A team of researchers from Singapore National University (NUS) has produced a novel film that is very effective in evaporating sweat from our skin to keep us cool and relaxed while exercising. To power wearable electronic devices such as watches, fitness trackers and more, the humidity extracted from human sweat can be used.
In order to relieve thermal tension, sweating is a normal mechanism for our bodies. “Sweat consists mostly of water.
It reduces the skin temperature as water evaporates from the surface of the skin and we feel cooler.
In our new innovation, we have created a new form of film that is extremely effective at evaporating sweat from our skin and then removing the moisture from the sweat.
The research team leader, Assistant Professor Tan Swee Ching, from the NUS Department of Material Science and Engineering, clarified that we are also going a step further by transforming the moisture from sweat into energy that can be used to power small wearable devices.
Two hygroscopic chemicals are the key components of the novel thin film – cobalt chloride and ethanolamine.
Not only is this film highly moisture-absorbent, but it can also release water easily when exposed to sunlight and can be “regenerated” and reused more than 100 times.
The NUS team also developed a portable energy harvesting system consisting of eight electrochemical cells (ECs) using the novel film as an electrolyte in order to completely exploit the absorbed sweat.
When absorbing moisture, every EC can produce about 0.57 volts of electricity.
To power a light-emitting diode, the total energy harvested by the system is sufficient.
This proof-of-concept demonstration shows the promise of human sweat-powered battery-free wearables.
In the September issue of Nano Energy, this technological advancement was published.
For personal comfort, consuming moisture
Traditional hygroscopic materials have poor water absorption and a rigid structure, such as zeolites and silica gels, rendering them unsuitable for absorbing moisture from the evaporation of sweat.
In contrast, the latest moisture-absorbing film produced by NUS researchers absorbs 15 times more moisture than traditional films and does so 6 times faster.
Moreover, as it consumes moisture, this groundbreaking film experiences a color shift from blue to purple and eventually pink.
This trait can be used as a measure of the degree of absorption of moisture.
The film was packaged by the NUS team in breathable and waterproof polytetrafluoroethylene (PTFE) membranes that are versatile and widely used in clothing, and the application of the moisture-absorbing film was successfully demonstrated for underarm pads, shoe linings, and shoe soles.
Asst.-Asst. Underarm sweating is embarrassing and irritating, said Prof. Tan, and this condition contributes to bacterial growth and leads to undesirable body odor.
Sweat accumulation in shoes can contribute to health problems such as blisters, calluses, and fungal infections. With the underarm pad, shoe lining, and shoe insert embedded in the film that absorbs moisture, sweat evaporation moisture is rapidly absorbed, preventing sweat accumulation, and providing personal comfort with a dry and cool microclimate.
The shoe insole prototype was developed using 3D printing.
The material used is a blend of soft and hard polymer, which provides adequate support and shock absorption, explains Professor Ding Jun, co-lead of the research team, also from the Department of Materials Science and Engineering of the NUS.
The NUS team is now planning to partner with businesses to integrate the new moisture-absorbing film into consumer goods.
By Xueping Zhang, Jiachen Yang, Ramadan Borayek, Hao Qu, Dilip Krishna Nandakumar, Qian Zhang, Jun Ding and Swee Ching Tan, 11 May 2020, Nano Energy.DOI: 10.1016/j.nanoen.2020.104873 Reference: ‘Super-hygroscopic film for wearables with dual functions of expediting sweat evaporation and energy harvesting’