Eco-friendly plastic crystals may make solid-state refrigeration possible

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food in refrigeratorEco-friendly plastic crystals may make solid-state refrigeration possible
Scientists from the United Kingdom and Spain have developed a way to replace the organic gases—hydrofluorocarbons (HFCs) and hydrocarbons (HCs)—used in most conventional refrigerators. These gases are toxic and flammable, and when they leak into the air, they also contribute to global warming.

“Refrigerators and air conditioners based on HFCs and HCs are also relatively inefficient,” said lead researcher Xavier Moya, Royal Society research fellow in the University of Cambridge’s Department of Materials Science and Metallurgy. “That’s important because refrigeration and air conditioning currently devour a fifth of the energy produced worldwide, and demand for cooling is only going up.”

To solve these problems, materials scientists around the world have sought alternative solid refrigerants. When put under pressure, plastic crystals of neopentylglycol (NPG) yield huge cooling effects—enough that they are competitive with conventional coolants. In addition, the material is inexpensive, widely available, and functions at close to room temperature. Details are published in the journal Nature Communications.

In the study, Moya and collaborators from the Universitat Politècnica de Catalunya and the Universitat de Barcelona describe the enormous thermal changes under pressure achieved with plastic crystals. Conventional cooling technologies rely on the thermal changes that occur when a compressed fluid expands. Most cooling devices work by compressing and expanding fluids such as HFCs and HCs. As the fluid expands, it decreases in temperature, cooling its surroundings.

With solids, cooling is achieved by changing the material’s microscopic structure. This change can be achieved by applying a magnetic field, an electric field, or through mechanic force. NPG’s molecules, composed of carbon, hydrogen, and oxygen, are nearly spherical and interact with each other only weakly. These loose bonds in its microscopic structure permit the molecules to rotate relatively freely.

The word “plastic” in “plastic crystals” refers not to its chemical composition but rather to its malleability. Plastic crystals lie at the boundary between solids and liquids.

In the future, solid-state refrigeration could lead to more compact and flexible devices compared to traditional ones. Moya is now working with Cambridge Enterprise, the commercialization arm of the University of Cambridge, to bring this technology to market.


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