The document discusses multiple emulsions, defined as the dispersion of one immiscible liquid in another, stabilized by an emulsifying agent. It details classifications (w/o and o/w systems), types (macroemulsion, nanoemulsion, microemulsion), methods of preparation (two-step emulsification, phase inversion, membrane emulsification), and factors affecting their stability and applications in pharmaceuticals, cosmetics, and drug delivery systems. Multiple emulsions show promise for prolonged release and enhanced absorption but face limitations due to thermodynamic instability.

1. Multiple EmulsionMultiple Emulsion

2. The emulsion can be defined as the dispersion of oneThe emulsion can be defined as the dispersion of one
immiscible liquid in another, stabilized by a thirdimmiscible liquid in another, stabilized by a third
component called the emulsifying agent. Simplecomponent called the emulsifying agent. Simple
emulsions are classified according to the nature of theiremulsions are classified according to the nature of their
continuous phase or dispersed phase, wherein twocontinuous phase or dispersed phase, wherein two
main classes can be identified:main classes can be identified:
 W/O system: Dispersion of droplets of aqueous phaseW/O system: Dispersion of droplets of aqueous phase
(dispersed phase) in oil (continuous) phase.(dispersed phase) in oil (continuous) phase.
 O/W system: Dispersion of oil droplets (dispersedO/W system: Dispersion of oil droplets (dispersed
phase) in aqueous (continuous) phase.phase) in aqueous (continuous) phase.

3. Types of Emulsions
Macroemulsion
Nanoemulsion
Microemulsion
Multiple emulsion

4. Nanoemulsion and
Microemulsion
 Nanoemulsions
 cover the size range of 50-200 nm
 Microemulsions

usually in the size range of 5-50 nm
 long term physical stability against creaming, flocculation and
coalescence
 Due to their small size they enhance penetration, spreading and will
give uniform distribution on the substrate on which they are
applied.
 application in personal care products and cosmetics, agrochemicals,
pharmaceuticals, household products etc.

5. Multiple emulsionMultiple emulsion
 Multiple emulsions are vesicular and complex systems. They can beMultiple emulsions are vesicular and complex systems. They can be
considered as emulsions of emulsions and have shown promise inconsidered as emulsions of emulsions and have shown promise in
cosmetic, pharmaceutical and separation sciences.cosmetic, pharmaceutical and separation sciences.
 Their potential pharmaceutical applications include uses such asTheir potential pharmaceutical applications include uses such as
taste masking, adjuvant vaccines, an immobilization of enzymestaste masking, adjuvant vaccines, an immobilization of enzymes
and sorbent reservoir of overdose treatments, and for enhancementand sorbent reservoir of overdose treatments, and for enhancement
of enteral or dermal absorption.of enteral or dermal absorption.
 Multiple emulsions have been formulated as cosmetics, such as skinMultiple emulsions have been formulated as cosmetics, such as skin
moisturizer.moisturizer.
 Prolonged release can also be obtained by means of multipleProlonged release can also be obtained by means of multiple
structures.structures.
 These systems have some advantages, such as the protection of theThese systems have some advantages, such as the protection of the
entrapped substances and the incorporation of several actives in theentrapped substances and the incorporation of several actives in the
different compartments.different compartments.
 Despite their potential usefulness, applications of multipleDespite their potential usefulness, applications of multiple
emulsions have been limited because of thermodynamic instabilityemulsions have been limited because of thermodynamic instability
and their complex structure.and their complex structure.

