WIXLIB

PENETRATIONOF OILS INTOHAIRFIBERS287hours.The major decreasein withdrawal forcefor sunfloweroil-treatedhair was foundto occur within 24 hours, whereas for coconut oil-treated hair the short-term heattreatment had the largesteffect.The lowest withdrawal force, i.e., the closestto theuntreated hair, was found for the coconut oil-treated hair after 24 hours with heattreatment.In Figures2-4 the typicalwithdrawalforcecurvesare shownfor mineral,coconut,and sunfloweroil-treated hair fibersafter 5 min, 24 h, and with heat treatment.The decreasein withdrawalforceis associatedwith changesin fiber-surfaceconditionandcanbe explainedasfollows.The forceof adhesionis determinedby the effectiveareaofthe liquid bridgesformed betweenfibers and by capillary pressure,which in turndependson the surfacetensionof the oil, the contactangle of the oil on the fiber, andthe curvatureof the liquid bridge.An equationfor the adhesiveforcedue to capillarityfor two parallelfibershasbeenderivedby Brookseta/. (7). A decreasein the amountofoil on the fiber surfaceby penetrationresultsin an increasein liquid bridgecurvatureand a decreasein contactarea,shownin Figure 5. From this combinedeffect,an initialincreasefollowed by a decreasein the withdrawal force is expected.Thus, decreasedwithdrawalforces found for sunflower and coconut oil-treatedhair fibers indicate thepenetrabilityof theseoils into the hair fibers,leadingto thinningof surfaceoil films.Unchangedwithdrawalforcesfor mineraloil imply the possiblelack of penetrationandfilm thinning. Thesefindingsare in good agreementwith fiber interior studiesperformedby secondaryion massspectrometry(SIMS)in combinationwith a time-of-flight(TOF) massspectrometer,where mineral oil was not detectedwithin the hair fiber crosssection,whereascoconutoil wasfound to penetratepartially or completely(2).EFFECTOF MINERALANDCOCONUTOILS ONGP MEASUREMENTSIt was the work of Stammet a/. (4) that showedthat the shift in the reflectance eaks160140'120A100602005 mmLength of Fiber MovedFigure 2. Typical withdrawal forcecurvesfor Indian hair fibers treatedwith coconutoil after 5 minutes(A), after24 hours(B), andafter24 hourswith heattreatment(C). Curvesshiftedarbitrarily.

288JOURNAL OF COSMETIC SCIENCE16014012010060402005 mmLength of Fiber MovedFigure 3. Typicalwithdrawalforcecurvesfor Indian hair fiberstreatedwith mineraloil after 5 minutes(A),after24 hours(B), and after24 hourswith heattreatment(C). Curvesshiftedarbitrarily.250200AE 5oE oo5OLength of Fiber Moved5mmFigure 4. Typicalwithdrawalforcecurvesfor Indianhair fiberstreatedwith sunfloweroil after5 minutes(A), after 24 hours(B), and after 24 hourswith heattreatment(C). Curvesshiftedarbitrarily.

PENETRATIONOF OILS INTOHAIRFIBERS289Figure 5. Schematicsof the oil liquid bridgebetweentwo fibers.Oil penetrationdecreasesthe contactarea,A rR2, andincreasestheLaplacepressure,P crcos0/r.wherecristhesurfacetensionofoil and0 isthecontactangle. The combinedeffectof thesetwo resultsin a decreasein adhesiveforce(P Al P2A2).for a hair fiber in the R-T and T-R modesat a given angleof incidencewasdue to thescaleangle. Depositionof thick oil films eliminated this shift by maskingthe scalestructurewith the oil film. For sucha system,the reflectancepeaksin the R-T and T-Rmodesoverlapped.In Figure6A the GP curvesrecordedin the R-T and T-R positionsfor an untreatedIndian singlehair fiber and for the samefiber treatedwith a mineraloilare shown.For the untreatedhair fiber the sharpspecularreflectancepeak occursat anangledifferentfromtheangleof incidence,dueto the inclinationof scalesrelativeto theaxisof the fiber. For R-T and T-R scans,the specularpeakshavea maximumat 38ø and52ø, respectively.From thesevaluesa scaleangle of 3.5ø for untreatedhair fiber iscalculated.After applicationof mineraloil, the specularreflectancepeaksoverlap,bothappearingat 45ø. The angleof reflectionbeingequalto the angleof incidenceindicatesthe formationof a smooth mirror-likeoil filmon the fiber surface. Hair-fiberscalestructureis no longerseen.Also, the sharperpeakswith higher reflectancecomparedtountreated hair fiber illustrate the lustrous surface withoutdiffuse reflectance. For mineraloil, the GP intensityscans,directlyafter oil treatment(not shownin Figure6A) andafter 24 hours,are similar regardingboth the peak positionas well as reflectedlightintensities.The additionalshoulderon the specularreflectancepeakfor R-T at a higherangleismostprobablycausedby thediscontinuityof film at certainlocations.After heattreatmentfor five minutes,the intensityof reflectancehasdecreasedby a factorof 1.6,as shownin Figure 6B. However,the shapeof the GP curveremainssimilar to thoseobtainedafter24 hours,with no separationindicativeof the scaleangle.Thus,evenafterthe heat treatment, most of the mineral oil remainson the hair surface.It is worthwhilementioning that the GP curvesremainedunchangedeven with heat treatment over alongerperiodof time (20 minutes).Finally, in orderto demonstratethe reproducibilityand reliability of the resultsand the method, the hair fiber was dipped into acetone,removingthe mineraloil film from the fiber surface.This resultedin the separationofscansfrom the R-T and T-R positions,giving a scaleangleof 3.4ø. Also, the reflectionintensitiesare comparableto onesobtained from the initial measurements.To some

