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March 6, 1997

Chemist's basic research moves closer to practical applications

"Isn't this a pretty one?" Pitt chemis- try professor Sanford "Sandy" Asher asked, holding up a vial containing a thick, milky, rainbow-streaked substance resembling a liquid opal.

"Oh, yes," Asher repeated to himself, peering at the material under a light in his Chevron Science Center office. "That's very pretty." Cheap to produce, too, this substance. Yet potentially precious because of its unique optical, thermal and chemical properties.

According to Asher and his research team, the material — called a polymerized crystalline colloidal array (PCCA) — may some day yield such commercially valuable products as improved laptop computer displays, "smart membranes" to dispense drugs within the body, highly sensitive lead sensors, and laser-resistant goggles for fighter pilots.

Last month, Asher's office itself looked like it had been strafed by enemy planes. Paper lay scattered over every surface that wasn't already covered by books, journals, molecular models and vials of PCCAs.

Any researcher would have recognized the scene: Asher was in the final throes of completing a research grant proposal.

He was applying to the U.S. Defense Department's Defense Advanced Research Projects Agency (DARPA) for a $3 million grant for research that could lead to a PCCA coating for pilot goggles. Such a coating would screen out lasers or other optical weapons without affecting pilots' vision.

Currently, Asher's PCCA research funding consists mainly of a $150,000-per-year grant from the Office of Naval Research, recently renewed for two more years, and a three-year, $380,000 National Science Foundation Grant that he shares with co-principal investigator Rob Coalson, also of the chemistry department.

"The DARPA funding represents a large opportunity for us, and I think we have a pretty good chance of success," Asher said. "I mean, we created this field of research. We think we can compete pretty well in the field we created." Ironically, Asher had "absolutely no practical applications in mind at all" when he began experimenting with crystalline colloidal arrays (CCAs) in 1980, he said. "This started off completely as basic research. We had no funding. It sort of took over my lab by itself." To understand how that happened, you need to know that a CCA is made up of highly charged, giant molecules that space themselves in a predictable order. "When we began working with this material in 1980, we quickly realized that it interacts very intensely with light. That led to the idea that it could be used for optical devices and optical filters," Asher said.

The problem was, a CCA's ordering is unsettled temporarily by shaking the substance. Also, the substance is easily contaminated. But then Asher came up with the idea of locking the CCA structure in place (polymerizing it) within a water-based binding material called a hydrogel.

The hydrogels used by Asher's team shrink or swell depending on the surrounding temperature. They also can be customized to respond to chemical changes. The polymerized CCA (that is, the PCCA) itself changes its dimensions when the hydrogel changes size — and so, the optical properties of the PCCA change.

"We first theorized six years ago that we could develop highly sensitive optical switches and optical limiters with this technology," Asher said. "But it wasn't until this past November that we managed to create this effect in the lab." Recently, Asher's team created a PCCA that changes color when it comes into contact with minute amounts of lead. "With this, we could develop a cheap but very reliable lead sensor that could be used in industry or in a device that you could attach to a kitchen faucet," Asher said.

The team also is developing a PCCA in which the macro-molecules are spaced in such a way that gaps between them act as pores. The pore sizes vary depending on temperature and their chemical surroundings. Using this material, Asher hopes to create "smart membranes" that can detect specific chemical conditions of the human body and dispense drugs accordingly.

According to Asher, the PCCA devices would represent an improvement over existing drug delivery systems such as time-release capsules and skin patches, which release a drug at a fixed rate regardless of whether the body requires it.

Another potentially lucrative application for PCCA technology is in the laptop computer market, which is huge and growing faster than the desktop market, Asher noted.

Laptop computers currently use liquid crystal displays, which polarize light. "Unfortunately, this liquid crystal technology is expensive and slow and requires a lot of power," Asher said. "The screen gets washed out by strong light. At this point, you can't take your laptop to the beach, for example, because there's not enough backlight for you to see anything on the screen.

"But our technology relies on refraction of light instead of transmission of the backlight. That means the display wouldn't be washed out by strong ambient light. It's also a technology that requires very low power." Asher will give a talk called "Giant, Smart and Hardworking Molecules: Cystalline Colloidal Array Self-Assembly Is a Motif for Creating Novel Optical and Chemical Sensing Devices" at a March 6 chemistry department colloquium in the Chevron Ashe Auditorium, beginning at 2:30 p.m.

— Bruce Steele

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