Making Photonic Crystals via Evaporation of Nanoparticle-Laden Droplets on Superhydrophobic Microstructures

Abstract

We employed a convenient evaporation approach to fabricate photonic crystals by naturally drying droplets laden with nanoparticles on a superhydrophobic surface. The final drying morphology could be controlled by the concentration of nanoparticles. A dilute droplet resulted in a torus, whereas a quasi-spherical cap with a bottom cavity was made from a concentrated droplet. Remarkably, the nanofluid droplets maintained high contact angles (≳120°) during the entire evaporation process because of inhomogeneous surface wetting. Bottom-view snapshots revealed that during evaporation the color of the contact area changed sequentially from white to red, orange, yellow, and eventually to green. Scanning electron microscopy and Voronoi analysis demonstrated that nanoparticles were self-assembled to a hexagonal pattern. Finally, based on the effects of particle size, material, and volume concentration on the reflected wavelengths, a model has been developed to successfully predict the reflected wavelength peaks from the contact area of evaporating colloidal droplets. Our model can be easily adopted as a manufacturing guide for functional photonic crystals to predict the optimal reflected color made by evaporation-driven self-assembly of photonic crystals.

Evaporation Dynamics of Surfactant-Laden Droplets on a Superhydrophobic Surface: Influence of Surfactant Concentration

“…Sessile droplet evaporation on a solid surface is a ubiquitous process relevant to myriads of scientific fields and technologies, including inkjet printing, − watercolor painting, DNA extraction, productions of biomaterials, and fabrications of photonics through evaporation-driven self-assembly. − Droplet evaporation dynamics is influenced by nanoparticle suspensions, , surface roughness, − and substrate wettability . Thus, a comprehensive understanding of the droplet evaporation characteristics quantified by the contact angle (CA) and base radius ( R B ) is essential to control the processes tailored for the particular applications.…”

A microfluidics‐dispensing‐printing strategy for Janus photonic crystal microspheres towards smart patterned displays

“…Meanwhile, the colloidal particles in another hemisphere undergo a self‐assembly process under 45°C for 24 h. With evaporation of water, the PS@poly(BA‐ co ‐AA) particles gradually self‐assembled into a tight ordered structure. When the volume fraction of particles exceeds the critical value, photonic band gaps can be generated, and thus the structure colors appear 32 . As shown in Figure 4B, magnetic Janus CPCs microspheres with bright red and green structural colors were successfully achieved.…”

Functional Colloidal Assemblies Based on Superwettable Substrates

“…As a droplet evaporates on a superhydrophobic substrate, the TCL continuously recedes and thus pushes the particles to induce their motion. [ 119 ] This pushing force provides an additional interaction for the colloidal assembly, offering a special method of creating novel assembly structures. Different from the traditional idea that (super)hydrophobic substrates do not favor latex assembly, the new understanding of the influence of wettability on this assembly process paves the way to the construction of novel assembly structures.…”