Thixotropy in Formulation describes reversible gel-to-sol transitions under shear, improving dosage form handling. Thixotropy In Formulation is a desirable property in liquid pharmaceutical systems, which should have: High consistency in the container. Yet pour or spread easily upon use. Procaine benzyl penicillin (procaine penicillin) combines benzyl penicillin with the local anaesthetic procaine. Thixotropy enhances suspension … Read more
Definition of Thixotropy (Time-Dependent Shear-Thinning): Thixotropy (Time-Dependent Shear-Thinning) is a time-dependent shear-thinning behavior. When a material is subjected to constant shear, its viscosity decreases over time. When the shear is removed, the material slowly regains its original viscosity. Key Features: Viscosity decreases with sustained shear. Recovery is reversible but time-dependent. Exhibits a hysteresis loop in … Read more
Definition of Dilatant Flow (Shear-Thickening): Dilatant Flow (Shear-Thickening) is seen in suspensions, protective gear, and industrial formulations. Dilatant fluids increase in viscosity with increasing shear rate. They become thicker and harder to move as more force is applied. Rheological Behavior: No yield stress Shear-thickening Flow curve is convex upward Equation (Power Law): $\tau = K … Read more
Definition of Pseudoplastic Flow (Shear-Thinning): Pseudoplastic Flow (Shear-Thinning) shows viscosity decreases with rising shear rate in fluids. Pseudoplastic fluids decrease in viscosity with increasing shear rate. The more you stir or apply shear, the thinner the fluid becomes. Here’s the graph showing the shear-thinning behavior of a pseudoplastic fluid. As shear rate increases, the … Read more
Definition of Plastic Flow (Bingham Plastic): A plastic fluid (Bingham Plastic) behaves as a solid until a certain yield stress is exceeded. Beyond this point, it flows like a Newtonian fluid with a constant viscosity. Rheological Behavior: Requires minimum force (yield value) to initiate flow. Once flow starts, shear stress and shear rate are linearly … Read more
Non-Newtonian systems are fluids that do not follow Newton’s law of viscosity. Unlike Newtonian fluids (such as water or alcohol), their viscosity is not constant and varies depending on factors like shear rate, shear stress, and, in some cases, time. This makes them essential considerations in the formulation and behavior of various pharmaceutical products. Common … Read more
Size & Shapes of Colloidal Particles range from 1–1000 nm, influencing stability and optical properties. Size & Shapes of Colloidal Particles include spherical, rod-like, lamellar, and irregular forms. Size of Colloidal Particles: Range: 1 nm to 1000 nm (i.e., 10⁻⁹ m to 10⁻⁶ m). Size influences: Surface area Stability Interaction with biological membranes Drug release … Read more
Effect of Temperature on Viscosity is key in drug formulation, lubrication, and industrial processes. Effect of Temperature on Viscosity shows liquids thin as heat rises and molecules move faster. Viscosity is inversely related to temperature – as temperature increases, viscosity usually decreases. Why? At higher temperatures, the kinetic energy of molecules increases. This reduces intermolecular … Read more
Definition of Kinematic Viscosity: Kinematic viscosity is the ratio of dynamic viscosity to the density of the fluid. $\nu = \frac{\eta}{\rho}$ Where: ν = kinematic viscosity (units: m²/s or centistokes, cSt) η = dynamic viscosity (e.g., poise, centipoise) ρ = density of the fluid (e.g., g/cm³) Why is it important? It relates viscosity to the … Read more
Law of Flow (Newton’s Law of Viscosity) states shear stress is directly proportional to velocity gradient. Law of Flow (Newton’s Law of Viscosity) explains Newtonian fluid behavior in pharmaceutical systems. This refers to the application of Newton’s law in describing fluid behavior. Newton’s Law (Restated): $\frac{F}{A} = \eta \cdot \frac{du}{dy}$ Where: F/A = applied force … Read more
