Complex 3D‐Printed Mechanochromic Materials with Iridescent Structural Colors Based on Core–Shell Particles

Abstract

A scalable protocol for design and subsequent 3D‐printing of polymeric core‐shell‐particles is reported. The particle synthesis by emulsion polymerization in starved‐feed mode is used for tailoring particle architecture and composition. Control of size, mechanical properties, and chemical functionalities allow to achieve the specific requirement profile for subsequent extrusion‐based additive manufacturing. The core‐shell particles consist of hard polystyrene cores and a comparably soft polyalkylacrylate‐based shell. Size and monodispersity, as well as core‐to‐shell ratio, are determined by means of dynamic light scattering and transmission electron microscopy. Thermal and rheological properties are investigated by means of dynamic scanning calorimetry and thermogravimetric analysis as well as oscillation and capillary rheometry. During 3D‐printing, the monodisperse particles self‐assemble into an ordered close packed lattice structure, leading to visible reflection colors according to Bragg's law of diffraction. Distinct and angle‐dependent reflection colors are recorded via UV‐vis spectroscopy. As the structural color depends, inter alia, on the underlying particle sizes, resulting colors are easily tunable by adjusting the applied synthesis parameters. Under mechanical deformation, the color changes due to controlled lattice deformation, which enables mechanochromic sensing with the printed objects. They are also promising candidates for decorative ornaments, smart optical coatings, or advanced security devices.

Bioinspired reflective display based on photonic crystals

“…Siegwardt and Gallei [145] proposed a scalable polymer core-shell particle design and printing method (Figure 11D). The core-shell particles are composed of a hard polystyrene core and a relatively soft polyalkyl acrylate-based shell.…”

“…In addition to innovative printing methods, variable color models of 3D structure assembly can also be obtained by constructing PhC substrates of different materials and structures. Siegwardt and Gallei [ 145 ] proposed a scalable polymer core–shell particle design and printing method (Figure 11D). The core–shell particles are composed of a hard polystyrene core and a relatively soft polyalkyl acrylate‐based shell.…”

Recent progress in low‐swellable polymer‐based smart photonic crystal sensors

“…To this end, we also expect more specific stimuliswelling materials and micro-nano structure-modulated color-changing mechanisms to be applied to the construction of SPCSs. A large number of stimuli-responsive micronano structures will play important roles in SPCSs, possibly including 2D nano-to-micro structures, [37,294] surface wrinkles, [295,296] photonic porous microparticles, [279,285] quasiamorphous structures, [289,297] diffraction gratings, [298,299] bilayer photonic structures, [26,82] photonic microcapsules, [208,275] stratified porous structures, [300] particle-nested nanostructures, [271,301] periodic wavy structures, [302] woodpile PCs, [303] micro-sized bowl-array, [39] core-shell particles, [304] microbubbles, [305] polyhedron particle-arrays, [306] and so on. Moreover, some novel sensing-material systems, such as cholesteric liquid crystal [307][308][309] and blue-phase liquid crystal, [310][311][312] also show extraordinary sensing properties.…”

Hierarchically Structured Deformation‐Sensing Mechanochromic Pigments

“…interesting strategies have been explored to produce structurally colored mechanochromic materials in other forms apart from films, for example with 3D-printing, [42] it remains difficult to apply these materials as general sensors for deformation within a range of different polymeric matrices. Moreover, the lack of universally applicable mechanochromic deformation sensors may be one key obstacle that has limited their widespread application in commercial products.…”

“…[ 30,38,40,41 ] However, these materials are limited in their capacity for sensing local strains in a substrate matrix, as they can only report the deformation at the surface of or at a certain depth within the substrate. While interesting strategies have been explored to produce structurally colored mechanochromic materials in other forms apart from films, for example with 3D‐printing, [ 42 ] it remains difficult to apply these materials as general sensors for deformation within a range of different polymeric matrices. Moreover, the lack of universally applicable mechanochromic deformation sensors may be one key obstacle that has limited their widespread application in commercial products.…”