Emulsions Flashcards
1
Q
What is the definition of Emulsion?
A
2 immiscible liquid phases, one of which is dispersed as fine globules throughout the other; System is stabilised by addition of emulsifying agent.
2
Q
What is Dispersed/Internal phase?
A
Liquid phase subdivided into globules
3
Q
What is Continuous/External phase?
A
Liquid in which the globules are dispersed
4
Q
What are the Application of emulsions?
A
~ Pharmaceutical & cosmetic products formulated as emulsions
~ May be adm orally, topically and parenterally
5
Q
What are Simple Emulsions?
A
o/w or w/o
6
Q
What are Multiple emulsions?
A
w/o/w: composed of w/o primary emulsion dispersed in water
o/w/o: composed of o/w primary emulsion dispered in oil
7
Q
What are Microemulsions?
A
Extremely small globules (10-75nm); transparent to naked eye
8
Q
What are Micellar emulsions?
A
Relatively high conc of surfactant and a small prop of disperse phase which is solubilised by the surfactant
9
Q
Surfactant exist as ________
A
micelles (5-20nm)
10
Q
Define o/w micellar emulsion.
A
oil is non-polar inferior of micelles; present in aqueous continuous phase
11
Q
Define reverse micellar emulsion.
A
water is polar inferior of micelles; present in oily continuous phase
12
Q
How to identify o/w or w/o using Dye test? Which dye is commonly used?
A
O/W emulsion: Globules coloured by oil-soluble dye while continuous phase by water-soluble dye
W/O emulsion: Globules coloured by water-soluble dye while continuous phase by oil-soluble dye
Sudan III oil soluble dye
13
Q
What will you observe in the Dilution method.
A
O/W emulsion: Miscible with water
W/O emulsion: Miscible with oil
14
Q
Oil phase examples
A
Mineral oils, Vege oils, Silicones, Waxes
15
Q
Properties of oil phase affects performance of emulsion (4 things)
A
Consistency, “Feel” or tactile characteristic, Stability, Drug solubility
16
Q
Emulsifying agents are ______
A
Emulgents stabilise emulsion
17
Q
Name the types of Emulsifying agents (3 categories)
A
- Surfactants
- Hydrophilic colloids
- Finely divided solids
18
Q
Surfactants are _______
A
Hydrophilic and lipophilic group; amphipathic –> molecules to become attached to interfaces, thus lowering interfacial tension
19
Q
Anionic surfactants are only for _______
A
Only for external preparations
20
Q
Anionic surfactants are incompatible with ______
A
Cationic compounds, low pH, high conc of electrolytes
21
Q
Effectiveness of anionic surfactants is enhanced by _______
A
nonionic surfactants
22
Q
Different types of anionic surfactants (there are 5)
A
- Soaps of monovalent bases
- Soaps of polyvalent bases
- Amine soaps
- Sulphated and sulphonated fatty acids and alcohols
- Quillaia saponins
23
Q
Soaps of monovalent bases examples:
A
Sodium; Potassium; Ammonium stearate
SPA
24
Q
Emulsion type of Soaps of monovalent bases o/w or w/o ?
A
O/W
25
Properties of Soaps of monovalent bases:
Presence of polyvalent cations will cause phase inversion
26
Sodium and Potassium soaps have __________
high pH and are unsuitable for emulsion where a high pH can't be tolerated.
27
Soaps of polyvalent bases examples:
Calcium, Zinc oleate
28
Soaps of polyvalent bases Emulsion Type o/w or w/o?
W/O
29
Properties of Soaps of polyvalent bases:
Presence of monovalent cations will cause phase inversion
30
Amine soaps examples:
Triethanolamine sterate
31
Emulsion type of Amine soaps o/w or w/o?
O/W
32
Properties of Amine soaps:
Suitable for o/w emulsions where a high pH can't be tolerated (not so high pH)
VS unsuitable in soaps of monovalent bases
33
Sulphated and sulphonated fatty acids and alcohols examples
Sodium lauryl sulphate
| Sodium cetyl sulphate
34
Emulsion type of Sulphated and sulphonated fatty acids and alcohols o/w or w/o?
O/W
35
Properties of Sulphated and sulphonated fatty acids and alcohols
Generally more effective than other types but strongly alkaline
36
SLS + CSA = _____
Emulsifying Wax
37
Cationic surfactants have ______ properties and only used for ______
Antiseptic > Emulsifying properties
| External prep only
38
Cationic surfactants incompatible with ________
Anionic compounds
39
Cationic surfactants examples
Quaternary ammonium compounds - cetrimide, cetyl pyridinium chloride and benzalkonium chloride
C, CP, BC
40
Cationic surfactants promote formation of o/w or w/o?
