Lipophilic linker impact on adsorption of and styrene adsolubilization in polyethoxylated octylphenols

The impact of lipophilic linkers (long chain linear alcohols) on the adsorption of and styrene adsolubilization in polyethyoxylated alkylphenols (Triton X) nonionic surfactants with varying EO units on amorphous precipitated silica (Hi-Sil(R) 233) was investigated. The surfactant adsorption and styrene adsolubilization isotherms with and without linkers were compared. Results show that the presence of lipophilic linkers increases both surfactant adsorption and styrene adsolubilization and the percent increase of styrene adsolubilization was greater than the percent increase of surfactant adsorption for all studied systems. The increases were much lower than those reported for oil uptake in microemulsions, which emphasizes the differences in the effect of linkers between two-dimensional (adsorbed surfactant aggregates or admicelles) and three-dimensional (micellar and microemulsion) systems. The adsolubilization capacity of surfactants increases, up to a certain value, with increasing lipophilic linker tail length or concentration. Styrene adsolubilization at the water-silica interface decreases with increasing numbers of ethyoxylated (EO) units in the surfactant, especially at higher styrene loading levels. The enhancement of adsorption and styrene adsolubilization is thought to be caused by the linkers increasing interactions between styrene and surfactant hydrophobic groups. Additionally, the adsolubilization isotherms provide indirect evidence for possible phase separation or phase transition within the admicelles. These results provide us with information about multicomponent behavior at the solid/liquid interface and highlight the differences that exist in two-dimensional admicelle behavior and three-dimensional micellar and microemulsion systems. (C) 2003 Elsevier B.V. All rights reserved.