Hydrophobic and Physical Properties of the Two Step Processed Ambient Pressure Dried Silica Aerogels with Various Exchanging Solvents |
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Authors: | Email author" target="_blank">A?Parvathy?RaoEmail author A?Venkateswara?Rao G?M?Pajonk |
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Institution: | (1) Airglass Laboratory, Physics Department, Shivaji University, Kolhapur, Maharashtra, 416004, India;(2) Laboratoire Des Materiaux et Procedes catalytiques, Universite Claude Bernard, Lyon1,43 Boulevard Du11Novembre 1918, Villeurbanne Cedex, 69622, France |
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Abstract: | The experimental results by using various exchanging solvents in the preparation of two step (acid and base) processed ambient
pressure dried hydrophobic silica aerogels, are reported. Silica alcogels were prepared by hydrolysis with oxalic acid and
condensation with NH4OH of ethanol diluted tetraethylorthosilicate (TEOS) precursor and hexamethyldisilazane(HMDZ) methylating agent. The exchanging
solvents used were: hexane, cyclohexane, heptane, benzene, toluene and xylene. The physical properties such as % of volume
shrinkage, density, pore volume, % of porosity, thermal conductivity, % of optical transmission, surface area, pore size distribution
and contact angle (θ) of the silica aerogels with water, were measured as a function of EtOH/TEOS molar ratios (R) for all the exchanging solvents. It was found that the physical and hydrophobic properties of the silica aerogels strongly
depend on the nature of the solvent and R. Heptane solvent resulted in highly transparent (≈90% optical transmission at 700 nm for 1 cm thick sample), low density
(≈0.060 g/cm3), low thermal conductive (≈0.070 W/m·K), high % of porosity (97%), high surface area (750 m2/g), uniform porosity and hydrophobic (θ ≈ 160°) aerogels compared to other solvents. On the otherhand, xylene resulted in aerogels with higher hydrophobicity (θ ≈ 172°) among other solvents. |
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Keywords: | microporous sol-gel chemistry hydrophobicity thermal conductivity optical transmission |
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