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Adsorption and Desorption of Nonionic Surfactants on Silica from Toluene Studied by ATR-FTIR

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journal contribution
posted on 2009-09-01, 00:00 authored by Rico F. Tabor, Julian Eastoe, Peter Dowding
The adsorption and desorption kinetics and equilibrium surface coverages for a range of poly(ethylene glycol) monoalkyl ether nonionic surfactants (CnEms) from toluene onto silica were studied using attentuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) coupled with a constant-flow liquid cell. The initial adsorption rate appears to be transport controlled, and broadly independent of molecular structure, whereas equilibrium adsorbed amounts are dependent on surfactant head group size (which controls both surface interactions and the surface−bulk partitioning). Desorption kinetic data are fitted to a simple two-step model based upon Langmuir-type kinetics. The results are interpreted in terms of a simple model comprising two modes of surfactant adsorption, each with a characteristic adsorbed amount and desorption rate constant; a possible physical basis for this observation is presented. Trace water levels appear to have a strong impact on the equilibrium surface coverages in these systems, possibly by influencing both surfactant interactions and solubility.