PHARMACEUTICAL DISPERSIONS Flashcards
Define dispersed and continous phase
Disperse phase, dispersed as particles/droplets/bubbles within a continuous phase
What is a colloidal system and name some examples
- If dispersed partices are 1-1000nm
- Thermodynamically unstable
- Suspensions and emulsions
How to prepare a suspension
How do we measure size of dispersed particles?
- Can be done by both kinetic and light scattering method
- Kinetic property: These will measure size dependant on the concentration so number of particles in the sample (total weight of particles divided by total number of particles).
- Light scattering will measure size based on weight as larger particles scatter light more so skewing (dominating) the measurement.
How do dispersed phases gain a charge
- Surfaces will have a surface electric charge when brought into contact with a polar medium
- Changes distribution of the ions in the solution
- Ions of opposite charge (counter-ions) are attracted to the surface
What is the electrical double layer?
- This is a region of charge that forms between a solid surface and liquid solution
- First layer is the ‘stern layer’ that are oppositely charged and strongly attracted
- Second layer ‘diffuse’ layer are ions that are less strong attracted and more spread out
Define counter ions and co ions in terms of distribution of of ions in a colloidal system
Ions of opposite charge (counter-ions) are attracted to the surface
Ions of like charge (co-ions) are repelled
Interactions between particles are depedent on which two forces
- Repulsive forces: Electrical double layer or steric repulsion
- Attractive forces: Van der Waals
What is dvlo theory, include equation
- Its the total interaction energy
Label interactive distance curve
Attractive interactions, Va
Attractive interactions, Va
- Depends on Van der Waals and hamaker constant
What are repulsive interactions dependent on
- Surface charge - as charge increases, repulsive interactions increase
- Conc of ions in solution - increased concentration, lead to increased , but reduced thickness of the double layer => repulsive interaction decrease
Do repulsive or attracted forces increase stability
REPULSIVE
Prevents aggregation and flocculation
What is steric hindrance
- Bulky molecules stop attractive forces from occurring
- Act as a barrier preventing molecules from getting close so now VDW forces
- This prevents aggregation and flocculation