A research team at the University of Colorado in Boulder is using liquid crystal technology, widely known for its use in smartphones and flat-panel HD televisions, to create a transparent, solid film for windows that could significantly improve energy efficiency in buildings. The film is thermally insulating, soundproof and protects against water condensation.
The Energy Dept.’s Advanced Research Projects Agency-Energy (ARPA-E) awarded CU Boulder a $1.8-million grant to develop the new window coating, led by researchers from the Renewable and Sustainable Energy Institute. RASEI is a joint institute of CU Boulder and the National Renewable Energy Laboratory, headquartered in Golden, Colo.
“Buildings consume about 40% of the energy expended annually in the United States,” says Ronggui Yang, a mechanical engineering professor who leads the team, along with associate professor of physics Ivan Smalyukh.
“We think we can dramatically increase the energy efficiency of windows without compromising transparency and other functions,” Yang says.
The liquid crystal-based aerogel—a synthetic, porous and ultra-light material—can be created by using rod-like cellulose nano-particles, each with a diameter nearly a million times smaller than a grain of sand, says Smalyukh.
Aerogels, which were developed in the 1930s, replace some of the liquid components of a gel with air, without excessively shrinking the gel in the process, and in turn produce a light, low-density solid that does not conduct heat or cold well. “Most aerogels are not transparent. Ours will be,” says Smalyukh.
The cellulose-based liquid crystals are designed to self-organize and can be “pre-engineered” to assure transparency in the visible light range as well as high reflectivity in a selected part of the infrared spectrum that keeps buildings cool or warm as needed. “It’s not a costly process because the nanorods self-assemble,” Smalyukh says. “There’s no need for us to align them or point them.”
Derived from food industry waste or glucose, with the help of a special bacteria grown by the research team, the nano-particles spontaneously self-assemble into a liquid crystal, Smalyukh says. A key step in the process is carefully replacing the water in the liquid-crystal material with air, thus transforming it into the flexible film.
“The material will be lightweight, insulating, mechanically stable, flexible and inexpensive,” says Smalyukh. The lower cost is possible in part because cellulose “is one of the most abundant and naturally occurring substances on Earth,” he says.
Dubbed “air film” by the team, the aerogel material is more than 99% air. The air, or thin polymer, film can be laminated onto the surface of existing windowpanes, Smalyukh says, perhaps at first by professionals, but the team aims to produce films that consumers can easily apply themselves. The target cost is less than $5.00 per sq ft. Consumers could order them in rolls or sheets, precut to the right size. That would decrease costs by eliminating professional-installation expenses, Smalyukh adds.
Sustainability experts estimate that retrofitting windows rather than replacing them could reduce heat loss and save roughly the amount of electricity needed to power 32 million U.S. homes and businesses each year. The air film will help insulate single-pane windows in particular, Smalyukh says.
The CU Boulder grant, which officially began on Aug. 1, was one of 14 grants totaling $31 million for window-efficient technologies awarded this spring by the U.S. Energy Dept.
The grant is part of the ARPA-E’s Single-Pane Insulating Efficient Lucid Design (SHIELD) program. It is expected to accelerate development of materials that could cut in half the amount of heat lost through single-pane windows without replacing them, Yang says.
In December, the DOE awarded another CU Boulder research team $4 million to develop over three years an inexpensive, paintable coating to retrofit energy-inefficient windows. The infrared-reflective coating is expected to drastically reduce cooling costs for both residential and commercial structures, thus helping to reduce greenhouse gas emissions.