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Enhanced Resonator Sensitivity with Nanostructured Porous Silica S. H. Bhansali, J. M. Jarvis, I. A. Aksay,* and J. D. Carbeck
 

Summary: Enhanced Resonator Sensitivity with Nanostructured Porous Silica
Coatings
S. H. Bhansali, J. M. Jarvis, I. A. Aksay,* and J. D. Carbeck
Department of Chemical Engineering, Princeton UniVersity, Princeton, New Jersey 08544-5263
ReceiVed July 21, 2005. In Final Form: March 15, 2006
We present a strategy to increase the sensitivity of resonators to the presence of specific molecules in the gas phase,
measured by the change in resonant frequency as the partial pressure of the molecule changes. We used quartz crystals
as the resonators and coated them with three different thin films (<1 Ám thick) of porous silica: silica xerogel, silica
templated by an ordered hexagonal phase of surfactant micelles, and silica templated by an isotropic L3 phase surfactant
micellar system. We compared the sensitivity of coated resonators to the presence of water vapor. The crystals coated
with hexagonal phase-templated silica displayed a sensitivity enhancement up to 100-fold compared to an uncoated
quartz crystal in the low-pressure regime where adsorption played a dominant role. L3 phase-templated silica displayed
the highest sensitivity (up to a 4000-fold increase) in the high partial pressure regimes where capillary condensation
was the main accumulation mechanism. Three parameters differentiate the contributions of these coatings to the
sensitivity of the underlying resonator: (i) specific surface area per unit mass of the coating, (ii) accessibility of the
surfaces to a target molecule, and (iii) distribution in the characteristic radii of curvature of internal surfaces, as
measured by capillary condensation.
Introduction
Theresonantfrequencyofamechanicaloscillator,orresonator,
is a function of the mass of the oscillating body. Resonators can

  

Source: Aksay, Ilhan A. - Department of Chemical Engineering, Princeton University

 

Collections: Materials Science