The effect of treatments on the shear modulus of human hair measured by the single fiber torsion pendulum.
Previous studies with the single fiber torsion pendulum have alluded to the ability of this device to selectively measure different regions of a fiber, namely, the core and the sheath. This selective ability of the torsion pendulum was explored further as a means of better understanding treatments effects. First, a substantial reduction in shear modulus was caused by simply abrading the hair fiber surface to remove the cuticle layer. In another experiment, bleaching was found to have a softening effect on the cuticle layer since the shear modulus was reduced significantly. Next, the fibers were subsequently treated with either Polyquaternium-10 or cetyl trimethylammonium bromide (CETAB) and measured again. The CETAB treatment resulted in an increase in the shear modulus indicating fortification of the cuticle layer. Polyquaternium-10 treatment increased the shear modulus slightly. These different effects are explained by the molecular sizes of these compounds-CETAB is a small molecule which can penetrate into the cuticle layer while Polyquaternium-10 is too large to do so. Lastly, the effect of moisture was evaluated by varying the humidity inside a chamber surrounding the sample mounted in the torsion pendulum. This showed a substantial inverse relationship between humidity level and shear modulus that was much more pronounced for bleached hair fibers than for untreated.
Harper
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TRI/Princeton, P.O. Box 625, Princeton, NJ 18542, USA.
Kamath
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D002482:Cellulose / Q000031:analogs & derivatives / Q000737:chemistry; D000077286:Cetrimonium; D002593:Cetrimonium Compounds / Q000737:chemistry; D004548:Elasticity; D006197:Hair / Q000737:chemistry*; D006203:Hair Preparations / Q000737:chemistry*; D006801:Humans; D000644:Quaternary Ammonium Compounds / Q000737:chemistry
D002593:Cetrimonium Compounds; D006203:Hair Preparations; C506623:PQ10 compound; D000644:Quaternary Ammonium Compounds; D002482:Cellulose; D000077286:Cetrimonium