Rheological and Mechanical Properties of Dispersed Systems
The response of pharmaceutical materials to an externally applied stress or strain is reflected in their rheological and mechanical properties. The study of the response is referred to as rheology and the application of measurement techniques and instrumentation is referred to as rheometry or viscometry. All pharmaceutical materials undergo flow or deformation when subjected to externally applied stress or strain. This includes pharmaceutical systems such as free-flowing elixirs, ointments and creams, foams, and compacted powders. Dispersed systems include such diverse systems as liquid suspensions, liquid emulsions, semisolid powder-filled systems, semisolid liquid-filled systems, foams, and powder-filled solid polymeric systems. Powder-filled solid polymeric systems are typified by pharmaceutical film coatings. The rheological and mechanical properties of dispersed systems are not well understood, especially when the droplets or solid particles of the dispersed phase interact with one another, or interact with the surrounding bulk phase.