Electrokinetic analysis reveals common conditioner ingredient interactions with human hair

This study aims to use electrokinetic analysis to investigate the deposition behaviour and conditioning efficacy of cationic surfactants on human hair, focusing on how surfactant structure, concentration and hair damage influence performance. It also aims to understand the mechanisms governing surfactant adsorption and their impact on hair manageability and health.

This research employed streaming potential measurements-including pH-dependent, time-dependent and concentration-dependent zeta (ζ)-potential studies-alongside wet combing analyses and ATR-FTIR spectroscopy to evaluate the adsorption affinity and conditioning effects of four cationic surfactants: behentrimonium chloride (BTMC), behentrimonium methosulfate (BTMS), hexadecyltrimethylammonium chloride (CTAC) and stearylalkonium chloride (STAC). A simplified model surface using silicon oxide (Si | SiO₂) wafers was also utilized to isolate the influence of hair's natural variability and fibrous structure.

Longer-chain surfactants like BTMC showed superior deposition and conditioning due to stronger van der Waals interactions, while bulky groups in STAC hindered deposition. BTMC outperformed BTMS, likely due to the chloride counterion's higher mobility. BTMC and BTMS were superior against CTAC and STAC due to their longer carbon chain length. Wet combing analyses revealed that BTMC significantly reduced combing forces, improving manageability, whereas STAC fared the worst due to its low adsorption. However, ATR-FTIR analysis indicated no reversal of oxidative damage, suggesting conditioners improve manageability without repairing structural damage.

The study highlights the importance of surfactant molecular structure-such as carbon chain length and counterion type-in deposition efficiency and conditioning performance, providing valuable insights for developing more effective hair care formulations. By leveraging electrokinetic analyses in the form of streaming potential experiments, we were able to quantitatively assess adsorption behaviour, ζ-potential changes and the dynamic interactions between surfactants and hair. These findings enhance the understanding of cationic surfactant-hair interactions, offering practical implications for optimizing conditioners to improve user experience and hair health.