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Shrinkage and Microstructural Development During Drying of Organically Modified Silica Xerogels

Published online by Cambridge University Press:  10 February 2011

N. K. Raman ,
S. Wallace  and
C. J. Brinker
N. K. Raman
Affiliation:
Center for Micro-Engineered Ceramics, University of New Mexico, Albuquerque, NM 87131
S. Wallace
Affiliation:
Nanopore Corporation, 2501 Alamo Ave., SE, Albuquerque, NM 87106.
C. J. Brinker
Affiliation:
Center for Micro-Engineered Ceramics, University of New Mexico, Albuquerque, NM 87131 Sandia National Laboratories, Advanced Materials Laboratory, 1001 University Blvd., SE, Albuquerque, NM 87106.
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Abstract

We have studied the different driving forces behind syneresis in methyltriethoxysilane/tetraethoxysilane (MTES/TEOS) gels by aging them in different H2O/EtOH pore fluids. We show using shrinkage, density, contact angle, and N2 sorption measurements, the influence of gel/solvent interactions on the microstructural evolution during drying. Competing effects of syneresis (that occurs during aging) and drying shrinkage resulted in the overall linear shrinkage of the organically modified gels to be constant at ∼50%. Increasing the hydrophobicity of the gels caused the driving force for syneresis to change from primarily condensation reactions to a combination of condensation and solid/liquid interfacial energy. In addition the condensation driven shrinkage was observed to be irreversible, whereas the interfacial free energy driven shrinkage was observed to be partially reversible. Nitrogen sorption experiments show that xerogels with the same overall extent of shrinkage can have vastly different microstructures due to the effects of microphase separation.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 435: Symposium V – Better Ceramics Through Chemistry VII , 1996 , 357
Copyright
Copyright © Materials Research Society 1996

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