Hard-to-burn ‘smart’ wallpaper even triggers alarms | Science News for Students

Hard-to-burn ‘smart’ wallpaper even triggers alarms

Embedded nanowires respond to heat in a way that can turn on buzzers and warning lights
May 9, 2018 — 6:45 am EST
Chevron wallpaper

Wallpaper can give a room pizzazz and personality that a simple paint job won’t achieve. But a new type of wall covering offers to do even more — serve as an alarm system that scouts for signs of fire.

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Wallpaper can transform the look of a room. A new type could also do double-duty as a 24/7 fire sentry. This novel “paper” is all but unburnable. And if it gets really hot, the paper will trigger warning lights and sound an alarm.

Researchers in China described their new wall covering March 13 in ACS Nano. They hope the product’s traits will make it attractive for use in homes. One added benefit: It’s nontoxic.

Ying-Jie Zhu works for the Shanghai Institute of Ceramics at the Chinese Academy of Sciences. He led a team that developed the new technology. As a nanostructured-materials scientist, he develops useful materials that contain tiny parts. How tiny? Some parts have a height, width or length that is less than 100 nanometers — or one thousandth the width of a human hair.

Regular paper, including wallpaper, contains cellulose. (Wood is an abundant source of this plant-based product.) But cellulose catches fire easily. So Zhu’s team designed their wall covering be fire resistant. That means it takes a long heating or very hot temperatures to ignite.

Key to the new wallpaper is a network of nanowires inside it. They’re made from hydroxyapatite (Hy-DROX-ee-APP-eh-tyte). It’s a mineral found in bones and teeth. The scientists chose this mineral because it is highly flexible and fire resistant. To make the tiny wires, they added three chemicals — calcium chloride, monosodium phosphate and sodium hydroxide — to a mix of water, an alcohol (methanol) and a dietary fat (oleic acid). Then they heated this recipe for a whole day.

fire alarm nanowires
After five minutes in the flame, the paper is intact and the warning light is still turned on.
F.-F. Chen et al/ACS Nano 2018

The nanowires are about 10 nanometers wide and at least 100 micrometers long (which is about the thickness of a sheet of printer paper). Those wires naturally weave together. The researchers strengthened the weave by adding glass particles. To make the paper, the scientists pour a liquid containing the nanowires through a paper-making machine. Like regular wallpaper, the end product is smooth and flexible. And though it starts out white, people can dye it different colors or print attractive patterns on it.

The woven network of fibers is linked to a temperature-sensitive sensor on the back of the paper. The sensor is made from a material called graphene (GRAA-feen) oxide. At room temperature, this carbon-based material is an electrical insulator. That means it won’t conduct electricity. But when the temperature climbs above 129° Celsius (264° Fahrenheit), this material’s structure changes. Now it can conduct electricity. And when this happens, the electricity turns on the fire-alarm lamp and buzzer.

To embed this sensor in the wallpaper, the scientists mix graphene oxide in water to create an ink. Then they print it onto the back of the wallpaper. To make the sensor sensitive and resist breakdown, Zhu’s team coats it with a chemical known as polydopamine (PAA-lee-DOAP-uh-meen). It protects the sensor from immediately breaking down in a fire. Within two seconds, high heat will turn on a sensor treated with this chemical. That sensor can survive flames for more than five minutes.

Qunfeng Cheng works at Beihang University in Beijing, China, and was not involved in the new study. As a bioinspired nanomaterials scientist, he looks to structures made by plants and animals as inspiration for new materials. The hardest part of bringing the new wallpaper to market, he suspects, will be to affordably make lots of it. So far, the scientists have only made enough nanowires to cover five square meters (54 square feet) of paper. That is barely enough to cover one wall. To make it attractive for home use, they will have to find a way to make a lot of it inexpensively.

Zhu says his group is talking with a few companies about collaborating. They’re hoping this could lead to enough wallpaper to sell.

“The smart-fire-alarm, fire-resistant wallpaper will be helpful for public safety,” Zhu hopes. If it indeed can be made affordable for widespread use, he said, it holds the prospect of “saving human lives and reducing the loss of property in a fire.”

