Superspreading of Trisiloxane Surfactant Mixtures on Hydrophobic Surfaces. 1. Interfacial Adsorption of Aqueous Trisiloxane Surfactant−N-Alkyl Pyrrolidinone Mixtures on Polyethylene

Interfacial adsorptions of aqueous solutions of trisiloxane surfactant (SILWET L77), N -alkyl pyrrolidinones [ N -butyl-(C4P), N -cyclohexyl-(CHP), N -hexyl-(C6P), N -2-ethyhexyl-(C2,6P), N -octyl-(C8P), and N -decyl-(C10P)], and their mixtures have been measured. The adsorptions at the air/aqueous solution interface were obtained from the plots of surface tension versus log( C ) by use of the Gibbs equation. The adsorptions onto the powdered polyethylene surface were determined by the use of UV spectroscopy for pyrrolidinones and two-phase titration for SILWET L77, respectively. The adsorptions at the solid/air interface were evaluated by the use of an equation derived from the Gibbs and Young equations. It was found that the addition of the N -alkyl pyrrolidinones to the solution produces little or no enhancement of the total surfactant adsorption at the air/aqueous solution interface. At the solid/aqueous solution interface, the enhancement effectiveness of the pyrrolidinones decreases in the order C2,6P > C8P > C6P > CHP > C4P, and their enhancement efficiency decreases in the order C2,6P > C8P > CHP > C6P > C4P. However, C10P, the most effective surface-active agent among the pyrrolidinones, produces no enhancement in the adsorption of L77 at both the air/aqueous solution and the solid/aqueous solution interfaces. The adsorptions of the individual surfactants and their mixtures at the solid/air interface are shown to be smaller by 1 order of magnitude than those at the air/aqueous solution and solid/aqueous solution interfaces. Consequently, the most significant fact of the addition of N -alkyl pyrrolidinones to an aqueous solution of L77 is the enhancement of the adsorption of L77 at the solid/aqueous solution interface.