Professor Hopkins and University of Virginia colleagues — in collaboration with materials scientists at Penn State, the University of Maryland, and the National Institute of Standards and Technology — have studied a material that can dynamically regulate its thermal properties, switching back and forth between insulating and cooling based on the amount of water that is present.

Dr. Patrick Hopkins

Tech Briefs: What got you interested in this project?

Dr. Patrick Hopkins: For several years, my research has been focused on methods to control thermal conductivity. We have been trying to find ways to regulate heat transfer and temperature by doing things like flipping a switch. I met Melik Demirel at Penn State, who was creating a squid ring-teeth-derived protein. When you hydrate that material, it undergoes a fascinating transition that changes all of its mechanical properties — the underlying reason behind its self-healing. I thought it would likely also change its thermal properties.

Tech Briefs: Is the thermal conductivity switched on and off, or can you control the amplitude?

Dr. Hopkins: Both — you can actually program the thermal conductivity based on the genetic sequence in the protein. With different sequences, you can end up with different thermal conductivities. So, when you hydrate it, the on/off ratio is different. You have the same protein, but by scrambling the sequences in different ways, you can actually program the thermal conductivity.

Tech Briefs: Could you actually make a garment from the material?

Dr. Hopkins: You can make this material into basically any geometry you want — textiles, strands, films — and with really small features. You could even integrate it into existing garments such as activewear, a jacket, or even a sock. One could envision that it could be a filler or a fraction of some type of garment. It would give a fabric the smart property to respond to hydration; for example, from human sweat.

Tech Briefs: Are there applications other than clothing?

Dr. Hopkins: It could be used for recovering waste heat. Think about a car exhaust, an airplane engine, even a computer — these things get very hot. This heat is usually just wasted and expelled into the atmosphere. Typical heat sources are DC or steady-state; for example, when a car is running, once it gets up to a couple of hundred degrees, its exhaust pipe is basically going to stay at that temperature throughout the trip.

However, you can have an order of magnitude more efficient thermal-to-electrical energy conversion if your heat source is alternating — if it’s an AC heat source. If you have a way to modulate the thermal conductivity of a material, then you can take a DC heat source and by putting a material in contact with it and changing its thermal conductivity, you could create an AC temperature change on the other side. This modulation of thermal conductivity is a way to produce DC-to-AC temperature conversion.

Tech Briefs: Using nature as inspiration seems to be a trend.

Dr. Hopkins: Yes, I think there is a lot of merit to this. Nature has been evolving and perfecting the material properties of everything around us — adapting to survive and optimize. So, let's harness some of that. We're seeing it in a lot of fields in materials, hydrodynamics, and aerodynamics. Bio-inspired engineering is, regardless of the discipline, a fascinating and very fruitful path forward.

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