Adsorption and Bulk Assembly of Quaternized Hydroxyethylcellulose–Anionic Surfactant Complexes on Negatively Charged Substrates

Abstract

This study examines the adsorption and bulk assembly behaviour of quaternized hydroxyethylcellulose ethoxylate (QHECE)–sodium dodecyl sulphate (SDS) complexes on negatively charged substrates. Due to its quaternized structure, QHECE, which is used in several industries, including cosmetics, exhibits enhanced electrostatic interactions. The phase behaviour and adsorption mechanisms of QHECE–SDS complexes are investigated using model substrates that mimic the wettability and surface charge of damaged hair fibres. Two preparation methodologies, high-concentration mixing and gradient-free mixing, were employed to examine their impact on the complex equilibrium, phase behaviour, and adsorption properties of the complexes. The measurements of turbidity, electrophoretic mobility, and conductivity demonstrate the existence of nonequilibrium dynamics during the mixing process, which exert a significant influence on the structural and functional characteristics of the complexes. The quartz crystal microbalance with dissipation monitoring (QCM-D) was employed to investigate the adsorption of the complexes onto the substrates. The results demonstrated the critical role of intermediate SDS concentrations in enhancing deposition. The findings emphasise the importance of formulation and preparation protocols in designing stable, high-performance cosmetic products. This research advances our understanding of polyelectrolyte–surfactant interactions and provides insights into optimising QHECE-based formulations.