Boundary Lubrication Performance of Polyelectrolyte-Surfactant Complexes on Biomimetic Surfaces

Area of Science:

• Surface science
• Materials science
• Computational chemistry

Background:

• Aqueous mixtures of oppositely charged polyelectrolytes and surfactants are widely used in personal care products like shampoos and conditioners.
• Understanding the interfacial behavior of these mixtures is crucial for optimizing product performance, such as hair feel and manageability.

Purpose of the Study:

• To investigate the friction between biomimetic hair surfaces in the presence of adsorbed complexes formed from cationic polyelectrolytes and anionic surfactants.
• To develop new computational parameters for cationic guar gum (CGG) and assess the lubrication performance of CGG-surfactant complexes.

Main Methods:

• Nonequilibrium molecular dynamics (NEMD) simulations were employed using the coarse-grained MARTINI model.
• New MARTINI parameters were developed for cationic guar gum (CGG).
• Sequential adsorption and squeeze-out/sliding simulations were performed to analyze CGG-SDS complexation and lubrication.

Main Results:

• The CGG-SDS complex exhibited synergistic friction reduction at low pressures, outperforming pure CGG or SDS.
• Friction at low pressures was dominated by viscous dissipation within an interfacial layer of SDS and water.
• At higher pressures, increased friction was observed due to interdigitation as SDS and water were squeezed out.

Conclusions:

• The CGG-SDS complex demonstrates potential for effective boundary lubrication between hair surfaces.
• These findings can guide the development of sustainable hair care formulations for improved smoothness and reduced entanglement.
• Computational modeling provides a valuable tool for screening and optimizing cosmetic ingredients.