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CUE 2007
Chemical & Biological Engineering:
Nanostructured Polymer Materials Offer Innovations From Hazmat Protection to Desalination

Civilian and military hazmat teams might one day wear suits made from a liquid crystal-butyl rubber composite, which is breathable, yet blocks out toxic chemicals. Above, graduate student Xiaoyun Lu works with Professor Douglas Gin to test the new composite material against chemical agents.

A breathable rubber suit? That might sound like an oxymoron until you talk to CU Professor Douglas Gin, co-inventor of an advanced material known as cross-linked lyotropic liquid crystal-butyl rubber composite. The new material could soon find its way into use by hazmat teams handling toxic chemicals as well as military and civil defense operations combating chemical warfare or terrorism.

The new material is as good or better at blocking out hazardous chemicals in aerosol and vapor form than is a typical cross-linked butyl rubber hazmat suit material, Gin says, while at the same time being more comfortable and safer to wear because it allows moisture vapor to flow in and out.

"Under heavy workload and warm temperatures, an individual wearing a butyl rubber protective garment can easily develop heat stress due to ineffective evaporative cooling," he says.

The new, selectively permeable material is made from cross-linking butyl rubber with liquid-crystal molecules, which arrange themselves into ordered, nanometer-scale, water-filled channels or pores. The channels allow water to pass in and out of the synthetic material. However, they block the passage of water-insoluble molecules such as most chemical warfare agents or any toxic molecules larger than the nanopores.

European rescuers train during a civil protection exercise in October 2002. (AP Photo/Lionel Cironneau)

Most chemical agents are hydrophobic (water-hating) and are larger than the material's pores, which are 1.2 nanometers in diameter, Gin says. A nanometer is one billionth of a meter, or about 75,000 times smaller than a strand of human hair. Even chemical vapor molecules that may be smaller tend to be water-repellent, so they would be blocked from passing through the ion-lined water channels, he adds.

The idea of a breathable liquid crystal-rubber suit was conceived by Dr. Brian Elliott of TDA Research, an advanced materials company located in Wheat Ridge, Colorado, which now owns the patent.

"The new invention built upon fundamental work in polymerizable liquid crystals that Dr. Gin started at the University of California, Berkeley, and added the idea of using these liquid crystals as pore-formers in a higher barrier material such as butyl rubber," says Elliott. "The goal was a material that was a good chemical barrier that only allowed water vapor to penetrate."

Gore-Tex operates on a similar principle, although its pores are 100 times larger. "Brian came up with the idea, and we made it work," says Gin, explaining that Elliott earned his doctorate in chemical engineering at CU-Boulder in 1998 and continues to collaborate with faculty and students.

Gin came to CU in 2001 from Berkeley, where he had been an assistant professor of chemistry. At CU-Boulder, he holds joint appointments in chemical and biological engineering and in chemistry and biochemistry, a situation he calls his "biggest challenge and his biggest opportunity."

"As a chemist, I had a great vision of making separating devices…but I didn't know how to make a membrane," he recalls. Now, his research group involves students from both fields, who benefit from being cross-trained in chemical synthesis, engineering, and analysis.

The combination of chemistry and chemical engineering is what led to Gin's current work in nanometer-scale architecture and development of new functional materials. In particular, Gin's research focuses on ordered liquid crystal materials and advanced polymer systems.

German members of the nuclear biological and chemical team spray down a Fox reconnaissance vehicle as part of an exercise to illustrate decontamination in February 2003.   (AP Photo/Kevork Djansezian)

Liquid crystals are molecules that self-assemble into organized phases that are in between crystalline solids and isotropic liquids, he explains. When polymerized, they form a robust network that maintains the molecules' nanostructure while providing new functional properties to a material.

Gin says cross-linking liquid crystals with other materials could  be an effective technique for making polymers with controlled, nanometer-size pores to purify drinking water or remove sodium  from seawater. While commercial desalination technologies use non-porous polymer membranes and require a large amount of energy, the same result could be achieved by controlling the size of liquid-crystalline nanochannels in a membrane to block out larger hydrated salt ions while letting smaller water molecules pass through. Gin's group has demonstrated this technology in the laboratory and says it could be competitive.

Faculty website: www.colorado.edu/che/research/faculty/gin
Department website: www.colorado.edu/che