Li is a professor in the Department of Materials Science and Engineering in the College of Engineering and head of the Soft Materials Lab.
You probably aren’t aware of the invisible carpets of polymers that keep everyday items from collecting dust and dirt. But there these so-called “polymer nanobrushes” are, protecting your glasses from getting smudged or keeping the underbellies of ships from corroding.
Polymer nanobrushes ensure that artificial joints don’t lock up and medical devices don’t gather germs. And Drexel researchers have come up with a way to make them better.
For years, the nanobrush production process has either involved “grafting-from” — similar to sprinkling seeds on soil and waiting for grass to grow — or “grafting-to” — more like transplanting individual blades of grass. The approach taken by Professor Christopher Li in the College of Engineering involves growing a functional, two-dimensional sheet of polymer crystals — something like a nanoscale piece of double-sided tape — and sticking it to an existing substrate, allowing the crystals to dissolve and the remaining polymer chains to spring up and form the brush’s bristles.
Drexel researchers’ new polymer nanobrushes, like those used to protect glasses from getting smudged, are more densely packed, and can help extend the life of various kinds of medical devices..
The relative amount of friction the brushes can eliminate by acting as a lubricant is determined by how long and rigid the polymers are and how far apart they’re spaced. Li’s method allows him to precisely tune those characteristics because he can control the formation of the two-dimensional crystal sheets, allowing for the creation of the most densely packed polymer brushes to date, with bristles less than a nanometer apart.
According to a paper in Nature Communications, Li’s team is even able to create polymer crystals with anchor points on both ends so they form a loop, which is a much sturdier bristle formation than a single-anchored polymer.
“One day engineers will be able to tailor-make incredibly durable polymer brush coatings to extend the usage lives of all kinds of uniquely shaped joints and couplings,” Li says.