In situ tensile deformation characterization of human hair with atomic force microscopy

Human hair fibers experience tensile forces as they are groomed and styled. Hence the behavior of hair under tension is of interest to beauty care science. Previous studies have used optical/scanning electron microscopy to characterize hair tensile response. For the first time, in situ tensile loading experiments on hair with atomic force microscopy (AFM) have been performed. A custom-built AFM sample stage allows loading hair fibers in tension. A technique to locate and image the same control area at different strains is developed. This is used to study morphology changes that occur with deformation. Caucasian virgin, chemically damaged and mechanically damaged hair samples are studied to assess the effects of damaging treatments and the differences between chemical and mechanical damage. Virgin and damaged samples treated with commercial conditioner are also studied to ascertain the effect of conditioner on the tensile response. Mechanisms for the observed results are discussed.