Abstract
18-MEA (18-Methyleicosanic acid) is an unusual branched-chain fatty acid covalently bound to the cuticle surface of hair. 18-MEA makes the surface hydrophobic and acts as a boundary lubricant to decrease frictional resistance. It can be easily removed in alkaline conditions such as hair color or perm, and the surface becomes hydrophilic and friction increases. This is one of the phenomena of hair damage. Focusing on the recovery of 18-MEA on hair surface, we found a persistent 18-MEA layer can be generated on the surface of hair by the use of a specific tertiary amine. The combination of 18-MEA with the specific tertiary amine (Stearoxypropyldimethylamine : SPDA) makes the bleached hair surface hydrophobic, and its hydrophobicity is maintained even after shampooing. Characterization of adsorbed layers of 18-MEA/SPDA on a mica surface, as a possible hydrophilic surface model, was performed using Atomic Force Microscopy (AFM) and Angle-resolved X-ray Photoelectron Spectroscopy (AR-XPS).The results revealed that 18-MEA/SPDA formed a layer with high wear resistance, with an alkyl chain, the hydrophobic moiety, oriented at an angle of around 35°to the air interface and the anteiso-branch moiety of 18-MEA providing higher fluidity to the upper part of the layer. Sensory evaluation of this technology was also performed and it was recognized that 18-MEA/SPDA could provide not only a silky, smooth and moisturized texture but also the right amount of body/bounce and less frizz and flyaway.
