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Respiratory Diseases & Dermatology > P7: Emulsions & Suspensions > Flashcards

P7: Emulsions & Suspensions Flashcards

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Dermatology Board Prep flashcards
1
Q

what are colloids

A

emulsions, microemulsions, creams

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2
Q

what are some examples of colloids

A

oral suspensions, topical dosage forms, injections, aerosols

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3
Q

what is the dispersion phase of an emulsion

A

phase that is sub-divided

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4
Q

what is the continuous phase of an emulsion

A

phase in which disperse phase is distributed

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5
Q

what are the steps of colloidal stability

A

high surface area -> high surface energy -> aggregation -> thermodynamically unstable

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6
Q

what are emulsions and suspensions

A

thermodynamically unstable two-phase systems

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7
Q

when do emulsions and suspensions attain equilibrium

A

when internal droplets coalesce to form one ‘macro-phase’

surface area is minimised

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8
Q

how do suspension particles achieve lower surface area

A

flocculating or aggregating (no coalescence)

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9
Q

how do fine particles dispersed in liquid encounter one another

A

brownian movement, creaming or sedimentation, convection

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10
Q

what is the effect on sedimentation rate when particle diameter increases

A

increased sedimentation rate

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11
Q

what is the effect on sedimentation rate when particle density increases

A

increased sedimentation rate

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12
Q

what happens to sedimentation rate when viscosity increases

A

decreased sedimentation rate

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13
Q

what happens to particles at short inter-particle distances

A

attractive forces predominate and particles tend to agglomerate

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14
Q

what happens to particles as inter-particle distance increases

A

sufficient energy is added to separate the particles, repulsive forces dominate and particles remain in suspension

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15
Q

what is flocculation

A

prevents rigid cohesion by forming loose aggregates

held together with comparatively weak interparticulate forces

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16
Q

what type of structure occurs with flocculation

A

lattice type structure; resists complete settling, reduces caking and aids re-dispersion

17
Q

what happens in flocculated systems

A

repulsive barriers have been reduced and particles form loosely bonded structures in secondary minimum
particles settle as flocculates not individual particles
sediment is not closely packed and caking does not occur
suspension formulation aims for partial or controlled flocculation

18
Q

what is caking

A

particles not associated in deflocculated systems; pressure on individual particles - their close packing

19
Q

what happens to particles in low cetrimide concentration

A

head-groups attach to kaolin
hydrophobic tails point out into aqueous phase
hydrophobic groups interact to form flocculates

20
Q

what happens to particles in high cetrimide concentration

A

cetrimide bilayer with head groups pointing out

interfacial tension reduced and deflocculation

21
Q

how is flocculation controlled

A

with non-ionic polymers to increase aqueous phase viscosity

22
Q

what are the characteristics of an ideal suspending agent for controlled flocculation

A

easily incorporated into formulation, readily dissolves/disperses in water without the need for special techniques, ensures formation of loosely-packed system that does not cake, does not affect dissolution rate or absorption rate of drug, is inert, non-toxic and free from incompatibilities

23
Q

how can colloids be stabalised

A

by repulsive forces due to adsorption of macromolecules or surfactants to their surfaces
in aqueous dispersions, absorbed molecules are hydrated

24
Q

why are non-ionic surfactants used in emulsions

A

to absorb onto oil droplets and increase stability by creating hydrated layer on hydrophobic particles

25
Q

what is HLB

A

measure of balance between hydrophobic and hydrophilic components of a surfactant

26
Q

what does HLB stand for

A

hydrophile-lipophile balance system

27
Q

what is the range of the HLB scale

A

1 to 20

28
Q

what does a low HLB value indicate

A

oil-soluble surfactants

29
Q

what are microemulsions

A

homogenous, transparent, low-viscocity colloidal solutions

Respiratory Diseases & Dermatology (34 decks)

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