A cellphone you never need to plug in. A watch, a television remote, or a key fob that runs forever without any battery to change. A self-contained pacemaker that need not be surgically removed every seven to ten years for replacement.
None of these 'green' products or technologies yet exists, but they might one day come to pass if new Stevens research into sustainable energy sources at very small scales proves fruitful.
Chang-Hwan Choi, a mechanical engineering professor at Stevens, was recently awarded a three-year grant and $200,000 in support by the National Science Foundation to explore a so-called nanofluidic energy harvesting system. Dubbed a "hydropower plant on a chip," the technology harvests energy from nanoscale water flows to create a self-sustaining energy supply.
“There is tremendous interest now in developing alternative energy sources such as wind and solar energy," explains Choi. “Our idea was to investigate the concept of using hydropower, at very small scales, to generate significant quantities of energy using another naturally abundant resource: water."
Leveraging the lotus effect
Choi's proposed system works like this: a tiny amount of water is circulated through extremely narrow channels just one to 100 nanometers wide each. (By comparison, a single human hair is approximately 80,000 to 100,000 nanometers wide.) The channels are not perfectly smooth; instead, they have been specially engineered with nanoscale roughness so that their surfaces can attract and hold tiny bubbles of air present in the water.
Some of the water flows around the bubbles without ever touching the solid channels, creating a super-slippery effect.
"The water on this superhydrophobic surface is moving on a thin layer of air, much like a puck glides on an air-hockey table," explains Choi. "Many natural surfaces, such as the leaves of plants, exhibit a similar water-repelling characteristic known as the 'lotus effect'. "
As the water streams over the frictionless surface, millions of ions formed in the nanoscale channel can be captured, transformed into electricity and temporarily stored — with almost no energy loss, compared with the 90-plus percent loss that occurs in conventional hydropower systems.
If his research proves fruitful, says Choi, the next step will be to develop larger, super-thin membranes incorporating arrays of the textured channels. Those membranes would theoretically be able to capture and store enough energy to power smaller electronic devices.