'Smart' paper detects water leaks, say scientists

Scientists at the University of Washington (UW) are aiming to simplify the process for discovering detrimental leaks having developed ‘smart' paper that can sense the presence of water.

Anthony Dichiara

According to the university, detecting a water leak in a complicated network of pipes in cities and large-scale manufacturing plants can take tremendous time and effort as technicians must disassemble many pieces to locate the problem. The American Water Works Association indicates that nearly a 250,000 water line breaks occur each year in the US, costing public water utilities about US$2.8bn (£2.1bn) annually.

Researchers at the University of Washington have developed smart paper which is laced with conductive nanomaterials. It can be employed as a switch, turning on or off an LED light or an alarm system indicating the absence or presence of water.

The researchers described their discovery in a paper appearing in the November issue of the Journal of Materials Chemistry A.

“Water sensing is very challenging to do due to the polar nature of water, and what is used now is very expensive and not practical to implement,” said lead author Anthony Dichiara, a UW assistant professor of bioresource science and engineering in the School of Environment and Forest Sciences. “That led to the reason to pursue this work.”

Along with Dichiara, a team of UW undergraduate students in the Bioresource Science and Engineering programme successfully embedded nanomaterials in paper that can conduct electricity and sense the presence of water. Starting with pulp, they manipulated the wood fibres and carefully mixed in nanomaterials using a standard process for papermaking, but never before used to make sensing papers.

Discovering that the paper could detect the presence of water came by way of a fortuitous accident. Water droplets fell onto the conductive paper the team had created, causing the LED light indicating conductivity to turn off. Though they thought they had ruined the paper at first, the researchers realised they had instead created a paper that was sensitive to water.

When water hits the paper, its fibrous cells swell to up to three times their original size. That expansion displaces conductive nanomaterials inside the paper, which in turn disrupts the electrical connections and causes the LED indicator light to turn off.

This process is fully reversible, and as the paper dries, the conductive network re-forms so the paper can be used multiple times.

The researchers envision an application in which a sheet of conductive paper with a battery could be placed around a pipe or under a complex network of intersecting pipes in a manufacturing plant. If a pipe leaks, the paper would sense the presence of water, then send an electrical signal wirelessly to a central control centre so a technician could quickly locate and repair the leak.

In addition, the paper is so sensitive that it can also detect trace amounts of water in mixtures of various liquids. This ability to distinguish water from other molecules is particularly valuable for the petroleum and biofuel industries, where water is regarded as an impurity.