Formation of a xerogel in reduced gravity using the acid catalysed silica sol-gel reaction

Christine L. Pienaar; Theodore A. Steinberg

doi:10.1117/12.640969

19 January 2006 Formation of a xerogel in reduced gravity using the acid catalysed silica sol-gel reaction

Christine L. Pienaar, Theodore A. Steinberg

Proceedings Volume 6036, BioMEMS and Nanotechnology II; 603609 (2006) https://doi.org/10.1117/12.640969
Event: Microelectronics, MEMS, and Nanotechnology, 2005, Brisbane, Australia

Abstract

An acid catalysed silica sol-gel reaction was used to create a xerogel in reduced gravity. Samples were formed in a special apparatus which utilised vacuum and heating to speed up the gelation process. Testing was conducted aboard NASA's KC-135 aircraft which flies a parabolic trajectory, producing a series of 25 second reduced gravity periods. The samples formed in reduced gravity were compared against a control sample formed in normal gravity. ²⁹Si NMR and nitrogen adsorption/desorption techniques yielded information on the molecular and physical structure of the xerogels. The microstructure of the reduced gravity samples contained more Q⁴ groups and less Q³ and Q² groups than the control sample. The pore size of the reduced gravity samples was also larger than the control sample. This indicated that in a reduced gravity environment, where convection is lessened due to the removal of buoyancy forces, the microstructure formed through cyclisation reactions rather than bimolecularisation reactions. The latter requires the movement of molecules for reactions to occur whereas cyclisation only requires a favourable configuration. Q⁴ groups are stabilised when contained in a ring structure and are unlikely to undergo repolymerisation. Thus reduced gravity favoured the formation of a xerogel through cyclisation, producing a structure with more highly coordinated Q groups. The xerogel formed in normal gravity contained both chain and ring structures as bimolecularisation reactions were able to effectively compete with cyclisation.

Citation Download Citation

Christine L. Pienaar and Theodore A. Steinberg "Formation of a xerogel in reduced gravity using the acid catalysed silica sol-gel reaction", Proc. SPIE 6036, BioMEMS and Nanotechnology II, 603609 (19 January 2006); https://doi.org/10.1117/12.640969

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