Boundary Lubrication Performance of Polyelectrolyte–Surfactant Complexes on Biomimetic Surfaces

Abstract

Aqueous mixtures of oppositely charged polyelectrolytes and surfactants are useful in many industrial applications, such as shampoos and hair conditioners. In this work, we investigate the friction between biomimetic hair surfaces in the presence of adsorbed complexes formed from cationic polyelectrolytes and anionic surfactants in an aqueous solution. We apply nonequilibrium molecular dynamics (NEMD) simulations using the coarse-grained MARTINI model. We first developed new MARTINI parameters for cationic guar gum (CGG), a functionalized, plant-derived polysaccharide. The complexation of CGG and the anionic surfactant sodium dodecyl sulfate (SDS) on virgin and chemically damaged biomimetic hair surfaces was studied using a sequential adsorption approach. We then carried out squeeze-out and sliding NEMD simulations to assess the boundary lubrication performance of the CGG−SDS complex compressed between two hair surfaces. At low pressure, we observe a synergistic friction behavior for the CGG−SDS complex, which gives lower shear stress than either pure CGG or SDS. Here, friction is dominated by viscous dissipation in an interfacial layer comprising SDS and water. At higher pressures, which are probably beyond those usually experienced during hair manipulation, SDS and water are squeezed out, and friction increases due to interdigitation. The outcomes of this work are expected to be beneficial to fine-tune and screen sustainable hair care formulations to provide low friction and therefore a smooth feel and reduced entanglement.

Molecular Dynamics Simulation on Polymer Tribology: A Review

“…It considers 3-4 non-hydrogen atoms in common organic molecules as a coarsegrained particle and compares the simulation results with experimental measurements to fit the resultant force field parameters. At present, the Martini force field has been updated to the third generation, with further improvements in the description of hydrogen bonding and electronic polarizability, making it better able to simulate ionic liquids and polymers [35][36][37][38][39].…”

Atomistic Characterization of Healthy and Damaged Hair Surfaces: A Molecular Dynamics Simulation Study of Fatty Acids on Protein Layer

“…When this happens, the structural features can no-longer be reinstated to bring back the quality of the damaged hair by replenishing free fatty acids. There are reported coarse-grained simulations that looked at the adsorption of cationic surfactants [32,52] and cationic polyelectrolytes [53] to the hair surface. These compounds can also be used to restore the hydrophobic, protective barrier on damaged hair.…”