Physical Pharmacy: Rheology, Colloids, and Flow Properties
English with a size of 2.89 KBPeptization
The process of converting a precipitate into a colloidal solution by shaking with a suitable electrolyte is called peptization. The electrolyte acts as a stabilizing agent, known as a peptizing agent.
Kinematic Viscosity
Defined as the ratio of viscosity to the density of a fluid. It is denoted by ν (nu), where ν = η/ρ.
Porosity
The ratio of void volume to bulk volume. It is denoted by ε.
Law of Flow
Shear stress is directly proportional to the rate of shear strain (τ ∝ dv/dr).
Newtonian and Non-Newtonian Fluids
- Newtonian Fluid: Obeys Newton's law of flow; viscosity remains constant. Examples: H₂O, glycerine, oil, glasses.
- Non-Newtonian Fluid: Does not obey Newton's law of flow; exhibits variable viscosity. Examples: Butter, gum, lava.
Particle Diameter Definitions
- Feret Diameter: Distance between two tangents on opposite sides of a particle parallel to a fixed direction.
- Martin Diameter: Length of the line that bisects the particle image.
- Projected Diameter: The diameter of a circle that has the same projected area as the particle when viewed under a microscope.
Schulze-Hardy Rule
A rule of coagulation stating that the power of coagulation is proportional to the valency of the ion. Coagulation power increases with the valency of the ion. Examples: Al³⁺, Ba²⁺, Na⁺.
Rheology
The science concerned with the flow of liquids and the deformation of solids under stress. It is the study of the flow of matter under the influence of stress.
Importance
- Crucial in the handling of drugs for dosage forms.
- Used in quality control and the identification of diseases.
HLB Scale (Hydrophilic-Lipophilic Balance)
A measure of the balance between the hydrophilic and lipophilic properties of emulsifiers. The range is 0 (lipophilic) to 20 (hydrophilic).
Flocculated vs. Deflocculated Suspensions
| Feature | Flocculated | Deflocculated |
|---|---|---|
| Sedimentation Rate | High | Low |
| Viscosity | More viscous | Less viscous |
| Sediment Packing | Loosely packed (soft cake) | Closely packed (hard cake) |
| Redispersion | Easily redispersed | Difficult to redisperse |
| Bioavailability | Lower | Higher |
| Formation | Rapidly formed | Slowly formed |
Multi-point Viscometer
Used to measure the viscosity of non-Newtonian fluids at several rates of shear stress. Examples include rotational viscometers such as cup and bob, cone and plate, and MacMichael viscometers.