O/W emulsions
41
Amphotetic surfactants are ________
Cationic at low pH and Anionic at high pH
42
Example of Amphotetic surfactant
Lecithin for I/V fat emulsions
43
Nonionic surfactants have ________
Low toxicity and irritancy
44
Nonionic surfactants are Less sensitive to pH changes as they are _________
they are uncharged
45
Nonionic surfactants less sensitive to _______
pH changes and addition of electrolytes
46
Nonionic surfactants used for _______
External + Internal prep
47
Types of nonionic surfactants
Sorbitan esters and Polyoxyethylene sorbitan esters (POE)
| Higher fatty alcohols (CSA)
48
Sorbitan ester trade name -
Span
49
POE trade name -
Tween
50
Blends of Span and Tween usually employed; Depending on ____ of blend
Depending on HLB of blend, it may promote formaiton of o/w or w/o emulsions
51
HLB full name
Hydrophilic-lipophilic balance
52
For span (sorbitan esters); as the hydrocarbon chain increases,
HLB decreases, but always <9.0
53
Lower HLB means
More lipophilic
54
Span sorbitan esters are generally
lipophilic surfactants
55
Tween (POE sorbitan esters) hydrocarbon chain increases,
HLB decreases; but >9.0 value
56
Tween (POE sorbitan esters) are
hydrophilic surfactants
57
Higher fatty alcohols example
cetostearyl alcohol
58
Higher fatty alcohols are
Auxillary emulsifying agents
59
Auxillary emulsifying agents definition
Not effective emulsifying agents when used by themselves (alone not good)
However, they can be combined with other emulsifying agents e.g. Non-ionic (CSA) with anionic (SLS) to enhance the effectiveness of the anionic surfactant.
60
Hydrophilic colloids are what type of agents?
More useful as auxillary emulsifying agents and as thickening agents
61
Hydrophilic colloids generally favour what type of emulsion?
Formation of o/w emulsions
62
Natural and synthetic clays example
Bentonite
63
Natural and synthetic clays properties
Bentonite swells in presence of water but rasies viscosity of medium only at pH 6 or higher
64
Natural and synthetic gum examples
Acacia, Tragacanth, Sodium Alginate, Carrageenan, Locust bean, Guar, Xanthan, Sodium CMC, methyl cellulose
65
Natural and synthetic gum properties
Polysaccharides
| Incompatible with certain cations or pH
66
Sodium alginate and Sodium CMC incompatible with
acids
67
Methyl cellulose is less soluble in
hot water
68
Proteins examples
Gelatin, soluble caesin
69
Are Proteins commonly used?
Less commonly used than gums
70
Gelatin prepared by
partial hydrolysis of collagen
71
Are Finely divided solids commonly used?
Limited use as primary emulsifying agents
72
Solids of mineral origin should be sterilised before use because
they may contain tetanus spores
73
Polar inorganic solids favour
Favour o/w emulsions
74
Polar inorganic solids examples
Heavy metal hydroxides, non-swelling clays
75
Non-polar solids favour
favour formation of w/o emulsions
76
Non-polar solids examples
Carbon, glyceryl tristearate
77
which 2 types of emulsions appear transparent to the naked eye?
microemulsions and micellar emulsions
78
what dye is used to differentiate o/w and w/o emulsion
an oil-soluble dye called sudan III
79
3 things needed to form an emulsion
emulsifying agent, oil, water
80
can hydrophilic colloids be taken orally?
yes
81
what kind of additives can be found in emulsions?
colors, sweetening agents, flavors and fragrance, antimicrobial preservatives, antioxidants chelating agents, buffers
82
3 theory of emulsification (how emulsification happens)?
