M98-A10

Lewis Slaten, Consumer Affairs , PI, German Mills, Chemistry; Roy

Broughton, Textile Engineering (Auburn)

Adaptive systems that exhibit desirable and predictable reversible alterations of their properties in response to external stimuli are very attractive, and are usually called "smart" systems. An important class of responsive systems are those that are photoadaptive, that is, systems experiencing reversible changes upon exposure to light. A simple example are photochromic glasses, where photoreducion of silver halides yields Ag particles that decay in a dark reaction with Cu2+ ions to reform the starting silver halides.

We developed a novel photoadaptive system in which light induces reduction of AuCl4¯ ions present in methanol-swollen crosslinked polymers of diallyldimethylammonium chloride (DADMAC) to generate nanometer-sized Au particles. They in turn are oxidized at room temperature in a dark reaction. The DADMAC gels are model systems for the photoadaptive fibers

that we are currently developing. These fibers are expected to operate in a fashion similar to photochromic glasses where particles of Ag or Au form by exposure to high intensity visible light, but decay once the intensity of light decreases to the level of ambient light. We are emphasizing the

preparation of photoresponsive fibers for applications such as reflection of infrared radiation, shielding of electromagnetic radiation, as well as 3D storage of data.

Sunlight illumination of polyvinylacetate (PVA) fibers generates nanometer-sized metallic particles when crosslinked with dimethylsulfoxide that contains DADMAC monomer or poly(acrylic acid) as well as metal complexes of Ag and Au. Formation of metal crystallites took place exclusively under high light intensity irradiation; no particles were generated under ambient light. This is encouraging; since, for practical applications, fast formation of particles is desired only at high photon fluxes such as during a fire. In addition, continuous crystallite generation with ambient light would inevitably lead to extensive oxidation of the PVA matrix and to deterioration of fiber properties. We could not detect particle decay at room temperature in the PVA fibers because constituents that destabilize the metal crystallites and facilitate their oxidation reactions had not yet been introduced into the fibers. However, the behavior of our model DADMAC gels is altered in the presence of water, which is significant because water is often present, either due to perspiration during use or by direct contact with this liquid during precipitation or fire-fighting activities.

If Au particles are made photochemically in gels containing 30% or more of water, they no longer decay in the dark at room temperature. Instead, the particles are oxidized at T>30oC, but they regenerate fast in the dark at room temperature (See Figure). This means that the behavior of the gels is transformed from only being photadaptive in the absence of water to both photo and thermo-adaptive after adding water. Thus, in the case of PVA fibers exposed to water, room temperature decay of the Au and Ag crystallites is no longer required, because heat produced during exposure to high photon fluxes will accelerate the decay of the metal crystallites.

We are also exploring the feasibility of incorporating water into PVA fibers to investigate the potential thermo and photo-adaptive properties of the resulting materials. If this approach is successful, simpler adaptive materials can be made without the need to incorporate additional components required to destabilize the metal crystallites in the fibers.

[Other Contributors: Graduate Student: Kelly Malone, Undergraduate Student: D. Taylor]

Industry interactions: 4

Project Web Site Address:

German Mills, an Associate Professor of Chemistry at Auburn since 1995, joined the faculty in 1989. He earned a Ph.D. in physical chemistry from the Technical University of West Berlin in 1985 and a MS in inorganic chemistry from the University of Chile in 1981. "Jimmy" has held postdoctoral positions at Caltech and Argonne National Lab. His research interests include synthesis and properties of nanometer-sized metal and semiconductor particles, "smart" materials and transformation of toxic chemicals.

millsge@mail.auburn.edu

(334)-844-6974

Roy M. Broughton, Jr, a Professor of Textile Engineering at Auburn since 1976, received his Ph.D. with concentrations in textile chemistry and fiber and polymer science from NC State. Before joining Auburn, Roy worked in polyester research at Goodyear Tire & Rubber. His research interests include manufacture, utilization and testing of fibers and nonwovens.

royalb@eng.auburn.edu

(334)-844-5460

B. Lewis Slaten, an Associate Professor at Auburn, joined the faculty in 1974 after receiving a M.S. in organic chemistry from University of Arkansas and a Ph.D. in chemical engineering from Maryland. Previously, Lew was a chemist for Freeport Minerals and the National Bureau of Standards' Fire Technology division. His research interests include fabric test methods, barrier textiles, protective clothing, environmental chemistry and chemistry of textile finishes.

blslaten@humsci.auburn.edu

(334)-844-1330