Physical properties of methyltrimethoxysilane based elastic silica aerogels prepared by the two-stage sol–gel process
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The experimental results on the physical properties of methyltrimethoxysilane (MTMS) based elastic silica aerogels prepared by the two stage sol–gel process, are reported. The molar ratio of methanol (MeOH)/MTMS, (M), was varied from 14 to 42 and the molar ratios of acidic water/MTMS, (A) and basic water/MTMS, (B) were each varied from 0.8 to 7.2. The acidic water and basic water concentrations were also varied from 0–0.1 M and 6–13.36 M, respectively. The MTMS based superhydrophobic elastic aerogels could be obtained by adding only distilled water without an acid in the first step which would prevent the possible corrosion of the autoclave during the supercritical drying. With an increase in the MeOH/MTMS molar ratio, the aerogels have been found to become flexible which was characterized by the Young’s modulus. The best quality elastic superhydrophobic aerogels in terms of contact angle (160°), density (37 kg/m3), volume shrinkage (6%), porosity (98%) and thermal conductivity (0.057 Wm−1 K−1) have been obtained for the molar ratio of MTMS:MeOH:acidic water:basic water:: 1:35:3.97:3.97, respectively. The hydrophobicity was confirmed by Fourier Transform Infrared (FTIR) spectroscopy and contact angle measurements. The microstructure of the aerogels has been studied by the transmission electron microscopy (TEM).
KeywordsContact Angle Silica Aerogel Gelation Time Volume Shrinkage Silica Network
The authors are grateful to the 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-01/2002). The authors are also thankful to Prof. Hiroshi Hirashima and Mr. Mitsutoshi INAGAKI, Faculty of Science and Technology, Keio University, Japan for the help in the TEM studies. One of the authors, Nagaraja D. Hegde, is highly thankful to the University Grants Commission (UGC), Government of India, New Delhi for the teacher fellowship awarded under the 10th Plan and gratefully acknowledges the encouragement by the Principal and members of staff of G.S.Science College, Belgaum, Karnataka, India.
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