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Synthesis and Characterization of Hydrophobic Silica Aerogels Using Trimethylethoxysilane as a Co-Precursor
Authors:Rao  A Venkateswara  Kulkarni  MM  Pajonk  GM  Amalnerkar  DP  Seth  T
Institution:(1) Air Glass Laboratory, Department of Physics, Shivaji University, Kolhapur, 416 004 Maharashtra, India;(2) Laboratoire d'Application de la Chimie a l'Environnent, Université Claude Bernard, Lyon I, 69622 Villeurbanne Cedex, France;(3) Centre for Materials for Electronics Technology, Off Pashan Road, Panchavati, Pune, 411 008 Maharashtra, India
Abstract:The hydrophobic property is one of the most important requirements for the long-term use of silica aerogels for transparent or translucent window insulation and opaque thermal insulating systems. Therefore, the present paper deals with the synthesis and characterization of hydrophobic silica aerogels using trimethylethoxysilane (TMES) as a co-precursor. Silica sol was prepared by keeping the molar ratio of tetramethoxysilane (TMOS) precursor, methanol (MeOH) solvent, water (H2O) and ammonia (NH4OH) catalyst constant at 1:12:4:3.7 × 10–3 respectively throughout the experiments and the TMES/TMOS molar ratio (A) was varied from 0 to 2.35. The resulting silica alcogels were dried supercritically by high-temperature alcohol solvent extraction. Hydrophobicity of the aerogels was tested by measuring the percentage of water adsorbed by the aerogels after putting them directly on the surface of water under humid conditions. Alternately, the hydrophobicity was also tested by contact angle measurements. It was found that as the A value increased, the hydrophobicity of the aerogels increased but the optical transmission decreased from 93% to less than 5% in the visible range. The thermal stability of the aerogels was studied in the temperature range from 25 to 400°C. The hydrophobic nature of the aerogels was maintained up to a temperature of 300°C. The aerogels were characterized by infrared spectroscopy, optical transmittance, Scanning electron microscopy (SEM) and contact angle measurements. The results have been discussed by taking into account the hydrolysis and condensation mechanisms.
Keywords:aerogels  hydrophobicity  water adsorption  IR spectroscopy  scanning electron microscopy
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