New Insight on the Friction of Natural Fibers. Effect of Sliding Angle and Anisotropic Surface Topography

The friction anisotropy of human hair has been investigated as a function of angle using AFM fiber probe;measurements to evaluate the role of cuticle alignment. It is found that friction hysteresis, the difference in friction coefficients between sliding with or against the cuticle direction, is essentially nonexistent for native human hair. For damaged human hair, however a clear. friction hysteresis is observed; which appears to be a periodic function of the angle between the fibers. The implication is that antiparallel sliding is not in itself sufficient for friction, isotropy but that lifting of the cuticle, edges is required. A methodology to perform friction analysis independently for trace and retrace was therefore developed, which is applicable to any type of AFM lateral force measurement. It explicitly accounts for roll, noncircular cross section, and off-axis alignment as well as baseline drift,. Which allows real anisotropy in the friction coefficient to be deconvoluted from these artifacts.