Theories of Dissolution: The Danckwerts' Model and Interfacial Barrier Model

Various dissolution theories elucidate factors impacting the dissolution rate.

Danckwert's model postulates that the dissolution medium shows turbulence at the solid-liquid interface instead of a stagnant layer.

The agitated solvent containing macroscopic packets moves to the interface via eddy currents, absorbing and delivering the drug to the bulk solution.

Regular replenishment of solvent packets maintains the concentration gradient.

Here, the drug transport to the bulk solution is the rate-limiting step.

The interfacial barrier model considers a drug particle as a crystal with distinct interfacial barriers on each face. An intermediate concentration, a solubility function, exists at the interface due to solvation.

The dissolution rate is calculated per unit area and depends on the interfacial transport constant and concentrations in the static layer and bulk solution.

The drug's solubilization rate in the static layer is the rate-limiting step.