Amid escalating threat of wildfires induced by climate change, researchers at Stanford have introduced an innovative long-lasting water-enhancing gel that could be sprayed on homes and critical infrastructure to mitigate the loss caused by the natural disaster.
The research, published in Advanced Materials, shows that the new gels are significantly more effective than existing commercial gels. Its enhanced performance and extended durability offer a promising solution to mitigate wildfire damage and safeguard vulnerable areas.
“Under typical wildfire conditions, current water-enhancing gels dry out in 45 minutes,” said Eric Appel, senior author of the paper and associate professor of materials science and engineering in the School of Engineering.
“We’ve developed a gel that would have a broader application window – you can spray it further in advance of the fire and still get the benefit of the protection – and it will work better when the fire comes.
Water-enhancing gels are made of super-absorbent polymers – similar to the absorbent powder found in disposable diapers. Mixed with water and sprayed on a building, they swell into a gelatinous substance that clings to the outside of the structure, creating a thick, wet shield.
But the conditions in the vicinity of a wildfire are extremely dry – temperatures can be near 100 degrees, with high winds and zero percent humidity – and even water locked in a gel evaporates fairly quickly, said Appel.
In the gel designed by Appel and his colleagues, the water is just the first layer of protection. In addition to a cellulose-based polymer, the gel contains silica particles, which get left behind when the gels are subjected to heat.
“We have discovered a unique phenomenon where a soft, squishy hydrogel seamlessly transitions into a robust aerogel shield under heat, offering enhanced and long-lasting wildfire protection. This environmentally conscious breakthrough surpasses current commercial solutions, offering a superior and scalable defense against wildfires,” said the lead author of the study, Changxin “Lyla” Dong.
“When the water boils off and all of the cellulose burns off, we’re left with the silica particles assembled into a foam,” Appel said. “That foam is highly insulative and ends up scattering all of the heat, completely protecting the substrate underneath it.”
The silica forms an aerogel – a solid, porous structure that is a particularly good insulator. Similar silica aerogels are used in space applications because they are extremely lightweight and can prevent most methods of heat transfer.
The researchers tested several formulations of their new gel by applying them to pieces of plywood and exposing them to direct flame from a gas hand-torch, which burns at a considerably higher temperature than a wildfire. Their most effective formulation lasted for more than 7 minutes before the board began to char. When they tested a commercially available water-enhancing gel in the same way, it protected the plywood for less than 90 seconds.
“Traditional gels don’t work once they dry out,” Appel said. “Our materials form this silica aerogel when exposed to fire that continues to protect the treated substrates after all the water has evaporated. These materials can be easily washed away once the fire is gone.”
