32 SCIENCE NEWS | November 20, 2021ALL: K. LIET AL/SCIENCE ADVANCES2021SCIENCE VISUALIZEDYou’ve heard of disappearing ink. Now get ready for suddenly
appearing ink. Using a clear liquid, researchers can print a
full rainbow of colors on transparent surfaces. The trick is
printing the liquid in precise, microscale patterns that create
structural color, researchers report September 22 in Science
Advances.
Structural color arises from the way different wavelengths
of light bounce off microscopic imperfections on surfaces
(SN: 6/11/16, p. 32). “In nature, there are many beautiful
structure colors, such as the wings of butterflies, the feathers
of peacocks, the skin of chameleons and so on,” says Yanlin
Song, a materials chemist at the Chinese Academy of
Sciences in Beijing.
Song and colleagues printed structural colors on trans-
parent silicone sheets using an ordinary ink-jet printer and
clear polymer ink. The printer studded the silicone sheets
with millions of microscopic ink domes. Each dome served
as a single pixel in the resulting images, including of butter-
flies (top) and celebrities such as Marilyn Monroe.
Adjusting a microdome’s size changed the wavelengths of
light that the dome reflected and therefore its color. (Scanning
electron micographs show domes with different diameters,Tiny domes of see-through ink create
these colorful butterfliesabove left, and dark-field optical micrographs show the corre-
sponding colors created by those domes, right).
The denser the domes were packed, the brighter the image.
And printing a medley of differently colored ink pixels across
a single area created blended shades, such as brown and gray.
“I was excited to see that somebody had used [structural
color] for this purpose,” says Lauren Zarzar, a materials
chemist at Penn State. The new images “illustrated the versa-
tility of this mechanism.” She imagines using structural colors
to create complex optical signatures for anti-counterfeiting
features on ID cards or currency. Such shimmery, colorfast
hues could also be used in cosmetics, clothing or architecture,
she says. — Maria Temming5 μm 100 μmscivis.indd 32scivis.indd 32 11/3/21 9:30 AM11/3/21 9:30 AM