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Abstract:

The sol to gel evolution of systems based on the hydrolysis of titanium n-butoxide, Ti(OBu n ) 4 , in 1-butanol was investigated by monitoring the changes of the radiative and nonradiative electronic excited state processes of embedded dyes (cresyl violet and 4-(dicyanomethylene)-2-methyl-6(p-dimethylaminostyryl-4H-pyran). Fluorescence anisotropy experiments (FA) allow determination of changes in the microviscosity of the medium surrounding the fluorophore through the sol-gel evolution. The increase of the anisotropy parameter, 〈r〉, is explained in terms of solvent confinement in cavities enclosed within cross-linked polymeric chains. The acoustic signal recorded in laser-induced optoacoustics experiments (LIOAS) is attenuated as the system loses fluidity, with a minimum at t g , thus providing an alternative method for determining the gelation point. In addition, within the theoretical approach of percolation theory, the exponent of the viscosity power law is obtained from the attenuation of the sound wave. Although both FA and LIOAS provide information on the degree of cross-linking between polymeric chains, there is a clear difference between the behavior of the macroscopic shear viscosity determined by LIOAS and the local friction or microviscosity obtained from FA.

Registro:

Documento: Artículo
Título:Radiative and nonradiative excited state processes for studying the sol to gel evolution
Autor:Marchi, M.C.; Bilmes, S.A.; Negri, R.M.
Filiación:Instituto de Quimica Fisica de los Materiales, Medio Ambiente y Energia (INQUIMAE), Departamento de Química Inorgánica, Analítica y Química Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón II, C1428EHA Buenos Aires, Ciudad Universitaria, Argentina
Palabras clave:Excited states; Anisotropy; Chromophores; Electron energy levels; Fluorescence; Gelation; Hydrolysis; Nanostructured materials; Neutron scattering; Nuclear magnetic resonance; Percolation (fluids); Photoacoustic effect; Raman spectroscopy; Sol-gels
Año:2002
Volumen:18
Número:18
Página de inicio:6730
Página de fin:6735
DOI: http://dx.doi.org/10.1021/la0117597
Título revista:Langmuir
Título revista abreviado:Langmuir
ISSN:07437463
CODEN:LANGD
Registro:https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_07437463_v18_n18_p6730_Marchi

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Citas:

---------- APA ----------
Marchi, M.C., Bilmes, S.A. & Negri, R.M. (2002) . Radiative and nonradiative excited state processes for studying the sol to gel evolution. Langmuir, 18(18), 6730-6735.
http://dx.doi.org/10.1021/la0117597
---------- CHICAGO ----------
Marchi, M.C., Bilmes, S.A., Negri, R.M. "Radiative and nonradiative excited state processes for studying the sol to gel evolution" . Langmuir 18, no. 18 (2002) : 6730-6735.
http://dx.doi.org/10.1021/la0117597
---------- MLA ----------
Marchi, M.C., Bilmes, S.A., Negri, R.M. "Radiative and nonradiative excited state processes for studying the sol to gel evolution" . Langmuir, vol. 18, no. 18, 2002, pp. 6730-6735.
http://dx.doi.org/10.1021/la0117597
---------- VANCOUVER ----------
Marchi, M.C., Bilmes, S.A., Negri, R.M. Radiative and nonradiative excited state processes for studying the sol to gel evolution. Langmuir. 2002;18(18):6730-6735.
http://dx.doi.org/10.1021/la0117597