Janus’ colorful, magnetic balls could help combat fraud

Traders selling a slew of popular shoes, handbags and other items are becoming increasingly sophisticated, forcing manufacturers to find new technologies to stay one step ahead. Now, researchers report ACS Nano have developed tiny “Janus balls” that show their colorful side under a magnetic field. These microparticles could be useful in ink for anti-blocking tags, which can be detected with a standard magnet, the researchers say.

In ancient Roman folklore, Janus was the god of two-faced intercession. Similarly, Janus balls are called microspheres that have two sides with specific properties. Shin-Hyun Kim and his colleagues wanted to make Janus balls out of two immeasurable resins: one containing magnetic nanoparticles, and another containing silica grains. The magnetic side of the ball would also absorb carbon black, causing that hemisphere to appear dark, whereas the silica particles on the other side of the ball would automatically accumulate. into a crystalline surface, emitting structural colors. The result is tiny balls in which their black sides usually look up, but when a magnetic field causes them to move to their colored sides.

To make Janus balls, the researchers used a microfluidic device to unite the drones of the two resins, with surfactant added to stabilize the bonded droplets in a spherical shape. Because the silica colored side in the droplets was heavier than the black magnetic side, the gravitational force of the black side suddenly caused a face, like a roly-poly toy, when the balls were immersed in water. The researchers then placed the magnetic nanoparticles steadily in the balls in the same direction. By placing a magnetic field on the other side, they could turn the balls to their colored sides.

The researchers made red and green Janus balls using different sizes of silica grains, with their magnetic nanoparticles on the same side. By changing the direction of the activated magnetic field, they could change the colors of 3-D printed chameleon shapes and butterflies. The use of different colors and directions of Janus balls in ink could lead to interactive, interactive anti-fraud tags, the researchers say.