title: Vapor detection enabled by self-assembled colloidal photonic crystals.
abstract: Here we report the sensitive and reversible detection of vapors by using self-assembled colloidal photonic crystals. The condensation of various vapors in the interstitials of silica colloidal photonic crystals leads to red-shift and amplitude reduction of optical stop bands. A linear relationship between wavelength shift and vapor partial pressure has been observed for a variety of vapors including ethanol, water, and toluene. Importantly, the sensitivity of colloidal photonic crystal-based vapor detectors can be improved by nearly two orders of magnitude by using a new full-peak analysis technique that takes advantage of the manifest amplitude reduction of optical stop bands during vapor condensation. Optical simulation based on a scalar-wave approximation model shows that the predicted optical responses during vapor condensation in colloidal photonic crystals agree well with experimental results. The condensation of vapors between submicrometer-scale microspheres, a topic that has received little examination, has also been investigated by both experiments and theoretical calculations. Predictions based on a modified Kelvin equation match with the experiments for a wide range of vapor partial pressures.
authors.affiliation: Department of Chemical Engineering, University of Florida, Gainesville, FL 32611, USA.
authors.forename: Hongta
authors.initials: H
authors.lastname: Yang
authors.forename: Peng
authors.initials: P
authors.lastname: Jiang
authors.forename: Bin
authors.initials: B
authors.lastname: Jiang