A flexible and stretchable photonic crystal film with sensitive structural color-changing properties for spoiled milk detection.

This study proposes a flexible and stretchable 3D polymer film with photonic crystals for the visible detection of spoiled milk. Thermoplastic polyurethane (TPU) was used as the substrate for the photonic crystal structure. The back barrier layer with a regular array of nanohemispheres of anodic aluminum oxide film was used as a template for electroforming a nickel mold. The nanohemisphere array was then nanoimprinted onto the TPU substrate to form a strain-controllable photonic crystal (SCPC) structure on it. Food spoilage can be easily detected by the structural color change caused by the gas it produces. Experimental results confirmed that the structural color change of the fabricated SCPC TPU film occurred when the elongation (ΔL) of the film reached 0.2 mm (1.2 %). Furthermore, spoiled milk detection experiments showed that the proposed SCPC TPU film is a highly intelligent and cost-effective biosensor for detecting spoiled food in a container.

Force-Induced Synergetic Pigmentary and Structural Color Change of Liquid Crystalline Elastomer with Nanoparticle-Enhanced Mechanosensitivity.

The ability of some animals to rapidly change their colors can greatly improve their chances of escaping predators or hunting prey. A classic example is cephalopods, which can rapidly shift through a wide range of colors. This ability is based on the synergetic effect of the change of pigmentary and structural colors exhibited by their own two categories of color-changing cells: supernatant chromatophores offer various pigmentary colors and lower iridophores or leucophores reflect the different structural colors by adjusting their periodicities. Here, a mechanochromic liquid crystalline elastomer with force-induced synergetic pigmentary and structural color change, whose mechanosensitivity is enhanced by the stress-concentration induced by the doped nanoparticle, is presented. The materials have a large color-changing gamut and high mechanochromic sensitivity, which exhibit great potential in the field of mechanical detectors, sensors, and anti-counterfeiting materials.

Temperature-Responsive, Multicolor-Changing Photonic Polymers.

A new principle is developed to fabricate temperature-responsive, multicolor photonic coatings that are capable of switching color. The coating is composed of a non-cross-linked liquid crystal siloxane-based elastomer that is interpenetrated through an acrylate-based liquid crystal network. Discrete temperature changes induce phase separation and mixing between the siloxane and the acrylate polymers and change the reflective colors correspondingly. The temperature-responsive color change of the coatings can be programmed by the processing conditions and coating formulation, which allows for the fabrication of photopatterned multicolor images. The photonic ink can be coated on flexible poly(ethylene terephthalate) films using roll-to-roll flexographic printing, making these temperature-responsive, multicolor-changing polymers appealing for applications such as responsive color decors, optical sensors, and anticounterfeit labels.