Hair-On-Hair Static Friction Coefficient Can Be Determined by Tying a Knot

The study validated an equation for determining the self-friction coefficient of elastic fibers using a relaxed overhand knot, initially derived by Audoly et al. The methodology was tested with nylon thread and applied to single hair fibers, showing its effectiveness in providing high-throughput data on hair friction under various conditions. It was found that treating hair with 1 M sodium hydroxide significantly increased the self-friction coefficient, making the fibers suitable for forming small knots in medical applications. This method could be broadly applied to measure the self-friction coefficients of various elastic fibers across different scales.