6.  Like simple emulsions, the multiple emulsions are also considered to be of
two types:
 Oil-in-water-in-oil (O/W/O) emulsion system
 Water-in-oil-in-water (W/O/W) emulsion system
 In O/W/O systems, an aqueous phase (hydrophilic) separates internal and external oil phases. In
other words, O/W/O is a system in which water droplets may be surrounded in an oil phase,
which in turn encloses one or more oil droplets. Mixing with an aqueous solution of hydrophilic
emulsifier W/O Span 80 W/O/W Tween 80 Mixing with the mixture of oil and hydrophobic
emulsifier O/W Tween 80 O/W/O Span 80The simplest multiple emulsions, sometimes called “
double emulsions, ” are in fact ternary systems, having either a water in oil in water or an oil in
water in oil structure, whereby the dispersed droplets contain smaller droplets of a different phase.
 In W/O/W systems an organic phase (hydrophobic) separates internal and external aqueous
phases. In other words, W/O/W is a system in which an oil droplet may be surrounded by an
aqueous phase, which in turn encloses one or several water droplets. These systems are the most
studied among the multiple emulsions. The immiscible oil phase, which separates the two
miscible aqueous phases is known as “liquid membrane” and acts as a diffusion barrier and
semi-permeable membrane for the drugs or moieties entrapped in the internal aqueous phase.

7. The hydrophilic emulsifier is dissolved in water.
The micellar phase of surfactant solution
solubilizes a small amount of oil, while a large
part of oil remains immiscible with the solution.
This area can be specified by the location for
providing O/W micro-emulsions, when one
makes disruption of the interface between the
two separate phases. On the other hand, a
variety of the hydrophobic emulsifiers dissolved
in oil phase assumable as reversed micelles
solubilizes a small quantity of water while a
large amount of residual water remains
separated from the reversed micellar solution.
This zone is featured by the area for preparing
W/O micro-emulsions due to disruption
between the two-separated phase.
Some emulsifiers can neither be dissolved in
water nor in oil, but they form their own
continuous phase that consists of the D-phase
and contains a certain amount of water and/or
oil among the lamellar structure of D-phase.
Such a phase can be provided by increasing
temperature of the non-ionic emulsifier or by
mixing the different types of emulsifiers. It
should be mentioned that the region for
obtaining W/O/W and O/W/O emulsions
should be located very closely to the either sides
of the D-phase. The two different types of
multiple emulsion may be prepared around the
D-phase by use of the similar constituents with
judicious selection of components and their
concentration levels.
W/O emulsion
W/O/W
Water OilReverse
Micelle
O/W emulsion
O/W/O
Micelle
Micelle
Phase volumeWater Oil
Hydrophobicity
Reverse
Micelle
PREPARATION ASPECTS OF MULTIPLE EMULSION

8. Method of preparationMethod of preparation
 Two-Step Emulsification (Double Emulsification)Two-Step Emulsification (Double Emulsification)
 Phase Inversion Technique (One step Technique)Phase Inversion Technique (One step Technique)
 Membrane Emulsification TechniqueMembrane Emulsification Technique

9. Two-Step Emulsification (Double Emulsification)Two-Step Emulsification (Double Emulsification)
Two-step emulsification methods involve re-emulsification of primary W/O orTwo-step emulsification methods involve re-emulsification of primary W/O or
O/W emulsion using a suitable emulsifier agent. The first step involves,O/W emulsion using a suitable emulsifier agent. The first step involves,
obtaining an ordinary W/O or O/W primary emulsion wherein anobtaining an ordinary W/O or O/W primary emulsion wherein an
appropriate emulsifier system is utilized. In the second step, the freshlyappropriate emulsifier system is utilized. In the second step, the freshly
prepared W/O or O/W primary emulsion is re-emulsified with an excess ofprepared W/O or O/W primary emulsion is re-emulsified with an excess of
aqueous phase or oil phase. The finally prepared emulsion could beaqueous phase or oil phase. The finally prepared emulsion could be
W/O/W or O/W/O respectively.W/O/W or O/W/O respectively.
Factors:Factors: ratio of the amount of Span 80 or hydrophilic emulsifiers.ratio of the amount of Span 80 or hydrophilic emulsifiers.
It was observed that twice or less Span 80 than Tween 80 is necessary forIt was observed that twice or less Span 80 than Tween 80 is necessary for
obtaining higher yields of O/W/O emulsions in contrast to the amount andobtaining higher yields of O/W/O emulsions in contrast to the amount and
ratio recommended for W/O/W emulsion (Kang and Matsumoto, 1988).ratio recommended for W/O/W emulsion (Kang and Matsumoto, 1988).
Aqueous
phase
Oil + Lipophilic
surfactant
W/O emulsion
Mix
Step 1
Hydrophilic
surfactant
W/O/W emulsion
W/O
emulsion
Mix
Step 2

