School of Chemical Engineering, University of Birmingham, Edgbaston, Birmingham, UK.
The Procter & Gamble Company, Mason Business Centre, Mason, Ohio, USA.
Int J Cosmet Sci. 2023 Apr;45(2):224-235. doi: 10.1111/ics.12834. Epub 2023 Mar 14.
The nature and magnitude of molecular interactions on hair surfaces underpin the design of formulated products, of which the application involves a competitive adsorption process between cationic surfactants, fatty alcohols and surface actives such as silicone. The knowledge of molecular interaction with hair surface will not only provide insight on the surface binding affinity but also offer an effective methodology in characterizing surface deposits.
Untreated and chemically treated hair samples were treated with either conditioner chassis alone (gel network) or conditioner chassis plus silicone (chassis/TAS). Hair surface interactions against four different chemical functional groups, namely methyl (-CH ), acid (-COOH), amine (-NH ) and hydroxyl (-OH), were quantified in both ambient and aqueous environment using Chemical Force Microscopy, a method based on atomic force microscopy (AFM).
Surface adhesion on hair in ambient is dominated by capillary force that is determined by both the wettability of hair fibre (hydrophobic vs. hydrophilic), presence of any deposits and the chemical functionality of the AFM cantilever. Capillary force is diminished and replaced by electrostatic interaction when polar groups are present on both hair and AFM cantilever. A distinctively different force, hydrophobic interaction, plays a major role when virgin hair and hydrophobic functionalized AFM cantilever make contact in water.
Results acquired by AFM cantilevers of different functional groups show that hydrophobic interaction is a key driver for deposition on virgin hair, whilst electrostatic interaction is the most important one for bleached hair. Interfacial conformation of chassis components upon deposition is determined by the hair surface properties. Our study highlights the possibility of a range of polar groups, not necessarily negatively charged, on the damaged hair. Unlike conventional surface chemical analysis method, it is possible to quantitatively evaluate the interfacial conformation of deposited surface actives on hair, which identifies the target moieties for conditioning products on different types of hair.
毛发表面分子相互作用的性质和大小是配方产品设计的基础，其应用涉及阳离子表面活性剂、脂肪醇和硅氧烷等表面活性剂之间的竞争吸附过程。了解与毛发表面的分子相互作用不仅可以提供对表面结合亲和力的深入了解，还可以提供一种有效的方法来表征表面沉积物。
使用化学力显微镜（基于原子力显微镜（AFM）的方法）在环境和水相两种条件下，定量研究了未经处理和化学处理的毛发样品与调理剂底盘（凝胶网络）或调理剂底盘加硅氧烷（底盘/TAS）的相互作用。对于四种不同的化学官能团，即甲基（-CH ）、酸（-COOH）、胺（-NH ）和羟基（-OH），在环境和水相两种条件下，定量研究了它们与毛发表面的相互作用。
在环境中，毛发表面的附着力主要由毛纤维的润湿性（疏水性与亲水性）、任何沉积物的存在以及 AFM 悬臂的化学官能团决定的毛细作用力决定。当毛发和 AFM 悬臂上都存在极性基团时，毛细作用力会减弱并被静电相互作用取代。当 virgin 毛发和疏水官能化的 AFM 悬臂在水中接触时，一种截然不同的力，即疏水相互作用，起着主要作用。
不同官能团的 AFM 悬臂获得的结果表明，疏水相互作用是 virgin 毛发沉积的关键驱动力，而静电相互作用是漂白发毛最重要的驱动力。沉积时底盘组件的界面构象取决于毛发表面的性质。我们的研究强调了受损毛发上可能存在一系列极性基团，而不一定是带负电荷的基团。与传统的表面化学分析方法不同，它可以定量评估沉积在毛发上的表面活性剂的界面构象，从而确定不同类型毛发的调理产品的目标部位。
