Evaporation powers a motor

Scientists at Columbia University have effectively harvested energy from evaporation in the environment to drive engines that start and run autonomously when placed near a water surface. Arrays of artificial “muscles” composed of bacterial spores on a polymer strip enhanced the water evaporation rates when scaled-up.

By harvesting the energy from water evaporation in the environment researchers demonstrated self-sustained power generation from engines placed at air-water interfaces. These evaporation-driven engines could power robotic systems, sensor, devices, and machinery.

Researchers, funded by the US Department of Energy, optimized the thickness of the spore layer for rapid water transport into and out of the nanopores. The energy of evaporation was harnessed to power the muscle. A small portion of the power operated a feedback mechanism to address the slow and variable rate of change in environmental humidity, enabling rapid cycling between spore swelling to stretch the muscle and shrinking to contract the muscle.

Upon stretching at a desired humidity, the self-regulating feedback mechanism allows the humidity to decrease. Precise control of this process enabled self-sustained power generation from piston-driven and rotary engines when placed at air-water interfaces—powering a light source and moving a miniature car forward. These results could enable evaporation-driven engines to power robotic systems and sensors.