In-situ Tensile Deformation and Surface Charging Characterization of Human Hair with Atomic Force Microscopy

Strong beautiful hair is universally desired across various cultures. Hence, the ways in which cleaning conditioning, grooming and styling processes affect the strength, feel and manageability of hair is of interest to beauty care science and technology. Human hair is a complex nanocomposite biological fiber. In this thesis, experiments are performed to better understand mechanical and electrical properties of human hair fibers. Human hair fibers experience tensile forces during many grooming and styling processes. Hence, characterizing the tensile response of human hair fibers is of considerable interest. The effect of tension on human hair is studied using an atomic force microscope (AFM) and a custom built tensile sample stage. The tensile sample stage allows loading a single hair fiber in tension. In the methodology used here, straining of the hair fiber is stopped intermittently and a marked control area is imaged with the AFM at different strains, upto break point. Morphological changes and deformation that occur with increasing strain are studied. Stress strain data is also simultaneously captured by the sample stage. To understand the effect of damage and treatment on hair fibers virgin, chemically damaged, virgin conditioner treated and chemically damaged conditioner treated, Caucasian hair fibers are studied. To understand differences between damaging processes, mechanically damaged hair is also studied and compared to chemically damaged and virgin hair. Hair from different ethnic types is known to have significantly different properties. In order to understand this difference better, the tensile response of virgin Caucasian, Asian and African hair is investigated. The wet tensile