290JOURNAL OF COSMETIC SCIENCEA0.05t Mineraloil24hiItiMineraloi124hII, R-T0.03I0.02j/'\untreatedT-RuntreatedR-T, 0.010.002O4O6080Scatteringangle(degrees)Bßral oil 24 h and heat0.025R-T0.020ß ' '0.015o.oo1 o,,eoveo,,eoveR-T l/vT-Ro.oo q[Io.ooo/I . .v'\' , ' \.020406080Scatteringangle (degrees)Figure 6. Goniophotometricintensityscans:(A) IndividualuntreatedIndianhair fiberand24 hoursaftermineraloil application.(B) 24 hoursaftermineraloil applicationwith short-termheattreatmentandafterremoval of oil film with acetone.

PENETRATIONOF OILS emay be explainedby mineraloil residues,especiallyaroundthe scaleedges.Thus, usinga goniophotometeras an optical tool to studythesurfacecondition of the hair fiber, we conclude that mineral oil forms a smooth andstablefilm on the top of the cuticularsheath.Mineral oil doesnot penetrateextensivelyinto the hairfiber in a 24-hourperiod,not evenat elevatedtemperatures.Reductioninpeak intensityafter heat treatmentis likely to be due to the penetrationof a smallamount of oil into the cuticularsheath,leavingmost of it on the surface.In Figure 7A the GP intensityscansare shownfor untreatedIndian hair fiber recordedin the R-T and T-R positions.Figure 7 alsodisplaysthe reflectancecurveswhen thesamefiberwastreatedwith coconutoil. As describedabove,a scaleangleof 3.6øis foundfrom the displacementof specularpeaksfrom the angle of incidence.Coconutoiltreatmentcoversthe scalestructureand resultsin sharpspecularreflectancewith increasedpeakintensities.After 24 hoursthe reflectionintensityhasdecreasedby a factorof 1.9 (seeFigure7B). However,peaksarestill positionedaroundthe angleof incidence.Applicationof heattreatmentfor onlya few minutesinducesa tremendouschangein theGP curves,with partial separation,as seenin Figure 7C. Intensity scansfrom the T-RandR-T positionsshowa reductionin total areobserved,indicatingthe changein the surfacedistributionof oil residues,the fiber scalestructureis likely to be exposed.Thus, the majoramountof depositedoilfilm on the surfacehasindeedpenetratedinto the hair fiber. Dipping the fiber intoacetoneremovesthe remainingoil and resultsin scansmatchingthoseof the untreatedfiber, as shownin Figure7D. The scaleangleis again3.5ø.Results from coconut oil treatmentdiffer fromthose from mineraloil treatmentinseveralways. Although measuredintensity does not allow exact quantification,thechangesin relative intensitiescan be usedas estimatesas long as measurementsareperformedon the samefiber underidenticalconditions.Hence,the reductionin intensityafter24 hourscouldindicatethe decreasein coconutoil film thicknesscoveringthehairfiber.For mineraloil, the reflectedlight at coconutoil may haveat leastpartiallypenetratedthe hair fiber within24 hours.After 24 hoursthe remainingsmoothcoconutoil film must be very thin,consideringthe effectof short-timeblow-drying.Severalstudiesconductedat TRI havedemonstratedthe looseningof scaleedgesand the formationof half-domesupon heattreatment of hair fibers. Under suchconditions,oil can wick into the cuticular structure.If so, then both mineral and coconutoil shouldpenetrateinto the hair becausetheirsurfacetensionsare similar.Although oils can wick by capillaritybetweenseparatedcuticlecellsat the surfacewherethe cellsmay be separated,their penetrationinto theentirecuticlesheathand the cortexdoesnot occurby capillarity.The fact that coconutoil wasfoundto penetrateandmineraloil doesnot supportsthis hypothesis.Becauseofthe much smaller volume, the cuticle can accommodateonly a small amount of oil.Therefore,theseGP observationsshowthat oilspenetrateinto the bulk of hair and skinby moleculardiffusion.EFFECTOF OTHEROILS ONGP MEASUREMENTSWe alsoconductedmeasurementswith variousotherplant-derivedoils. For hair treatedwith mustard oil, the scalestructure remained coveredafter 24 hours, even after addi-

