
A new material has been developed that can block microwaves, infrared (IR) heat, and light, and can also become transparent by being stretched or contracted. The inspiration for this material comes from the properties of squid skin, which can shift from translucent to opaque due to the presence of iridocytes and chromatophores. This material has many potential applications, such as safeguarding electronic devices, improving energy efficiency in commercial buildings, protecting against microwave weapons, and yes, creating invisibility cloaks for young wizards.
Using current technologies, specific wavelengths can be blocked or transmitted in order to switch materials from being dark to light or cold to hot. But now, researchers in ACS Nano have developed a soft film inspired by squid skin that can regulate its transparency across a wide range of wavelengths simultaneously, including visible, infrared, and microwave. They demonstrated its use in smart windows and in health monitoring and temperature management applications.
Squid and other cephalopods have unique skin features called iridocytes and chromatophores which can alter the animals’ appearance by changing their orientation. Iridocytes are specialized cells found in the skin of some animals, such as cephalopods (e.g. squid, octopuses), fish, and reptiles. These cells contain reflective platelets or crystals that can change the color and reflectivity of the skin. In some species, iridocytes can produce iridescent colors that seem to shimmer and change when viewed from different angles.
Chromatophores, on the other hand, are pigment-containing cells found in the skin of many animals, including fish, reptiles, amphibians, and cephalopods. Unlike iridocytes, chromatophores contain pigments that allow animals to rapidly change the color and pattern of their skin. This is achieved through the expansion and contraction of the cells, which can reveal or hide the pigments. Chromatophores can produce a wide variety of colors, from reds and yellows to blues and greens, and can also create patterns such as stripes or spots.
Scientists have developed artificial materials that mimic the behavior of iridocytes and chromatophores by transitioning from reflecting to transmitting visible and infrared wavelengths by shifting from stretched to contracted. Microwaves are much larger than these surface structures and are not impacted. However, recently, researchers discovered that dense networks of electrically conductive materials, such as silver nanowires, can block microwaves. Therefore, Yi Yang, Guangbin Ji, Zhichuan J. Xu, and colleagues aimed to integrate surface structures with a conductive network in a soft film that could quickly transition between shielding visible-to-microwave bands and allowing them through.
The researchers developed a two-layer film by spraying a thin coating of silver nanowires onto a stretched elastomer. This process produced cracks and bumpy wrinkles in the metal surface when the material was stretched and contracted, respectively. When the material was contracted to a -30% strain, it blocked light, trapped infrared heat, and shielded up to 99.9% of microwaves that could interfere with devices. Even more surprising, the material’s transparency and heat and microwave transmission increased as it stretched apart.
The material can be applied in various ways, such as blocking or transmitting wireless electrocardiography signals, trapping or allowing body heat to escape, and tracking movements through temperature changes that can be detected by infrared cameras. The researchers believe that their system’s ability to rapidly and repeatedly change transparency could benefit dynamic camouflage technologies, energy-efficient buildings, and adaptive personal and healthcare devices.