In this study, we investigated how the lipids bound to the outermost surface of human hair are affected by chemical treatments such as hair bleach and ultraviolet (UV) radiation using time-of-flight secondary ion mass spectrometry (ToF-SIMS). Many lipid components are bound covalently via a thioester or ester linkage on the outermost surface of hair. We studied how these components are changed by chemical treatment. It was found that the fatty acids covalently bound via a thioester linkage are removed more easily than those with an ester linkage. Eighty percent of the 18-MEA (18-methyleicosanoic acid), which is a major component of lipids, was removed in a single bleach treatment, and most had vanished entirely after three treatments. We also investigated the influence of UV radiation and found that the amount of 18-MEA decreased with the radiation time. More than 90% of the 18-MEA was removed by UV radiation with corresponding exposure of three summer months. Copyright

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Viscoelasticity of monolayers of fluorocarbon/hydrocarbon tetrablock amphiphiles di(FnHm) ((CFCH)(CH)CH-CH(CFCH)(CH)) was characterized by interfacial dilational rheology under periodic oscillation of the moving barriers at the air/water interface. Because the frequency dispersion of the response function indicated that di(FnHm) form two-dimensional gels at the interface, the viscosity and elasticity of di(FnHm) were first analyzed with the classical Kelvin-Voigt model. However, the global shape of stress response functions clearly indicated the emergence of a nonlinearity even at very low surface pressures (π ≈ 5 mN/m) and small strain amplitudes (u = 1%). The Fourier-transformed response function of higher harmonics exhibited a clear increase in the intensity only from odd modes, corresponding to the nonlinear elastic component under reflection because of mirror symmetry. The emergence of strong nonlinear viscoelasticity of di(FnHm) at low surface pressures and strain amplitudes is highly unique compared to the nonlinear viscoelasticity of other surfactant systems reported previously, suggesting a large potential of such fluorocarbon/hydrocarbon molecules to modulate the mechanics of interfaces using the self-assembled domains of small molecules.

Films of mesoscopic domains self-assembled from fluorocarbon/hydrocarbon diblock copolymers (FnHm) at the air/water interface were found to display highly elastic behavior. We determined the interfacial viscoelasticity of domain-patterned FnHm Langmuir monolayers by applying periodic shear stresses. Remarkably, we found the formation of two-dimensional gels even at zero surface pressure. These monolayers are predominantly elastic, which is unprecedented for surfactants, exhibiting gelation only at high surface pressures. Systematic variation of the hydrocarbon (n=8; m=14, 16, 18, 20) and fluorocarbon (n=8, 10, 12; m=16) block lengths demonstrated that subtle changes in the block length ratio significantly alter the mechanics of two-dimensional gels across one order of magnitude. These findings open perspectives for the fabrication of two-dimensional gels with tuneable viscoelasticity via self-assembly of mesoscale, low-molecular-weight materials.

In this study, the effect of the damage level of 18-MEA on the hydrophobicity of hair surfaces and the mechanism of technology for replenishment of the lipid on damaged hair surfaces were examined using Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). The surface amount of 18-MEA was measured in Japanese women by ToF-SIMS. It was obvious that the 18-MEA was decreased drastically by coloring treatments, especially in individuals who underwent such treatments more than two times per year. Additionally, even in hair without any chemical treatments, more than 80 percent of 18-MEA was removed at the portion 40 cm from the hair root. The relationship between the surface contact angle of the hair fiber and the 18-MEA amount showed that 18-MEA played an important role in surface hydrophobicity. It was found that, as a replenishment technology of the surface lipid layer, 18-MEA conditioner treatment combined with a specific cationic surfactant (Stearoxypropyldimethylamine: SPDA) effectively results in persistent hydrophobicity and low friction on damaged hair surfaces. ToF-SIMS analyses revealed that the homogeneous adsorption layer provided by 18-MEA/SPDA treatment resulted in effective hydrophobicity in damaged hair.