We will present a simple and low cost method to visualize local strain distribution in deformed aluminum plates. In this
study, aluminum plates were coated with opal photonic crystal film with tunable structural color. The photonic crystal
films consist of a silicone elastomer that contains an array of submicron polystyrene colloidal particles. When the
aluminum sheets were stretched, the change in the spacing of the colloidal particles in the opal film alters the color of the
film. This approach could be useful as a new strain gauge having a visual indicator to detect mechanical deformation.
We report the application of a photonic crystal sensor for the components of a liquid mixture by a simple and easy
technique. A closely packed colloidal crystal film is made of arrayed 202-nm PS particles and PDMS elastomer is used
for filling the voids in the film. Bragg's diffraction in the visible wavelength region causes the formation of a structural
color in the colloidal crystal. The structural color varies according to the solvents depending on the swelling ability of the
PDMS elastomer. We can perform the quantitative analysis of the swelling phenomena by measuring Bragg's diffraction
peaks. The peak shifts as a function of the mixing ratio of the solvents, i.e., methanol, ethanol, and propanol. The peak
position is proportional to the solvent concentration. In the case of a water-ethanol system, there is little peak-shift up to
80 vol.% of ethanol concentration. Above this concentration, the rate of peak shift increases beyond 50 nm. A reflectance
spectrometer enables the detection of the components of ethanol liquids with the volume concentration of water ranging
from 0 to 10%. In this study, a commercially available optical fiber spectrometer detects the volume concentrations of
water of the order of 1 vol.% in ethanol. The photonic sensor has the potential to be used in a rapid analysis method that
employs a portable optical fiber spectrometer.
We have developed a simple method to produce large colloidal crystal films for a like-charged particles system, where
particle arrays with single-crystalline-like characteristics are made by a flow-induced process. A poly-crystalline
suspension was charged in a flat capillary and processed by strong shear flow. Optical characterizations for the uniform
samples indicate that almost all the capillary space (several square centimeters wide and 0.1mm thick) is filled with a
single-domain crystal with a fixed crystallographic orientation determined by the cell geometry. The single-domain
crystal can be fixed in a self-standing hydro-gel film by polymerizing gelation agents added in the suspension. Upon
gelation, the optical quality was found to be well preserved. We also show tunable characteristics of the gelled crystals in
some different aspects. They can be contracted by changing the composition of the solvent. The stop-band width can be
effectively expanded by adjusting the fabrication condition. These transformations can be made as single domains that
should be advantageous to application purposes.
This paper describes an elastic colloidal crystal, soft opal, with tunable stop band and its potential application for mechanical strain sensing. A poly-dimethylsiloxane, PDMS, rubber sheet was coated with a thin layer of the soft opal. In the layer, polystyrene, PS, submicron particles were cubic-closely packed, CCP, and among the particles filled with PDMS elastomer. We design the array of CCP (111) planes selectively diffracts light in visible wavelength. The wavelength, i.e. photonic stop band, was reversibly tuned by tensile strain. As the PDMS sheet was stretched in horizontal direction, the film becomes compress in vertical direction. As a result, the lattice distance of CCP (111) planes decreased and the stop band shifted to shorter wavelengths. As released the mechanical strain on the PDMS sheet, the stop band completely returned to the initial wavelength. The PDMS sheet also displays reversible change of the structural color during elastic deformation. The potential application is a simple stress sensor enables visual judgment of the intensity of tensioning.