No abstract

To obtain high-quality homogeneous photonic glass-based structural color films over large areas, it is essential to precisely control the degree of disorder of the spherical particles used and reduce the crack density within the films as much as possible. To tailor the disorder and quality of photonic glasses, a heteroaggregation-based process was developed by employing two oppositely charged equal-sized polystyrene (PS) particle types. The influence of the particle size ratio on the extent of heteroaggregation in the suspension mixes is investigated and correlated with both the morphology and the resultant optical properties of the films. The results show that the oppositely charged particle size ratio within the mix greatly influences the assembled structure in the films, affecting their roughness, crack density, and the coffee-ring formation. To better differentiate the morphology of the films, scanning electron microscopy images of the microstructures were classified by a supervised training of a deep convolutional neural network model to find distinctions that are inaccessible by conventional image analysis methods. Selected compositions were then infiltrated with TiO2 via atomic layer deposition, and after removal of the PS spheres, surface-templated inverse photonic glasses were obtained. Different color impressions and optical properties were obtained depending on the heteroaggregation level and thus the quality of the resultant films. The best results regarding the stability of the films and suppression of coffee-ring formation are obtained with a 35 wt % positively charged over negatively charged particle mix, which yielded enhanced structural coloration associated with improved film quality, tailored by the heteroaggregation fabrication process.

Macroporous structures are of interest for several technological applications such as catalysis, sensors, filters, membranes, batteries, energy conversion devices, structural colors, and reflective thermal barrier coatings. Ceramic‐based inverse opal macroporous structures are especially interesting for high‐temperature applications. However, the interrelation between the structural parameters, mechanical properties, and thermal stability of such structures is not yet clarified. In this work, we analyzed the mechanical properties as well as the thermal stability of aluminum oxide inverse opal three‐dimensional macroporous structures with different macropore sizes and shell thicknesses produced by atomic layer deposition. Our results show that the structures’ thermal stability increased with increasing shell thickness and macropore size, however, their higher stability was not linked to their mechanical properties. To be able to explain this unexpected behavior, finite element modeling simulations were performed, showing that bending stresses became more pronounced with increasing shell thickness, potentially creating additional critical sites for crack initiation and consequent structural failure.

strategies. [4] Here, on-chip microfluidics could aid to effectively remove heat. [4] This requires processing techniques with great design and material flexibility. However, current processes for microfluidics rely mainly on lithography techniques, which are limited in materials selection and restricted to rather 2D designs. [5] Hence, the development of novel processing routes is required that allow design flexible processes such as AM and greater materials variety. [4] Next to thermal management in highpower electronics, thermal shielding in high-temperature applications requires consistent enhancement toward higher working temperatures: here, next-generation reflective thermal barrier coatings (rTBCs) with tailored microstructures have lower thermal conductivity in comparison to traditional TBCs, [6] but most importantly are capable of additionally scatter heat radiation. [7] The emittance of heat radiation scales with temperature by T 4 , hence obstructing radiative heat transport becomes very relevant with increasing working temperatures (>1000 °C). Therefore, coating components for high-temperature applications with such rTBCs could allow the devices to work at higher operating temperatures.