbon dioxide in glass nanopores with diameter of several nanometers was 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 medium 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 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 [5 6].
The other goal of presented approach is the characterization of nanoporous structures. The level of nonresonant background in CARS signal is caused by the host material, therefore the void space of host can be defined. The phase behavior of a medium confined in nanopores is naturally defined by morphology and dimensions of pores as well as by internal surface area. Thus, the analysis of spectroscopic data based on thermodynamical conceptions gives a fundamental opportunity to characterize the structure the transparent nanoporous materials.
References:
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