The Fundementals of Polymer-Micelle Interactions in Shampoo Formulations

At present the Unilever shampoo formulations are under preforming in categories of deposition efficiency and aesthetic appeal. It is hypothesised that the performance is being hindered by complexation in the shampoo. Understanding the complexation and the driving forces behind it was an essential process in the efforts to resolve the performance issues and to better understand the system microstructure. The shampoo formulation was broken down into its key components and investigated as primary systems of molecular and micellar surfactant (CAPB & SLES) solutions, secondary systems of surfactant and deposition polymer (quaternary ammonium modified hydroxyethyl cellulose) & surfactant and structuring polymer (hydrophobically modified alkali swellable emulsion polymer, HASE) micellar solutions, and ternary systems of surfactant, deposition polymer and structuring polymer micellar solutions. Surface tension and zeta potential measurements found that the surfactant head and tail group determine the interfacial properties of the system. SAXS and rheology experiments identified the formation of oblate ellipsoidal homo-micelles of SLES and CAPB at low concentrations (1 – 5 % w/w). Above 10 % w/w surfactant, SLES forms a cubic mesophase which transforms into lamellar at 70 % w/w, while the CAPB micelles transition into a novel A15 Frank-Kasper phase at 60 % w/w. A phase diagram was constructed depicting the surfactant-deposition polymer structural transitions as a function of concentration, from string-of-pearls to worm-like micelles bridging polymer chains. Surface tension experiments identified the presence of the critical aggregation concentration (CAC), the critical neutralisation concentration (CNC) and the critical micelle concentration (CMC) for the systems. At the CNC phase separation was observed by rheology and dynamic light scattering. The reversible swelling behaviour of the HASE polymer particles, of 90 nm, was determined to be induced by both increases in pH and addition of surfactant above a threshold concentration (1 % w/w). At low pH and in the presence of surfactant the HASE polymer formed a hexagonally packed mesophase. At high pH, the HASE polymer formed an undefined, entangled polymer gel network. At high concentrations of HASE polymer (20 % w/w) a surfactant-polymer lamellar phase was formed. The formation of a hexagonally packed cylinder mesophases was also identified in the ternary systems at low pH (4 – 6) and above surfactant concentrations of 2 % w/w. The concentration and ratio of surfactant and structuring polymer in the systems determines the packing of the formed mesophases. When the surfactant and structuring polymer are in ratio, the mesophase is highly ordered and contracted. However, when the surfactant is in excess the mesophase is much less defined and has a larger value associated with the d-spacing.