Swelling and dissolution of onion phases : The effect of temperature

Contact experiments have been performed between an onion lamel-lar phase and brine, in the SDS/octanol/brine system. Using video mi-croscopy we have studied the nonequilibrium behaviour of the swelling and dissolution process of onions. Experiments at T = 20 • C 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 sightly. However by increasing the temperature we induce the formation of sponge phase (L 3) at the onion/brine interface. Onions that initially swell then dissolve into L 3 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 co-alescence leading to the formation of large onions of up to ∼ 100µm diameter. These huge onions have a radial distribution of domains, or solvent cavities, within them.