disperse systems(suspensions )
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suspension
A two-phase system consisting of a finely divided solid dispersed in a liquid vehicle
in suspensions, the substance distributed is referred to as the …………………. and the vehicle is termed the ………………. or dispersion medium.Together, they produce a ……………..
dispersed phase dispersing phase dispersed system
in suspensions, what name is given to what forms when the particles sink to the bottom
a sediment forms
difference between a stable and unstable suspension
particles evenly dispersed in a stable suspension while particles eventually sink to the bottom to form a sediment, in an unstable suspension(i.e not evenly dispersed)
name some desirable properties of an oral suspension
No grittiness Uniform dispersion. Easy to pour yet not watery Particles should settle slowly (so that an accurate dose can be taken out) Does not form a hard cake and the particles are readily re-dispersed upon shaking. A flocculated suspension is desirable than a deflocculated suspension. Palatable, pleasing odour and colour. Temperature insensitive
name some desirable properties of suspensions for injections
Particle size such that they can pass freely through the syringe needle – called “syringeability”. should be sterile
name some desirable properties of an ophtalmic suspension
Should be formulated such that particles do not exceed 10 μm. (< 10 μm, the patient experiences no pain when instilled into the eyes) Should be sterile
desirable properties of topical suspensions
Fine particles are desired to avoid grittiness when applied to the skin.
sedimentation
settling of particles or floccules in a suspension Occurs under gravitational force in a liquid dosage form
Is it possible to make a permanently well-dispersed suspension?
it is possible, but can be rather challenging
factors affecting sedimentation
particle size density of particle dispersed viscosity of the dispersion phase/medium Sedimentation velocity(v) is directly proportional to r2 of particle(i.e it.s size) Sedimentation velocity is inversely proportional to viscosity of dispersion medium
caking
the undesired agglomeration or clumping of particles in a solid material, leading to the formation of a solid mass.
when particles in a suspension are neutral, which is more likely to happen, van der waals attraction, or repulsion ?
Van der waals attractions
supernatant
to the liquid portion that remains above a solid residue after a mixture has undergone a settling or centrifugation process
the supernantant of floculated suspensions appear clear, while that of defloculated suspensions appear cloudy. true or false? give a reason for your answer
true in deflocculated suspensions, larger particles settle faster and smaller ones remain in the supernatant liquid, therefore they supernatant appears cloudy whereby in flocculated suspensions, even the smallest particles are involved in flocs, so supernatant does not appear cloudy.
which are more likely to result to caking over time, flocculated or deflocculated suspensions?
deflocculated suspensions
differences between flocculated and deflocculated suspensions
Particles link together to form a loose structure while Particles remain independent Big and small particles settle together in the loose structure while Particles settle at differentrates, but overall slowly Supernatant quickly becomes clear (different sizes link and settle together) while Supernatant remain turbid for a long time The sediment remains loose and easy to re-disperse while Settled particles may form a hard cake which is difficult to re-disperse