Abstract
Evaporation is a ubiquitous phenomenon in the natural environment and a dominant form of energy transfer in the Earth's climate. Engineered systems rarely, if ever, use evaporation as a source of energy, despite myriad examples of such adaptations in the biological world. Here, we report evaporation-driven engines that can power common tasks like locomotion and electricity generation. These engines start and run autonomously when placed at air–water interfaces. They generate rotary and piston-like linear motion using specially designed, biologically based artificial muscles responsive to moisture fluctuations. Using these engines, we demonstrate an electricity generator that rests on water while harvesting its evaporation to power a light source, and a miniature car (weighing 0.1 kg) that moves forward as the water in the car evaporates. Evaporation-driven engines may find applications in powering robotic systems, sensors, devices and machinery that function in the natural environment.
Highlights
Evaporation is a ubiquitous phenomenon in the natural environment and a dominant form of energy transfer in the Earth’s climate
Nanoscale confinement of water in hygroscopic materials provides a means to convert energy from evaporation by generating mechanical force in response to changing relative humidity[6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21]. Scaling up this phenomenon to create macroscopic devices faces multiple challenges: unfavourable scaling of hydration kinetics slows down actuation speeds at large dimensions; small strains complicate energy transfer to external systems; and, importantly, the slow rate of change of relative humidity in the environment limits the power output
Working with bacterial spores that exhibit strong hydration-driven actuation[20], we present strategies to circumvent these challenges described above to create macroscale evaporation-driven engines. These engines start and run autonomously when placed at air–water interfaces, and operate as long as the air is not saturated. We demonstrate that these engines are able to power an electricity generator to light up light-emitting diodes (LEDs) and drive a miniature car as the water evaporates
Summary
Evaporation is a ubiquitous phenomenon in the natural environment and a dominant form of energy transfer in the Earth’s climate. Nanoscale confinement of water in hygroscopic materials provides a means to convert energy from evaporation by generating mechanical force in response to changing relative humidity[6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21] Scaling up this phenomenon to create macroscopic devices faces multiple challenges: unfavourable scaling of hydration kinetics slows down actuation speeds at large dimensions; small strains complicate energy transfer to external systems; and, importantly, the slow rate of change of relative humidity in the environment limits the power output. We demonstrate that these engines are able to power an electricity generator to light up LEDs and drive a miniature car as the water evaporates
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