A dynamic thermoregulatory material inspired by squid skin

Erica M. Leung, Melvin Colorado Escobar, George T. Stiubianu, Steven R. Jim, Alexandra L. Vyatskikh, Zhijing Feng, Nicholas Garner, Priyam Patel, Kyle L. Naughton, Maurizio Follador, Emil Karshalev, Matthew D. Trexler & Alon A. Gorodetsky
Nature Communicationsvolume 10, Article number: 1947 (2019) | Download Citation

Abstract
Effective thermal management is critical for the operation of many modern technologies, such as electronic circuits, smart clothing, and building environment control systems. By leveraging the static infrared-reflecting design of the space blanket and drawing inspiration from the dynamic color-changing ability of squid skin, we have developed a composite material with tunable thermoregulatory properties. Our material demonstrates an on/off switching ratio of ~25 for the transmittance, regulates a heat flux of ~36?W/m2 with an estimated mechanical power input of ~3?W/m2, and features a dynamic environmental setpoint temperature window of ~8?°C. Moreover, the composite can manage one fourth of the metabolic heat flux expected for a sedentary individual and can also modulate localized changes in a wearer’s body temperature by nearly 10-fold. Due to such functionality and associated figures of merit, our material may substantially reduce building energy consumption upon widespread deployment and adoption.

Introduction
Effective management of heat transfer enables the operation of many ubiquitous modern technologies, including electronic circuits1, aircraft and spacecraft components2, clinical warming devices3, power generation platforms4, shipping and packaging containers5, specialty textiles and garments6, and building environment control systems7. Within this context, building operation accounts for ~40% of global energy consumption (with heating and cooling alone requiring ~36% of this amount)7,8, and as such, the development of novel personal (localized or wearable) thermoregulatory platforms represents an exciting opportunity and can dramatically diminish energy use worldwide9. To date, the great variety and abundance of indoor thermal management systems have been classified as either “passive” or “active,” depending on the underlying mode of operation10,11,12,13. Specifically, representative passive heating technologies, such as insulation, textiles, and reflective coatings, employ materials with low thermal conductivities and/or high infrared reflectances, and thus regulate temperature by blocking heat transfer (Supplementary Table 1). These systems are low cost, energy efficient, and simple to implement but are also static and unresponsive to changing conditions10,11,12,13. In contrast, representative active heating technologies, such as electrothermal devices and heating/ventilation/air conditioning platforms, regulate temperature by driving the flow of heat through the external input of electrical and/or mechanical energy (Supplementary Table 1). These systems are dynamic and readily allow for user control but are also relatively expensive, energy inefficient, and complex to install10,11,12,13. Consequently, it is highly desirable to develop an “ideal” thermal management platform that merges the advantages of passive systems (i.e., low cost, straightforward implementation, and energy efficiency) with the on-demand dynamic control capabilities of active systems.

Among passive thermal management systems, the “space blanket,” which was introduced by NASA in the 1960s to mitigate temperature fluctuations in space, represents arguably one of the most famous and impactful wearable technologies reported to date (Fig. 1a)14. In its standard configuration, the space blanket consists of a plastic sheet (e.g., polyethylene terephthalate) overlaid with a thin continuous layer of metal (e.g., aluminum) (Fig. 1a, inset and Fig. 1b, left)—an architecture that is highly effective at reflecting infrared radiation (e.g., heat)14. Various incarnations of the space blanket have found applications in packaging, emergency portable shelters, clinical warming devices, and protective or performance apparel3,5,6,14,15,16,17. However, the space blanket’s application scope has been limited by its static thermal properties, which cannot be reconfigured on demand or adjusted in any way (Fig. 1b). Indeed, as a technology, the space blanket has remained fundamentally unchanged over the past 50 years14.

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