Morphological change in drop structure with time for abnormal polymer/water/surfactant dispersions

The morphological variation of complex drops of oil/water/oil (O/W/O) in un stable polymer/water/surfactant systems was investigated. A new, but simple , technique was developed to measure the internal phase ratio of multiple d rops. The morphology change occurred because of inclusion of oil droplets i nto the dispersed water drops which contained water-soluble surfactant. The variation in morphology can lead to a delayed phase inversion if a substan tial variation in the effective volume fraction of the dispersed phase occu rs. The time sequence of the morphology change of complex drops is as follo ws: In the early stage of stirring, most water drops that are formed contai n no internal oil droplets but some contain large internal oil droplets. As time proceeds, the relative size of the internal oil droplets to that of s urrounding water drops is appreciably reduced, while the water drops become richer in the continuous phase. The progressive increase in the internal p hase ratio of the dispersed phase will continuously increase the effective volume fraction of the dispersed phase and hence enlarge the water drop siz e. Eventually a balance might be reached between drop inclusion and escape, to give a steady-state, at which the drop morphology and size reach a cons tant value. If the rate of inclusion exceeds that of escape, so that a stea dy-state is not reached, a phase inversion will occur. The extent of variat ion in drop morphology with time was found to depend on the size of drops, which is highly influenced by the volume fraction of the dispersed phase, a nd the surfactant concentration in the system, which enables the water drop s to entrain a larger volume of the continuous phase. The large drops are a ble to entrain a larger volume of the internal oil phase and, thus, contrib ute more to increasing the effective volume fraction of the dispersed phase and to inducing a phase inversion.