Surface properties of hair

Breuer, M. M., The binding of small molecules and polymers to keratin and their effects on the physicochemical and surface properties of hair fibers, in Hair Research Status and Future Aspects, Orfanos, C. E., Montagna, W., and Stuttgen, G., Eds., Springer-Verlag, Berlin, 1981, 96. 

Measuring Changes of Intrinsic Surfaces Properties of Hair and Skin... 

The pH at which a protein or particle has an equivalent number of total positive and negative charges as determined by proton exchange is the isoionic point. The pH at which a protein or a particle does not migrate in an electric field is called the isoelectric point. The isoionic point is a whole fiber property of hair and is reflected in the equilibrium acid-base properties of the total fiber the isoelectric point is related to the acid-base properties of the fiber surface. 

Tensile properties are obviously whole hber properties, as opposed to surface properties, and it has been suggested that they are cortical properties not related to the cuticle. This is because of experimental evidence and is, in part, due to the importance of the alpha to beta transformation that occurs on stretching [5]. Wolfram and Lindemann [6] have suggested that the cuticle does contribute to the tensile properties, especially in thin hair. However, Scott [7] has provided support for the no cuticle involvement hypothesis, by evaluating the tensile properties of hair hbers that were abraded under controlled conditions. In no instance could he demonstrate a signihcant change in tensile properties where only cuticle had been abraded. 

Vibrational spectroscopy has had a profound effect on our understanding of the surface chemistry of silica. Indeed, it has been the model system for the use of IR spectroscopy for probing the surface chemistry of oxides, the first studies having been carried out in late 1950. The books written by Hair [1] and Little [2] in the sixties have become classics with respect to the early use of IR spectroscopy for studying the surface properties of silica and adsorbed species thereon. 

Infrared spectra can provide direct evidence on the chemical and physical processes that lead to adsorption on surfaces, and these reactions may, in turn, serve to differentiate the various types of surface present in such heterogenous systems as soil clays. Changes in the concentration or structure of the adsorbed species on aging or other treatments are readily followed in a single small specimen without the necessity for destructive analyses. The surface properties of clay minerals and other colloids of importance in soil have been studied particularly by Fripat and his colleagues, who have made considerable use of infrared spectroscopy. A review (Fripiat [1964]) of their work in this field has appeared. Studies of adsorbed species on silica, silica-alumina, alumina, and zeolites have been principally concerned with the highly dehydrated systems of interest in catalytic applications. This field has been reviewed by Little [1966] and Hair [1967]. 

In selecting cloths made from synthetic materials, one must account for the fact that staple cloths provide a good retentivity of solid particles due to the short hairs on their surface. However, cake removal is often difficult from these cloths - more than from cloths of polyfilament and, especially, monofilament fibers. The type of fiber weave and pore size determine the degree of retentivity and permeability. The objective of the process, and the properties of particles, suspension and cake should be accounted for. The cloth selected in this maimer should be confirmed or corrected by laboratory tests. Such tests can be performed on a single filter. These tests, however, provide no information on progressive pore plugging and cloth wear. However, they do provide indications of expected filtrate pureness, capacity and final cake wetness. 

In the category of silicone coatings used for surface modification of the specific substrates, functional silicone fluids are often used, which can selectively interact with the chemical groups of the substrate, thus modifying its surface properties. The use of functional silicones in the textile industry has been discussed in a number of recent publications.5 421 422 The use of different types of high-performace silicone-coated textiles, which include elastomers and resins, has recently been reviewed.423 The use of functional silicones in personal-care products, for example, in shampoos and hair conditioners, mentioned before,381 provides another well-known example. 

So far, only a limited number of full dielectric relaxation spectra for well defined systems are available. Apart from the technical problems involved in the measurements (sec. 4.5e) there is the colloidal problem of synthesizing sufficiently concentrated sols with homodisperse spherical particles, preferably having different radii but fixed surface properties. Latices are popular objects because the particles are easily made homodisperse and spherical. Nevertheless they are somewhat suspect because there may be hairs on the surface, drastically affecting lateral hydrodynamic motion close to the surface. Moreover, changing the radius requires new syntheses and it is difficult to guarantee exact reproducibility of the surface structure. Inorganic particles do not have these drawbacks but it is not so ea to synthesize these as perfect spheres. 

Scheuplein (1) concluded that diflFusion rates are high but transport capacities are limited in hair and ducts because these structures occupy only one-thousandth of the total skin surface area. The present data suggest that intercellular cement and desmosomes occupy 0.001-0.004 of the remaining area. Accordingly, penetration through the interspaces will be limited by their relatively small area for exposure. However, the interspace route could be significant for molecules that penetrate SC cells poorly. As with asphalt tile, properties of the solvent and composition of the cellular tile must be considered. 

Water soluble polymers are frequently incorporated in aqueous surfactant solutions in many domestic and technological applications (in formulations such as shower gels and hair shampoos), as viscosity modifiers, stabilisers and deposition aids. Water soluble polymers often interact strongly with surfactants in aqueous solution, giving rise to a rich pattern of behaviour in properties such as surface tension. The bulk properties of a variety of polymer/... 

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