1. Surface and Interfacial Phenomena Presented by the Pharmacist
Presented by the Pharmacist
Muhanad S. Al-Ani

2. Interface is the boundary between two or more phases
exist together
The properties of the molecules forming the interface are
different from those in the bulk that these molecules are
forming an interfacial phase.
Several types of interface can exist depending on whether
the two adjacent phases are in solid, liquid or gaseous state.
If one of the phases is gas we use the term surface tension ,
other that we use interfacial tension.
No interface can be observed between two gas phases
because they are miscible in all proportions.

3. Important of Interfacial phenomena in pharmacy:
Adsorption of drugs onto solid adjuncts in
dosage forms
2. Penetration of molecules through biological
membranes
3. Emulsion formation and stability
4. The dispersion of insoluble particles in liquid
media to form suspensions.

4. Interfaces Gas/Liquid S.T. Liquid/Liquid I.T. Liquid/Solid I.T.
Gas/Solid
S.T.
Solid/Solid
I.T.
Gas/Liquid
Bubbles/Foam
Surfactants
Adsorption
Liquid Crystals
Liquid/Liquid
Emulsions
Detergency
Aerosols
Gas/Solid
solid surface
liquid/Solid
suspension
Solid/Solid
powder particles in contact

5. The molecules of solid and
liquid have an inter molecular
forces ,the gas have low to a
negligible forces .
The molecules in the bulk of
the liquid are surrounded by
other molecules for which
they have equal attraction,
these forces tend to cancel
each other and the net
attraction at any point in the
bulk will be zero.

6. The molecules at the surface do not have
this balance of attraction ,
they experience an in
word force of attraction
to word the bulk of the
liquid the surface
gets contracted and the
molecules at the
surface are pulled together ,the force
which has been applied to counter balance
this in word pull is known as the surface
tension which has a unit dyne/cm

7. Long legged bugs called “water striders” can skate
How is this possible?
Long legged bugs called “water striders” can skate
along the surface of a body of water

8. In case of liquids
The grater the tendency of the substance to
interact the less is the interfacial tension.
If two liquids are completely miscible no I.T.
exist between them, example: Glycerin
interact with water to the extent that no I.T.
exist.

9. Increasing the temperature cause increasing the
The surface tension depend on the nature of intermolecular forces
Example: the molecules of mercury are held together by strong
metallic Bonds ( S.T. is 476 dyne/cm), while water molecules are
held together By hydrogen bonds ( S.T. is 72.8 dyne/cm)
Surface tension (g) decreases with increasing temperature, why ?
Increasing the temperature cause increasing the
kinetic energy of the molecules which lead to decrease the surface tension ex. water S.T. is
76.5 dyne/cm at 0 C° and
72.8 dyne/cm at 20 C°.

10. At and above the critical temperature the surface tension become zero ,Why ?
At the critical temperature , the liquid exists as a vapor ( gaseous state ) rather than in the liquid state.

11. Adhesional forces :forces acting between
molecules of different phases which tend to
increase the affinity of the phases, so if the
adhesional forces increase the two phases
tend to miscible with each other
Cohesional forces: act between molecules
of the same phase and tend to keep the
two phases separate .

12. In general, interfacial tensions are less than the surface tensions, why ?
The adhesive forces between two liquids at the interface are greater than when liquid and gas exist together ,the interfacial tension indicates the strength of the adhesive forces between immiscible liquids, whereas surface tension indicates the cohesive forces in the liquids.

13. The surface tension are responsible for the following processes;
1.Formation of spherical globules in emulsions.
2.Formation of nearly spherical shape of falling water droplets.
3.Formation of spherical shape of mercury particles on a flat surface
4.Rise of liquid in capillary tube .
5.Formation of hemispherical surface when water is filled in a glass tube.

14. Expression of surface tension
The S.T. can be expressed in one of the following
ways
1. in terms of force per unit length (dyne/cm)
let us consider a 3 sided wire
frame fitted with a movable bar if the wire frame is dipped into soap solution and taken out, a soap film is formed over the area
ABCD
This soap film tend to contract
in an attempt to decrease the surface area and pulls the movable bare to words the stationary bare .
Stationary bar L B C
Force:2Lg
Soap film
Movable bar A D
Force=weight x gravity

15. F = У 2L F = weight X gravity(981cm/sec)
L : is the length of the movable bar
we multiply by 2 because the soap form an
interface on both sides of the movable bar.
F = У 2L
У = W x gravity
2 L

16. the mass required to break a soap film is 0.5 g , what is the surface
Example:
If the length of the bar is 5 cm and
the mass required to break a soap
film is 0.5 g , what is the surface
tension of the soap solution.

