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 (SIL WET L77), N-alkyl pyrrolidinones [N-butyl-(C4P), N-cyclohexyl-(CHP), N-hexy l-(C6P), N-2-ethyhexyl-(C2,6P), N-octyl-(C8P), and N-decyl-(C10P)], and the ir 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 an d two-phase titration for SILWET L77, respectively. The adsorptions at the solid/air interface were evaluated by the use of an equation derived from t he 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 to tal surfactant adsorption at the air/aqueous solution interface. At the sol id/aqueous solution interface, the enhancement effectiveness of the pyrroli dinones decreases in the order C2,6P > C8P > C6P > CHP > C4P, and their enh ancement efficiency decreases in the order C2,6P > C8P > CHP > C6P > C4P. H owever, C10P, the most effective surface-active agent among the pyrrolidino nes, produces no enhancement in the adsorption of L77 at both the air/aqueo us solution and the solid/aqueous solution interfaces. The adsorptions of t he 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 sign ificant fact of the addition of N-alkyl pyrrolidinones to an aqueous soluti on of L77 is the enhancement of the adsorption of L77 at the solid/aqueous solution interface.