Division of Surface and Corrosion Science, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden.
Institut Laue-Langevin, 71 avenue des Martyrs, CS 20156, 38042 Grenoble cedex 9, France.
Soft Matter. 2024 Oct 2;20(38):7634-7645. doi: 10.1039/d4sm00784k.
The surface of human hair is normally hydrophobic as it is covered by a lipid layer, mainly composed of 18-methyleicosanoic acid (18-MEA). When the hair is damaged, this layer can be partially or fully removed and more hydrophilic, mainly negatively charged surfaces are formed with a wide variety of physical and chemical characteristics. The cosmetic industry is currently embracing the opportunity of increasing the sustainability of their hair-care products whilst improving product performance. To do this, it is vital to have a deeper understanding of the hair surface and how it interacts with hair-care ingredients. This work contributes to this by harnessing the potential of neutron reflectometry (NR) with scattering contrast variation to describe hierarchical adsorption. Three types of hair-mimetic surfaces have been produced: two "healthy hair" models to probe the role of lipid structure, and one "damaged hair" model, to consider the effect of the surface charge. Adsorption of hair-care ingredients has then been studied. The results for these relatively short lipid models indicate that a methyl branch has little effect on adsorption. The "damaged hair" studies, however, reveal the unexpected apparent adsorption of an anionic surfactant to a negative surface. This preferential adsorption of the otherwise solubilised neutral components demonstrates a facile route to selectively deliver a protective film on a damaged hair fibre, without the need for a cationic species. On a more general note, this study also demonstrates the feasibility of using NR to characterize such complex systems.
人的头发表面通常是疏水的，因为它被一层脂质层覆盖，主要由 18-甲基二十烷酸（18-MEA）组成。当头发受损时，这层脂质层可能会部分或完全被去除，形成更多亲水的、主要带负电荷的表面，具有各种物理和化学特性。化妆品行业目前正在抓住机会提高其护发产品的可持续性，同时提高产品性能。为此，深入了解头发表面以及它与护发成分的相互作用至关重要。这项工作通过利用中子反射测量（NR）与散射对比度变化的潜力来描述分层吸附，从而为此做出了贡献。已经制备了三种头发模拟表面：两种“健康头发”模型用于探测脂质结构的作用，以及一种“受损头发”模型，用于考虑表面电荷的影响。然后研究了护发成分的吸附。对于这些相对较短的脂质模型，结果表明甲基支链对吸附几乎没有影响。然而，“受损头发”的研究揭示了阴离子表面活性剂出乎意料地优先吸附到负表面。这种对原本溶解的中性成分的选择性吸附表明，在不需要阳离子物质的情况下，在受损的头发纤维上选择性地输送保护膜的简便途径。更一般地说，这项研究还证明了使用 NR 来表征这种复杂系统的可行性。
