Hair fibers change

Weathering, Contaminants, and Color Change to Hair Fibers.128... 

Solid particles usually adhere to the hair surface through van der Waals or ionic forces [116-118], In water, the ease of removing these soils from a surface depends upon the relative affinities for each other of the water, soil, and substrate. These affinities are expressed as Wa, the work of adhesion, which is defined as the free energy change per unit area involved in removing an adhered solid particle from a surface (in this case the hair fiber) to which it is adhered. In water, Wa can be expressed as... 

Volume Changes During Water Binding to Hair Fibers... 

Experimental Determination of Hair Fiber Diameter Changes at Various Humidities... 

In this study, hair effects were measured by following changes in hair fiber friction. In general, the effect of chlorine was to increase the coefficient of fiber friction and to decrease the differential friction effect in hair. Changes in hair friction were observed even at parts-per-million levels of chlorine. Effects increased with the number of treatments and with decreasing pH from 8 to 2. 

Although human hair fibers vary in cross-sectional shape, from nearly circular to elliptical, normalizing most elastic and other properties to fiber thickness can significantly reduce experimental scatter. Thickness is usually characterized as fiber diameter or cross-sectional area. Corrections to diameter for ellipticity are generally not employed. Hair fiber dimensions are also necessary to calculate fundamental elastic properties, and dimensional changes are often employed to follow the course of chemical reactions with hair. 

Both single-fiber and multiple-fiber methods are available for determining hair fiber cross-sectional dimensions or changes. Single-fiber methods include linear density, microscope (light or electron), vibrascope, micrometer caliper, and laser beam diffraction. For multiple-fiber determinations, a centrifuge may be used. 

Curvature is perhaps the most important fiber characteristic for styling, combing, and other aspects of hair behavior. Permanent waves and hair relaxers function primarily by changing fiber curvature to produce either a curlier or a straighter hair fiber. When curvature is low (the hair is straight—... 

Scott and Robbins [123] found that high-load friction is independent of hair fiber diameter, in agreement with theory and with the results of Fishman et al. [128]. However, others [129] have reported a slight increase in friction with wool fiber diameter. For low-load hair on hair friction, this variable would be difficult to test because as fiber diameter increases, the load also changes appreciably. 

When hair fibers of an assembly are aligned parallel, maximum specular (mirror) reflectance can be obtained with minimum scattering [155]. The problem of consistently aligning the fibers of a tress or head exactly parallel or comparably perhaps produces the largest variance in shine evaluations and, therefore, interferes with the ability to see small changes in hair shine—thus, the obvious advantage of the instrumental methods that evaluate either single hairs or a parallel array of hairs [150-154]. 

Mechanical Hygrometers Materials such as human hair, wood fiber, and plastics have been used to measure humidity. These methods rely on a change in dimension with humidity. 

Postmortem changes at the hair root (proximal) end in 22 forensic hair samples derived from decomposed scalps included fibers with dark stained bands located toward the proximal end, defined as postmortem root banding, as well as unstained fibers with hard points or brush-like ends (Linch and Prahlow 2001). There remains little evidence as to how these different microscopic features originate, but postmortem root banding probably results from putrefaction and is not noted in older hair from archeological remains. 

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