Devices and methods for electric field driven on-demand separation of liquid-liquid mixtures are provided. For example, methods for separating liquid-liquid mixtures, such as free oil and water, oil-in-water emulsions and water-in-oil emulsions, are provided that have separation efficiencies up to about 99.9%. The liquid-liquid mixture is contacted with a separator membrane assembly comprising a separator membrane formed of a porous oleophobic (or superoleophobic) material and an electrically conductive member. An electrical potential is applied across the porous oleophobic (or superoleophobic) material of the separator membrane to facilitate passage and separation of at least a portion of the first component through the separator membrane. Separation devices and such separator membrane assemblies are also provided.