17. 2. In terms of energy per unit area increase.
If we consider the work required to increase the
surface area of the film.
let dw be the work (surface free energy ) needed to
displace the movable bar by a small distance ds
Stationary bar
work = force x distance
dw =F x ds
F =У x 2L
dw = У x 2L x ds
(2L x ds) is the area
dw = У x dA
Dw : is the work (ergs)
У : is the surface tension
dA : is the increase in area cm² L B C
Force:2Lg
Soap film
Movable bar A D ds

18. Example
What is the work required in the previous
example to pull the wire 1 cm.
A soap solution having surface tension of dy/cm is applied to the metal frame bar of 5 cm. calculate the work required to pull the wire down by 2 cm.

19. 3.in terms of pressure across curved surface
In this soap bubble the total surface free energy is
W = 4 πr²У
4 πr² :is the area of soap babble .
If the soap babble is caused to shrink so that its‘ radius decreased by dr so the final surface free energy will be given by
W = 4 πУ (r- dr)²
W = 4 πУ r² - 8 πУ r dr + 4 πУdr²
dr :is quite small compared to r
So 4 πУdr² is disregarded so the equation will be
W = 4 πУ r² - 8 πУ r dr
So the change in surface free energy is
8 πУ r dr dr r

20. This is opposed by the pressure difference ΔP across the wall of the bubble
pressure = force / area
force = pressure x area
= ΔP x 4 πr²
so at equilibrium
ΔP = 2 У r
So as the radius of the babble decrease the pressure of the air inside the babble increase relative to the radius.
For non spherical surface
ΔP = У ( )
r r2
r1 and r2 are the two radii of curvature of non spherical surface

21. Measurement of surface and interfacial tension: θ
1. Capillary rise method
This method is suitable for
measuring surface tension and
not for interfacial
tension .Why ?
If a capillary tube is immersed in a liquid such as water contained in beaker the liquid immediately rises up the tube to a certain height , this rise of a liquid in the tube occurs because the force of adhesion between water molecule and the capillary wall is greater than the force of cohesion between water molecules.
By measuring the rise in the capillary , it possible to determine the surface tension of the liquid. θ
easu

22. Force due to the surface tension
The liquid in the capillary tube continuous to rise till the up word movement is just balanced by the down word force of gravity due to the weight of the liquid .
So we have two forces opposing each other the up word force due to the surface tension and the counteracting force due to the weight of the column of liquid in the tube.
Force due to the surface tension
The S.T. at any point on the circumference of the capillary tube is given by the equation:
a = У cos θ cos θ :is the angle between
surface of liquid and capillary wall
So the total up word force along the inside circumference of the capillary is given by
a = 2π r У cos θ r: is the inside radius of the
capillary tube
When the liquid such as water wets the surface of the capillary tube the θ is taken as unity, then the up word force is given by
a = 2π r У

23. Force due to the weight of the liquid column
d = π r²h(P P˚) g + W
π r² : is the cross sectional area of the capillary tube
h: is the height of liquid column in the capillary tube up to the lowest point of the meniscus.
P and p˚ are the densities of the liquid and its vapor.
g: is the acceleration due to gravity.
W: is the weight of the liquid above h in the meniscus.
The density of liquid is being much greater than the density of its vapor , the weight of the liquid in the column being much greater than the weight of the liquid above h in the meniscus.
So P˚ and w will be disregarded
So d = π r²hP g
at equilibrium the up word force is equal to the down word force thus
2 π r У = π r²hP g
У = π r²hP g = 1 r h p g
2π r

24. Example
A sample of chloroform rise to a height of 3.67 cm at 20 c˚ in capillary tube having an inside radius of 0.01 cm. what is the surface tension of chloroform at this temperature ?
The density of chloroform is g/ml

25. 2. drop weight and drop count method
If a liquid is allowed to fall slowly through
a capillary tube the liquid 1st.
forms a drop at the tip
of the tube which gradually
increase in size and finally
detaches from the tip
when the weight of the
drop = to the surface tension at the
circumference of the tube.
W x gravity = 2prg
W = weight of drop
r = radius of tube
g = surface tension

