Silica hydrogel formation and aging monitored by pyrene-based fluorescence probes |
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Authors: | Tomá? Nedel?ev Igor Krupa Pavol Hrdlovi? Jozef Kollár Jr" target="_blank">Du?an ChorvátJr Igor Lacík |
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Institution: | 1.Polymer Institute of the Slovak Academy of Sciences,Bratislava,Slovak Republic;2.International Laser Center,Bratislava,Slovak Republic |
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Abstract: | Fluorescent probes pyrene (Py), di(1-pyrenylmethyl)ether (DiPyM) and newly synthesized 2,3-bis-4-(1-pyrenemethoxy)methylphenyl]butane
(DiPyS) were used to monitor the formation and aging of silica hydrogel prepared from poly(glyceryl silicate) (PGS) sol. The
fluorescence emission spectra of these probes are sensitive to their environment and this feature is utilized for monitoring
the evolution of silica hydrogels prepared in this work. The polarity of hydrogel matrix during sol–gel transition assessed
by all three pyrene probes decreases in the first stage of hydrogel formation, for about 2 h, followed by a gradual increase
in polarity and reaching the constant level after 24 h for at least 2 weeks. The process of crosslinking was assessed by DiPyM
and DiPyS. These fluorescent probes possess two pyrene structures, which ability to form a dynamic intramolecular excimer
can be used to monitor the degree of hydrogel crosslinking with time. These data support the polarity measurements that the
hydrogel network is predominatly formed within the first 2 h, stabilized within the 24 h, and that there is a minor increase
in the network density for about 10 days until reaching the constant level. In addition, utilizing the second-order diffraction
of scattered excitation light may also be used to obtain an adequate information about the silica hydrogel evolution. In summary,
this paper demonstrates that pyrene-type fluorescent probes represent simple and precise tool for characterization of formation
and aging of the silica hydrogels. |
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