COADSORPTION OF SODIUM DODECYL-SULFATE AND DODECANOL AT A HYDROPHOBICSURFACE

Sum-frequency spectroscopy has been used to study coadsorption of dode canol and sodium dodecyl sulfate (SDS) at the interface between aqueou s solutions and a monolayer of octadecanethiol on gold. Selective deut eration was employed to distinguish between the two adsorbed surfactan ts. Mixed monolayers were studied over a range of SDS concentrations w ith dodecanol present at a level of 1 mol %. The results are compared with other data published previously and with literature studies of th e air/water interface. A quantitative analysis of the monolayer adsorb ed from 6 mM SDS + 10 mu M dodecanol showed that the monolayer compris ed 63% dodecanol and 37% SDS and had a packing density comparable to t hat of a monolayer of pure dodecanol. The composition of the monolayer was found to be isotope dependent. This dependence might arise from a highly surface active impurity in the SDS but can also be explained q uantitatively by a lattice model of the monolayer within regular solut ion theory.