Materials
Ethanol was purchased from Sinopharm Chemical Reagent Co., Ltd. Pure
water was provided by the water purification systems (Direct-Q8UV-R,
Merk Millipore, Germany). Human hair was provided by the author Qian-Ru
Xiao, who has no objection to the hair being used in this study.
Preparation and
characterization of the twisted hair fibers
Long black hair with a diameter of 90-100 μm was cleaned and used in
this study. The length of the hair fibers ranges from 40 to 70 cm. For
preparation of the twisted hair fiber, a raw hair fiber was placed
vertically with a weight hanging on its bottom end. Twist was inserted
at the top end of the hair fiber by a motor in the counter-clockwise
direction. Meanwhile, the weight at the bottom was tethered to avoid
twist release during the twist insertion. After twisting, the fiber was
folded at its middle point and formed a torque-balanced two-plied
structure. Then the single twisted hair filament was attached to a
folded paper with an observation window and observed with a macro lens.
ImageJ was used to measure the helical angles.