Differences between African, Caucasian and Asian Hair

Researchers of IQAC-CSIC, in collaboration with the ALBA Synchrotron, demonstrate that African hair has more lipids that are highly disordered. This distinction with Caucasian and Asian hair might be relevant to develop new ethnic hair-care products.

Cerdanyola del Vallès, 14th December 2021Researchers from the Institute for Advanced Chemistry of Catalonia (IQAC-CSIC) in collaboration with the ALBA Synchrotron have studied and compared the lipid distribution of African, Caucasian and Asian hair fibers. More specifically, the work has determined the presence, distribution, and function of lipids of each ethnicity. The differences observed can explain some of the barrier properties against external substances that each hair type presents. In particular, African hair was demonstrated to have more lipids that are highly disordered, which can explain its differentiation from Asian and Caucasian hair concerning moisturization and swelling (when water content inside the fiber increases).

Read more on the ALBA website

Image: Left: Cross-sections observed by optical microscopy for Caucasian hair selected to analyze by μ-FTIR, regions were manually determined. Right: Chemical map of second derivative obtained at 2850 cm−1 (CH2 symmetric stretching) of Caucasian virgin hair (a) and Caucasian delipidized hair (b).

Credit: ALBA

A powerful infrared technique broadens its horizons

Infrared light has the right energy range to probe many interesting material properties, including the vibrational modes of molecules and the way electrons interact with external photons. As devices get smaller and faster, the ability to study the way light and matter interact at the nanoscale will become crucial for the development of quantum and microelectronic technologies.

A powerful infrared method for probing such phenomena is called scattering-type scanning near-field optical microscopy (s-SNOM), which uses the tip of an atomic force microscope (AFM) to focus infrared light down to about 10 nm, below the wavelength of the light itself (i.e., below the diffraction limit). However, because of the elongated geometry of the AFM tip, oriented perpendicular to the sample, s-SNOM is less sensitive to features of interest that lie parallel to the sample surface.

“Probing in-plane responses at the subwavelength scale has been a long-time hurdle for the technique,” said Ziheng Yao, a former ALS doctoral fellow and co-first author of a Nature Communications paper that reports on a way around this hurdle. “With our results, we can get not only the the top view of the object, but also the side views.”

At ALS Beamline 2.4, the researchers used s-SNOM to study samples of sapphire and LiNbO3, two well-characterized, prototypical materials suitable for a proof-of-concept demonstration. Both have a property (the dielectric function) that varies along different in-plane crystal axes.

Read more on the ALS website

Image: Schematic of the s-SNOM nanospectroscopy setup and the crystal orientation of the sample (a, b, and c axes). Red arrow indicates the in-plane component of the incident light, kin-plane. Rotating the sample changes θ, the angle between kin-plane and the c-axis. Inset: Image of the gold disk on sapphire (m-cut Al2O3). Sdark and Sbright are the two locations were spectra were collected. Scale bar = 1 µm.

Credit: Xinzhong Chen and Ziheng Yao/Stony Brook University