Although spills inside a lab can often spell trouble, a University of Washington scientist found a way to turn an accidentally doused conductive material into an inventive new sensor. The lab mishap led to a “smart” paper that conducts electricity and provides wireless detection of water pipe leaks.
According to the American Water Works Association, nearly a quarter-million water line breaks occur annually in the U.S., costing public water utilities $2.8 billion each year. UW researcher Anthony Dichiara believes that the affordable nature of the “smart paper” and its sustainable ingredients could provide a low-cost, scalable solution for municipalities, and help conserve one of Earth's most precious resources.
Dichiara, a UW assistant professor of bioresource science and engineering in the School of Environment and Forest Sciences, and his team described their discovery in a paper appearing in the November issue of the Journal of Materials Chemistry A.
From Spills to Sensors
The electrically conductive paper, laced with conductive materials, senses the presence of water and alerts a user via switch, LED light, or alarm.
In a factory or municipal setting, the smart paper, wrapped around a pipe, could theoretically sense the presence of water and relay that information wirelessly. In such a scenario, a chip, attached to the paper, would monitor electrical resistivity levels.
“Basically, when there is a major change that’s up to a couple 1000 percent of the resistivity of the material, then it could trigger a signal or an alarm that can be sent to some technicians and say, ‘You have a leak on this particular pipe,’” Dichiara told Tech Briefs.
When water touches the paper, the material’s fibrous cells swell. The expansion displaces the paper’s conductive nanomaterials, disrupting the electrical connections and switching off the LED indicator light.
The discovery that the paper could detect the presence of water began with an accident.
“We were simply testing if the material was conductive, and basically how many nanomaterials we needed to put there to make it conductive,” said Dichiara.
A student, he said, spilled water onto the conductive paper, deactivating the LED used to indicate conductivity. Instead of ruining the paper, however, the scientists realized they made a material that changes its conductivity depending on the presence of water.
The process is fully reversible. As the paper dries, the conductive network re-forms so the paper can be used multiple times.
“After a little bit of time, we let it dry. We tested it again and the conductivity was back on,” said Dichiara. “That’s when I realized that now we can actually use it as a sensor.”
How to Make ‘Smart’ Paper
Typical leak-detection technology employs polymer composites. Although some composites with matrices like poly(ethylene terephthalate), poly(ethylene-co-vinyl acetate), poly(vinyl alcohol), or chitosan react to water, the non-polar character of most polymers make the materials insensitive to polar water molecules.
The smart paper provides a stronger and more sustainable process, according to the UW researchers, as the entire paper-making process can be completed with cheap, natural materials like wood scraps.
“You don’t have to amplify the electrical signal from the material because the paper, compared to other polymers, is already very sensitive,” said Dichiara.
The recipe: Dried sheets of softwood pulp are added to water, and then mixed in a machine to create a slurry-like substance. After the pulp is diluted, nanomaterials, in black liquid form, are slowly poured into the pulp mixture.
The nanomaterials, made of extremely conductive carbon, are added to the paper without having to modify the paper making process.
The solid materials are next pressed to create a circular shape of paper, and a roller squeezes out remaining water. The carbon from charcoal creates the rich, black paper that is stiff and smooth in texture.
Although the team created 8-inch prototype disks, the researchers hope to next test the process on an industrial-sized paper-making machine, which will require a greater amount of nanomaterials and paper pulp.
The nanomaterials help to improve strength properties of the material, according to the team, which maintains the same level of resistance when immersed in water 20 times.
“It won’t be dissolved, and will be fairly strong underwater,” said Dichiara, adding that the smart paper exhibits a wet strength of about 60% compared to a typical paper’s 10% amount.
According to the professor, the true value for users is the technology’s simplicity.
“It can be literally a copy paper that’s embedded with those nanomaterials,” said Dichiara. “It’s extremely cheap.”
A Flood of Ideas
The University of Washington team is currently working to develop a full remote sensor and electronic chip that can be placed on the paper. Once completed, Dichiara and his team will begin practical testing in an industrial or municipal setting.
The researchers envision an application in which a combination of conductive paper and a battery could be placed around a pipe, or under a manufacturing plant’s network of intersecting pipes. The paper could then sense the presence of water, and send an electrical signal wirelessly to a central control center or a technician could quickly find and repair the leak.
Additionally, the smart material detects trace amounts of water in mixtures of various liquids – a particularly helpful capability for petroleum and biofuel industries needing to distinguish water from other molecules.
“I believe that, for large-scale applications, this is definitely doable,” Dichiara said in a university press release. “The price for nanomaterials is going to drop, and we’re already using an established papermaking process. You just add what we developed in the right place and time in the process.”
Funding for this research came from the U.S. Department of Agriculture’s National Institute of Food and Agriculture, McIntire Stennis project, and from the UW School of Environmental and Forest Sciences.
Other co-authors are Sheila Goodman, a UW graduate student, and Delong He and Jinbo Bai of Universite Paris-Saclay in France. UW undergraduate students Jimeng Cui, Riley Fitzpatrick, Sydney Fry, Demi Lidorikiotis, Anna Song and Zoie Tisler completed additional lab work.
What do you think? Will smart paper prevent leaks? Share your thoughts below.
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