Fabrication of Photonic Microbricks via Crack Engineering of Colloidal Crystals

Abstract

Evaporation-induced self-assembly of colloidal particles is one of the most versatile fabrication routes to obtain large-area colloidal crystals; however, the formation of uncontrolled "drying cracks" due to gradual solvent evaporation represents a significant challenge of this process. While several methods have been reported to minimize crack formation during evaporation-induced colloidal assembly, here we report an approach to take advantage of the crack formation as a patterning tool to fabricate microscopic photonic structures with controlled sizes and geometries. This is achieved through a mechanistic understanding of the fracture behavior of three different types of opal structures, namely, direct opals (colloidal crystals with no matrix material), compound opals (colloidal crystals with matrix material), and inverse opals (matrix material templated by a sacrificial colloidal crystal). Our work explains why, while direct and inverse opals tend to fracture along the expected {111} planes, the compound opals exhibit a different cracking behavior along the non-close-packed {110} planes, which is facilitated by the formation of cleavage-like fracture surfaces. We utilize the discovered principles to fabricate photonic microbricks by programming the crack initiation at specific locations and by guiding propagation along predefined orientations during the self-assembly process, resulting in photonic microbricks with controlled sizes and geometries.Received: ((will be filled in by the editorial staff))Revised: ((will be filled in by the editorial staff))

Enhanced Phase-Change Condensation Using Inverse Opals

“…Faster condensate removal through the cracks refreshed the surface and prepared it for renewed droplet nucleation and growth. These results suggest that hierarchical (two-level) porosity, which can be achieved by engineering cracks in colloidal crystals, 32 has a potential for faster condensate removal that can translate to improved phase-change condensation heat transfer rate.…”

“…Using the bottom-up colloidal co-assembly technique, [30][31][32] we coated copper tubes (length = 60 mm, external diameter = 6.35 mm, internal diameter = 4.57 mm) with silica inverse opals; a highly porous material consisting of sub-micron voids in a support matrix (see materials and methods for material synthesis and sample fabrication). Typical scanning electron micrograph (SEM) images of the porous inverse opal coating at different magnifications are shown in Fig.…”

Improvement of the Centrifugal Force in Gravity Driven Method for the Fabrication of Highly Ordered and Submillimeter-Thick Colloidal Crystal

“…The measured reflectance values of silica colloidal crystals stacked at different rotational speeds (150, 200, and 250 rpm) and radii of rotation (8,16,24,32, and 40 cm) are presented in Figure 2. The concentration of the colloidal silica solution was 30 wt %.…”

“…The two glass plates were treated to possess hydrophobic and hydrophilic properties, respectively, to allow the colloidal crystals to easily remain on the hydrophilic-treated glass plate [26]. These glass plates were fixed by magnets and placed in humid dishes that were placed at various positions (8,16,24, 32 and 40 cm) on the rotator, as shown in Figure 1. The positions of the samples were defined by their distances from the rotating axis.…”

Self‐Assembly of Colloidal Nanoparticles into Well‐Ordered Centimeter‐Long Rods via Crack Engineering

“…[ 15,16 ] Therefore, most of previous efforts were devoted to circumventing them. [ 15,17,18 ] Recently, it has been demonstrated that regulated crack patterns could be useful in some applications, such as fabrication of microchannels, [ 9,19 ] photonic microbricks, [ 20 ] and sensors, [ 21 ] due to their excellent controllability of morphology and periodicity. Herein, we utilized rational designed cracks to obtain uniform CRs.…”