| Full text | |
| Author(s): |
Fermino, Taina Z.
[1]
;
Awano, Carlos M.
[1]
;
Moreno, Leandro X.
[1]
;
Vollet, Dimas R.
[1]
;
de Vicente, Fabio S.
[1]
Total Authors: 5
|
| Affiliation: | [1] Univ Estadual Paulista, UNESP, Inst Geociencias & Ciencias Exatas, Dept Fis, BR-13506900 Rio Claro, SP - Brazil
Total Affiliations: 1
|
| Document type: | Journal article |
| Source: | Microporous and Mesoporous Materials; v. 267, p. 242-248, SEP 1 2018. |
| Web of Science Citations: | 3 |
| Abstract | |
Hydrophobic ambient pressure drying (APD) aerogels were prepared from hydrolysis of tetraethylorthosilicate (TEOS) in solutions with different concentrations of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (F127). APD was carried out after silylation of wet gels with 20% by volume of hexamethyldisilazane (HMDZ) in n-hexane. The samples were analyzed by small-angle X-ray scattering (SAXS) and nitrogen adsorption. The APD aerogels obtained in this process were submitted to heat treatment at 300, 500, 700 and 900 degrees C to study the pores stability. The samples were characterized by nitrogen adsorption. Wet gels are formed by massfractal domains, with fractal dimension close to 2.1 and characteristic size (xi) spanning from about 9 nm (for the gel prepared without the addition of F127) up to values that exceed the maximum limit of the SAXS experimental setup, with increasing the concentration of F127. Nitrogen adsorption data showed that the pore volume (V-P) and the mean pore size (l(p)) of the aerogels increased with increasing the concentration of F127. The drying process diminished the characteristic size xi and increased the dimension D of the mass-fractal domains and the size (r(0)) of the primary particles of the aerogels with respect to the wet gels. The characteristic size xi of the massfractal of the aerogels was found significantly larger with increasing the concentrations of F127. Thermally treated aerogels exhibited a similar general behavior with temperature independent of the concentration of F127. The porosity was found fairly stable up to about 500 degrees C. The porosity started to be eliminated at 700 degrees C and it was found practically collapsed at 900 degrees C. The silylation layer on the silica surface of the present APD aerogels was promptly eliminated at about 350 degrees C yielding complete loss of hydrophobicity. (AU) | |
| FAPESP's process: | 11/18149-5 - Study of Photosensitivity and photoluminescence in organically modified silicates films prepared by sol-gel |
| Grantee: | Fábio Simões de Vicente |
| Support Opportunities: | Regular Research Grants |