SynopsisThe wetting behavior of human hair in water has been investigated using a technique based on the Wilhelmy balance principle. The experimental technique makes it possible to study the relaxation effects occurring at the solid-liquid-air interface. The results strongly suggest that interactions between the solid and the liquid make important contributions to wettability of the solid surface because of reversible reorientation of polar groups at the interface. The effects of scale structure, weathering, and mechanical damage on wettability of the fiber surface are discussed. Surface roughness of the fiber plays an important role in wetting hysteresis.

A technique is presented for characterizing the surface wettability of relatively long filaments based on scanning the filament with a liquid membrane. This technique overcomes the limitations of specimen size and crimp, which are inherent in the bulk immersion method for evaluating wettability changes along a filament. The technique can be used to study the surface distribution of finishes on long filaments, provided the wettability characteristics of the finished surface are significantly different from those of the untreated filament under the conditions of measurement. If the method is to be used to study finish distribution, an appropriate liquid must be used for the membrane, and guidelines for selection of such a liquid are discussed.

The stress relaxation process of keratin fibers may be divided into two stages, the first rapid stage involving hydrogen bond breakdown and the second slower stage being connected with disulfide bond scission. The temperature dependence of the second disulfide-controlled stage of stress relaxation of wool fibers from extensions of 20 and 40% was investigated at pH 7.0, both in the presence and absence of the sulfhydrylblocking agent N-ethylmalimide (NEMI). By plotting the relaxation modulus E r as a function of temperature, a transition at 70°C was observed for untreated wool fibers.An increase in the SH content by partial reduction of the wool cystine decreases this transition temperature, as was expected from previous evidence of the SH dependence of the transition temperature under stress obtained from stress-strain curves [20].By normalizing the stress at any time with a stress value in the presence of the SH-group blocking agent, it was possible to eliminate the first stage of stress relaxation without losing any component of the second stage. The viscoelastic behavior of the second stage was found to approximate that of a single Maxwellian element. The controlling mechanism in 'this stage appears to be a disulfide interchange catalyzed by free. SH groups, with an activation energy of approximately 23 kcal mole, which is independent of the strain level.

SynopsisMonitoring the wetting force exerted on a single fiber while the fiber is slowly and continuously immersed in a liquid and then withdrawn can provide several kinds of information about the physicochemical heterogeneity of the fiber surface. This method for scanning the fiber surface with an appropriate liquid has been found useful for studying the distribution of materials deposited on the surface of human hair to improve hair assembly properties, such as cationic polymers used in hair conditioners. It is shown how wetting force vs. immersion depth curves can reflect not only the average distribution of the material on the surface, but also the degree of uniformity of the deposit; further, wetting force curves for multiple immersions of the same treated fiber indicate the ease of desorption of the surface material. The results for the systems studied, which include mildly oxidized hair and smooth nylon fibers for comparisop, show how the relation between the critical surface tension of the fiber and the surface tension of the treating solution influences distribution and substantivity. Finally, data on the difference between advancing and receding wettability indicate how this hysteresis is related to the nature of the surface and to surface coverage by treating agents.