Non – Newtonian systems The majority of fluid pharmaceutical products are not simple liquids and do not follow Newton’s law of flow. These systems are referred to as non-Newtonian. Non-Newtonian behavior is generally exhibited by liquid and solid heterogeneous dispersions such as colloidal solutions, emulsions, liquid suspensions, and ointments. When non- Newtonian materials are analyzed in a rotational viscometer and results are plotted, various consistency curves, representing three classes of flow, are recognized, plastic, pseudoplastic and dilatant. Plastic Flow The curve for the plastic flow represents a body that exhibits plastic flow, such materials are known as Bingham bodies. Plastic flow curves do not pass through the origin but rather intersect the shearing stress axis at a particular point referred to as the yield value. (obtain after the straight part of the curve is extrapolated to the axis). A Bingham...
