Block copolymer structural color strain sensor

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 self-assembled 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. A strain sensor that changes color when stretched has been developed by a team in Korea. Flexible sensors that measure pressure or strain could find application as wearable health monitors. One route to achieve such sensors is to use dielectric films whose capacitance changes in response to mechanical stimulus. However, an easy way is needed for wearers to read the output. Cheolmin Park from Yonsei University and colleagues constructed a polymer-based material with a periodic structure that reflects light of different colors depending on the degree to which it is extended. Specifically, they created a block copolymer soft-solid film with one-dimensional periodic layers. The capacitance changes under strain as a result of the dimensional change of the elastomer film, causing the initially red sensor to turn blue when fully stretched. A novel block copolymer structural color strain sensor was developed, capable of electrically sensing a strain in capacitance change with simultaneous visualization of the strain. A thin mechanochromic bilayer of a block copolymer structural film with 1-D periodic lamellae placed on an ionic gel layer allowed for direct visualization of strain while sensing in capacitance when embedded in an elastomeric dielectric medium. Our block copolymer structural strain sensor was suitable for a reflective mode electronic skin which readily recognized human motion of the finger, elbow, and knee.