10. Phase Inversion Technique (One step Technique)Phase Inversion Technique (One step Technique)
An increase in volume concentration of dispersed phase may cause an increase in
the phase volume ratio, which subsequently leads to the formation of multiple
emulsions.
The method typically involves the addition of an aqueous phase containing the
hydrophilic emulsifier [Tween 80/sodium dodecyl sulphate (SDS) or Cetyl
trimethyl ammonium salt (CTAB)] to an oil phase consisted of liquid paraffin and
containing lipophilic emulsifier (Span 80).
A well-defined volume of oil phase is placed in a vessel of pin mixer. An aqueous
solution of emulsifier is then introduced successively to the oil phase in the vessel
at a rate of 5 ml/min, while the pin mixer rotates steadily at 88 rpm at room
temperature. When volume fraction of the aqueous solution of hydrophilic
emulsifier exceeds 0.7, the continuous oil phase is substituted by the aqueous
phase containing a number of the vesicular globules among the simple oil
droplets, leading to phase inversion and formation of W/O/W multiple
emulsion
Aqueous phase
containing hydrophilic
emulsifier
Oil + Lipophilic
surfactant
W/O/W emulsion
Mix
b
•Volume fraction of the aqueous phase
should be higher than 0.7.
•Molar ratio of the hydrophobic and
hydrophilic emulsifier should be
optimized

11. Membrane emulsification procedureMembrane emulsification procedure
Recently, a membrane emulsificationRecently, a membrane emulsification
procedure has been developed as a novelprocedure has been developed as a novel
emulsification method (Higashi et al., 1995;emulsification method (Higashi et al., 1995;
Higashi et al., 1999). In this method, a W/OHigashi et al., 1999). In this method, a W/O
emulsion (a dispersed phase) is extruded intoemulsion (a dispersed phase) is extruded into
an external aqueous phase (a continuousan external aqueous phase (a continuous
phase) with a constant pressure through aphase) with a constant pressure through a
Porous Glass Membrane, which should havePorous Glass Membrane, which should have
controlled and homogeneous pores. Thecontrolled and homogeneous pores. The
particle size of the resulting emulsion can beparticle size of the resulting emulsion can be
controlled with proper selection of Porouscontrolled with proper selection of Porous
Glass Membrane as the droplet size dependsGlass Membrane as the droplet size depends
upon the pore size of the membrane. Theupon the pore size of the membrane. The
relation between membrane pore size andrelation between membrane pore size and
particle size of W/O/W emulsion exhibitsparticle size of W/O/W emulsion exhibits
good correlation as described by the followinggood correlation as described by the following
equation:equation:
Y = 5.03 X + 0.19Y = 5.03 X + 0.19
Where X is the pore size and Y is the meanWhere X is the pore size and Y is the mean
particle size of the multiple emulsionparticle size of the multiple emulsion
prepared using membrane emulsificationprepared using membrane emulsification
technique.technique. Mechanical stirring
External aqueous
phase
Porous membrane
W/O emulsion
Pressure
gauge
Nitrogen
gas

12. Characterization of multipleCharacterization of multiple
emulsionsemulsions
 Average globule size, size distribution andAverage globule size, size distribution and
yield of multiple emulsionyield of multiple emulsion
 Area of interfacesArea of interfaces
 Number of globulesNumber of globules
 Rheological evaluationRheological evaluation
 Zeta potentialZeta potential
 Percent drug entrapmentPercent drug entrapment
 In vitroIn vitro drug releasedrug release
 In vitroIn vitro stability studiesstability studies

