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Despite the remarkable progress in the development of sweat sensors, self‐powered sweat‐responsive sensing displays that detect sweat in electric signals with simultaneous and direct visualization of the sweat is rarely demonstrated. Here, a self‐powered sweat‐responsive structural color (SC) display enabled by ionomer‐doped block copolymer (BCP) photonic crystals (PCs) is presented. The sweat‐responsive BCP PC is developed by employing a cross‐linking single‐mobile ionomer (SMI) with mobile anions anchored to immobile polycations to a 1‐D BCP PC. The hydrophobic SMI‐doped BCP PC is mechanically robust as well as water and temperature‐resistive, exhibiting ionomer concentration‐dependent full visible SCs. Moreover, the mobile anions periodically confined in the SMI‐doped BCP PC harvest triboelectric energy, giving rise to a high‐power density of ≈0.774 Mw cm−2. Cation‐sensitive SC variation is observed in the SMI‐doped BCP PC, allowing the visualization of sweat containing various cations. A skin‐patchable self‐powered sweat‐responsive display is demonstrated in which kirigami‐patterned SMI‐doped BCP PC incorporated in the display can withstand up to 50% strain during exercise. Sweat from the exercise is visualized via SC display and measured using both ionic resistance changes and triboelectric signals. In addition, the integration of sweat sensing membrane into SMI‐doped BCP PC enables the quantification of sweat. [ABSTRACT FROM AUTHOR] more...

Displays are an effective way for humans to recognize information instantly and intuitively without linguistic barriers. Electrical sensors detect diverse human and environmental changes through variations in electrical signals; these data are delivered to a display connected to a sensor via a microprocessor, facilitating human/machine interface technologies. The development of an innovative one-integrated platform with optimized architectures, where a sensor and a display are converged, is essential for achieving efficient and rapid information management with low power consumption. These integrated stimuli-adaptive and human-interactive sensing displays (HISDs) electrically detect external stimuli and display an optical visualization simultaneously. Among numerous materials suitable for stimuli-adaptive displays and HISDs, self-assembled photonic crystals (PCs) of block copolymers (BCPs) are promising because of their structural colors (SCs) resulting from constructive interference of incident light. This review provides a comprehensive overview of recent developments in stimuli-adaptive SC displays using self-assembled BCP PCs. The responses of BCP SC displays, operating in liquid cells and solid-type films, to various external stimuli are described. Furthermore, emerging HISDs based on BCP PCs are discussed wherein external stimuli are electrically detected and simultaneous visualization of stimuli-adaptive SCs occurs. A perspective on the development of next-generation stimuli-adaptive BCP SC displays and HISDs is also provided. [ABSTRACT FROM AUTHOR] more...

For changing environmental circumstances, interactive structural color (SC) observation is a promising strategy to store and express external information. SCs based on self-assembled block copolymer (BCP) photonic crystals have been a research focus due to their facile and diverse nanostructures relying on the volume ratio of blocks. Their unique nano-architectonics can reflect incident light due to constructive interference of the two different dielectric constituents. Their excellent ability to change nano-architectonics in response to external stimuli (i.e. humidity, temperature, pH, and mechanical force) allows for a programmable and stimuli-interactive BCP SC display. In this review, recent advances in programmable and stimuli-interactive SC displays with the 1-dimensional self-assembled BCP nano-architectonics are comprehensively discussed. First, this review focuses on the development of programmable BCP SCs that can store various information. Second, stimuli-interactive BCP SCs capable of responding reversibly to external stimuli are also addressed. Particularly, reversible BCP SC changes are suitable for rewritable displays and emerging human-interactive BCP SC displays that detect various human information through changes in electric signals with the simultaneous alteration of the BCP SCs. Based on previously reported literature, the current challenges in this research field are further discussed, and the perspective for future development is presented in terms of material, nano-architectonics, and process. [ABSTRACT FROM AUTHOR] more...

[Display omitted] Dual-mode optical encryption based on holographic metasurfaces and color components is of great attraction because of their enhanced information security and storage; however, the realization of independently as well as reversibly encodable holographic metasurfaces and color components remains unreported. Herein, we present reconfigurable dual-mode encryptions of structural colors (SC) and holograms, achieved through stimuli-responsive block copolymer (BCP) photonic crystals (PCs) with micro-imprinted holographic metasurfaces. Holographic images appear when the micro-imprinted BCP PCs, consisting of self-assembled alternating lamellae of two dielectrics, are exposed to an incident laser. A characteristic SC develops in the visible range when the imprinted film is immersed in a liquid agent that can swell one of the dielectrics, allowing for dual-mode holographic and SC encodings in the solid and liquid states, respectively. The dual-mode optical encoding is reconfigured. The holographic image can be erased and replaced with another micropattern, while preserving the SC. Moreover, an SC, set by crosslinking of the swellable lamellae, is reset by chemical de-crosslinking and subsequent transient re-crosslinking, enabling the SC reconfigurability of the BCP PC film. A prototype of a high-security reconfigurable dual encryption has been developed, wherein true information is decrypted when holographic passwords are confirmed with full-color visible SC passwords. [ABSTRACT FROM AUTHOR] more...

