Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

PSF > Emulsions > Flashcards

Emulsions Flashcards

1
Q

Define emulsion

A

An emulsion is a disperse system where atleast one liquid is dispersed in another immiscible liquid as droplets

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Is an emulsion thermodynamically stable or unstable?

A

It is thermodynamically unstable due to the interfacial energy associated with the huge interfacial area. All emulsions are doomed to break – it is just a matter of time

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Typical droplet sizes of emulsions

A

0.1–100μm, though some as small as 0.01μm or as large as 1000 μm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What can emulsions be used for

A

oral, topical and parenteral applications

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Submicron emulsions

A

up to 500nm, milky white emulsions. E.g. Intralipid®, Diprivan®.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Nanoemulsions

A

Clear or translucent emulsions, <200nm (0.2μm)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Microemulsions

A

Strictly speaking these are not emulsions. They are single-phase, transparent systems. They represents a intermediate state between solubilised systems and emulsions. There are different understandings on this topic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Emulsion types

A 
Oil-in-water(o/w):
• Water-in-oil(w/o)
• Oil-in-water-in-oil(o/w/o)
• Water-in-oil-in-water(w/o/w)
• For oral use:o/w(viscosity, aqueous feel)
• For external use: o/w or w/o
• For oral application: o/w
•For i.v. application: o/w, average diameter <1μm. No droplets > 5 μm.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

which should have a

higher conductivity, o/w or w/o?

A

o/w

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Theories of emulsification - by adding surface active agents ..

A

by adding surface active agents, the surface energy and interfacial energy can be reduced and stability is increased

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Theories of emulsification - interfacial film strength

A

emulsifiers can form a stable film between the oil droplets and the dispersion medium, which stabilises emulsion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Zeta potential

A

– charge repulsion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Interfacial energy

A

E=γA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What are the 2 types of interfacial films?

A

monolayer and multilayer films

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are monolayer films?

A 
Monolayer films (more important) – surface active agents, e.g. Span 80 and Tween 80
– Surface tension is usually reduced, so is interfacial energy
– A mixture of emulsifiers is usually better than a single emulsifier
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What are multilayer films?

A

hydrophilic colloids (some naturally occurring polymers), e.g. acacia gum

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Are all emulsifiers surface active agents?

A

Not all emulsifiers are SAA.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is a common feature of surfactants.

A

must have a hydrophilic section and a lipophilic (hydrophobic) section in the same molecule

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is not easily soluble in water and shows surface activity?

A

chain of carbons is not easily water soluble, the longer the carbon chain, the more lipophilic the molecule is.
CH3(CH2)14OH

20
Q

Define HLB

A

Hydrophile-lipophile balance.

First designated by Griffin to indicate how hydrophilic or lipophilic an surfactant is

21
Q

Low HLB is

A

lipophilic eg. oleic acid

22
Q

High HLB is

A

hydrophilic eg. potassium oleate

23
Q

Which phase is the external phase

A

The phase in which the emulsifiers have higher solubility tends to be the external phase. i.e.
– hydrophilic emulsifiers, o/w emulsions
– Hydrophobic emulsifiers, w/o emulsions