13.  Average globule size and size distributionAverage globule size and size distribution
 Optical microscopy,Optical microscopy, Malvern Mastersizer, Coulter counter, freeze-Malvern Mastersizer, Coulter counter, freeze-
fracture electron microscopy and scanning electron microscopy.fracture electron microscopy and scanning electron microscopy.
Multiple emulsions as coarse (>3µm diameter), fine (1-3µmMultiple emulsions as coarse (>3µm diameter), fine (1-3µm
diameter) and micro-multiple emulsion (<1 µm diameter)diameter) and micro-multiple emulsion (<1 µm diameter)
 Area of interfacesArea of interfaces
The average globules diameter determined can be used in the calculationThe average globules diameter determined can be used in the calculation
of the total area of interface using the formula:of the total area of interface using the formula:
 S = 6/dS = 6/d
 S = Total area of interface (sq.cm)S = Total area of interface (sq.cm)
 D = Diameter of globules (cm)D = Diameter of globules (cm)
 Number of globules (Number of globules (hemocytometer cellhemocytometer cell))
No of globules X Dilution X 4000
No of small squares counted
No of globules/mm3
=

14.  Rheological evaluationRheological evaluation
 The rheology of multiple emulsion is an important parameter as itThe rheology of multiple emulsion is an important parameter as it
relates to emulsion stability and clinical performance. The viscosityrelates to emulsion stability and clinical performance. The viscosity
and interfacial elasticity are two major parameters, which relate toand interfacial elasticity are two major parameters, which relate to
product rheology. The viscosity of the multiple emulsions can beproduct rheology. The viscosity of the multiple emulsions can be
measured by Brookfield rotational viscometer.measured by Brookfield rotational viscometer.
 Zeta potentialZeta potential
 The zeta potential measurements are pivotal in the designing ofThe zeta potential measurements are pivotal in the designing of
surface modified or ligand anchored multiple emulsion systems. Thesurface modified or ligand anchored multiple emulsion systems. The
zeta potential and surface charge can be calculated usingzeta potential and surface charge can be calculated using
Smoluchowski’s equation from the mobility and electrophoreticSmoluchowski’s equation from the mobility and electrophoretic
velocity of dispersed globules using the Zeta-potentiometer.velocity of dispersed globules using the Zeta-potentiometer.
Electrophoretic mobility of the diluted W/O/W emulsion and usingElectrophoretic mobility of the diluted W/O/W emulsion and using
the following equation, zeta potential was calculated.the following equation, zeta potential was calculated.
Where,Where,
ζζ = Zeta potential (mV)= Zeta potential (mV)
ηη = Viscosity of the dispersion medium (poise)= Viscosity of the dispersion medium (poise)
µµ = Migration velocity (cm/s)= Migration velocity (cm/s)
εε = Dielectric constant of the dispersion medium= Dielectric constant of the dispersion medium
E = Potential gradient (Voltage applied/ Distance between electrodes)E = Potential gradient (Voltage applied/ Distance between electrodes)
ζ =
4πηµ
εE
× 103

15.  Percent drug entrapmentPercent drug entrapment
 nn10 = Initial concentration of drug in inner aqueous phase10 = Initial concentration of drug in inner aqueous phase
 nn1 = Concentration of drug in dialysate1 = Concentration of drug in dialysate
 VV1,1, VV2 and2 and VV0 represent the volume of inner and outer aqueous and middle oil phase0 represent the volume of inner and outer aqueous and middle oil phase
respectively, andrespectively, and VVs ands and VVd represent volume of dialyzing media and dialyzed emulsiond represent volume of dialyzing media and dialyzed emulsion
respectively.respectively.
 In vitroIn vitro drug releasedrug release
 The drug released from the aqueous inner phase of a W/O/W emulsionThe drug released from the aqueous inner phase of a W/O/W emulsion
can be estimated using the conventional dialysis technique.can be estimated using the conventional dialysis technique.
V = V2 +
Vd (V1+V2+V0)
Vs
C = 100/[1-n1V*/n10-n1)V1]
Water out
Water in
Receptor compartment
Dialysis bag
Sampling pipette
Temperature jacket

16. ApplicationApplication
 Controlled and sustained drug deliveryControlled and sustained drug delivery
 Drug targetingDrug targeting
 Absorption enhancement through GITAbsorption enhancement through GIT
 Vaccine adjuvantVaccine adjuvant
 Immobilization of enzymeImmobilization of enzyme
 As a preparative tool for microencapsulation technologyAs a preparative tool for microencapsulation technology
 Food and cosmetics applicationsFood and cosmetics applications
 MiscellaneousMiscellaneous
 As sorbent reservoir in drug overdose treatmentAs sorbent reservoir in drug overdose treatment
 Protection actionProtection action
 Taste masking actionTaste masking action

