Pseudoternära

Pseudoternära, or pseudo-ternary, is a concept used in colloid and interface science to describe a ternary phase diagram that represents a multi-component system by collapsing two or more components into a single pseudo-component. In such diagrams, the three corners typically correspond to oil, water, and a pseudo-component that represents a mixture of one or more real constituents, such as a surfactant and a co-surfactant. The pseudo-component is defined by a fixed internal composition (for example, a fixed surfactant-to-co-surfactant ratio), while its overall amount can vary.

Construction and interpretation of a pseudoternary diagram start from a complex system containing several chemical species. One or more components are combined into the pseudo-component, with the internal make-up kept constant across the diagram. The diagram then plots the three effective components on a triangular graph, with every point representing a specific overall composition of oil, water, and the pseudo-component. Phase behavior is read from regions separated by binodal curves, with tie-lines indicating coexisting phases. The approach simplifies analysis by reducing dimensionality, while preserving essential trends in phase behavior.

Applications are common in areas such as microemulsions, emulsification, detergency, cosmetic formulations, and certain polymer or pharmaceutical systems. Pseudoternary diagrams help formulators optimize stability, clarity, and texture by visualizing how changing the overall fractions of oil, water, and the pseudo-component affects phase structure.

Limitations include the requirement that the internal composition of the pseudo-component remains fixed for the diagram to be valid, and the results can depend on temperature, pressure, and other conditions. The method provides a practical but conditional view of multi-component systems rather than a universal description.