Soft‐solid photonic crystals (PCs) based on periodically ordered block copolymer (BCP) nanostructures demonstrate stimuli‐adaptive structural colors (SCs) and desirable mechanical properties suitable for reflective‐mode electric‐switching (E‐switching) displays. However, the low electrochemical stability and humidity‐dependent E‐switching performance of hygroscopic ionic salts, often employed for E‐field‐adaptive structural alteration, limit their applications. In this study, a low‐powered capacitive E‐switching BCP SC display with an organohydrogel (OH) humidity controller is proposed, where a bilayer of a BCP and a polymer blend with hygroscopic E‐field‐adaptive ionic salts is sandwiched between Au electrodes. The display reliably exhibits reversible full‐color E‐switching (100 on/off cycles) at operating voltages of +2.5 to −2 V within the ionic salts' electrochemical window at ≈50% humidity. A patchable and reusable OH serves as a water reservoir (with optimized geometries and dimensions) to improve the display's humidity tolerance, providing a target humidity (≈50%). The proposed display performs at ambient humidity lower than 60% for over 10 days because of the long water retention and mechanical integrity properties of OH. Additionally, the topologically micropatterned BCP PC allows lateral diffusion of ionic salts through the sides of the patterned domain under E‐field, facilitating E‐switching speeds of ≈30 s. [ABSTRACT FROM AUTHOR] more...

Structural color (SC) arising from a periodically ordered self‐assembled block copolymer (BCP) photonic crystal (PC) is useful for reflective‐mode sensing displays owing to its capability of stimuli‐responsive structure alteration. However, a set of PC inks, each providing a precisely addressable SC in the full visible range, has rarely been demonstrated. Here, a strategy for developing BCP PC inks with tunable structures is presented. This involves solution‐blending of two lamellar‐forming BCPs with different molecular weights. By controlling the mixing ratio of the two BCPs, a thin 1D BCP PC film is developed with alternating in‐plane lamellae whose periodicity varies linearly from ≈46 to ≈91 nm. Subsequent preferential swelling of one‐type lamellae with either solvent or non‐volatile ionic liquid causes the photonic band gap of the films to red‐shift, giving rise to full‐visible‐range SC correlated with the pristine nanostructures of the blended films in both liquid and solid states. The BCP PC palette of solution‐blended binary solutions is conveniently employed in various coating processes, allowing facile development of BCP SC on the targeted surface. Furthermore, full‐color SC paintings are realized with their transparent PC inks, facilitating low‐power pattern encryption. [ABSTRACT FROM AUTHOR] more...

Keywords: multilevel information storage; nonvolatile photothermal writing; self-assembled block copolymers; structural colors; thermally induced crosslinking In article number 1904055, Youngjong Kang, Cheolmin Park, and co-workers demonstrate multilevel nonvolatile memory bits by utilizing photothermal control of the structural color of a block copolymer photonic crystal deposited on the photothermal-conversion layer. Multilevel information storage, nonvolatile photothermal writing, self-assembled block copolymers, structural colors, thermally induced crosslinking. [Extracted from the article] more...

In spite of efforts to fabricate stimuli‐sensitive structural colors (SCs) of self‐assembled block copolymer (BCP) photonic crystals (PCs) with potential applications in displays, media boards, and sensors, few studies have demonstrated BCP PCs suitable for high‐density nonvolatile information storage. Herein, a simple but robust route for multilevel nonvolatile information recording using a BCP PC is presented. The proposed method is based on the spatially controlled crosslinking of microdomains of a BCP PC induced by photothermal conversion. Photothermal SC writing is accomplished via time‐ and position‐controlled laser exposure on thin poly(styrene‐block‐quaternized 2‐vinyl pyridine) (PS‐b‐QP2VP) PC films deposited on a layer of poly(3,4‐ethylenedioxythiophene) doped with tosylate (PP‐PEDOT). Upon near‐infrared (NIR) irradiation of this structure, the PP‐PEDOT underlayer converts the NIR light into thermal energy in the locally irradiated region, which is subsequently transferred to the BCP top layer consisting of alternating in‐plane PS and QP2VP lamellar stacks. The QP2VP layers are vulnerable to thermal crosslinking, giving rise to locally programmable SCs. The degree of crosslinking of the QP2VP domains depends on the laser power and exposure time, which allows for multi‐SC recording per spot, leading to a novel multilevel optical recording medium based on BCP PCs. [ABSTRACT FROM AUTHOR] more...