High-fidelity patterns form spontaneously when solvent evaporates

Resembling neatly stacked rows of driftwood abandoned by receding tides, particles left by a confined, evaporating droplet can create beautiful and complex patterns. The natural, pattern-forming process could find use in fields such as nanotechnology and optoelectronics.

“A lot of work in nanotechnology has been directed toward the bottom-up imposition of patterns onto materials,” said Steve Granick, a professor of materials science, chemistry and physics at the University of Illinois at Urbana-Champaign. “We found that beautiful patterns of high fidelity and regularity could form naturally and spontaneously, simply by allowing a drop to evaporate in a confined geometry.”

Granick and former postdoctoral research associate Zhiqun Lin (now a professor of materials science at Iowa State University) describe their work in a paper that has been accepted for publication in the Journal of the American Chemical Society, and posted on its Web site. Funding was provided by the U.S. Department of Energy.

To produce the patterns, Granick and Lin began by gluing two small mica sheets to cylindrical mounts. With the cylinders at right angles, a droplet of volatile solution containing small polymer chains was inserted between the curved mica sheets. The sheets were then brought into contact and left undisturbed until evaporation was complete.

Because evaporation in this geometry is restricted to the edge of the droplet, the process results in hundreds of concentric rings with regular spacing, very much resembling a miniature archery target. Each ring – composed of polymer chains abandoned as the solvent receded – is several nanometers high and several microns wide.

The droplet evaporates in a jerky, stick-slip fashion, said Granick, who also is a researcher at the Frederick Seitz Materials Research Laboratory and at the Beckman Institute for Advanced Science and Technology.

“While the droplet is sticking to the surface, a ring of polymer is deposited,” he said. “As evaporation continues, tension builds in the droplet. Eventually the droplet jerks to a new position, the tension is temporarily relieved, and another ring is deposited.”

The simple evaporative process could be used to form patterns with many other materials, such as electrically conducting polymers, nanoparticles and proteins. Pattern formation could be controlled by altering the size of the material, changing the solvent, or modifying the surfaces.

“The pattern emerges spontaneously from the geometry in which we put the droplet,” Granick said. “This means we could make other kinds of patterns by using different geometries or surfaces with tailored wettability.”

Source: University of Illinois at Urbana-Champaign

Related stories:

Miniature lab can detect deadly bird flu virus in 30 minutes
Researchers at the Institute of Bioengineering and Nanotechnology (IBN), Institute of Molecular and Cell Biology (IMCB) and Genome Institute of Singapore (GIS) have successfully developed a miniaturized device that can be used to detect the highly pathogenic avian flu (H5N1) virus.
Widespread 'Twilight Zone' Detected Around Clouds
There seems to be something new under the sun -- in the sky, specifically -- that could complicate scientists' efforts to get a fix on how much the world will warm in the future. Greenhouse gases are not the only things in the air that influence the temperature of our atmosphere. Clouds and small airborne particles called aerosols also play an important and complicated role. And now a new ingredient has been discovered: an extensive and previously unseen “twilight zone” of particles that represents a gradual transition from cloud droplets to dry particles.
Protein's tail may be flu virus's achilles heel
Striking new research from Rice University and the University of Texas at Austin (UT) has revealed a potential new target that drug makers can use to attack several strains of influenza, including those that cause bird flu as well as the common variety that infects millions each flu season.
Single-particle interference observed for macroscopic objects
With a variation on the famous double-slit experiment of quantum mechanics, scientists Yves Couder and Emmanuel Fort from the University of Paris 7 are rewriting the textbooks. Their accomplishment, however, has less to do with quantum mechanics than with an observation once considered experimentally impossible: the wave-particle double nature of a macroscopic object (an oil droplet and its associated surface wave).
NASA Africa Mission Investigates Origin, Development of Hurricanes
Scientists from NASA, the National Oceanic and Atmospheric Administration, universities and international agencies will study how winds and dust conditions from Africa influence the birth of hurricanes in the Atlantic Ocean.
Magnetism and mimicry of nature hold hope for better medicine, environmental safety
Critical advances in medicine and environmental protection promise to emerge from a new method for biochemical analysis of fluids developed by an international science team led in part by Arizona State University researchers.
Researchers make long DNA 'nanowires' for future medical and electronic devices
Ohio State University researchers have invented a process for uncoiling long strands of DNA and forming them into precise patterns. Ultimately, these DNA strands could act as wires in biologically based electronics and medical devices, said L. James Lee, professor of chemical and biomolecular engineering at Ohio State University.
Researchers Improve Predictions of Cloud Formation For Better Global Climate Modeling
Atmospheric scientists have developed simple, physics-based equations that address some of the limitations of current methods for representing cloud formation in global climate models – important because of increased aerosol pollution that gives clouds more cooling power and affects precipitation.
The National Science Foundation (NSF)-funded researchers, led by scientists at the Georgia Institute of Technology, also have developed a new instrument for measuring the conditions and time needed for a particle to become a cloud droplet. This will help scientists determine how various types of emissions affect cloud formation.

News discussion:

Physics news