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Polymerized polyHEMA photonic crystals: pH and ethanol sensor materials

Xu, X and Goponenko, AV and Asher, SA (2008) Polymerized polyHEMA photonic crystals: pH and ethanol sensor materials. Journal of the American Chemical Society, 130 (10). 3113 - 3119. ISSN 0002-7863

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The surface of monodisperse silica particles synthesized using the Stober process were coated with a thin layer of polystyrene. Surface charge groups were attached by a grafting polymerization of styrene sulfonate. The resulting highly charged monodisperse silica particles self-assemble into crystalline colloidal arrays (CCA) in deionized water. We polymerized hydroxyethyl methacrylate (HEMA) around the CCA to form a HEMA-polymerized crystalline colloidal array (PCCA). Hydrofluoric acid was utilized to etch out the silica particles to produce a three-dimensional periodic array of voids in the HEMA PCCA. The diffraction from the embedded CCA sensitively monitors the concentration of ethanol in water because the HEMA PCCA shows a large volume dependence on ethanol due to a decreased Flory-Huggins mixing parameter. Between pure water and 40% ethanol the diffraction shifts across the entire visible spectral region. We accurately modeled the dependence of the diffraction wavelength on ethanol concentration using Flory theory. We also fabricated a PCCA (which responds to pH changes in both low and high ionic strength solutions) by utilizing a second polymerization to incorporate carboxyl groups into the HEMA PCCA. We were also able to model the pH dependence of diffraction of the HEMA PCCA by using Flory theory. An unusual feature of the pH response is a hysteresis in response to titration to higher and lower pH. This hysteresis results from the formation of a Donnan potential at high pH which shifts the ionic equilibrium. The kinetics of equilibration is very slow due to the ultralow diffusion constant of protons in the carboxylated PCCA as predicted earlier by the Tanaka group. © 2008 American Chemical Society.


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Item Type: Article
Status: Published
CreatorsEmailPitt UsernameORCID
Xu, X
Goponenko, AV
Asher, SAasher@pitt.eduASHER
Date: 12 March 2008
Date Type: Publication
Journal or Publication Title: Journal of the American Chemical Society
Volume: 130
Number: 10
Page Range: 3113 - 3119
DOI or Unique Handle: 10.1021/ja077979+
Schools and Programs: Dietrich School of Arts and Sciences > Chemistry
Refereed: Yes
ISSN: 0002-7863
MeSH Headings: Colloids--chemistry; Electrodes; Ethanol--chemistry; Hydrogen-Ion Concentration; Particle Size; Polyhydroxyethyl Methacrylate--chemistry; Sensitivity and Specificity; Silicon Dioxide--chemical synthesis; Silicon Dioxide--chemistry; Surface Properties; Time Factors; Water--chemistry
PubMed ID: 18271586
Date Deposited: 08 Feb 2013 21:05
Last Modified: 02 Feb 2019 16:55


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