Gold- and bronze-like paints that don't contain metal

Date:
October 14, 2020
Source:
American Chemical Society
Summary:
Lustrous metallic paints are used to enhance the beauty of many
products, such as home decorations, cars and artwork. But most
of these pigments owe their sheen to flakes of aluminum, copper,
zinc or other metals, which have drawbacks. Now, researchers have
developed organic-only dyes that can form films resembling gold
or bronze, without the need for metals.



FULL STORY ========================================================================== Lustrous metallic paints are used to enhance the beauty of many products,
such as home decorations, cars and artwork. But most of these pigments owe their sheen to flakes of aluminum, copper, zinc or other metals, which
have drawbacks. Now, researchers reporting in ACS Omega have developed organic-only dyes that can form films resembling gold or bronze, without
the need for metals.


==========================================================================
In paints, metal flakes tend to settle to the bottom of the can, requiring regular stirring during use and storage. Multiple coats of metallic paint
are often needed to provide good coverage, which adds weight to the object being painted. Also, when used in ink-jet printers, metallic pigments can
clog ink nozzles. For these and other reasons, researchers are trying to develop nonmetallic, organic paints with metal-like luster. But so far,
few candidates have displayed all of the desired qualities of solubility
in solvents, good film-forming properties and excellent stability over
time. Katsuyoshi Hoshino and colleagues from Chiba University in Japan
recently introduced a perchlorate-doped 3-methoxythiophene oligomer that checked all of these boxes, but it had to be dissolved in solvents that
are considered unsafe for painters.

To develop an industrially acceptable metal-effect dye, the researchers
wanted to make and test chloride-doped 3-methoxythiophene oligomers.

The team made two different versions of the chloride-doped oligomers,
which, unlike their previously reported perchlorate-doped counterpart, dissolved in water. They coated glass plates with solutions of the
new dyes and allowed them to dry. The two chloride-doped oligomers
produced lustrous gold- or bronze-like films, respectively, but they
each had a non-glossy dark stain, which resembled a coffee ring stain,
near the center. Although more research is needed to determine how to
prevent this stain from forming, both films had higher reflectance than
the one made by the perchlorate-doped oligomer. The paints are soluble
in water but can be made water-resistant by dehydration, which makes
their industrial implementation feasible. The new dyes could be used in commercial ink-jet printers, and they also might someday be implemented
in organic electronic systems, the researchers say.


========================================================================== Story Source: Materials provided by American_Chemical_Society. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Minako Tachiki, Reo Tagawa, Katsuyoshi Hoshino. Oligo(3-
methoxythiophene)s as Water-Soluble Dyes for Highly Lustrous Gold-
and Bronze-like Metal-Effect Coatings and Printings. ACS Omega,
2020; 5 (38): 24379 DOI: 10.1021/acsomega.0c02752 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201014141100.htm

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