Characterisation of asphaltene monolayers using a Langmuir trough and an atomic force microscope at air-water and n-heptane-water interfaces

The Langmuir trough is a useful tool for studying surfactant behaviour at interfaces and interfacial phenomena in emulsions. The behaviour of different asphaltene fractions at air-water and n-heptane-water interfaces have been characterised by pressure-area isotherms, monolayer compression-expansion hysteresis, and relaxation characteristics.; Asphaltene monolayers were transferred to silicon wafer and mica substrates using the Langmuir-Blodgett and Langmuir-Schaefer method at a number of surface pressures. The topography of the Langmuir-Blodgett films was analysed using an atomic force microscope and the contact angle of the deposited films was measured by a drop shape analyser.; When comparing Langmuir-Blodgett films at different interfaces, asphaltene molecules were found to be more closely packed at the n-heptane-water interface than at the air-water interface.; The effects of two commercial demulsifiers on asphaltene monolayers at n-heptane-water interfaces were also analysed with regard to reduction of film rigidity.