26. So S.T. can be determined using this principle by using stalagmometer
1.drop weight method
the liquid is allowed to drop slowly from the tip of the pipette, drops are collected from the pipette into a clean vessel and the weight of one drop of liquid is determined
W x g = 2 π r У
У = w x g
2 π r
W : is the weight of one drop of liquid
It is general practice to determine the S.T. of
a liquid with respect to water ,so 1st. The weight of one drop of liquid is determined (W1) ,then the weight of one drop of water (W2) is obtained
Relative S.T. = S.T. of liquid =W1 g/2 π r =W1
S.T. of water W2 g/2 π r W2

27. 2. drop count method
This method is similar to the drop weight method except that the number of drops of the liquid are counted instead of weight.
У = W1 x g in that W1: is the weight one drop
2 π r
density = weight
volume
W1 = density x volume of one drop
Volume of one drop = total volume
number of drop
W1 = density x total volume
У = density x total volume x g
2 x π x r x n
У = d x V x g
V : is the total volume of the liquid
n : is the number of drop

28. For the determination of the relative surface tension
No. of drop of liquid is counted
No. of drop of water is counted using the same volume by the same tube and at the same temperature.
Уrelative = V d1 g / 2 x π x r x n1
V d2 g / 2 x π x r x n2
Уrelative = d1 x n2
d2 x n1
d1 : is the density of liquid
n2 : is the number of drop of water
d2 : is the density of water
n1 : is the number of drop of liquid

29. Example:
Calculate the surface tension of a liquid, by
using a capillary tube, knowing that the
weight of one drop of the liquid is g
at 25 Cº, the surface tension of water is 72
dyn/cm and 2 ml of water produce 50 drop
at the same temperature by the use of the
same capillary tube.

30. Spreading
If a small quantity of an immiscible liquid is placed on the surface of another liquid it will be either spread as a film on the surface of the liquid or remain as a drop or lens . This depends on the achievement of a state of minimum free energy.
This spreading can be assessed in terms of spreading coefficient , its‘ value should be either zero or positive for the spreading to occur.
This spreading is important for products prepared for external use or application such as lotions and creams

31. Spreading coefficient
In general spreading of a liquid on the surface of another occurs when the work of adhesion between the 2 liquids exceeds the work of cohesion between the molecules of each liquid.
in general
work = surface tension x unit area change
work of cohesion
surface free energy increase
By separating a column of pure
Liquid into two halves which
mean Surface free energy increase
by Increasing surface area. L
Cohesion

32. Wc =УL x ΔA + УL x ΔA = УL (ΔA + ΔA ) Wc = УL ( 1+ 1) 1cm²
if the column surface area is 1cm²
Wc = УL ( 1+ 1)
Wc = 2 УL
1cm² УL L
Cohesion

33. so energy required to separate УL УL S
Work of adhesion
if we have 2 immiscible liquids
Wa = УL x ΔA +Уs x ΔA - УLS x ΔA
Why ? We have this( - УLS x ΔA )
because these 2 immiscible liquids is already separated
by a boundary in that we have cohesion forces > adhesion forces.
1cm²
so energy required to separate
УL УL S УS
2 immiscible liquids is less by
an amount of - УL S x ΔA than
that required to separate the same liquid. L S i
Adhesion

34. If the column have a sectional surface area of 1cm² Wa = УL + УS – УLS
Spreading coefficient S
S = Wa – Wc = УL + УS - УLS - 2УL
= УS - УL - УLS = УS – (УL + УLS)
УS : is the surface tension of the sub layer
УL : is the surface tension of the layer
УLS : is the interfacial tension between the 2 layer
So spreading occur when the УS is ≥ (УL + УLS)
If the S is negative the spreading liquid will form a globule or a floating lens and the spreading will not takes place.

35. Cohesive forces: Factor affecting Spreading Coefficient
Molecular Structural:
The greater the polarity of the molecule the more positive [S]
as ethyl alcohol and propionic acid
Non polar substances as Liquid petrolatum have negative [S] fail
to spread on water
For organic acids, as Oleic acid,
the longer the carbon chain decrease in polar character decrease [S]
Some oils can spread over water because they contain polar groups
as COOH and OH
Cohesive forces:
Benzene spreads on water not because it is polar but because the cohesive forces between its molecules are much weaker than the adhesion for water.

