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Cover The Physicochemical Basis of Pharmaceuticals

The Theory of Disperse Systems  

This chapter focuses on the theory of disperse systems. Various types of disperse system can be formed depending on the state of the disperse phase and the continuous phase. The chapter then looks at the drug distribution in pharmaceutical disperse systems. Drug molecules usually partition between the disperse phase and the continuous phase and can be present in both phases, but the concentration of drug is usually much greater in one phase. Disperse systems can be classified as molecular, colloidal, and coarse dispersions, according to the properties exhibited. Dispersed entities move in dispersions due to Brownian motion, diffusion, and sedimentation. Viscosity describes the resistance of a liquid to flow and the higher the viscosity of a liquid the greater the resistance of the liquid to flow when shear stress is applied. Increases in interfacial tension and interfacial contact area increase interfacial free energy and can destabilize disperse systems.