Scanning the scientific literature for applications based on graphene quickly turns up examples such as electronics, sensors, and energy storage devices. Here comes a new one—hair care products.
Researchers at Northwestern University report that the ultrathin carbon material can dye hair in a range of dark colors (Chem 2018, DOI: 10.1016/j.chempr.2018.02.021).
The product, for which the team has filed a provisional patent application, can be prepared as a low-cost, durable, water-based, formulation that does not include toxic compounds commonly used in hair dyes. As an added bonus, graphene-colored hair effectively combats electrostatic frizz.
Long-lasting commercial hair dyes typically alter hair color through a number of chemical reactions. An alkaline solution, generally ammonia-based, swells and opens the cuticles on the surface of hairs so color-changing compounds can penetrate the hair’s cortex. In the presence of an oxidizer such as hydrogen peroxide, the compounds, which include aromatic amines and phenols, react with the hair’s melanin pigments.
In contrast to those products, the graphene colorant forms a smooth coating on hair surfaces. To make the dye, the Northwestern group, which includes Chong Luo, Lingye Zhou, and Jiaxing Huang, used the biopolymer chitosan and ascorbic acid (vitamin C) to disperse flakes of graphene oxide (GO)—and the darker derivative, reduced GO—in water. GO is the common form of the material made by exfoliating graphite with strong oxidizers.
The researchers showed that the dye, which can be applied by spraying or brushing, binds tightly to hair, resisting fading for at least 30 washings. They attribute the tight binding to several factors including graphene’s thinness, which helps it conform to uneven surfaces; hydrogen bonding between graphene and chitosan; and chitosan’s ability to bind tightly to keratin, a protein on the surface of hair.
The coatings boast other advantages relative to commercial dyes. For example, due to graphene’s electrical conductivity, dyed hair resists electrostatic charging and unsightly flyaways common on dry winter days. And due to the material’s thermal conductivity, the dye may help dissipate heat on hot summer days.
“This multifunctional hair dye is an ingenious use of graphene-based materials that solves a problem in everyday life,” says Hui-Ming Cheng, a carbon nanomaterials specialist at Tsinghua University and the Chinese Academy of Sciences. He adds, it’s great that this application does not require high-quality graphene, which is often quite expensive to scale up.
CORRECTION: This story was updated on March 18, 2018, to correct the identity of the journal in which the graphene hair dye study was published. It was published in Chem, not Cell.