Phenomenological properties and phase behavior of benzylalkyldimethylammonium salts in the presence of benzene and electrolyte solutions

The solubilities of benzylalkyldimethylammonium salts (BADAX) in benzene we re characterized by the specific Krafft boundaries, depending on their mole cular structures. BADAX affords not only the Krafft boundary but also the i mmiscibility gap in water or aqueous electrolyte solutions. BADAX formed ag gregates in aqueous solution or in benzene when its concentration was above the critical solubility concentration (csc) of the Krafft boundary. It is assumed that the aggregate structure varies successively with the change in electrolyte concentration or oil-water ratio, The phase behavior of the mi xture of BADAX, benzene, water, and electrolyte was examined as a function of temperature or a function of component composition. The conditions under which a microemulsion phase appears or coexists with other phases are clar ified, and the change in aggregate structure is discussed, on the basis of the solubility and immiscibility gap.