New sweat absorbing material is designed to keep you cool and power your devices

Summary

A new kind of moisture-absorbing material was developed to speed up the evaporation of sweat from skin. The so-called Co-SHM films change color as they absorb moisture and have so far been tested in various personal comfort applications. Integrating the absorbent film with a wearable energy transducer shows potential for the future smart-clothes for fitness or everyday use.

 

What if you could turn sweat stains into electrical power? 

Imagine: An absorbent band powering your smart-watch, shoes that unlock more features the farther you run in them, and business casual clothing designed to prevent sweat stains and keep your phone charged. Last year, a team from the National University of Singapore invented a new hygroscopic material that rapidly absorbs moisture from sweat, which is converted into energy using electrochemical cells, unlocking the potential for novel wearable tech (2).

 

Despite a boom in the development of atmospheric water-harvesting technologies, most of which capture dew and traces of humidity in the environment, few researchers have explored moisture capture elsewhere. The team wanted to explore wider applications (1). Capturing the moisture humans release to use in a productive way is largely unexplored outside of the Fremen stilsuits on Arrakis.

 

Capturing sweat with this new material has additional benefits, like:

  • Comfort - the wearer doesn’t feel damp and overly aware of moisture deposits on their clothes.
  • Odor control - in capturing sweat, the material inhibits the growth of odor-causing bacteria.



How do hygroscopic materials absorb water?

Hygroscopic materials are good at absorbing moisture and retaining water. They’re all around us. Paper, sugars, wood, salts, and silica gels used in commercial packaging all fall under the hygroscopic umbrella.

 

Generally, materials with absorbent properties are porous and hydrophilic, which means the chemical structure may include groups like alcohols, ionic charges, and/or carboxylic acids. Since water is a polar molecule, slight charges can cause electrostatic attractions with other polar molecules or salts. This works so that each molecule of the hygroscopic substance can be surrounded by a group of sticky water molecules.

 

What are the current and future uses?

The Co-SHM film releases absorbed moisture on contact with sunlight and can be regenerated over 100 times, indicated by the color change from blue to pink (2).

Researchers used 3D printing to encase the hygroscopic films in a breathable PTFE plastic membrane to improve waterproofing and durability. A video of the waterproofed properties of the Co-SHM membranes is included with the published manuscript (1).

Another key finding from this project was the integration of the sweat-harvesting film with a wearable energy transducer. The energy device included eight electrochemical cells, which drew a current from electrolytes in the Co-SHM membrane (2). Early trials were able to generate about 0.54 volts after 10 minutes, or enough energy to light a small LED bulb (2).

While the current energy output is not high enough to power most small devices, the authors suggest that scaling up to practical applications is likely (1).

With advances in moisture harvesting materials coupled with wearable technologies, it’s easy to imagine a wave of new inventions on the horizon.

 

References:

  1. Zhang, X., Yang, J., Borayek, R., et al. Super-hygroscopic film for wearables with dual functions of expediting sweat evaporation and energy harvesting. Nano En. 75 (2020) 104873. https://doi.org/10.1016/j.nanoen.2020.104873
  2. National University of Singapore. Film can grab your sweat to power your watch. Futurity (2021) Retrieved from https://www.futurity.org/wearable-devices-sweat-skin-clothing-2501002/