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Abstract Printable structural colors, originating from the interaction of light with micro- and nanostructures, have emerged as a promising approach for creating vibrant, durable, and environmentally friendly coloration. The mechanisms of natural structural colors are introduced. Current printing techniques, including nozzle-based and light-based methods, are discussed, along with their respective color generation strategies. These strategies are categorized into three main approaches: nanostructure self-assembly, high-resolution printing, and total reflection interfaces. Additionally, this review addresses the current challenges within the field for each strategy and proposes potential future directions for the development of printable structural colors. Graphical abstract 

Abstract The ability to modulate polyacrylamide hydrogel surface morphology, rheological properties, adhesion and frictional response is demonstrated by combining acrylic acid copolymerization and network confinement via grafting to a surface. Specifically, atomic force microscopy imaging reveals both micellar and lamellar microphase separations in grafted copolymer hydrogels. Bulk characterization is conducted to reveal the mechanisms underlying microstructural changes and ordering of the polymer network, supporting that they stem from the balance between hydrogen bonding in the substrate‐grafted hydrogels, electrostatic interactions, and a decrease in osmotically active charges. The morphological modulation has direct impacts on the spatial distribution of surface stiffness and adhesion. Furthermore, lateral force measurements show that the microphase separations lead to speed and load‐dependent lubrication regimes as well as spatial variation of friction. A proof of concept via salt screening demonstrates the dynamic control of surface morphology and adhesion. This work advances the knowledge necessary to design complex hydrogel interfaces that enable spatial and dynamic control of surface morphology and thereby of friction and adhesion through modulation of hydrogel composition and surface confinement, which is of significance for applications in biomedical devices, soft tissue design, soft robotics, and other engineered tribosystems. 

Large modulation of the microphase separated morphology and structural color of PS-b-PLA BBCPs using single materials by exploiting selective solubility of the two blocks in a series of structurally similar solvents. 

Additive manufacturing capable of controlling and dynamically modulating structures down to the nanoscopic scale remains challenging. By marrying additive manufacturing with self-assembly, we develop a UV (ultra-violet)-assisted direct ink write approach for on-the-fly modulation of structural color by programming the assembly kinetics through photo-cross-linking. We design a photo-cross-linkable bottlebrush block copolymer solution as a printing ink that exhibits vibrant structural color (i.e., photonic properties) due to the nanoscopic lamellar structures formed post extrusion. By dynamically modulating UV-light irradiance during printing, we can program the color of the printed material to access a broad spectrum of visible light with a single ink while also creating color gradients not previously possible. We unveil the mechanism of this approach using a combination of coarse-grained simulations, rheological measurements, and structural characterizations. Central to the assembly mechanism is the matching of the cross-linking timescale with the assembly timescale, which leads to kinetic trapping of the assembly process that evolves structural color from blue to red driven by solvent evaporation. This strategy of integrating cross-linking chemistry and out-of-equilibrium processing opens an avenue for spatiotemporal control of self-assembled nanostructures during additive manufacturing. 

Favorable polymer-substrate interactions induce surface orientation fields in block copolymer (BCP) melts. In linear BCP processed near equilibrium, alignment of domains generally persists for a small number of periods (∼4–6 D 0 ) before randomization of domain orientation. Bottlebrush BCP are an emerging class of materials with distinct chain dynamics stemming from substantial molecular rigidity, enabling rapid assembly at ultrahigh (>100 nm) domain periodicities with strong photonic properties (structural color). This work assesses interface-induced ordering in PS- b -PLA bottle b rush diblock copolymer films during thermal annealing between planar surfaces. To clearly observe the decay in orientational order from surface to bulk, we choose to study micron-scale films spanning greater than 200 lamellar periods. In situ optical microscopy and transmission UV-Vis spectroscopy are used to monitor photonic properties during annealing and paired with ex situ UV-Vis reflection measurement, cross-sectional scanning electron microscopy (SEM), and small-angle X-ray scattering (SAXS) to probe the evolution of domain microstructure. Photonic properties were observed to saturate within minutes of annealing at 150 °C, with distinct variation in transmission response as a function of film thickness. The depth of the highly aligned surface region was found to vary stochastically in the range of 30–100 lamellar periods, with the sharpness of the orientation gradient decreasing substantially with increasing film thickness. This observation suggests a competition between growth of aligned, heterogeneously nucleated, grains at the surface and orientationally isotropic, homogeneously nucleated, grains throughout the bulk. This work demonstrates the high potential of bottlebrush block copolymers in rapid fabrication workflows and provides a point of comparison for future application of directed self-assembly to BBCP ordering.