Scientists are closer to understanding the forces that conspire to create a bad hair day, thanks to a new technique that allows researchers to probe friction and other forces between two hairs.
Understanding such hair-on-hair interactions may lead to new cosmetic products for taming hair or to more realistic computer-animated coifs. It also may help researchers better understand the interactions between other fibers, such as textiles for clothing or bandages.
“What is interesting about hair — while it has been with us for a long time, it is still very unknown,” says Gustavo Luengo, a research scientist with L’Oréal in Paris. Luengo and coauthors Mark Rutland and Hiroyasu Mizuno of KTH Royal Institute of Technology in Stockholm describe the new work in a paper published online November 30 in Langmuir.
Much work has been done on the surface structure of hair, but getting at how hairs behave when in each others’ company has been more difficult. To spy on these interactions, the researchers delicately attached a hair snippet 50 micrometers long to the tip of an atomic force microscope probe, which measures forces present at a surface. Bringing that hair-topped tip into close proximity with other strands of hair allowed the team to assess how the strands attract and repel each other at various distances and under particular conditions.
The researchers found that ordinary washed hairs are stand-offish at a distance, but get them as close as 15 nanometers and attractive forces kick in. A protective layer of fatty acids sits on a hair’s surface along with an unusual cocktail of molecules, says Rutland. Bleaching hair removes much of the fatty-acid layer, which affects the resulting interaction: charge builds up on bleached hair and seems to mask the closer-range attractive forces, the team reports. This can lead to fly-away hair.
Future work will look at the effects of high humidity — a notorious cause of bad hair days — on one hair’s relationship to another.
Translating these hair-hair interactions into how an entire head of hair — typically with more than 100,000 strands — behaves will also take more research. A broader understanding of the forces at play could lead to products that overcome or enhance these forces for a particular desired effect, says Luengo.
The new work is an interesting proof of principle, says mechanical engineer Jian Cao of Northwestern University in Evanston, Ill., whose research focuses on interactions between bundles of lightweight fibers for use in airplane wings or bicycle frames. “Friction forces are always something we have to deal with,” she says.