36. Application of Spreading coefficient in pharmacy
The requirement of film coats to be spreaded over the
tablet surfaces
The requirement of lotions with mineral oils to spread on
the skin by the addition of surfactants

37. Surface Active Agents
Molecules and ions that are adsorbed at interfaces are
termed surface active agents, surfactants or amphiphile
The molecule or ion has a certain affinity for both polar and
nonpolar solvents.
Depending on the number and nature of the polar and
nonpolar groups present, the amphiphile may be hydrophilic,
lipophilic or be reasonably well-balanced between these two
extremes.

38. Surfactants Molecules
Depending on the number
and nature of the sites the
Surfactants may be
Predominantly Hydrophilic or
Hydrophobic or there is a
balance between these two
sites.
So in this figure as the no. of
Carbon atoms increase it will
change from being
predominantly Hydrophilic to
Hydrophobic
Hydrophilic ( lyophobic, water-loving) head containing a charged functional group
Hydrophobic ( lyophilic, water-fearing ) tail containing a hydrocarbon chain

39. At the water air interface ,the lyophilic chains are directed
upward into the air , and
the hydrophilic head toward water
At the water oil interface
,the lyophilic chains are
directed upward into
the oil, and the hydrophilic
head toward water
Oil
WATER

40. In order for the amphiphile to be concentrated at the interface , it must be balanced with the proper amount of water- and oil soluble groups.
If the molecule is too hydrophilic it remains within the body of the aqueous phase and exerts no effect at the interface.
If the molecule is too lyophilic it dissolve completely in the oil and also exerts no effect at the interface.

41. Classification of Surface Active Agents
Functional Classification
According to their pharmaceutical use, surfactants can be divided into the following groups:
Wetting agents
Solubilizing agents
Emulsifying agents
Dispersing, Suspending and Defloculating agents
Foaming and antifoaming agents
Detergents

42. Wetting agents Wetting agent is a surfactant that when dissolved in
water, lower the contact angle and aids in displacing the air phase at the surface and replacing it with a liquid phase.
Solids will not be wetted if their surface tension
is exceeded by the surface tension of the liquid. Thus water with a value of 72 dynes/cm will not wet polyethylene with a surface tension of 3 1 dynes/cm.
Based on this concept we should expect a good wetting
agent to be one which reduces the surface tension of a liquid to a value below the solid surface tension.

43. According to the nature of the liquid and the solid, a drop of liquid placed on a solid surface will adhere to it or no. which is the wettability between liquids and solids.
When the forces of adhesion are greater than the forces of cohesion, the liquid tends to wet the surface and vice versa.
Place a drop of a liquid on a smooth surface of a solid. According to the wettability, the drop will make a certain angle of contact with the solid.
A contact angle is lower than 90°, the solid is called wettable
A contact angle is wider than 90°, the solid is named non-wettable.
A contact angle equal to zero indicates complete wettability.

44. Wetting Phenomena No wetting Absolute wetting  = 0o =180o No wetting
Partial wetting
 = 90o
УSL =УS
Partial wetting
> 90o
Negligible wetting

45. Example in pharmaceutical field :
1. The displacement of air from the surface of
sulfur, charcoal, and other powders for the
purpose of dispersing these drugs in liquid
vehicles.
2. The displacement of dirt and debris by the
use of detergents in the washing of wounds.
3. The application of medicinal lotions and sprays
to the surface of the skin and mucous
membrane.
4. Wet ability of tablet surfaces influences disintegration and dissolution and subsequent release of the active ingredient(s) from the tablet

46. Micellar Solubilization
Surfactant molecules accumulate in the interfaces between water and water
insoluble compound. Their hydrocarbon chains penetrate the outermost
layer of insoluble compound which combine with the water­insoluble
molecules. Micelles form around the molecules of the water­insoluble
compound inside the micelles’ cores and bring them into solution in an
aqueous medium. This phenomenon is called micellar solubilization.
As Micellar solubilization depends on the existence of micelles; it does not take
place below the CMC. So dissolution begins at the CMC. Above the CMC, the
amount solubilized is directly proportional to the surfactant concentration
because all surfactant added to the solution in excess of the CMC exists in
micellar form, and as the number of micelles increases the extent of
solubilization increases .

47. Foaming and Anti Foaming agents
Foams are dispersion of a gas in a liquid
(liquid foams as that formed by soaps and
detergents ) or in a solid (solid foams as
sponges ).
Foaming agents
Many Surfactants solutions promote the formation of foams and stabilize them, in pharmacy they are useful in toothpastes compositions.
Anti Foaming agents
They break foams and reduce frothing that may cause problems as in foaming of solubilized liquid preparations. in pharmacy they are useful in aerobic fermentations, steam boilers.

