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Cuticle Surface Damage & Repair
Contact Angle Measurements
Contact angle measurements are used to measure the degree of cuticle surface damage on the hair. These measurements can be used to support cuticle surface protection and repair claims. Contact angle tests can also be used for more fundamental research.
Our hair has been designed, through evolution, to have a water-repellent surface. This helps drive-off rain droplets, making our hair more shower-proof. It also helps our hair, when it is wet, to detangle more easily. The water-repellent surface on hair is made from a combination of tightly bound surface lipids and a loose covering of sebum. An important tightly bound cuticle surface lipid is 18-MEA. 18-MEA is found nowhere-else in the human body and is perfectly designed for its role in the hair.
Many chemical treatments, for example hair bleaches and semi-permanent hair dyes, have been shown to remove tightly bound surface lipids, including 18-MEA, making hair less water-repellent, more tangly and harder to comb when it is wet. Treatments for the prevention and repair of this surface damage have become increasingly popular in the hair category.
Contact angle measurements measure how easily water spreads over the surface of the hair, and so can quantify cuticle surface damage. TRI Princeton offers an imaging method for measuring contact angle between hair and water droplets, using the Ramé-Hart Goniometer (Model 190 F2t). The measurement of the spreading of a water droplet on the hair over time allows us investigate surface wetting behaviour immediately after the water is applied and at different time-points. Images of droplets spreading on the hair over time can also be used to bring your claims stories more to life.
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Ramé-Hart Goniometer (Model 190 F2t)
The contact angle, qc, is the angle between the outside-edge of a water droplet and the hair surface. qc can be related to surface tensions by Young’s equation:
gSG = gSL + gLG cos qc
Where gSG, gSL and gLG are the surface tensions between the surface and gas, surface and liquid and liquid and gas, respectively.
Example image of a water droplet placed on a small bundle of hair fibres. Images such as this are taken at different time-points in the experiment.
Typical results showing the effects of bleach damage and a repair treatment on the contact angle of water directly after application (t = 0 seconds) and over 5 minutes. Data show that hair surface wettability increases with bleach treatment, and that the treatment product reverses some of these changes. Differences are most marked at 5 minutes.