The surface of a healthy hair is covered in a lipid coating known as the F-layer (Figure 1). When hair is damaged and the F-layer is stripped away, hair can become dry and frizzy. Conditioners are used to help solve such problems by replenishing the lipids in the F-layer.
In recent years, research into hair damage and the texture of hair after using hair products has advanced rapidly, reflecting a drive to develop new hair care products. Numerous papers have been written about structural changes to hair, such as the lift-up of the scale-like structures of the cuticle on the hair’s surface. Lion’s research has focused on the friction between hairs, one of the factors that influence the texture of hair and the way it feels to the touch. Using a frictional force microscope (FFM), a type of scanning probe microscope (SPM), we are advancing research at the nano-level into the microscopic structure and friction characteristics of the outermost cuticle layer.
We treated a gold-coated cantilever with octadecanethiol to create a hair model probe with a chemical structure similar to that of the outer surface of a hair (Figure 2) to use in FFM. This enabled us to measure friction between hairs at the nano level.
Applying this technology, we were able to compare recently grown hair near the root with hair that had grown about 20 months earlier and had since been exposed to and damaged by external stimuli, such as environmental ultraviolet rays. We found that the surface structure and nano-level friction characteristics of these hairs differed (Figure 3). Furthermore, we were able to perform nano-level evaluations of how the basic hair conditioner ingredients repaired hair surfaces that have been damaged by perms or bleaching. We are using this approach to advance R&D in order to create hair care products that offer superior hair texture.