AFM Based Single Hair Interaction Measurements

New material development and understanding existing market products requires detailed testing of treated surfaces and thin films. The effects of hair care products like shampoo and conditioner show in properties like combability and haptic perception of hair. Therefore, systematic investigations are carried out in order to improve the understanding and the quality of ingredients. The search for adequate physical test methods is motivated by the fact that a personal care ingredient supplier like BASF screens new, toxicologically not yet approved chemistries only in-vitro for improved application properties on human hair. Our aim is to provide methods that allow quantifying friction and interactions (Fig. 1) as a consequence of hair treatment on the single hair fiber level. We have developed an approach in which hair-hair interactions can be detected using Atomic Force Microscopy (AFM) force spectroscopy. We use hair fragments for our measurements, which were cut from Caucasian hair and immobilized on tipless AFM cantilevers. Our technique allows in-situ force measurements in a closed liquid cell to quantify those hair's force properties. For this, we collect different signals of the modified cantilevers in aqueous environment to measure mechanical properties like friction or adhesion in a subnanoscale. Subsequently, different active ingredients of hair care products are added, rinsing cycles are performed, and the resulting changes in friction and interactions are monitored.