dispersed phase

Think of chocolate chips scattered through cookie dough: the chips are the bits that are spread out and surrounded on all sides. In a disperse system, the dispersed phase is exactly that — the discontinuous material broken into small particles or droplets and distributed throughout the surrounding medium.

The dispersed phase is also called the internal phase, because each particle is isolated and enclosed by the continuous (external) phase. In a suspension the dispersed phase is solid drug particles; in an emulsion it is droplets of one liquid suspended in another. Its amount is usually given as the dispersed-phase volume fraction, which strongly affects how thick the product is and how stable it stays.

Properties of the dispersed phase drive the whole product. Particle or droplet size sets the settling or creaming rate and the visual appearance; surface charge governs whether particles repel or clump; and the total interfacial area created when one phase is finely divided is enormous, which is exactly why these systems are thermodynamically unstable and need stabilising agents.