Quantum dots display promise for polymers

Rice scientists simplify process to make polymers with light-triggered nanoparticles

Rice University scientists plan to employ the power of the sun to build functional synthetic polymers using photosensitive quantum dots — microscopic semiconducting particles — as a catalyst.

Rice graduate student Yifan Zhu holds a vial of photosensitive, semiconducting quantum dots. Photo by Jeff Fitlow

The luminescent dots are only a few nanometers wide, but are highly tunable for their unique optical and electronic properties. They are beginning to show up in modern displays, but lend themselves to industrial chemistry as well.

The Rice lab of materials scientist Eilaf Egap focused on the latter with its demonstration of a stable and economical method to make polymers through photo-controlled atom-transfer radical polymerization. The method could replace molecular catalysts or expensive transition metals currently used to make things like methacrylates (common in plastics), styrene and block copolymers.

Rice University researchers, from left, Yiming Huang, Eilaf Egap and Yifan Zhu are employing the power of the sun to build functional synthetic polymers using photosensitive, semiconducting quantum dots as a catalyst. They said the living polymerization process could lead to the creation of novel polymers. Photo by Jeff Fitlow

The work by Egap, Rice postdoctoral researcher and lead author Yiming Huang and graduate student Yifan Zhu is detailed in the American Chemical Society journal ACS Macro Letters.

The lab used various light sources, including the sun and even a household lamp, to illuminate a solution of dispersed cadmium selenide quantum dots. That introduced the generation of free radical atoms from a bromide-based initiator, which in turn triggered acrylate monomers in the solution to link. Because the monomers tested in Egap’s lab had no ability to terminate propagation of the chain, the process is called living polymerization.

“It will keep going until it consumes all the monomers or you decide to terminate,” Egap said.

Egap, an assistant professor of materials science and nanoengineering and chemical and biomolecular engineering, said quantum dot polymerization shows promise for highly controlled growth of sophisticated polymers. “The beauty of this is, if you have monomer A and you want to add monomers B and C in a specific sequence, you can do that,” she said. “In a random polymerization, they would be randomly dispersed along the polymer backbone.

Rice University’s Eilaf Egap, an assistant professor of materials science and nanoengineering and chemical and biomolecular engineering, holds a vial of quantum dots her lab is using to catalyze the creation of functional polymers. Photo by Jeff Fitlow

“The implication here — and part of our broader goal – is that we can synthesize organic-inorganic hybrid structures in a controlled and periodic way for many applications,” Egap said.

She anticipates the process could also lead to the discovery of novel polymers. One might be a quantum dot photocatalyst with an attached semiconducting polymer that would simplify the manufacture of solar cells and other devices.

“These could also be relevant to light-emitting diodes, magnetoelectronics and bioimaging,” she said. “We could grow them all at once. That’s the dream, and I think we are within reach.”

The National Science Foundation supported the research.