A small section of a tungsten-oxide, nanocomposite film processed in an oxygen-enriched background. The left side of the film has turned blue after exposure to ultraviolet light while the right side was masked and was not exposed.

A small section of a tungsten-oxide, nanocomposite film processed in an oxygen-enriched background. The left side of the film has turned blue after exposure to ultraviolet light while the right side was masked and was not exposed.

This research focuses on a new class of polymer matrix nanocomposites that display photochromic behavior. When exposed to ultraviolet light, these materials darken and the process is reversed when UV exposure ceases. The process used to produce these materials is highly scalable and could lead to a new class of energy-conserving products for window and roofing applications.

An in situ vapor deposition process has been used to create a photochromic, tungsten-oxide, polymer matrix nanocomposite. Under specific processing conditions, the composite consists of discrete tungsten-oxide nanoparticles distributed uniformly throughout the bulk of an optically transparent fluoropolymer matrix. Ultraviolet exposure of the nanocomposite produces characteristic photochromic changes that result in a 40% change in optical transmission. Optical absorption measurements yield a value of 3.08 eV for the bandgap of the tungsten-oxide particles. Incorporating oxygen as a supplementary deposition agent in the synthesis process increased the transparency of the films in the visible region, increased the change in transmission due to the photochromic effect, and led to the percolation of larger nanoparticles near the film surface. Growth of particles in this region allowed the nanocomposite to be bleached readily in an oxygen atmosphere while retaining photochromic activity.

 

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