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Janus particles can offer a range of improvements in standard paints

Materials World magazine
29 Sep 2020

Particles with different chemistries and physical properties on both sides could transform a lick of paint. Idha Valeur reports. 

Named after the Roman mythology god Janus, property-altering nanoparticles could offer better water resistance, surface hardness and reduced levels of volatile organic compounds (VOCs) in coatings, especially waterborne emulsion paints – all without altering the bulk material. 

A team from Binghamton University and Iowa State University, USA, have synthesised these particles from acrylic monomers to have different chemistries and physical properties on both sides. One combination ‘is to have one side hydrophilic and the other hydrophobic, which makes them behave uniquely at interfaces and surfaces. Janus particles can be viewed as a particle version of a surfactant’, explains Shan Jiang, Assistant Professor at the Department of Materials Science and Engineering at Iowa State. 

‘We discovered that these Janus nanoparticles would adsorb onto the surface when formulated with coatings and improve the surface properties through a unique self-stratification and self-assembly process.’ The resulting layer on the coating’s surface, when engineered properly, improves the paint’s performance while still being applied as normal paint would.  

To ascertain the performance, the team has measured the water contact angle and hardness, as well as testing the coating film’s durability against an organic solvent rinse. 

‘The testing showed that adding Janus particles can effectively convert a hydrophilic economic primer into a water-resistant hydrophobic surface, while maintaining the adhesion of the primer. The surface hardness is boosted significantly and tackiness is reduced. In addition, the coating is resistant to solvent rinsing,’ Jiang states. He adds that a surface force study shows the stickiness reduces by up to three times.

As the synthesis process is based on commonly used emulsion polymerisation, it is said to be easily scalable. The team foresees multiple areas of application outside paints, for example, in cosmetics, construction, chemicals, ink formulations or in biomedical applications. Jiang explains that in creating functional surfaces, Janus particles offer a straightforward approach. 

Currently, they are working on both understanding the detailed mechanisms of self-stratification and synthesising smaller particles, as well as being actively on the hunt for industry partnerships to progress commercialisation.