Ian Burgess, Bryan Nerger, Kevin Raymond, Alexis Goulet-Hanssens, Thomas Singleton, Mackenzie Kinney, Anna Shneidman, Natalie Koay, Christopher Barrett, Marko Lončar, Joanna Aizenberg
We provide an overview of our recent advances in the manipulation of wetting in inverse-opal photonic crystals.
Exploiting photonic crystals with spatially patterned surface chemistry to confine the infiltration of fluids to liquidspecific spatial patterns, we developed a highly selective scheme for colorimetry, where organic liquids are distinguished based on wetting. The high selectivity of wetting, upon-which the sensitivity of the response relies, and the bright iridescent color, which disappears when the pores are filled with liquid, are both a result of the highly symmetric pore structure of our inverse-opal films. The application of horizontally or vertically orientated gradients in the surface chemistry allows a unique response to be tailored to specific liquids. While the generic nature of wetting makes our approach to colorimetry suitable for applications in liquid authentication or identification across a broad range of industries, it also ensures chemical non-specificity. However, we show that chemical specificity can be achieved combinatorially using an array of indicators that each exploits different chemical gradients to cover the same dynamic range of response. Finally, incorporating a photo-responsive polyelectrolyte surface layer into the pores, we are able to dynamically and continuously photo-tune the wetting response, even while the film is immersed in liquid. This in situ optical control of liquid percolation in our photonic-crystal films may also provide an error-free means to tailor indicator response, naturally compensating for batch-to-batch variability in the pore geometry.
Whereas considerable interest exists in self-assembly of well-ordered, porous "inverse opal" structures for optical,
electronic, and (bio)chemical applications, uncontrolled defect formation has limited the scale-up and practicality of
such approaches. Here we demonstrate a new method for assembling highly ordered, crack-free inverse opal films over a
centimeter scale. Multilayered composite colloidal crystal films have been generated via evaporative deposition of
polymeric colloidal spheres suspended within a hydrolyzed silicate sol-gel precursor solution. The co-assembly of a
sacrificial colloidal template with a matrix material avoids the need for liquid infiltration into the preassembled colloidal
crystal and minimizes the associated cracking and inhomogeneities of the resulting inverse opal films. We demonstrate
that this co-assembly approach allows the fabrication of hierarchical structures not achievable by conventional methods,
such as multilayered films and deposition onto patterned or curved surfaces, and can be transformed into various
materials that retain the morphology and order of the original films. We show that colloidal co-assembly represents a
simple, low-cost, scalable method for generating high-quality, chemically tailorable inverse opal films for optical
applications.
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