Zwitterionic alkyldimethylammonium carboxybetaines are used in applications which require mildness, e g cosmetics and isolation of membrane proteins, although they interact strongly with other charged surfactants. They have an unusually high solubility and their surface behaviour suggests a large conformational change as the alkyl spacer length in the head group is increased. We have started a study the structural changes associated with the large change in limiting surface tension as a function of 3 different spacers by synthesizing and measuring the neutron reflectivity of all our isotopic species (9) in NRW. We need further time to complete the structural characterization with D2O measurements and the study of the interactions with anionic (SDS) and cationic (C12TAB) surfactants