Synthesis of transparent silica aerogels with low density and better hydrophobicity by controlled sol–gel route and subsequent atmospheric pressure drying
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In the present paper, attempts have been made to produce transparent silica aerogels with low density and better hydrophobicity by controlled sol–gel route and subsequent atmospheric pressure drying. The hydrogels were prepared by hydrolysis and polycondensation of sodium silicate (Na2SiO3) in the presence of acetic acid catalyzed water followed by several washing steps with water, methanol and hexane, respectively. The surface modification of the wet gel was carried out using a mixture of hexamethyldisilazane (HMDS) in hexane. Since, the sol–gel chemistry provides a straightforward method to control the physical and optical properties of the aerogels, the influence of various sol–gel parameters viz. gel washing time, molar ratios of CH3COOH/Na2SiO3 and HMDS/Na2SiO3 and silylation period on the physical and optical properties of the aerogels have been investigated. The aerogels have been characterized by bulk density, Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric and Differential Thermal Analysis (TG-DTA), Atomic Absorption Spectroscopy (AAS), Scanning Electron Microscopy (SEM) studies and Contact angle measurements.
KeywordsSodium silicate Ambient pressure drying Aerogel Hydrophobic Transparent
The authors are grateful to the Condensed Matter Advisory Committee, Department of Science and Technology (DST), New Delhi, Government of India, for the financial support for this work through a major research project on “Aerogels” (no. SR/S2/CMP-67/2006). Poonam M. Shewale is highly thankful to the Shivaji University Kolhapur for providing ‘Departmental Research Fellowship’. One of the authors Dr. A Parvathy Rao is highly thankful to the DST for the Senior Research Associateship.
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