Researchers have combined a polymer material with the shape of a common kitchen tool to help better control the design and application of coatings for various products and surfaces. A team at Rice University’s Brown School of Engineering developed a technique that shows how microscopic bottlebrush polymers are drawn to the top and bottom of a coating applied to a surface. The discovery could lead to a way to customize the properties of coatings for specific applications.

microscopic bottlebrush copolymer materials, Rice University, Brown School of Engineering
Rice University graduate student Hao Mei holds a plate with a pattern of bottlebrush polymers spelling “RICE.” The microscopic polymers could give industry exquisite control over the properties of surface coatings. (Image source: Jeff Fitlow)

The research was led by Rafael Verduzco, an associate professor and chemical and biomolecular engineer at Rice who has been studying so-called bottlebrush copolymers for some time. He and his collaborators now have developed models and methods to refine surface coatings to make them, for instance, more waterproof or more conductive, depending on what an application demands.

Coatings are a key interest for Verduzco because they can be the difference between a successful product and one that fails, he said. “Coatings are ubiquitous,” he said in a press statement. “If we didn’t have the right coatings, our materials would degrade quickly. They would react in ways we don’t want them to.”

Because of this, coating a surface is a separate and different way of thinking than the product itself. Therefore, different processes have to be applied to this part of creating something new, he said. “You make something and then you have to find a way to deposit a coating on top of it,” said Verduzco.

Same name, different use

Resembling the kitchen implements of the same name, bottlebrushes consist of small polymer chains that radiate outward from a linear polymer rod.  The bottlebrushes self-assemble in a solution, which researchers than can work with to adjust their properties. “What we’re looking at is a kind of universal additive, a molecule you can blend with whatever you’re making that will spontaneously go to the surface or the interface,” said Verduzco. “That’s how we ended up using bottlebrushes.”

What researchers discovered in their work is that bottlebrushes mixed with linear polymers tend to migrate to the top and bottom of a thin film as it dries. These films, as coatings, are ubiquitous in products; for instance, they are currently used as waterproof layers to keep metals from rusting or fabrics from staining.

During this migration, the linear polymers hold the center while the bottlebrushes migrate to the air above or to the substrate below. This, in effect, decouples the properties of the coating from its exposed surfaces. “The chemistry of these materials is advanced sufficiently that you can pretty much put just about any kind of polymer as one of these bristles on the side chain,” said Verduzco. “You can put them in different order.”

Researchers published a paper on their work in the American Chemical Society journal Macromolecules.

The team conducted computational models and experiments demonstrating that variations in the bottlebrush itself could be used to control surface characteristics, making these polymers useful in coating applications.

Applications for these materials include drug delivery via functionalized bottlebrushes that form micelles; lubricants; soft elastomers; and even surfaces that heal themselves. However, one challenge researchers still face is that bottlebrush polymers are still difficult to make in bulk.

Elizabeth Montalbano is a freelance writer who has written about technology and culture for more than 20 years. She has lived and worked as a professional journalist in Phoenix, San Francisco and New York City. In her free time she enjoys surfing, traveling, music, yoga and cooking. She currently resides in a village on the southwest coast of Portugal.

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