Biophysics of Human Hair

Humanhairisananocompositebiological?ber. Maintainingthehealth, feel, shine, color, softness, andoverallaestheticsofthehairishighlydesired. Haircarepr- ucts such as shampoos and conditioners, along with damaging processes such as chemical dyeing and permanent wave treatments, affect the maintenance and groomingprocessandareimportanttostudybecausetheyaltermanyhairprop- ties. Nanoscalecharacterizationofthecellularstructure, mechanicalproperties, and morphological, frictional, andadhesive properties(tribologicalproperties)ofhair areessentialtoevaluateanddevelopbettercosmeticproductsandtoadvancethe understandingofbiologicalandcosmeticscience. Theatomic/frictionforcemic- scope(AFM/FFM)andnanoindenterhavebecomeimportanttoolsforstudyingthe micro/nanoscalepropertiesofhumanhair. Inthisbook, wepresentacomprehensive review of structural, nanomechanical, and nanotribological properties of various hairandskinasafunctionofethnicity, damage, conditioningtreatment, andvarious environments. Variouscellularstructuresofhumanhairand?nesublamellarstr- turesofthecuticleareidenti?edandstudied. Nanomechanicalpropertiessuchas hardness, elasticmodulus, tensiledeformation, fatigue, creep, andscratchresistance arediscussed. Nanotribologicalpropertiessuchasroughness, friction, andadhesion are presented, as well as investigations of conditioner distribution, thickness, and bindinginteractions. Tounderstandtheelectrostaticchargebuilduponhair, surface potentialstudiesarealsopresented. Thebookshouldserveasareferencebookonthebiophysicsofhumanhairand hairtreatments. TheresearchreportedinthisbookwassupportedbyProcter&GambleCo. in Cincinnati, Ohio, andKobe, Japan. IwouldliketothankCarmenLaTorrewhohad assistedinvariouspublicationsonhairresearch. Iwouldalsoliketothankmywife Sudha, whohasbeenforbearingduringthepreparationofthisbook. Powell, OH BharatBhushan November2010 v Contents 1 Introduction-Human Hair, Skin, and Hair Care Products. . . . . . . . . . . 1 1. 1 HumanHair . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1. 1. 1 TheCuticle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. 1. 2 TheCortexandMedulla. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1. 2 Skin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1. 3 HairCare: CleaningandConditioningTreatments, andDamaging Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 1. 3. 1 CleaningandConditioningTreatments: Shampoo andConditioner. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 1. 3. 2 DamagingProcesses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 1. 4 OrganizationoftheBook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 2 Experimental Methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 2. 1 ExperimentalApparatuses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 2. 2 ExperimentalProcedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 2. 2. 1 StructuralCharacterizationUsinganAFM. . . . . . . . . . . . . . . . 26 2. 2. 2 SurfacePotentialStudiesUsingAFM-Based KelvinProbeMicroscopy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 2. 2. 3 NanomechanicalCharacterizationUsingNanoindentation . . . 30 2. 2. 4 InSituTensileDeformationCharacterizationUsingAFM . . . 32 2. 2. 5 M