This work is concerned with the interfacial behaviour of a range of non-ionic and anionic surfactants mainly at the sapphire/water interface. At the air/liquid interface, the adsorption of a series of a series of specially synthesized pentaethylene oxide surfactants was characterized at the molecular level by using specular neutron reflection in conjunction with isotopic labeling. Ihe information obtained about composition and the fragment distributions in the adsorbed layers helps to explain the variations in their macroscopic properties. The results indicate that the architecture of the surfactant hydrophobe, such as the branching and the position of aromatic group in the alkyl chain, has a strong influence upon the surface absorbed amount and limiting surface tension.