In this proposal we request beamtime on the Inter reflectometer to study the unexpected adsorption behaviour of the surfactant bis(2-ethylhexyl) sulfosuccinate caesium salt (Cs(AOT)) on both silica and mica surfaces as a function of temperature. This builds on previous ISIS work where the nature of the cation was found to have a big effect on the surprising adsorption of organic anions to an anionic surface. In particular, extending the work where we have observed a big difference in adsorption of the sodium and calcium AOT salts (on both mica and silicon substrates). In this work we directly challenge the ‘divalent ion bridging’ mechanism for this anion on anion adsorption by adsorption with a monovalent cation.