皮肤中表面能检测方案(接触角测量仪)

KRUSS Surface free energy of skin Application report： AR252e Industry sector： Cosmetics Author： F. Thomsen Date： 03/2006 Method： Drop Shape Analyzer- DSA100 Keywords： cosmetics， contact angle， surface free energy， wettability， wetting envelope Measuring the surface free energy of human skin Abstract Previously the wetting properties of cosmetic products could only be determined when sufficient"helping hands" wereavailable. Tests were carried out which in the product was applied to the skin and the result then assessed. It would behelpful if a prediction about the wettability on the skin could be made in advance， particularly as interactions between thevarious additives make the behavior more complicated. This gap in our knowledge can now be closed by making contactangle measurements with the DSA100. Method Human skin， just like any other surface， has a specificenergy that can be measured. And it is just this physicalproperty that， in combination with the surface tension ofthe cosmetic product， is responsible for its wettability. However， a single energy value for the human skin is notenough. Various skin types must also be taken intoaccount： skin can be dry， greasy， normal or even mixed. Ifthe energy profiles of all these skin types are known thenthe wetting behavior with various liquids can bepredicted. This ensures that different cosmetics can beperfectly matched to the particular user. Fig. 1： Schematic diagram of a sessile drop Experimental part Both Owens/Wendt and Fowkes describe the relationshipbetween the contact angle on a solid surface and thepolar and disperse fractions oand o of the surfacetensions of the two phases： With the aid of a drop shape analysis system contactangles are determined on the skin for different liquids.The surface free energy can then be determined directlyfrom these values， provided that the polar and dispersefractions of the liquids are known. Fig. 2： Drop shape analysis system DSA100 A collection of data for all skin types drawn up in this waymakes it possible to selectively alter the formulation ofcosmetics by making use of molecular parameters suchas polar behavior. This means that the number ofmeasurements that have to be carried out on volunteerscan be dramatically reduced. Result The following table shows the differences in energyresulting from different degrees of greasiness of the skin： Skin not degreased Skin degreased Surface free energy (mN/m) 43.7 32.9 Polar fraction(mN/m) 8.0 1.6 Disperse fraction(mN/m) 35.7 31.3 If the polar fractions of the surface tension are plottedagainst the disperse fractions then the result is the"wetting envelope"，which is shown here using non-degreased skin as an example.(see Figure 3). All liquidswhose data lie beneath the curve will provide completewetting. Fig. 3： Wetting envelope for non-degreased forehead skin Summary With the determination of the surface free energy ofhuman skin only the surface tension components of theliquidsinvolved are requiredtopermit reliablestatements to be made about the wetting behavior forarious types of skin. Literature C. Rulison： Two-Component Surface EnergyCharacterization as a Predictor of WettabilityandDispersability. KRUSS Application Note #213 (2000). A. Mavon， H. Zahouani， D. Redoules， P. Agache， Y. Gall，Ph. Humbert： Sebum and Stratum Lipids Increase HumanSkin Surface Free Energy as determined from ContactAngle Measurements： A Study on two Anatomical Sites.In： Colloids and Surfaces B： Biointerfaces. Vol 8， 1997.147-155. D.K. Owens， R. C. Wendt. In： Jour. Applied Polymer Sci.13，1741 (1969). F.M. Fowkes. In： Industrial and Engineering Chemistry， 56，12， 40 (1964). KRUSS GmbH|IBorsteler Chaussee Hamburg| Germany |\www.kruss.de|