Novel film keeps wearer cool and powers devices

This is the claim of a team from the National University of Singapore (NUS) whose proof-of-concept device can power an LED. The team’s breakthrough has been reported in Nano Energy.

According to NUS’ Assistant Professor Tan Swee Ching, sweat is mostly composed of water that evaporates from the surface of skin to lower skin temperature.

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“In our new invention, we created a novel film that is extremely effective in evaporating sweat from our skin and then absorbing the moisture from sweat. We also take this one step further - by converting the moisture from sweat into energy that could be used to power small wearable devices,” he said in a statement.

The main components of the novel thin film are cobalt chloride and ethanolamine. Besides being extremely moisture-absorbent, this film can rapidly release water when exposed to sunlight, and it can be ‘regenerated’ and reused over 100 times. To make full use of the absorbed sweat, the NUS team has also designed a wearable energy harvesting device comprising eight electrochemical cells (ECs), using the novel film as the electrolyte. Each EC can generate about 0.57 volts of electricity when they absorb moisture and the NUS team believe the proof-of-concept demonstration illustrates the potential of 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, whereas the NUS film is said to absorb 15 times more moisture and does this six times faster than conventional materials. The film also changes colour when absorbing moisture, turning from blue to purple, and finally pink. This feature can be used 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 already used in clothing, and demonstrated the application of the moisture-absorption film in an underarm pad, shoe lining and shoe insole.

Asst Prof Tan 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.