Hairy, expanding nanoparticles produce versatile coatings

A team of European scientists think about hairy polymer nanoparticles much like Cruella de Vil thought about furry Dalmation pups: Both would make fine coats. But chemistry, rather than cruelty, is helping these researchers achieve their goals.

Nanoparticle-based coatings help researchers tailor the optical and mechanical surface properties of the objects they cover. For example, researchers at Toyota Central R&D Laboratories recently showed that silica particles could help make flexible, antiglare coatings. Creating coatings with different surface properties, however, typically demands that researchers make different suspensions filled with different nanoparticles tailored for each new application.

Joseph L. Keddie of the University of Surrey and his colleagues have now developed “hairy,” growing particles that could simplify that process. Working with chemists at France’s National Center for Scientific Research (CNRS) in Lyon, Keddie and his crew created spherical copolymer particles adorned with mops of poly(methacrylic acid) chains that extend with increasing pH (ACS Appl. Mater. Interfaces 2016, DOI: 10.1021/acsami.6b12015).

At low pH, the chains cling to a particle’s core, leading to spheres with a diameter of roughly 50 nm. But as the pH becomes basic and the chains extend, the nanoparticle’s diameter grows, reaching more than 90 nm above pH 7. By mixing these size-shifting particles with larger, fixed-size acrylate particles, the team created a variety of coating motifs.

For instance, at low pH, these two-particle suspensions dry to form layered coatings with smaller particles sitting atop the larger ones. But at basic pH values, particles are “jammed” into place as they dry, resulting in homogenous coatings, Keddie says. This variety of coating styles should allow researchers to use a single colloidal suspension to tune a variety of surface properties, such as hardness, reflectivity, and potentially even stickiness, the Surrey team says.

John G. Tsavalas, a polymer chemist at the University of New Hampshire, agrees. “This is the one stone, two birds, analogy where a single composition can be triggered to be suited to a wide variety of end use applications.”