South SFV Today

As climate change creates hotter, drier conditions, fire seasons are becoming longer with larger and more frequent wildfires. These catastrophic events have destroyed homes and infrastructure, caused significant losses in lives and livelihoods, and damaged wildland resources and the economy. The need for new solutions to combat wildfires is pressing.

Researchers at Stanford University have developed a water-enhancing gel that can be sprayed on homes and critical infrastructure to help prevent them from burning during wildfires. According to research published on August 21 in Advanced Materials, these new gels last longer and are significantly more effective than existing commercial gels.

"Under typical wildfire conditions, current water-enhancing gels dry out in 45 minutes," said Eric Appel, associate professor of materials science and engineering at Stanford's School of Engineering, who is the senior author of the paper. "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 composed of super-absorbent polymers similar to those found in disposable diapers. When mixed with water and sprayed on a building, they form a gelatinous substance that clings to surfaces, creating a thick wet shield. However, under extreme wildfire conditions—temperatures near 100 degrees Fahrenheit with high winds and zero percent humidity—these gels dry out quickly.

The gel designed by Appel’s team includes silica particles along with a cellulose-based polymer. When exposed to heat, these components transform into an aerogel shield that offers enhanced wildfire protection. “We have discovered a unique phenomenon where a soft, squishy hydrogel seamlessly transitions into a robust aerogel shield under heat,” said Changxin “Lyla” Dong, lead author of the study.

“When the water boils off and all of the cellulose burns off, we’re left with silica particles assembled into a foam,” Appel explained. “That foam is highly insulative and ends up scattering all of the heat.”

The researchers tested various formulations by applying them to plywood pieces exposed to direct flame from a gas hand-torch. Their most effective formulation lasted over seven minutes before charring began; commercially available gels protected plywood for less than 90 seconds under similar conditions.

“Traditional gels don’t work once they dry out,” noted Appel. “Our materials form this silica aerogel when exposed to fire that continues to protect after all the water has evaporated.”

This development builds on Appel’s previous work using similar gels as vehicles for holding fire retardants on vegetation for extended periods. After initial success with transforming their properties under heat exposure, several years were spent optimizing storage stability, sprayability with standard equipment, surface adherence, non-toxicity approved by U.S Forest Service standards, and biodegradability by soil microbes.

“They’re safe for both people and the environment,” Appel emphasized.

Appel holds multiple affiliations within Stanford including senior fellow at Stanford Woods Institute for Environment among others; additional co-authors include Andrea I d’Aquino Samya Sen graduate students Changxin Dong Anthony C Yu undergraduate student Ian A Hall alongside California Polytechnic State University collaborators supported by funding from Gordon & Betty Moore Foundation Schmidt Science Fellows National Science Foundation

Media contact: Jill Wu School Engineering jillwu@stanford.edu

© Copyright Stanford University

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