But when the nanoparticles were left in the dark, distinct, long, straight ribbons formed.
"We discovered that if we make flat ribbons in the dark and then illuminate them, we see a gradual twisting, twisting that increases as we shine more light," Kotov said. "This is very unusual in many ways."
The light twists the ribbons by causing a stronger repulsion between nanoparticles in them.
The twisted ribbon is a new shape in nanotechnology, Kotov said. Besides superchiral materials, he envisions clever applications for the shape and the technique used to create I it. Sudhanshu Srivastava, a postdoctoral researcher in his lab, is trying to make the spirals rotate.
"He's making very small propellers to move through fluid---nanoscale submarines, if you will," Kotov said. "You often see this motif of twisted structures in mobility organs of bacteria and cells."
The nanoscale submarines could conceivably be used for drug-delivery and in microfluidic systems that mimic the body for experiments.
This newly-discovered twisting effect could also lead to microelectromechanical systems that are controlled by light. And it could be utilized in lithography, or microchip production.
Glotzer and Aaron Santos, a postdoctoral researcher in her lab, performed computer simulations that helped Kotov and his team better understand how the ribbons form. The simulations showed that under certain circumstances, the complex combination of forces between the tetrahedrally-shaped nanoparticles could conspire to produce ribbons of just the width observed in the experiments. A tetrahedron is a pyramid-shaped, three-dimensional polyhedron.
"The precise balance of forces leading to the self-assembly of ri
|Contact: Nicole Casal Moore|
University of Michigan