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Pharmaceutics > M7 Emulsions pt 2 > Flashcards

M7 Emulsions pt 2 Flashcards

1
Q

What is the relationship between surfactant concentration and interfacial tension?

A

As we increase surfactant concentration, we decrease interfacial tension – up to a point, which is the CMC of the surfactant

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2
Q

what is interfacial tension

A

force that resist it from breaking up into smaller particules is interfacial tension

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3
Q

What is the relationship between the location of the surfactant monomers and interfacial tension?

A

Monomeric surfactant molecules accumulating at the surface and interface decrease surface/interfacial tension

* air considered hydrophobic -> will go to surface and orient which will dec interfacial tension

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4
Q

Explain the log concentration of surfactant vs. interfacial tension curve.

A

A: interfacial tension

B: log concentration of surfactant

C: critical micellar concentration

D: surfactant molecules without full coverage of surface

E: surface adsorption of monomeric surfactant molecules with full coverage of surface

F. air/oil – water interface G. micelle formation

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5
Q

What happens to surfaceant molecules in dilute dispersions vs more saturated

A

dilute: surfaceants orient themselves at oil.water interface
- as conc of surfactnat inc surface alyer will becomes saturated
- once saturated further increases will no longer affect interfacial tension or stability of system
- surfacnts mols will start forming mmicelles

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6
Q

What is the effect of micellization on interfacial tension?

A

Micelles formation after the CMC is reached does not influence interfacial tension

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7
Q

what is CNC

A

point at which michelle formation begins

  • depends on structural characteristics to depends on surfactant
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8
Q

what happens to tendency to form michelles as the legnth of hydrocarbon chain inc

A
  • increases the tendency to form micelles
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9
Q

micelle formation of non ionic surfactants vs ionic

A

ionic surfactants -> get repulsion between adjacent charged head groups that opposes michelle formation

*non ionic surfactants for micheles art conc << ionic ones

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10
Q

what does a higher CMC mean

A
  • more monomers can go to interface ( more efficient)

*low CMC wll form micelles before oil ro water droplets are coated -> less efficient

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11
Q

What is meant by surface excess concentration of surfactant in the Gibbs equation?

A
  • Γ = surface excess surfactant concentration
    • portion of surfactant occupying the interface and contributes to lowering the interfacial tension
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12
Q

calc Q 32

A
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13
Q

when do you get mixed micelles

A

* some micelles ahve toils pointed out others with heads pointed out

If a blend of surfactants is used in the preparation of an emulsion → formation of mixed micelles

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14
Q

what is aggregation number

A

number of surfactant molecules that form one micelle

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15
Q

what are association colloids

A

micelles

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16
Q

what forms of surfactants are found below CMC and Above CMC

A

Below CMC: monomers
Above CMC: micelles

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17
Q

what does each varaible mean

A
  • Γ: surface excess or surfactnat (surfactant mol at surface)
    • moles/Cm2
  • R: universal gas cosntant (8.314 x 107 erg/mole/K aka g cm2/s2
  • T: abolute temp in K
  • ∆γ: change in surface tension of mixture with change in surfactant conc
    • dynes/cm OR g cm /s2
  • C: concentration of surfactant in liq bulk
    • unitless bc log
18
Q

What is HLB

A

Hydrophile - Lipophile Balance

describing the hydrophilic-hydrophobic characteristics

ie. solubility of surfactants

the HLB scale ranges from1-20 (in some special cases up to 50)

19
Q

HLB of something Lipophilic? Hydrophilic

A

HLB 0-10 = lipophilic

HLB: 10-20 = hydrophilic

20
Q

What type of emulsion is formed when a surfactant of HLB=14 is used?

A
  • o/w

*Hlb over 10 - hydrophilic

21
Q

What type of emulsion is formed when a surfactant of HLB=5 is used?

A

w/o

22
Q

Using the Tables below, select a pair of emulsifiers to prepare 100 g of an w/o emulsion containing 50g olive oil and 10g beeswax requiring a total of 7% w/w surfactant concentration

A
23
Q

What emulsifying agents form monomolecular film around the disperse phase?

