title: The effect of treatments on the shear modulus of human hair measured by the single fiber torsion pendulum.
abstract: 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.
authors.affiliation: TRI/Princeton, P.O. Box 625, Princeton, NJ 18542, USA.
authors.forename: D L
authors.initials: DL
authors.lastname: Harper
authors.forename: Y K
authors.initials: YK
authors.lastname: Kamath
mesh_terms: 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
chemical_list: D002593:Cetrimonium Compounds; D006203:Hair Preparations; C506623:PQ10 compound; D000644:Quaternary Ammonium Compounds; D002482:Cellulose; D000077286:Cetrimonium