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Melting Gel Films for Low Temperature Seals

Published online by Cambridge University Press:  05 April 2013

Mihaela Jitianu ,
Andrei Jitianu ,
Michael Stamper ,
Doreen Aboagye  and
Lisa C. Klein
Mihaela Jitianu
Affiliation:
Department of Chemistry, William Paterson University, 300 Pompton Road, Wayne, New Jersey 07470
Andrei Jitianu*
Affiliation:
Department of Chemistry, Lehman College, CUNY, Davis Hall, 250 Bedford Park Boulevard West, Bronx, New York 10468
Michael Stamper
Affiliation:
Department of Chemistry, William Paterson University, 300 Pompton Road, Wayne, New Jersey 07470
Doreen Aboagye
Affiliation:
Department of Chemistry, Lehman College, CUNY, Davis Hall, 250 Bedford Park Boulevard West, Bronx, New York 10468
Lisa C. Klein
Affiliation:
Department of Materials Science and Engineering, Rutgers University, 607 Taylor Road, Piscataway, New Jersey 08854
*
*Email: ANDREI.JITIANU@lehman.cuny.edu
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Abstract

Melting gels are silica-based hybrid gels with the curious behavior that they are rigid at room temperature, but soften around 110°C. A typical melting gel is prepared by mixing methyltriethoxysilane (MTES) and dimethyldiethoxysilane (DMDES). MTES has one methyl group substituted for an ethoxy, and DMDES has two substitutions. The methyl groups do not hydrolyze, which limits the network-forming capability of the precursors. To gain insight into the molecular structure of the melting gels, differential scanning calorimetry and oscillatory rheometry studies were performed on melting gels before consolidation. According to oscillatory rheometry, at room temperature, the gels behave as viscous fluids, with a viscous modulus, G″(t,ω0) that is larger than the elastic modulus, G′(t,ω0). As the temperature is decreased, gels continue to behave as viscous fluids, with both moduli increasing with decreasing temperature. At some point, the moduli cross over, and this temperature is recorded as the glass transition temperature Tg. The Tg values obtained from both methods are in excellent agreement. The Tg decreases from -0.3oC to -56oC with an increase in the amount of di-substituted siloxane (DMDES) from 30 to 50 mole %. A decrease of the Tg follows an increase of the number of hydrolytically stable groups, meaning a decrease in the number of oxygen bridges between siloxane chains.

Keywords

sol-gelviscoelasticitySi
Type
Articles
Information
MRS Online Proceedings Library (OPL) , Volume 1547: Symposium M – Solution Synthesis of Inorganic Functional Materials—Films, Nanoparticles and Nanocomposites , 2013 , pp. 81 - 86
Copyright
Copyright © Materials Research Society 2013 

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