A

Ionic and non-ionic surfactants

*act by dec interfacial tension

24
Q

What emulsifying agents form multimolecular film around the disperse phase?

A

Hydrocolloids such as polymers, acacia, gelatin

*sterioc hinderance (forming solid particle film)

25
Q
A
26
Q

What emulsifying agents form solid particle film around the disperse phase?

A
27
Q

How does bentonite exert its emulsifying properties?

A

It forms a solid particle film on the surface of oil droplets

28
Q

What are the desirable properties of surfactants?

non-ionic emulsifiers

A

*Depends on the emulsifying ability desired and the toxicity (determines route of administration) of each emulsifying agent.

less toxic and less iritant

29
Q

What are the desirable properties of surfactants?

ionic emulsifiers

A

should not be given orally (irritant to GIT)

Cationic: toxic at low concentrations ⇒ limited to external use when antiseptic properties are required

Anionic: have high pH (alkaline) ⇒ unsuitable for broken skin

30
Q

what is phase inversion? how can it be utilized?

A
  • change in emulsion type w/o -> o/w
    ex: during prep of o/w the water phase is poured into oil-> first add small amount of water to form w/o then subsequent addition of water will form an o/w
  • this order of addition results in better physical stability of final product
31
Q

List a few frequently used antioxidant.

A

BHA, BHT, α-tocopherol, alkyl gallates (Propyl Gallate B.P.), ascorbic acid, ascorbyl palmitate

32
Q

What equipment can be used for emulsification?

A
  • Mechanical stirrers (rotating blades)
    • used for low viscosity prep
    • large quantities may be mixed
  • Homogenizers
    • small inlet orifice and presssure used to nicorporate oil
    • not suitable for viscosity > 2000 cP
  • ultrasonifiers
    • sonic saves break down emulsified droplets
    • produces uniform emulsion
    • gentle -> powerful
  • colloid mills (rotor/stator)
    • common
33
Q

What is creaming?

A

Emulsion instability caused by flocculation and upward sedimentation of oil droplets

reversible process

34
Q

What is coalescence?

A
  • complete fusion of droplets within an emulsion

leads to a ↓ number of droplets and ultimately separation of the two immiscible phases

– irreversible process

35
Q

how do you determine rate of creaming or rate of sedimentation in an emulsion

A

Stokes law of sedimentation can be used to calculate sedimentation rate

in case of creaming sedimentation rate will be a negative number

36
Q

what kind fo stress conditions are used for assessing emulsion shelf lfie

A

Aging and temperature increase
Centrifugation (to accelerate separation into two layers)
Agitation (to reflect conditions of shipping)

37
Q

What is the reason for coalescence and what steps would you take to prevent coalescence in an emulsion?

A
  • can be caused by low zeta potential, high surface free energy or high interfacial tension

to mitigate: add protective colloids, optimize carticle size, add more surfactant

*coalesence in w/o emulsions is prevented by presence of long hydrocarbon changs of surfactant molecules that project into oil phase

38
Q

What is the reason for creaming and what steps would you take to prevent this in an emulsion?

A
  • caused by flocculation and upward sedimentation
  • add more rpotective colloids

add more surfactant

39
Q

What is the reason for foaming and what steps would you take to prevent foaming in an emulsion?

A

too muhc surfactant

reduce the surfactant conc

40
Q

What is the reason for microbial growth in an otherwise preserved emulsion and what steps would you take to prevent this in an emulsion?

A

preservative – surfactant interaction reduced antimicrobial function; add more or different preservative

41
Q

What is the reason for unpleasant taste and what steps would you take to achieve palatability in an emulsion?

A
  • inappropriate amount fo certain excipients: propylene glycol, glycerol, preservatives
  • lack or inappropriate amount of sweetnener or flavouring agent

*reduce/optimize excipient conc, add more or diff sweetener or flavour

42
Q

how to reduce rate of creaming/sedimentation

A

Pharmaceutics (19 decks)

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