Untangling Hair Dynamics

Got limp, lifeless locks? Or is your hair frazzled by frizz? Perhaps your mane is mangy-looking. You can blame all of these bad-hair scenarios on subtle molecular interactions between strands of hair. Scientists in Germany have developed a new tool for quantifying those interactions. The setup, they say, could help researchers study the effects of hair-care products in a more quantitative fashion than has been possible. And that, in turn, could lead to products that leave hair smoother and silkier.

Current ways of testing the effectiveness of hair-care products are either highly subjective or provide a disheveled pile of data. For example, some scientists gauge a hair’s silkiness simply by touching it. Some measure the forces required to run a comb through treated tresses—a calculation that weighs not only the interaction between hairs but also a hair’s interaction with the comb.

Chemists at the University of Bayreuth, in Germany, reasoned that they could get a simpler, yet quantitative and more reproducible, measurement of hair-hair interactions by attaching a short length of hair to the cantilever of an atomic force microscope (AFM) and then studying the subtle chemical and physical forces it exerts when pressed against another hair. Graduate student Eva Max presented the work during a symposium sponsored by the Division of Polymeric Materials Science & Engineering on Aug. 17 at the American Chemical Society national meeting in Philadelphia.

The length of the hair that Max glues onto the AFM cantilever is shorter than the hair’s diameter, which is on the order of tens of micrometers. Figuring out how to slice the hair so that it has a clean cut turned out to be the project’s biggest challenge, she said. Ultimately, Max found that a specialized microbeam laser gave her the precise trim she was looking for. To attach the tiny hair to the cantilever, Max used a micromanipulator that’s more commonly used to steady ova during in vitro fertilization.

“To optimize something, you first have to quantify it,” Max said. The modified AFM cantilever will allow hair-care product makers to quantify, for example, how subtle interactions, such as friction, change with different types of conditioners. “We now have a tool to optimize conditioners on a molecular scale,” added Andreas Frey, Max’s research mentor.