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Fei Lectures > L4: Emulsions > Flashcards

L4: Emulsions Flashcards

0
Q

Why could an emulsifying agent be nessecary?

A

To stabilise the emulsion

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1
Q

What is an emulsion?

A

System consisting of two IMMISCIBLE LIQUID phases,

One of which is dispersed throughout the other as fine droplets.

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2
Q

How could you achieve a very low interfacial tension? (Micro emulsions)

A

Include a second surfactant, co surfactant, that is corporated into the interfacial film around the droplets.

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3
Q

Name the 3 forms of administration of emulsions

A

Topical

Oral

Parenteral

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4
Q

How can emulsions be administered orally? (3)

A

Administration of oils in nutritional products

Administration of oil soluble drugs as a liquid

Can enhance oral absorption of some drugs

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5
Q

How can emulsions be administered parenterally? (2)

A

Oils May be injected intramuscularly, in small volumes.

Emulsions for intravenous injections must be o/w
–> to avoid embolic effect.

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6
Q

What can multiple emulsions and micro emulsions be used for?

A

Controlled release drug delivery systems

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7
Q

Name an advantage for using emulsions.

Delivery

A

Delivery of drugs with low aqueous solubility.

  • -> drug dissolved in oily phase.
  • -> oil droplets absorbed via fat adsorption mechanism
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8
Q

Name an advantage for using emulsions.

Taste

A

Taste masking.

  • -> drug dissolved in the internal phase
  • -> sweeteners added to external phase
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9
Q

Name an advantage for using emulsions.

Ease

A

Ease of swallowing than solid dosage forms

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10
Q

Name an advantage for using emulsions.

Reduction

A

Reduction of irritation of topical drugs

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11
Q

Name advantages for using emulsions (4)

A

1) Drugs with low aqueous solubility can be delivered.
2) Taste masking.
3) Ease of swallowing than solid dosage form.
4) Reduction of irritation of topical drugs.

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12
Q

Name 4 disadvantages of using emulsions

A

1) needs to be shaken before use
2) storage conditions may affect stability
3) bulky, difficult to transport, container breakage
4) liable to microbial contamination

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13
Q

What are the 4 different stability problems which can happen with emulsions?

A

Flocculation
Coalescence
Creaming
Breaking

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14
Q

What is flocculation?

A

The AGGREGATION of the dispersed globules into LOOSE cluster within the emulsion.

(Before coalescence).

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15
Q

What is coalescence?

A

Droplets coalesce, form larger clusters.

After flocculation

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16
Q

What is creaming?

A

The SEPARATION of an emulsion into 2 regions, one which is richer in disperse phase than the other.

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17
Q

How can creaming be reduced?

A

By reducing rate of sedimentation.

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18
Q

How can phase inversion occur?

A

When changing the phase volumes.

Addition of an electrolyte

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19
Q

Name 3 ways the viscosity of an emulsion can be modified

A

Increase the CONCENTRATION of dispersed phase.

Increase the NUMBER of droplets

Add a viscosity MODIFIER

20
Q

How does increasing concentration of the dispersed phase, increase the viscosity of emulsions?

A

It impedes/obstructs the movement if individual droplets.

21
Q

How does increasing the no of droplets (by homogenisation), increase the viscosity?

A

Reduces droplet size, hence increases number.

–> causes continuous phase to be trapped between droplets.

22
Q

What are the 3 groups of emulsifying agents

A

Surfactants

Hydrophilic colloids

Finely divided solid particles

23
Q

What do emulsifying agents do?

A

Form coating round the dispersed globules

24
Q

How do surfactants work, as emulsifying agents?

A

ADSORBED at oil-water interface,
to form MONOMOLECULAR FILMS around droplets,
to REDUCE interfacial tension

25
Q

How do hydrophilic colloids work, as emulsifying agents?

A

Form a MULTIMOLECULAR FILM around the droplets of oil in o/w emulsion.

26
Q

How do finely divided solid particles work, as emulsifying agents?

A

Absorbed at the interface, between 2 immiscible liquid phases and form a FILM OF PARTICLES around the globules.

27
Q

What are the mechanisms of emulsifying agents? (4)

A

1) DECREASE interfacial tension at water/oil interface
2) provide PHYSICAL BARRIER between droplets to prevent coalesce
3) provide droplets with ELECTRICAL charge (repulsion)
4) increase VISCOSITY of continuous phase

28
Q

What are the 3 types of monomolecular films?

A

Gaseous

Condensed

Expanded

29
Q

Explain gaseous monomolecular films

A

Large spaces between surfactants allowing lots of molecular motion

30
Q

Explain condensed monomolecular films

A

High density film with little repulsion between groups.

31
Q

Explain condensed monomolecular films

A

Branched or rigid hydrocarbons prevent high density.

32
Q

What is HLB?

A

Hydrophile-lipophile balance

33
Q

What type of stability does a mixture of high HLBs and low HLBs give?

A

Good/better stability.

34
Q

What type of surfactants have a high HLB; low HLB?

A

Water soluble surfactant –> high HLB.

Oil soluble surfactant –> low HLB.

35
Q

Why might antioxidants be added to the formulation of emulsions?

A

Some oils may be susceptible to oxidation.

36
Q

Why might humectants be added to the formulation of emulsions?

A

(Topical)
Reduces rate of EVAPORATION of water from formulation on skin.

  • -> increased hydration of skin.
  • -> moisturising capability of formulation is enhanced.
37
Q

Why might viscosity enhancers be added to the formulation of emulsions?

A

To improve stability.

38
Q

Why might preservatives be added to the formulation of emulsions?

A

To prevent growth of micro organisms.

39
Q

Name 2 problems with adding preservatives to emulsions

A
  • they can be solubilised by surfactant micelles.
  • they can partition into oil phase.

–> reduces concentration of preservative in aqueous phase.

40
Q

Name 3 ways the stability of an emulsion can be assessed.

A

Microscopic examination

Globules size analysis

Viscosity.

41
Q

What is microscopic examination?

A

–> observe the extent of creaming/coalescence over a period of time.

–> droplet sizes can be determined by microscopy

42
Q

What can be assessed by globule size analysis

A

Coalescence leads to the increase of mean globule size with time.

43
Q

How is viscosity an assessment of stability?

A

Droplet growth will be accompanied by decrease in no of particles.

–> viscosity will decrease.

44
Q

Name 4 accelerated test techniques

A

Store at increased temp.

Freeze-Thaw cycling

Centrifugation

Rheological assessment

45
Q

What does ‘storing at increased temp’ do to an emulsion?

A

Decreases viscosity of emulsion

–> droplet coalescence accelerated.

46
Q

What does ‘freeze-thaw cycling’ do to an emulsion?

A

Microcrystals of ice disrupt the film at the o/w interface of droplets.

47
Q

What does ‘centrifugation’ do to an emulsion?

A

Increases droplet acceleration.

48
Q

What does ‘rheological assessment’ do to an emulsion?

A

Measure the residual apparent viscosity after destroying the structure of the emulsion.

Fei Lectures (8 decks)

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