The first detailed analysis of what happens to individual hair fibres as they rub past each other when tresses are tossed has been conducted down to a billionth of a metre, showing how to make hair smooth to the touch.
This nanoscale analysis is seen as the key to the next generation of shampoos, conditioners, and other products for repairing damaged, dry and lifeless hair.
The advanced presented today to one of the biggest gatherings of scientists on the planet, the American Chemical Society's national meeting in Philadelphia, could end frizzy perms, over-bleached waves and other mishaps that affect a global industry now worth some $60 billion annually.
"Given all the new hair treatments out there, there's a growing need to make hair feel more natural," says study co-author Eva Max, a doctoral student in chemistry at the University of Bayreuth in Germany. She and her colleagues have found a new way to measure the silkiness and softness of individual hairs.
"For the first time, we present an experimental setup that allows measuring the subtle forces, both physical and chemical, that arise when single hairs slide past each other or are pressed against each other," Max says.
The German team has used one of the most sensitive microscopes on the planet, an atomic force microscope that traces out individual atoms with an ultrafine tip.
Max has found how to mount individual hairs on the tip of an atomic force microscope and measure their interactions as they touch each other.
Max points out that this will be a major advance over conventional methods for testing hair care products which involve measuring the force required to comb hair under standardized laboratory conditions, and subjective measurements of hair feel.
The nanoanalysis with what they call "single hair force spectroscopy" reveals that hair feels rough and difficult to comb for two main reasons: mechanical damage to a hair's surface, or cuticle, creates scaly projections that jut out.
When hair fibres slide past each other, these scales create more friction than smooth hairs, causing a rough feel and making hair more difficult to comb.
To soften hair, conditioners must contain active agents to smooth-out these scales so that they produce less friction, the researchers say.
The second key mechanism sees negative charges build up on the surface of hair that causes repulsion between single hairs.
This repulsion causes friction and makes hair rough and difficult to comb.
To solve the problem, positively-charged chain line molecules (polymers) that neutralize the negatively charged surfaces are included in conditioner formula to provide a silky feel to hair.
But finding the right formula for repairing damaged hair is no easy task, notes Dr Claudia Wood, , a senior scientist at the chemical company BASF in Bayreuth, Germany, which funded the work.
In addition to hair interactions, many other factors, such as humidity, water content of hair, and hair stickiness, all affect silkiness, Dr Wood says.