Butterfly-Inspired Films Passively Cool Structures

MONDAY, AUGUST 7, 2023


According to reports, researchers have developed new films that don’t absorb light to potentially reduce the energy needed for cooling in buildings or vehicles, while still maintaining vivid colors. The films were reportedly inspired by the nanostructures in butterfly wings.

The research, which was recently published in the journal Optica, has found that the films lower the temperature of colorful objects to about 2 degrees Celsius below ambient temperatures.

About the Films

The study explains that a car with blue paint appears blue because it absorbs yellow light and reflects blue light, absorbing heat into the car. However, Morpho butterflies produce their blue color based on the nanostructure of their wings.

The scientists say that the design of the cooling nanofilm mimics these structures to produce vibrant colors that don’t absorb light like traditional paint.

The nanofilms are reportedly created by placing a disordered material, or rough frosted glass, under a multilayer material made of titanium dioxide and aluminum dioxide. They then placed the structure on a silver layer that reflects all light, consequently preventing the absorption of solar radiation and the heating associated with that absorption.

“In buildings, large amounts of energy are used for cooling and ventilation, and running the air conditioner in electric cars can reduce the driving range by more than half,” said research team leader Guo Ping Wang from Shenzhen University in China. “Our cooling films could help advance energy sustainability and carbon neutrality.”

Additionally, the film’s color is determined by how components within its multilayered structure reflect light. For example, to create blue, the multilayer material is designed to reflect yellow light in a very narrow range of angles while the disordered structure diffuses the blue light across a broad area.

Prior to this research, this type of passive photonic thermal management has reportedly only been used with wide or clear objects since it is hard to maintain a wide viewing angle and high color saturation.

“With our new films, excellent cooling performance can be achieved, no matter the desired color, saturation or brightness,” said Wang. “They could even be used on textiles to create clothes of any color that are comfortable in hot temperatures.”

For the testing, the research team reportedly created blue, yellow and colorless films. These were placed outdoors at Shenzhen University on surfaces such as roofs, cars, cloth and cell phones throughout the day in both winter and summer weather.

Then, thermocouple sensors and infrared cameras were used to measure the temperature. The scientists reportedly found that the cooling films were about 15 C cooler than surfaces they were placed on in the winter and about 35 C cooler in the summer.

“Thanks to the layered structure we developed, we were able to extend the passive cooling method from colorless objects to colorful ones while preserving color performance,” said Wang. “In other words, our blue film looks blue across a large range of viewing angles and doesn’t heat up because it reflects all the light. In addition, high saturation and brightness can be achieved by optimizing the structure.”

The researchers note that replacing the silver film with an aluminum film would make the films less expensive and manufacturable by a scalable fabrication method. In the future, team plans to study and optimize other properties such as mechanical and chemical robustness.

Other Butterfly-Inspired Paint

Earlier this year, in March, a researcher from the University of Central Florida also reportedly drew inspiration from butterflies to create what he says is the first environmentally friendly, multicolor alternative to pigment-based colorants.

The work from Debashis Chanda, a professor in UCF’s NanoScience Technology Center, could potentially help with energy-saving efforts and reduce global warming.

According to the university, Chanda’s research team developed a bio-inspired plasmonic paint, which utilizes nanoscale structural arrangement of colorless materials such as aluminum and aluminum oxide instead of pigments to create colors.

Pigment colorants can control light absorption based on the electronic property of the pigment material, requiring every color to need a new molecule. However, structural colorants control the way light is reflected, scattered or absorbed based purely on the geometrical arrangement of nanostructures.

The researchers reportedly combined their structural color flakes with a commercial binder to form a long-lasting paint in various colors.

The paint is also the “lightest paint in the world,” Chanda says, due to the paint’s large area-to-thickness ratio. Full coloration is reportedly achieved at a paint thickness of only 150 nanometers.

Additionally, the researcher reports that the paint is so lightweight that only about 3 pounds of plasmonic paint could cover a Boeing 747, which normally requires more than 1,000 pounds of conventional paint.

In terms of sustainability, the structural colors use metals and oxides, whereas current pigment-based colors use artificially synthesized molecules. The plasmonic paint also reportedly reflects the entire infrared spectrum, meaning less heat is absorbed by the paint.

The university reports that the surface underneath the paint has stayed 25 to 30 degrees Fahrenheit cooler than it would if it were covered with standard commercial paint.

   

Tagged categories: Asia Pacific; Coating Materials; Coating Materials - Commercial; Coatings Technology; Coatings Technology; Coatings technology; Color; Color + Design; Cool Coatings; EMEA (Europe, Middle East and Africa); Green coatings; Latin America; Nanotechnology; North America; Research; Research and development; Sustainability; Z-Continents

Join the Conversation:

Sign in to our community to add your comments.