1. Formation of rigid interfacial film
(cholesterol + sodium cetyl sulfate - closely packed condensed complex)
2. Formation of an electric double layer (applies ONLY to ionic surfactants); electric double layer = electrical barrier
3. Increase viscosity of continuous phase; (gums for water and waxes for oil) -> increase viscosity, better stability
83
3 theories of how o/w or w/o emulsions is formed
1. Bancroft's theory: disperse phase is the greater interfacial tension
IF (film/oil) > IF (film/water) --> O/W
IF (film/oil) < IF (film/water) --> W/O
2. oriented wedge theory:
- o/w: one polar head + one non-polar tail (monovalent soap)
- w/o: one polar head + 2 non-polar tail (divalent soap)
3. Based on angle of contact (finely divided solids(
- >90: w/o
- <90: o/w (preferentially wetted by water)
84
oriented wedge theory applies to?
soaps as emulsifying agents
85
Theory based on angle of contact applies to what type of emulsifying agent?
finely divided solids as emulsifying agents
86
What do emulsifying agents in the theory of angle of contact have to have _____________
1. insoluble in both aq and oil phase
2. preferentially wetted by one of the phase
3. able to form thin interfacial film
4. of colloidal size (<1 micron in size)
87
HLB range for w/o emulsifying agents
4-6
88
HLB range for o/w emulsifying agents
8-18
89
how to determine the optimal HLB
Step 1: after finding proportion for a specific HLB (e.g. 12), change the proportion according to HLB of 11 to 13)
Step 2: identifying the most stable emulsion (let's say 12.5)
Step 3: select another pair of surfactants to give HLB 12.5
Step 4: using these new surfactants, change proportion of surfactant according to HLB e.g. 11.5-13.5; find the most stable emulsion (e.g. 12.3)
90
4 techniques of emulsification
1. Agent in water method
2. Agent in oil method
(1) & (2) both form o/w first, then phase inversion to w/o with greater addition of oil (oil > water)
3. Nascent soap method: applicable when emulsifying agent is soap (fatty acid in oil, base in water -> in situ soap
monovalent soap = o/w
polyvalent soap = w/o)
4. Alternate addition method (suitable for vege oil) -> water, and oil added alternately in small amount
91
types of emulsifying machines
- simple stirring (propeller, turbine, paddle)
- colloid milling
- vibration and ultrasonication
further homogenization to improve stability
92
what is creaming?
globules that rise = disperse phase at the top
globules that sediment = disperse phase bottom
reversible with shaking
93
Factors affecting creaming?
Based on stokes' Law
- radius (Dec r value - v decreases
Shear/agitate the emulsion repeatedly many more times --> reduce the r -->more stable emulsion)
- density of continuous - disperse phase
- viscosity of continuous phase (E.g. If o/w emulsion - hydrophilic colloid gum; E.g. If w/o emulsion - add wax)
- viscosity of continuous phase --> inversely proportional
- increasing vol fraction of disperse phase reduces rate of creaming (not from stokes law)
- flocculation: aggregates behave as single particles (increase radius) increases rate of creaming
94
why doesnt particles coalescence during flocculation?
droplets have mechanical barrier or electrical barrier
95
coalescence can lead to
cracking
96
process of coalescence is __________
irreversible, droplets join to form larger drops
97
how to know whether an emulsion has cracked?
separation of two phases into two layers
98
what can cause emulsions to crack?
- incompatible emulsifying agent
- pH changes
- temp change
- bacterial and fungal action
99
which emulsifying agents are incompatible with what
anionic x cationic vice verse
strong acid x alkali-metal soaps
high conc electrolytes x soaps
alcohol x gum
100
ways to speed up stability test?
1. centrifugation
2. agitation
3. freeze-thaw cycles
4. heating-cooling cycles
101
what do we analyse for during such stability test (4 things)
1. degree of separation on standing (vol of separated phase/total vol emulsion)
2. Size analysis of globules (microscopic/coulter/laser diffraction) -> greater increase in mean globule size ---> more unstable
3. electrophoretic property: reduction in conductivity in o/w when oil aggregate
- increase in conductivity in w/o when water aggregate
- platinum electrodes used
4. determining viscosity changes: emulsion viscosity is affected by globule size and number
- thus increase viscosity indicated instability
102
Flocculation causes
Creaming
103
Coalescence causes
Cracking
104
Stoke's Law applies to
an isolated sphere in an infinitely large mass of liquid
factors of stoke's law are used to determine the rate of creaming and improve stability of emulsion
105
advantages and limitations of emulsions over other dosage forms?
Adv:
- easily swallowed
- mask objectionable taste
- enable IV administration of lipid nutrients via O/W emulsion (w/o will clog the IV access)
- has a cost advantage over single-phase preparation (solvents for lipids cost more than water; thus use v little lipid content to make O/W compared to making a solution made wholly from lipids)
- allow formulation to have high degree of flexibility (vary the ratio of the phases; greasiness)
- topical emulsions = aesthetically pleasing, elegance