24
Q

Emulsifiers with HLB 4-6

A

w/o emulsions

25
Emulsifiers with HLB 8-16
o/w emulsions | more soluble in water
26
Required HLB of an oil phase for producing stable emulsions
Different oils require different HLB of emulsifiers for the best stability of emulsions produced Note: the required HLB of an oil is the HLB of the emulsifiers required by the oil to form a stable emulsion. A typical oil does not have a HLB
27
The HLB of a mixture of non-ionisable surfactants A and B is given by
(HLB )m = | xa (HLB )a + xb (HLB )b / xa+xb
28
Where xa is the quantity of surfactant A, and xb is the quantity of surfactant B, (HLB)a and (HLB)b are the HLB values of A and B, (HLB)m is the HLB of the mixture
(HLB)m = xa / xa +xb (HLB)a + xb / xa +xb (HLB)b (HLB)m = A% x (HLB)a + B% x (HLB)b A% + B% = 100%
29
How to work out A% and B% to achieve a required (HLB)m?
A% = (HLB)m − (HLB)b / (HLB)a −(HLB)b (REMEMBER THIS) B% = 100% - A%
30
Types of surfactants
• Anionicsurfactants – Soaps, e.g. sodium stearate – Sulfated and sulphonated compounds, e.g. sodium dodecyl sulfate • Cationic surfactants – Cetrimide (cetyl trimethylammonium bromide) • Non-ionic surfactants – Glycol and glycerol esters – Sorbitan esters(Spanseries,Span60,Span80) – Polysorbates (Tween series, Tween 80= polysorbate 80) – Fatty alcohol polyglycol ethers – Poloxamers (Pluronic Series, Pluronic F68= poloxamer 188) • Amphoteric surfactants,e.g.lecithin • Naturally occurring polymers, e.g. Acacia • Semi synthetic polysaccharides, e.g. cellulose derivatives, methyl cellulose
31
Preparation of emulsions
- Mechanical mixing device, e.g. Silverson homogeniser - High shear homogeniser – liquid samples passes through narrow gaps under high pressure - Microfluidizer – split feed into twin jets and collide at supersonic speed - Ultrasonication – for laboratory and small samples only
32
Why is work required in prep of emulsions
Work is required due to the increased interfacial energy
33
Define creaming (physical stability)
Emulsion droplets moves up to the top of the emulsion and form a droplet-rich layer (cream). When the oil layer forms on the top – The droplets remain independent (separate) – Redispersible – May eventually lead to the breaking of emulsions
34
How to avoid creaming
* Reduction of droplet size. The creaming velocity will be reduced according to Stokes’ law. For the same formulation, use a more powerful homogenisation device generate relatively more stable emulsions * Small particles have stronger Brownian motion,which helps the droplets remain dispersed * Control viscosity–this is possible for oral emulsions. * Screen for best formulations
35
Factors leading to flocculation (physical stability)
– Charge reduction by the addition of electrolytes (compression of diffuse layer) – Charge neutralisation by oppositely charged ions, e.g. Ca2+ or cationic polymers (for negatively charged emulsion droplets) – Bridge flocculation by added polymers (refer to lecture slides on colloidal dispersions)
36
How to avoid flocculation
- Avoid the addition of charge reducing agents and maintain sufficient zeta potential - Steric stabilisation
37
What is flocculation
Flocculation is the prelude of coalescence
38
Define coalescence and breaking (cracking) - (physical stability)
- Coalescence – refers to the process that two or more droplets merge together to form a bigger droplet. - Breaking – coalescence occurred substantially in an emulsion so that a free clear oil layer can be seen. This is an irreversible process (in contrast to creaming which is a reversible process
39
What prevents coalescence
A stable/strong interfacial film helps to prevent coalescence
40
How can creaming and coalescence be reversed
creaming can be reversed by shaking but coalescence is irreversible
41
Physical Stability – Ostwald ripening
Smaller droplets get smaller (have larger solubility) and larger droplets get larger (have smaller solubility)
42
Chemical aspects of emulsions
The active pharmaceutical ingredients must be compatible with the excipients in the emulsions – Most emulsions are negatively charged, so any positively charged materials may disturb the stability of emulsions, e.g. some proteins, Ca2+ – Most electrolytes will destabilise emulsions due to • compression of the diffuse layer • salting - out effect (on the hydrated layer of emulsifiers) – The addition of acidic materials to emulsions stabilised by soap-type emulsifiers: destabilise the emulsion.
43
Preservation of emulsions
Preservatives are needed to prevent the growth of bacteria for non-sterile products • Even for sterile products preservatives are sometimes required to minimise the impact of in- use contamination (e.g. Diprivan®) • Preservatives exert their effect in the aqueous phase where bacteria growth occurs
44
Preservatives –general requirements
A wide spectrum of activity against all bacteria • Tolerability-Non-toxic,non-irritant and free from sensitisation activities • High aqueous solubility–preservatives work in the aqueous phase as bacteria grow there • Stability and effectiveness over a wide range of pH and temperature. pH of some emulsions tend to drop during storage • The preservative activity needs to be tested by appropriate microbiological tests
45
Other additives in emulsion formulations
Antioxidants–some oil and emulsifiers are susceptive to oxidation, e.g. lecithin. Vitamin E can be used as antioxidant. • Flavours • Colours • Sweetening agents
46
Assessment of emulsion stability
Macroscopic examination – Creaming–cream ratio against time – Breaking? – Changing colour? • Microscopic examination - Select suitable magnification so that enough number of droplets are examined – Examine sufficient area under the microscope and avoid selecting rare exotic objects – Beware of alien particles (not from emulsions) • Particle size analysis –laser diffraction, Coulter counter, single particle optical counting etc. • Rheological (viscosity) test– – A change in size may result in a change of viscosity • Accelerated stability test – centrifugation, freeze-thaw cycling, temperature cycling
47
Formulations of some emulsions
``` Diazepam emulsions – Fractionated soy bean oil – Diacetylated monoglycerides – Fractionated egg phospholipids – Glycerol (anhydrous-used for stability) – Sodium hydroxide (to pH8) – Water for injections ``` ``` • Diprivan® - a propofol emulsion – Glycerol – Purified egg phosphatide – Sodium hydroxide – Soya-bean oil, refined – Nitrogen – Disodium edetate – Water for injections ```

PSF (11 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions