(64h) Polymer-Surfactant Complex and Shear Mediated Non-Equilibrium Colloidal Deposition Trajectories

This talk will present findings on colloidal deposition mechanisms in personal care products during rinsing processes involving formulation dilution and shear flow. We employ a laser based microscopy method to directly, sensitively, and simultaneously measure colloidal interactions, dynamics, and deposition for a broad range of polymer-surfactant compositions. Measured colloid-substrate interactions and deposition behavior in quiescent conditions show non-monotonic trends vs. polymer-surfactant composition and are synergistic in that they are not easily explained as the simple combination of single component mediated interactions. We then employ a flow cell/microscopy assay that provides in situ characterization of colloidal deposition and detachment as a function of dilution and shear flow. Results show initial shear-mediated detachment of colloids in the presence of polymer-surfactant complexes that produce depletion attraction, which does not produce tangential forces that can resist shear detachment. Further rinsing produces preferential dilution of surfactants, which causes re-deposition of colloids due to the increasing number and strength of cationic polymer bridges between anionic colloids and substrates. By decreasing the initial surfactant to polymer ratio, preferential surfactant dilution yields enhanced cationic bridging to resist shear detachment, produce more re-deposition, and the highest deposited colloid amounts. The success of capturing the role of formulation components on deposition during rinsing using the flow cell assay suggests it is well suited to screen new formulation compositions, materials, and processing methods.