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Published on: January 29, 2013
Polymerized PolyHEMA photonic crystals: pH and ethanol sensor materials.
Xiangling Xu1, Alexander V Goponenko, Sanford A Asher
1Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA.
Journal of the American Chemical Society
|February 15, 2008
Summary
Highly charged crystalline colloidal arrays (CCAs) were fabricated and coated with polymers. These photonic crystals act as sensitive ethanol and pH sensors, with tunable diffraction properties modeled by Flory theory.
Area of Science:
- Materials Science
- Nanotechnology
- Colloid Science
Background:
- Monodisperse silica particles are synthesized via the Stober process.
- Surface modification is achieved through polystyrene coating and grafting polymerization of styrene sulfonate, creating charged particles.
Purpose of the Study:
- To create self-assembled crystalline colloidal arrays (CCAs) and develop polymer-infiltrated CCAs (PCCAs).
- To investigate the sensing capabilities of PCCAs for ethanol concentration and pH.
- To model the optical response of PCCAs using theoretical frameworks.
Main Methods:
- Stober process for silica synthesis, followed by polystyrene coating and sulfonation.
- Polymerization of hydroxyethyl methacrylate (HEMA) around CCAs to form PCCAs.
- Etching silica cores with hydrofluoric acid to create 3D void arrays.
- Incorporation of carboxyl groups for pH sensitivity through secondary polymerization.
Main Results:
- HEMA PCCAs exhibit sensitive diffraction shifts with ethanol concentration, covering the visible spectrum.
- Flory theory accurately models the ethanol concentration dependence of diffraction wavelength.
- Carboxylated PCCAs respond to pH changes in varying ionic strengths, showing hysteresis due to Donnan potential formation.
Conclusions:
- Fabricated PCCAs serve as effective photonic crystal sensors for ethanol and pH.
- The optical response of PCCAs can be tuned and modeled using Flory theory.
- Hysteresis in pH response is attributed to Donnan potential, with slow kinetics due to low proton diffusion.
