CHAMPAIGN, Ill. - A University of Illinois researcher has developed a class of miniature polymers that self-assemble into mushroom-shaped nanostructures that in turn organize into macroscopic films that exhibit two dissimilar surfaces. The films should prove useful in a variety of applications, from the repair of human tissue to keeping aircraft wings free of ice.
"These mushroom-shaped nanostructures open up a new dimension in materials design," said Samuel I. Stupp, a U. of I. Swanlund Professor of materials science and engineering and of chemistry. "Now, instead of designing new materials with individual molecules, we can design them with these nanostructures that exhibit their own physical and chemical properties."
To fabricate films, Stupp first synthetically engineers the basic building blocks miniature polymers he calls "rodcoils" because they have a rigid, rod-like base attached to a flexible, coil-like top. These molecules self-assemble into bundles, forming nanostructures of a specific size and shape.
"The rod segments of the miniature polymers attract, while the coil segments which have a wider cross section repel," Stupp said. "As the rodcoils aggregate, the repulsive forces of the coils eventually balance the attractive forces of the rods and stop further growth. This balance of forces results in the formation of adjacent mushroom-shaped nanostructures, each containing about one hundred rodcoils."
The "mushrooms" continue to self-organize into films containing 100 or more layers stacked in polar alignment, Stupp said. Because the films possess polar order, they can be engineered for a variety of electrical, optical, mechanical and biological applications.
"For example, the films can exhibit an adhesive tape-like character, with one side sticky while the other side remains slick," Stupp said. "Such films could be used as protective coatings on computer disks or to reduce the buildup of ice on aircraft wings. The anti-icing application is currently being explored through a joint collaboration with government and industry."
Because of the polar stacking of nanostructures, the films could be designed to have piezoelectric or nonlinear optical properties. By presenting two different surfaces in a biological environment, the nanostructured films could aid in tissue repair and in the construction of artificial blood vessels. And, applied to metal or concrete surfaces, the films could serve as moisture barriers, effectively reducing corrosion in buildings, bridges and other structures.
"This is supramolecular materials science," Stupp said. "The organization of nanostructures into macroscopic materials allows us to design materials at a level of structure beyond that of simple molecules. Now we can tailor materials based upon something much bigger supramolecular units offering enormous diversity in shape and chemical structure, and therefore function, as well."
Stupp's latest findings appear in the April 18 issue of Science.