Swelling and dissolution of onion phases: the effect of temperature

Contact experiments have been performed between an onion lamellar phase and brine in the SDS/octanol/brine system. Using video microscopy we have studied the non-equilibrium behaviour of the swelling and dissolution process of onions. Experiments at T=20 and 30°C showed that temperature has a strong effect on their behaviour. At low temperature onions are observed to diffuse away from the onion phase and only swell slightly. However, by increasing the temperature we induce the formation of sponge phase (L3) at the onion/brine interface. Onions that initially swell then dissolve into L3 phase expel a stable core which moves to the micellar phase and remains there. Over a longer period of time (several days) we have also observed coalescence leading to the formation of large onions of up to ∼100 μm diameter. These huge onions have a radial distribution of domains, or solvent cavities, within them.