Paintable Encapsulated Body-Temperature-Responsive Photonic Reflectors with Arbitrary Shapes

A temperature-responsive photonic coating on a flexible substrate was prepared by a photoinduced phase-separation process. In this coating a low molecular weight cholesteric liquid crystal (Ch-LC) mixture was encapsulated between the substrate and an in situ formed protective polymer top layer. The photonic coating showed a blue-shift of the photonic reflection band of 100 nm by heating from 22 to 23 °C due to the close proximity to the smectic to cholesteric phase transition and an overall 330 nm blue-shift while heating from 22 to 45 °C. Hence, the red coating turned green upon contact with skin within seconds. Furthermore, the coating structure and composition were investigated in detail, revealing a thick top coat. The adhesion of the coating was improved by providing trays on the substrate (by etching or 3D printing), resulting in a link between arbitrary-shaped substrates and the protective polymer top layer. These bendable coatings could be of interest for sensors, anticounterfeit labels, or customizable aesthetic applications.</p

Paintable Encapsulated Body-Temperature-Responsive Photonic Reflectors with Arbitrary Shapes

A temperature-responsive photonic coating on a flexible substrate was prepared by a photoinduced phase-separation process. In this coating a low molecular weight cholesteric liquid crystal (Ch-LC) mixture was encapsulated between the substrate and an in situ formed protective polymer top layer. The photonic coating showed a blue-shift of the photonic reflection band of 100 nm by heating from 22 to 23 °C due to the close proximity to the smectic to cholesteric phase transition and an overall 330 nm blue-shift while heating from 22 to 45 °C. Hence, the red coating turned green upon contact with skin within seconds. Furthermore, the coating structure and composition were investigated in detail, revealing a thick top coat. The adhesion of the coating was improved by providing trays on the substrate (by etching or 3D printing), resulting in a link between arbitrary-shaped substrates and the protective polymer top layer. These bendable coatings could be of interest for sensors, anticounterfeit labels, or customizable aesthetic applications

Ink-Deposited Transparent Electrochromic Structural Colored Foils

Despite progress in the field of electrochromic devices, developing structural color-tunable photonic systems having both high transparency and flexibility remains challenging. Here, an ink-deposited transparent electrochromic structural colored foil displaying reflective colors, tuned by an integrated heater, is prepared in a single-substrate method. Efficient and homogeneous heating is induced by a gravure printed silver nanowire-based substrate, delivering an electrothermal response upon applying an electrical potential. On top of this flexible, transparent heater, a cholesteric liquid crystal ink is bar-coated and subsequently photopolymerized, yielding a structural colored film that exhibits temperature-responsive color changes. The transparent electrochromic foils appear colorless at room temperature but demonstrate structural color tuning with high optical quality when modifying the electrical potential. Both optical and electrothermal performances were preserved when deforming the foils. Applying the conductive and structural colored inks via the easy processable, continuous methods of gravure printing and bar-coating highlights the potential for scaling up to large-scale stimuli-responsive, transparent optical foils. These transparent structural colored foils can be potentially used for a wide range of photonic devices including smart windows, displays, and sensors and can be directly installed on top of curved, flexible surfaces