Janus particles, named after a two-faced Roman God of the same name, are special types of nanoparticles or microparticles whose surfaces have two or more distinct physical properties. The god Janus had two faces so that he could see clearly into both the past and future.
Janus particles have a similar dual nature, as they are engineered to have two surfaces each with distinct physical properties. One combination for a Janus particle is to have one side hydrophilic (attracted to water) and the other hydrophobic (water repellant).
Until now, Janus particles could not be produced in large quantities because of their limited commercial applications. A new study by Binghamton University, State University of New York and Iowa State University offer a new application for the Janus Particles.
Their study has shown that the nanoparticles could be the key to more environmentally friendly paints and coatings.
Xin Yong—an assistant professor in the Department of Mechanical Engineering at Binghamton University’s Thomas J. Watson College of Engineering and Applied Science said, “Previous studies are heavily focused on structures formed by these particles at a very small scale, because they have unique surface properties. In this study, we are trying to use these particles to improve the performance of paints and coating, which no one has ever thought about.”
“Think for a minute about painting a wall in your house or apartment. To do it properly, there are a few general methods. You can do a primer layer and then a paint layer, which can take twice the time. You can mix paints with solvents, but solvents are a health risk and fumes can be an issue in poorly ventilated spaces. Or you can use water-based paints such as latex or acrylic latex, but many of those still contain solvents and may not be as durable.”
For the study, scientists mixed hydrophilic/hydrophobic Janus particles with commercial paints, then painted surfaces to see how the particles would react.
They found that the hydrophilic side oriented to the surface and helped the coatings adhere better, while the hydrophobic side faced toward the surface and made it water-repellant. The scientists also found that the particles diffused and arranged themselves into self-stratifying layers more quickly and in ways that did not completely follow their hypotheses.
Iowa State’s Shan Jiang (an assistant professor in the university’s Department of Materials Science and Engineering) said, “Currently no theory can be used to explain the self-stratification behaviors of Janus particles. However, more studies are warranted to probe the detailed mechanism [of the particles]. I hope by fully understanding the principles in Janus particle self-stratification, we will be able to design next-generation ‘smart’ coating materials that are more environmentally friendly with better properties.”
Scientists believe that Janus particles can prove to be beneficial in many other applications, including cosmetics, 3-D printing and drug formulations.
- Yifan Li et al, Self-stratification of amphiphilic Janus particles at coating surfaces, Materials Horizons (2020). DOI: 10.1039/D0MH00589D