In a New Light

Summer 2013

Designer Composites

Laser light can be precisely directed and focused on tight spots to unleash big bursts of energy. And because laser light interacts with materials in unique ways, lasers give researchers a means to tweak materials at extremely small dimensions.

Spicer’s goal is to develop a laser-based technique to grow nanoparticles and tailor their compositions, shapes, and sizes directly inside polymers.

James Spicer, professor of materials science, is taking advantage of lasers to add new members to a family of materials known as polymer matrix nanocomposites. Composite materials, made by adding fillers to polymers, are stronger or more heat resistant, and are found in the Boeing 787 and in re-entry heat shields for spacecraft.

Using nanoparticles as fillers takes composites to the next level. Materials with nanometer dimensions have surprising properties that depend on the particle’s size, shape, and spacing. Until now, the potential of polymer nanocomposites has remained untapped largely because it is difficult to make the specialty materials affordably in large quantities.

Spicer’s goal is to develop a laser-based technique to grow nanoparticles and tailor their compositions, shapes, and sizes directly inside polymers. This would make it easier for scientists and industry to engineer nanocomposites with novel properties. They could, for instance, create polymers that are tough and scratch-proof, that conduct electricity, or are fire-retardant.

Today, making polymer nanocomposites involves generating the nanoparticles in a solution, separating them, and then distributing them in a liquid matrix that is subsequently cured. “The issue is that the nanoparticles can stick to one another, making it difficult to distribute them uniformly and get the properties you want,” Spicer says.

His approach is considerably simpler and more versatile. He starts with a clear, inert polymer that acts like a matrix to hold nanoparticles in place. The nanoparticles, depending on the application, can be metals, semiconductors, or ceramics.

First, he infuses the polymer with molecules containing atoms of the target nanoparticle. Heat decomposes the molecules, leaving behind atoms that clump into nanoparticles, which are dispersed randomly in the polymer matrix.

“Now we want to tweak the nanoparticle to give it a personality,” Spicer says. Change its chemical structure, say, or give it a coating of some other useful material.

This is where light enters the picture. After adding carefully chosen photonic materials to the nanocomposite, Spicer exposes the composite to short bursts of light from high energy, ultrafast lasers. Under the light pulses the photonic materials heat up and interact in sophisticated ways with the nanoparticles, tweaking their properties.

By selectively shining certain kinds of laser light and using multiple photonic materials, Spicer says it should be possible to control the structure, shape, size, and distribution of nanoparticles in the polymer. In other words, he gains the ability to quickly conjure different types of polymer nanocomposites with desired properties. “The real advantage of our approach is that it’s very scalable,” he says. “We want to make a lot of these materials.”

“We’re trying to engineer complicated nanostructures within polymers using photonic methods,” he says. “We want to understand how to engineer these particles, to form particles with desired features in order to carry out a specific task.”

His research could have broad applications. But one area he is focusing on is making photocatalytic materials, which speed up chemical reactions under light irradiation. Such composites could be tailored to split water and create hydrogen fuel, or to break down contaminants and purify water.