48. Detergents Detergents are surfactants used for removal of dirt.
Detergency involves:
Initial wetting of the dirt and the surface to be
cleaned.
Deflocculation and suspension, emulsification or
solubilisation of the dirt particles
Finally washing away the dirt.

49. Structural Classification
A single surfactant molecule contains one or more
hydrophobic portions and one or more hydrophilic
groups.
According to the presence of ions in the surfactant
molecule they may be classified into:
Ionic surfactants
Anionic surfactants: the surface active part is anion
(negative ion ) e.g. soaps, sodium lauryl sulfate
Cationic surfactants: the surface active part is cation
(positive ion) e.g. quaternary ammonium salts
Ampholytic surfactants: contain both positive and
negative ions e.g. dodecyl-B-alanine.

50. Ionic surfactants Anionic surfactants
They are the metal salts of long ­ chain fatty acids as lauric acid.
Sodium dodecyl sulfate or Sodium Lauryl Sulfate is used in toothpaste and ointments
Triethanolamine dodecyl sulfate is used in shampoos and other cosmetic preparations.
Sodium dodecyl benzene sulfonate is a detergent and has germicidal properties.
Sodium dialkvlsulfosuccinates are good wetting agents.

51. Cationic surfactants
These are chiefly quaternary ammonium compounds. They have bacteriostatic activity probably because they combine with the carboxyl groups in the cell walls of microorganisms by cation exchange, causing lysis.

52. Non-ionic surfactants
Widely used in pharmaceutical formulations e.g. Tweens, Spans.
They are polyethylene oxide products.
Esterification of the primary hydroxyl group with lauric, palmitic, stearic or oleic acid forms sorbitan monolaurate, monopalmitate, monostearate or monooleate
These are water-insoluble surfactants called Span 20, 40, 60 or 80, respectively.
Addition of about 20 ethylene oxide molecules produces the water-soluble surfactants called polysorbate or Tween 20, or 80.

53. Oriented Adsorption of surfactant at Interfaces
As a Surface active substance contains a hydrophilic and a hydrophobic portions, it is adsorbed as a monolayer at the interfaces.
At water-air interface
Surface­active molecules will
be adsorbed at water-air
interfaces and oriented so
that the hydrocarbon chains are pushed out of the water and rest on the surface, while the polar groups are inside the water. Perhaps the polar groups pull the hydrocarbon chains partly into the water.
At oil-water interface
Surface­active molecules will be oriented so that the hydrophobic
portion is inside the oil phase and the hydrophilic portion inside
the water phase.

54. At low surfactant concentrations:
The hydrocarbon chains of surfactant molecules adsorbed in the interface lie nearly flat on the water surface.
At higher concentrations:
They stand upright because this permits more surfactant molecules to pack into the interfacial monolayer.
As the number of surfactant molecules adsorbed at the water­air interface increased, they tend to cover the water with a layer of hydrocarbon chains. Thus, the water-air interface is gradually transformed into an non polar-air interface. This results in a decrease in the surface tension of water.

55. Micelle Formation Micelles.
When the surfactant molecules adsorbed as a monolayer in the water-air interface have become so closely packed that additional molecules cannot be accommodated with ease, the polar groups pull the hydrocarbon chains partly into the water. At certain concentration the interface and the bulk phase become saturated with monomers. Excess surfactants add will begin to agglomerate in the bulk of the solution forming aggregates called
The lowest concentration at which micelles first appear is called the critical concentration for micelle formation [CMC ]
Micelles.
CMC

56. At a given concentration, temperature, and salt content, all micelles of a given surfactant usually contain the same number of molecules, i.e. they are usually monodisperse.
For different surfactants in dilute aqueous solutions, this number ranges approximately from 50 to 100 molecules.
Micelles are not permanent aggregates. They form and disperse continually.

