Crafting polymer composites in one step with light

Polymer-nanoparticle composites are used in batteries, construction materials, nonstick coatings, and electronic and medical devices. But making them requires multiple steps or a lot of heat and chemicals. Plus, it’s hard to control where the nanoparticles end up in the material, which can hamper its functionality.

Now researchers can make such composites in one step, precisely placing nanoparticles, by using patterned light to cure resin-nanoparticle mixtures. “The key here is simplicity and rapidness,” said Ian D. Hosein, a materials science and engineer at Syracuse University who leads the work presented at the ACS Fall 2021 meeting. “We mix the formulation, cast it over a surface, cure it, and it’s done,” said Hosein, whose graduate student Shreyas Pathreeker presented the work in the Division of Polymeric Materials: Science and Engineering.

Since it can work with a wide range of mix-and-match materials and generate a variety of carefully controlled nanoparticle patterns, this low-cost technique could enable composites for a variety of applications. The team recently used the method to make superhydrophobic films. These consist of a dense, thin layer of titanium dioxide nanoparticles sitting atop a bumpy polymer surface (ACS Applied Polymer Materials 2021, DOI: 10.1021/acsapm.1c00744).

Composites are routinely made by curing light-sensitive monomers. But Hosein and his colleagues, he said, use masks—which are akin to photographic negatives—to spatially control where the resin polymerizes. The researchers also tune the intensity of light to speed or slow polymerization reactions. As the material’s density changes with polymerization, it gathers in some areas and also pushes the nanoparticles to control where they aggregate. “So we can pattern and direct where the nanoparticles are located while we’re synthesizing the material,” Hosein said.

To make the superhydrophobic material, they placed a mixture of titania nanoparticles and light-sensitive trimethylolpropane triacrylate monomer on a masking sheet riddled with a regular array of 40 μm wide holes and then illuminated it with UV light.

As the light polymerized the monomer through the holes, the material expanded and formed an array of bumps, and the nanoparticles were pushed to the surface. The combination of the micrometer-sized bumps and the nanoparticles makes water bead up and roll off the surface, which would be useful for nonstick and self-cleaning coatings.

Hosein said the researchers are using a similar technique to make stable, high-energy lithium-ion battery anode materials composed of silicon-carbon composite pillars with silicon nanoparticles. The team is also exploring light-harvesting coatings for solar cells that consist of metal nanoparticles periodically arranged in a polymer matrix.

Hong Yee Low, a materials scientist at the Singapore University of Technology and Design, said one limitation of this technique’s practical application could be the time and energy required for the UV curing. But the technique’s room-temperature process and minimal use of solvents, she said, make it stand out.