292JOURNAL OF COSMETIC SCIENCEA0.12 coconutoil 2 min.Ii0.10 T-RIiIiIiß 0.08ß --I0.06lcoconutoil2min.0.04untreatedR-T/k,,,111 ;. n eatedT-R0.02---iß lBI0.0020406O80Scatteringangle (degrees)B0.07coconut oil 24 hrs.5o.o5 T-Roi 0.04. ß o.o3 coconutoil24 hrs.'l lR-TT-RuntreatedR-' '\ 11 1 untreated0.010.00. . .,, -.,--,a ,- a ---- ,, '- --,02o40 , --' - .60 -,,,,80Scatteringangle (degrees)Figure 7. Goniophotometricintensityscans:(A) tercoconutoil application.(B)24 hoursaftercoconutoil applicationcomparedto untreatedfiber.(C)24 hoursaftercoconutoil applicationwith short-termheat treatment.(D) After removalof oil film with acetone.tional heat treatment. Also, for hair treated with sesame,ricebran,and olive oils, thescalestructurewasnot apparentfromthe GP curvesevenafter24 hours,suggestingnopenetration.For olive oil, however,partial separationof reflectancepatternsfrom the

PENETRATIONOF OILS INTOHAIRFIBERS293c0.0250.020coconutoil 24 hrs. w. heat0.0150.010O.0O50.0000iiii20406080Scattering angle (degrees)D0.05oilremovedI/0.03o ,l removed0.020.010.00020406080Scattering angle (degrees)Figure 7. Continued.T-R and R-T positionsappearedafter additionalheat treatment.Surprisingly,for hairtreatedwith sunfloweroil, the scaleedgeswerepartly exposedafter24 hours,indicatingat leastpartial penetrationof sunfloweroil into the fiber. As GP scanscharacterizeonly

