Novel film absorbs sweat to power wearable devices

A film that effectively evaporates sweat from skin while using the moisture to power wearable electronics has been developed by researchers from the National University of Singapore (NUS).

 The main components of the thin film are two hygroscopic chemicals – cobalt chloride and ethanolamine.

Besides being extremely moisture-absorbent, the film can rapidly release water when exposed to sunlight, and it can be ‘regenerated’ and reused more than 100 times.

The researchers designed a wearable energy-harvesting device comprising eight electrochemical cells (EC), using the novel film as the electrolyte.

Each EC can generate about 0.57V of electricity upon absorbing moisture and the overall energy harvested by the device is sufficient to power a light-emitting diode. The researchers believe their proof-of-concept demonstration could enable battery-less wearables powered using human sweat.

Conventional hygroscopic materials such as zeolites and silica gels have low water uptake and bulk solid structures, making them unsuitable for absorbing moisture from sweat evaporation. In comparison, the new film can absorb 15 times more moisture at a rate six times faster than conventional materials.

It shows a colour change upon absorbing moisture, from blue to purple, and finally pink which can be used as an indicator of the degree of moisture absorption.

The NUS team packaged the film into breathable and waterproof polytetrafluoroethylene (PTFE) membranes, which are flexible and commonly used in clothing, and successfully demonstrated the application of the moisture-absorption film for an underarm pad, shoe lining and shoe insole.

Assistant professor Tan Swee Ching said: “Underarm sweating is embarrassing and frustrating, and this condition contributes to the growth of bacteria and leads to unpleasant body odour.

“Accumulation of perspiration in the shoes could give rise to health problems such as blisters, calluses, and fungal infections. Using the underarm pad, shoe lining and shoe insole embedded with the moisture-absorbing film, the moisture from sweat evaporation is rapidly taken in, preventing an accumulation of sweat and provides a dry and cool microclimate for personal comfort.”

“The prototype for the shoe insole was created using 3D printing. The material used is a mixture of soft polymer and hard polymer, thus providing sufficient support and shock absorption,” explained research team co-leader Professor Ding Jun.

The NUS team now hopes to work with companies to incorporate the novel moisture-absorption film into consumer products.