Infrared External Reflection Spectroscopy of Sodium Dodecyl Sulfate Monolayers at the Air−Solution Interface: Removal of Bulk-Phase Water Concentration Effects

Abstract

Infrared external reflection (IER) spectra of a Gibbs monolayer of sodium dodecyl sulfate (SDS) at the air−solution interface were obtained at various concentrations of aqueous SDS. A new method is used to remove the effect of SDS dissolved in the bulk water phase on measured IER spectra. Corrected IER spectra reveal that (i) conformational order of the alkyl chain of SDS at the air−solution interface improves with increasing the SDS concentration, (ii) conformational order at concentrations >3 mM is nearly constant, and (iii) the alkyl chain of SDS is in a liquid crystalline state.