Adaptive materials are finding considerable interest because of their ability to change shape under an applied stimulus, such as an electric current or heat. These materials have a broad range of aerospace applications ranging from the deployment of large-area solar arrays and antennas for satellites to "morphing" aircraft. A considerable amount of work has focused on the development of piezoelectric polymers that can change shape under an applied electric current. More recently, researchers have demonstrated that liquid crystalline elastomers that are doped with a photochromic dye will also change shape (bend) when exposed to ultraviolet light of a certain wavelength. Upon irradiation, the photochromic dye changes shape, disrupts the packing of the liquid crystalline elastomers, and causes the polymer film to bend. These materials, known as photomechanical polymers, offer some distinct advantages over piezoelectric systems. They have faster response times, are not sensitive to electromagnetic interference, and are more compatible with the advanced fly-by-light (fly-by-fiber) approaches being proposed for future aircraft.
Schematic representation of photomechanical polymers showing the isomerization of a photochromic additive and its incorporation in a polymer.
Researchers at the NASA Glenn Research Center have developed a new class of photomechanical polymers that incorporate a photochromic unit into a series of rod-coil block copolymers. These materials are designed to undergo a controlled phase separation leading to regions of highly ordered rods and coils (see the chemical diagram). Incorporation of the photochromic unit as part of the rods leads to an ordered environment similar to that in liquid crystalline materials. The advantage of this approach over previously reported dye-doped systems is that attachment of the dye to the polymer chain enables the control of its placement within the film and ensures that the dye does not leach out or evaporate during use.
The photographs show a film from one of these polymers before irradiation (top) and after 15 min irradiation with short-wavelength (200- to 400-nm) light (center). After just a few minutes of short-wavelength irradiation, the film begins to display signs of curling, and after 15 min it has nearly curled into a cylinder. Irradiation of the curled film with longer wavelength (400- to 500-nm) ultraviolet light causes the film to relax, and it becomes flat again (bottom). Further modifications of these polymers and a more thorough investigation of the photomechanical effects in these materials are underway.
Top: Polymer film before irradiation. Center: Polymer film after irradiation at 200 to 400 nm. Bottom: Polymer film after irradiation at 400 to 500 nm. Initially, the film is flat and has some surface roughness; upon irradiation, the sample begins to curl; irradiation with longer wavelength light causes the film to flatten out. Surprisingly, the films are now smooth.
Find out more about the research of Glenn’s Polymers Branch: http://www.grc.nasa.gov/WWW/5000/MaterialsStructures/polymers/
Glenn contact:
Dr. Michael A. Meador, 216-433-9518, Michael.A.Meador@nasa.gov
Ohio Aerospace Institute (OAI) contact:
Dr. Daniel S. Tyson, 216-433-3188, Daniel.S.Tyson@nasa.gov
Authors:
Dr. Michael A. Meador, Dr. Daniel S. Tyson, and Pushan Dasgupta (participant in NASA’s 2005 Summer High School Apprenticeship Research Program, SHARP)
Headquarters program office:
Aeronautics Research
Programs/Projects:
Vehicle Systems, Exploration Systems
Last updated: October 16, 2006
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