57. Factors affecting CMC For nonionic surfactants Temperature CMC
For ionic surfactants
The CMC are higher for ionic than nonionic surfactants
The charges in the micelle of ionic surfactant are in close, to overcome the resulting repulsion an electric work is required but nonionic surfactants have no electric repulsion to overcome in order to aggregate.
Effect of electrolytes on the CMC of ionic surfactants
The addition of salts to ionic surfactant solutions reduces the electric repulsion between the charged groups and lower CMC values

58. Effect of Surfactant’s structure on CMC
Branched chain systems and double bonds raise CMC
Since the chains must come together inside the micelles
Length of hydrocarbon chain and polarity of Surfactants
Increase in chain length of hydrocarbon facilitate the transfer from aqueous phase to micellar form cause decrease in CMC
Greater interaction with water will retard micelle formation thus ionized surfactants have higher CMC in polar solvents than nonionic Surfactants.
In polar solvents:
Polarity of Surfactant molecules CMC
Length of hydrocarbon chain CMC
In non-polar solvents:
For mixed anionic-cationic surfactants, CMC much lower compared to those of pure components.

59. Incompatibilities Involving Surfactants
Nonionic surfactants
Nonionic surfactants have few incompatibilities with drugs and are preferred over ionic surfactants. even in formulations for external use, except when the germicidal properties of cationic and anionic surfactants are important.
Nonionic surfactants form weak complexes with some preservatives as phenols, including esters of p­hydroxybenzoic acid (Parabenzes) and with acids like benzoic and salicylic via hydrogen bonds. This reduces the antibacterial activity of these compounds.

60. Ionic surfactants
Ionic surfactants capable of reacting with compounds possessing ions of the opposite charge. These reactions
sometimes cause precipitation. The compounds which react with the surface active ions are also changed, and this may be harmful from the physiological or pharmacological point of view.

61. Anionic surfactants
React with Cationic drugs (local anesthetics, most skeletal muscle relaxants, antihistamines and antidepressant agents) cause precipitation or the drugs lose potency or availability.
Cationic surfactants
form complex with water soluble polymers containing negatively charged groups, as natural gums (acacia, tragacanth), sodium carboxy methylcellulose.

62. Anionic
Cationic
Zwitterionic
Nonionic
Sodium dodecylsulfate (SDS)
Cetylpyridinium bromide
Dipalmitoylphosphatidylcholine (lecithin)
Polyoxyethylene(4) lauryl ether

63. HLB and Use of Surfactants
This system measure the hydrophilic - lipophilic balance of S.A.A. which is needed for the emulsification of the oil phase
The oil phase of emulsions ( W/O ,O/W )
required a specific HLB which is called
RHLB .
The same oil phase in W/O emulsion have
another RHLB which is differ from that of
O/W emulsion

64. emulsification
Due to the large specific interfacial area, emulsion is not stable thermodynamically. In order to stabilize an emulsion a third substance known as an emulsifying agent should be added.
water in Oil type
W/O emulsion
oil in water type
O/W emulsion

65. 1. Calculate the required HLB for the oil phase of the following o/w emulsion:
HLB o/w (from reference)
Cetyl alcohol g
White wax g
Lanolin g
emulsifier q.s
water Q.S g
Required HLB is calculated as a sum of their respective HLB multiplied by the fraction of each.
fraction of each = weight of each
total weight

66. Usually a mixture of 2 S. A. A
Usually a mixture of 2 S.A.A. is used as an emulsifying agent in that one of them have HLB bellow RHLB of the oil phase and the other have HLB higher than that of the oil phase
% of surfactant = RHLB – HLB low
of high HLB HLB high – HLB low

67. Calculate the amount of each of Tween 80 ( HLB = 15 ) and of span 80 ( HLB = 4.8 )
that will be used as an emulsifying agent for the following O/W emulsion:
HLB o/w
oil A g
oil B g
oil C g
oil D g
emulsifying agent g
water Q.S g

68. If the amount of the emulsifying agent is not given, how we can calculate it
Qs = 6 ( Ps / P ) Q
RHLB
Qs: is the quantity of S.A.A.
Ps: is the density of surfactant mixture
P : is the density of the eternal phase
(dispersed phase)
Q : is the percent of the continuous phase
( dispersant phase )
RHLB : is the RHLB of the oil phase.

69. Emulsion containing 40g of mixed oil phase and 60g of water, how can you formulate this as O/W and W/O emulsion
The oil phase consists of
HLB (w/o) HLB(o/w)
Paraffin %
Bees wax %
The density of oil phase is 0.85 g/ml
The density of aqueous phase 1g/ml
The density of mixture of surfactant for W/O
emulsion is 0.87 g/ml
The density of mixture of surfactant for O/W
emulsion is 1.05 g/ml