Suspensions Flashcards
What is the Tyndall effect used for?
Distinguishes between solutions and colloidal dispersion
Def of suspensions:
preparations w/ finely divided particles
- distributed somewhat uniformly
Pharmaceutical suspensions are…
insoluble solid particles dispersed in liquid
- ready to use and dry powder forms
Pharmaceutical suspensions are necessary because…
- drug can be insoluble
- drug can be unstable as liquid
- masks bad tastes
What are some desired features of pharmaceutical suspensions?
- settle slowly
- easily redispersible when shaken
- relatively constant particle size
What law is involved in sedimentation?
stoke’s law
What are some ways to decrease the rate of settling?
- smaller and lighter particles
- smaller difference in densities between particles and medium
- increase in viscosity
Def of flocculation:
light and fluffy conglomerates held together via weak Van der Waals forces
- reversible
Def of caking:
particles adhere by stronger forces to form aggregates
- irreversible
What are some ways to stabilize suspensions?
decrease surface free E by:
- decreases interfacial area and interfacial tension
What happens in deflocculated suspensions?
vehicle traps particles so that less settling occurs
- compact cake might form though
What happens in flocculated suspensions?
- optimum stability obtained
- sedimentation might occur, but easily fixed
Flocculated suspensions with electrolytes:
- most commonly used one
- reduces repulsion between drug particles by adsorbing to opposite charges
Flocculated suspensions with polymers:
- needs to have affinity for drug particles
- builds inter-particle bridge
What happens when particles are not wetted properly?
powder particles will float
