The development of electrically responsive sensors based on the capacitance, voltage, and resistance that can detect and simultaneou sly visualize the large strain involved with human motion is in great demand. Here, we demonstrate a highly stretchable, large strain capacitive sensor that can visualize strain based on the strain-responsive structural color (SC). Our device contains an elastomeric sensing film that produces a capacitance change under strain, in which a selfassembled block copolymer (BCP) photonic crystal (PC) film with 1D periodic in-plane lamellae aligned parallel to the film surface is embedded for the efficient visualization of strain. The capacitance change arises from changes in the dimensions of the elastomer film under strain. The mechanochromic BCP PC film responds to strain, giving rise to an SC change with strain. The initial red SC of the sensor blueshifts and turns blue when the sensor is stretched to 100%, resulting in a full-color SC alteration as a function of the strain. Our BCP SC strain sensor exhibits a fast strain response with multi-cycle reliability of both the capacitance and SC changes over 1000 cycles. This property allows for efficient visible recognition not only of the strained positions during finger bending and poking with a sharp object but also of the shapes of the strained objects.

The development of a lightweight, low-power, user-interactive three-dimensional (3D) touchless display in which a human stimulus can be detected and simultaneously visualized in noncontact mode is of great interest. Here, we present a user-interactive 3D touchless sensing display based on multiorder reflection structural colors (SCs) of a thin, solid-state block copolymer (BCP) photonic crystal (PC). Full-visible-range SCs are developed in a BCP PC consisting of alternating lamellae, one of which contains a chemically cross-linked, interpenetrated hydrogel network. The absorption of a nonvolatile ionic liquid into the domains of the interpenetrated network allows for further manipulation of SC by using multiple-order photonic reflections, giving rise to unprecedented visible SCs arising from reflective color mixing. Furthermore, by using a hygroscopic ionic liquid ink, a printable 3D touchless interactive display is created where 3D position of a human finger is efficiently visualized in different SCs as a function of finger-to-display distance.

Flexible electronics that enable the visualization of thermal energy have significant potential for various applications, such as thermal diagnosis, sensing and imaging, and displays. Thermo‐adaptive flexible electronic devices based on thin 1D block copolymer (BCP) photonic crystal (PC) films with self‐assembled periodic nanostructures are presented. By employing a thermo‐responsive polymer/non‐volatile hygroscopic ionic liquid (IL) blend on a BCP film, full visible structural colors (SCs) are developed because of the temperature‐dependent expansion and contraction of one BCP domain via IL injection and release, respectively, as a function of temperature. Reversible SC control of the bi‐layered BCP/IL polymer blend film from room temperature to 80 °C facilitates the development of various thermo‐adaptive SC flexible electronic devices including pixel arrays of reflective‐mode displays and capacitive sensing display. A flexible diagnostic thermal patch is demonstrated with the bi‐layered BCP/IL polymer blend enabling the visualization of local heat sources from the human body to microelectronic circuits.

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-blockquaternized 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.

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 solutionblending 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.