294JOURNAL OF COSMETIC SCIENCEthe hair surfacecondition,it is not possibleto determineif sunfloweroil penetrationhasoccurredonly within the cuticularlayer or throughoutthe hair fiber, involving thecortex.In general,polyunsaturatedoils do not seemto diffuseinto hair. SaturatedandmonounsaturatedDIFFUSIONoils seem to diffuse into the hair structure.MECHANISMIt is known that diffusionof small moleculessuchasdyesand surfactantsin wool l membranecomplexes,CMCs (8). Itis alsoknown that surfactantssuchas sodiumlauryl sulfatediffuseinto protein structureseffectivelybecauseof their ability to solubilizeproteinsby complexation(9). Sincewe are consideringthe diffusionof oils that are unchargedtriglycerides,this may beirrelevantin this instance.Basedon the work referencedabove,the diffusionor penetrationability of small moleculeswould be expectedto be throughthe CMCs, controlled by the affinity of the moleculesfor nonkeratinousproteinsin the CMCs, molecularstructure,and molecularweight. For example,mineraloil doesnot diffuseintohair becauseit is nonpolar,containinglonglinearhydrocarbonchainswith lengthsaboveC-20. Eventhoughthe straight-chainmolecularstructureis favorablefor diffusionbyreptation,lackof affinityseemsto preventit fromdiffusinginto hair.Vegetableoils,onthe otherhand,consistof triglyceridemoleculesin which threefatty acidmoleculesarenaturallyesterifiedto the three hydroxylgroupsof a glycerolbackbone.For example,coconutoil is rich in lauricacid(C-12 triglyceride),whereasin sunfloweroil linoleicacid(C-18:2 triglyceride)is predominant.Becauseof its polarcharacter,coconutoil seemstohavean affinity towardproteinmoleculesin the CMCs, and, therefore,this oil penetratesmorereadilyinto hair fiberscomparedto mineraloil. SinceC-12 fatty acidis a straightchainfatty acid,the molecularstructureof the triglycerideis alsofavorablefor diffusion.Diffusionoccursby an acid-basetype of interactioninvolvingthe estergroupsin the oiland the carboxyland amine groupsin the protein. Oils containingtriglycerideswithunsaturatedfatty acidsseemto encountergreaterresistanceto diffusion.Thesemoleculestend to be more spreadout becauseof the presenceof multiple doublebondsand arethereforedifficult to enter and movethroughthe narrowchannelsof the CMCs. Theseaspectsneed to be exploredfurther, basedon the dynamicsof thesemoleculesin aprotein environment.CONCLUSIONSThe work reportedin this paper showsthat the formationof oil films in hair fiberassembliescan be studied by two very different methods,interfiber adhesionand reflectanceof light. There seemsto be goodcorrespondencebetweenthe two methods,asshownby the agreementbetweenthe two methodsfor coconut,mineral,sunflower,andoliveoils.In to the hair becauseof a compactmolecularstructureandthe polarheadgroupof the triglyceridemoleculesthat constitutetheseoils. In a dynamicmode thesemoleculescan reptateand squeezethroughthe CMCs. On the other hand,polyunsaturatedoils do not penetrateinto hair,most likely becauseof the more open and spread-outstructuresof their triglyceridemoleculesandbecauseof the presenceof multiple doublebonds.The resultsreportedin

PENETRATIONOF OILS INTOHAIRFIBERS295thiswork showa complexrelationshipbetweencapillaryliquid films, interfibercapillaryadhesion,light reflectance,fiber surfaceand bulk structure,and moleculardiffusion.ACKNOWLEDGMENTSThese studieswere carried out in conjunctionwith the TRI project "AnalysisandQuantificationof Hair Damage,"supportedby a group of TRI corporateparticipants.This study was also partially funded by Marico IndustriesLtd. We thank Mr. R. B.Mohile for his support.REFERENCES(1) A. S. Rele andR. B. Mobile, Effectof coconutoil on preventionof hair damagePart I,J. Cosmet.Sci.,50, 327 (1999).(2) S. B. Ruetsch,Y. K. Kamath, A. S. Rele, and R. B. Mohile, Secondaryion massspectrometricinvestigationof penetrationof coconutand mineraloils into humanhair fibers:Relevanceto hair damage,J. Cosmet.Sci.,52, 169 (2001).(3) Y. K. Kamath and H.-D. Weigmann, Measurementof interfiber adhesion,J. Cosmet.Sci., 51, 351(2000).(4) R. F. Stamm,M. g. Garcia,andJ. j. Fuchs,The opticalpropertiesof humanhair. II. Lusterof hairfibers,J. Soc.Cosmet.Chem.,28, 601 (1977).(5) A. Guiolet,J. C. Garson,andJ. L. Levecque,Studyof the propertiesof humanhair, I,t.J. Cosmet.ScL,9, 111 (1987).(6) C. ReichandC. R. Robbins,Light scatteringandshinemeasurementof humanhair:A sensitiveprobeof the hair surface,J.Soc.Cosmet.Chem.,44, 221 (1993).(7) J. H. Brooks,U.K. Das, and L.J. Smith, Effect of lubricationon tensile frictional and weavingpropertiesof sirospunwool yarn, TextileRes.J., 59, 382 (1989).(8) P. N. Moore, S. Puvvada,and D. Blanckschtein,Role of surfactantpolar headstructurein proteinsurfactantconcentration,Langmzdr,19, 1009 (2003).(9) V. Sideris,L.A. Holt, and I.H. Leavet, A microscopicalstudy of the pathway for diffusionofrhodamineB and octadecylrhodamineB into wool fibers,J. Soc.DyersColorists',106, 1 (1990).

The hair used in this study was black hair of Indian origin supplied by Marico Industries Ltd., Mumbai, India. Pure coconut oil, mineral oil, and ricebran oils were also provided by Marico Industries Ltd. Cold-pressed extra-virgin olive oil (Filippo Berio, Italy), expeller pressed sunflower oil (Hain Pure Foods, Inc., New York), pure sesame oil