A new approach to the analysis of special disturbance spreading phenomena and problems of interfacial instability at the boundary surface between two immiscible liquids is proposed. The stability of the secondary liquid-liquid droplet or droplet-film structure in a polydispersed system is discussed. Three interrelated forms of instability are postulated : rigidity, elasticity, and plasticity. These events are understood as interactions between the internal and external periodical physical fields. The particular secondary liquid-liquid polydispersed system examined was a heavy-phase droplet (phosphoric acid)-light-phase firm (the synergistic mixture D2EHPA-TOPO in kerosene) structure submerged into a heavy-phase continuum. This system was obtained from a pilot plant for uranium extraction from wet phosphoric acid by the D2EHPA-TOPO process. A method and apparatus were developed to monitor voltammetrically the interfacial electrical potential appearing during the formation of the double electrical layer while two-phase contact occurs. NMR spectrometry was used to determine the resonant/characteristic frequency of the molecular complex which builds the secondary liquid-liquid droplet-film structure. The experimental results were in fair agreement with the postulated theory.