Breaking emulsions at a silicon surface studied by neutron reflectometry

Neutron reflectivity has allowed the measurement of the structures formed when high internal phase water-in-oil emulsions are in contact with hydrophilic oxide surfaces prepared at planar faces of silicon blocks. The emulsions were a dispersion of micrometre sized droplets of saltwater-in-hexadecane stabilised by various oligomeric amphiphiles such as sorbitan monooleate. Contrast variation by selective deuteration of different components of the emulsion shows that for highly stable emulsions an oil rich layer is produced at the solid-emulsion interface. There is an almost complete surfactant monolayer at the hydrophilic solid face, then a hexadecane-rich layer that persists for 150 Angstroms. For emulsions less stable to phase separation, a more complex structure involving broken aqueous droplets forms with aqueous lamellae spread over the oxide surface, again stabilised by adsorbed amphiphile layers