The flame activates the temperature-sensitive sensor, turning on an alarm and light.
F.-F. Chen et al/ACS Nano 2018

Power Words

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calcium chloride     A compound made of calcium and chlorine. It has a strong affinity for water and chemists use it to dry out liquid solutions. It can also be used to help de-ice slippery roads in the winter.

carbon     The chemical element having the atomic number 6. It is the physical basis of all life on Earth. Carbon exists freely as graphite and diamond. It is an important part of coal, limestone and petroleum, and is capable of self-bonding, chemically, to form an enormous number of chemically, biologically and commercially important molecules.

cellulose     A type of fiber found in plant cell walls. It is formed by chains of glucose molecules.

ceramic     A hard but brittle material made by firing clay or some other non-metal-based mineral at a high temperature. Bricks, porcelain and other types of earthenware are examples of ceramics. Many high-performance ceramics are used in industry where materials must withstand harsh conditions.

chemical     A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.

electricity     A flow of charge, usually from the movement of negatively charged particles, called electrons.

graphene     A superthin, superstrong material made from a single layer of carbon atoms connected together.

hydroxyapatite     A mineral containing calcium and phosphorus, found in human bone.

insulator     A substance or device that does not readily conduct electricity.

materials science     The study of how the atomic and molecular structure of a material is related to its overall properties. Materials scientists can design new materials or analyze existing ones. Their analyses of a material’s overall properties (such as density, strength and melting point) can help engineers and other researchers select materials that are best suited to a new application. A scientist who works in this field is known as a materials scientist.

methanol     A colorless, toxic, flammable alcohol, sometimes referred to as wood alcohol or methyl alcohol. Each molecule of it contains one carbon atom, four hydrogen atoms and an oxygen atom. It is often used to dissolve things or as a fuel.

micrometer     (sometimes called a micron) One thousandth of a millimeter, or one millionth of a meter. It’s also equivalent to a few one-hundred-thousandths of an inch.

mineral     Crystal-forming substances that make up rock, such as quartz, apatite or various carbonates. Most rocks contain several different minerals mish-mashed together. A mineral usually is solid and stable at room temperatures and has a specific formula, or recipe (with atoms occurring in certain proportions) and a specific crystalline structure (meaning that its atoms are organized in regular three-dimensional patterns). (in physiology) The same chemicals that are needed by the body to make and feed tissues to maintain health.

nano     A prefix indicating a billionth. In the metric system of measurements, it’s often used as an abbreviation to refer to objects that are a billionth of a meter long or in diameter.

nanowire     A wire or rod on the order of a billionth of a meter in cross-section or in circumference. It is usually made from some type of semiconducting material. However some bacteria make string-like anchoring structures on the same size scale. Like the semiconductor wire, the bacterial ones also can transport electrons.

oleic acid     A monounsaturated fatty acid that is an ingredient of many vegetable oils and beef tallow. In the diet, it's a relatively heart-healthy type of fat. Industrial uses for this natural product include soap-making, cosmetics, lubricants and polishing compounds.

oxide     A compound made by combining one or more elements with oxygen. Rust is an oxide; so is water.

particle     A minute amount of something.

phosphate     A chemical containing one atom of phosphorus and four atoms of oxygen. It is a component of bones, hard white tooth enamel, and some minerals such as apatite.

polydopamine     An important polymer (chainlike chemical made from repeating units) used as a coating for many products, as an adhesive and as a surface to support the growth of cells.

sensor     A device that picks up information on physical or chemical conditions — such as temperature, barometric pressure, salinity, humidity, pH, light intensity or radiation — and stores or broadcasts that information. Scientists and engineers often rely on sensors to inform them of conditions that may change over time or that exist far from where a researcher can measure them directly.

sodium hydroxide     A chemical that is used in the production of paper and soap. It is used to make solutions more basic (alkaline).

technology     The application of scientific knowledge for practical purposes, especially in industry — or the devices, processes and systems that result from those efforts.

trait     A characteristic feature of something. (in genetics) A quality or characteristic that can be inherited.

Citation

Journal: F.-F. Chen et al. Fire alarm wallpaper based on fire-resistant hydroxyapetite nanowire inorganic paper and graphene oxide thermosensitive sensor. ACS Nano. Published online March 13, 2018. doi: 10.1021/acsnano.8b00047.