17. Application(s) Drug Entrapped
Enhanced oral bioavailability Heparin, Insulin Greseofulvin
Masking action Chlorpromazine HCl Chloroquin
Enzyme immobilization Urease, Lipase, Amylase, Pancreatic enzymes α-Chymotrysin, L-
leucine dehydrogenase
Drug over dosage treatment Salicylates, Barbiturates Quinine sulphate
Vaccine adjuvants Influenza virus, Tetanus toxoid
Separation and extraction
technique
Different hydrocarbons, Copper separation, purificaton of waste water
and Amine extraction
In the fabrication of
microcapsulated dosage form
Three ply system, Salbutamol sulphate, Pseudo Ephedrine HCl.
Vitamin-B6, Diclofenac sodium.
Prolonged action Naltrexone HCl, Pilocarpine HCl, Ephendrine HCl, Pentazocine,
Xylocaine HCl, Sulfacetamide sodium, Chloroquin phosphate,
Terbutaline sulphate, Haemogobin, Nitrofurantoin, Rifampicin,
Diclofenac
In cancer therapy and drug
targeting
5-Fluorouracil, Bleomycin, Methotrexate, Cysteamine, Adriamycin
HCl
Other applications Food and cosmetics

18.  Delivery of labeled 5-fluorouracil (5-FU) to regional lymph nodesDelivery of labeled 5-fluorouracil (5-FU) to regional lymph nodes
following intratesticular administration. They found that thefollowing intratesticular administration. They found that the
emulsion droplets reached the regional lymph nodes within 15emulsion droplets reached the regional lymph nodes within 15
minutes and remained there for more than 7 days.minutes and remained there for more than 7 days.
 Local administration of Bleomycin into tumors in animals and humanLocal administration of Bleomycin into tumors in animals and human
subjects by slowly delivered to regional lymph node.subjects by slowly delivered to regional lymph node.
 14C tripalmitin labeled sesame oil and 131I- iodohippuric acid (as14C tripalmitin labeled sesame oil and 131I- iodohippuric acid (as
model drug) entrapped in gelled gelatin phase of W/O emulsionmodel drug) entrapped in gelled gelatin phase of W/O emulsion
could be converted into a crude Gel/O/W type emulsion which wascould be converted into a crude Gel/O/W type emulsion which was
then transported to regional lymph nodes.then transported to regional lymph nodes.
 Deliver immunosuppressive agents (tacrolimus) locally to the site ofDeliver immunosuppressive agents (tacrolimus) locally to the site of
the target organsthe target organs
 The emulsion incorporating C18 unsaturated fatty acids orThe emulsion incorporating C18 unsaturated fatty acids or
docosahexaenoic acid (DHA) markedly enhanced drug absorptiondocosahexaenoic acid (DHA) markedly enhanced drug absorption
after colonic and rectal dosing. These results indicated that W/O/Wafter colonic and rectal dosing. These results indicated that W/O/W
emulsions incorporating C18 unsaturated fatty acid or DHA wereemulsions incorporating C18 unsaturated fatty acid or DHA were
useful carriers for improving the absorption of poorly absorbableuseful carriers for improving the absorption of poorly absorbable
drugs via the intestinal tract without gross changes to tight junctiondrugs via the intestinal tract without gross changes to tight junction
function.function.
 increased oral absorption of griseofulvin from W/O/W emulsion inincreased oral absorption of griseofulvin from W/O/W emulsion in
comparison to O/W emulsion and tablet dosage forms.comparison to O/W emulsion and tablet dosage forms.
 W/O/W emulsion for oral application of Salmon calcitonin used forW/O/W emulsion for oral application of Salmon calcitonin used for
the treatment of osteoporosis, Paget's disease and hypercalcaemiathe treatment of osteoporosis, Paget's disease and hypercalcaemia