Chapter 6 emulsification and
emulsification by surfactants
2006.4.19.
§1. Introduction
1. Emulsion – immiscible liquid phase, multiphase
dispersion, thermodynamics unstable system
(from a few minutes to a few years)– e.g. milk ,
soybean milk, bearnaise, finishing oil etc.
2. Formation
(1) Emulsification – one fluid dispersed in a second
 dispersephase – 分散相, inner phase , discontinuous phase
 dispersion medium – 分散介质，outer phase ，continuous
phase
 Three types: o/w, w/o, and w/o/w or o/w/o
 two immiscible, pure liquids cannot form emulsion.
(2) Emulsifying agents – the third component – surfactants
3. Properties
(1) Size and aspect of particles
 Macroemulsions: d>400nm, creamy white
 Miniemulsions: 400nm>d>100nm, blue-white
 Microemulsions: 100nm>d>50nm, translucence
 Nanoemulsions: 50nm<d, transparence
(2) Viscosity – Einstein’s eq.
 = 0 (1 + 2.5)
0 – viscosity of outer phase
 - volume fraction of inner phase
(3) Electric conductivity – outer phase
o/w 》w/o ,
ionics 》nonioncs
4. Differentiation of emulsion types
(1) Dilution method
(2) Dyeing method
(3) Electric conductivity
(4) Filter paper method
(5) Light reflectance
(6) Fluorescence method
§2. Theoretics and types of emulsions
Conversion in different types of emulsion
o/w  w/o
1. Phase volume ratio
if particles(inner phase) are rigid ball with same
size, then volume fraction of inner phase
  74.02%
 water > 74%, then w/o  o/w
 water < 26%, then o/w  w/o
monodisperse & rigid ball – polydisperse & elastic
ball(w/o of oil=99%)
2. Wedge theory – geometry theory Match model
3. Solubility rule – hydrophilicity of surfactants
(1) Hydrophilic surfactants – o/w
(2) Lyophilic surfactants – w/o
4. Effects of wall
(1) Hydrophilic wall (high energy surface) – o/w
(2) Lyophilic wall (low energy surface) – w/o
5. Kinetic theory of emulsion type
Davies(1957)developed a quantitative theory of
emulsion type relating the type of emulsion formed to
kinetics of coalescence(聚集) of the two types of
droplets present: oil droplets & water droplets
Rate of coalescence of the particles:
dv/dt = Ae-E/kT
A – collision factor; E – energy barrier to coalescence
 hydrophilic surfactants: Eoli, dv/dt of oil droplets,
dv/dt of water droplets, to form o/w emulsions
 lyophilic surfactants: Ewater, dv/dt of water droplets,
dv/dt of oil droplets, to form w/o emulsions
6. Powder for emulsification
(1) Condition of emulsification
 V/L Young’s eq. SV = SL + LV cos
Spreading S = SV - SL - LV = LV (cos-1)  0
 O/w Young’s eq. SO = SW + OW cosW
or SW = SO + OW cosO
W+ O=180º
SV
OW
vapor
oil
 liquid
SV
SL
O
SO
w water
SW
Spreading SW = SO - SW - OW = OW
(cosW-1)  0
or SO = SW - SO - OW =
OW (cosO-1)  0
 If so  ow + sw then W  0, the
powder is in water phase
If sw  ow + so then o  0, the powder
is in oil phase
Else the powder is adsorbed at O/W
interface
0º < W < 180º or 0º < O < 180º
(2) According O/w Young’s eq.
SO = SW + OW cosW or cosW = (SO - SW)/ OW
 if SO > SW, W < 90º, hydrophilic , mostly in
water phase o/w
 if SO < SW, W > 90º, lyophilic , mostly in oil
phase w/o
 if SO = SW, W = 90º, balance, o/w or w/o , but
unstable
§3. Factors of effect on stability of emulsion
1.Reduces of interfacial tension between two liquids
e.g. 10ml n-octane(正辛烷) is dispersed in water to
0.1 m emulsion, then its surface area is 300m2,
L/L= 50.8mJ/m2, then total surface energy=15.24J
if the surfactants are added into the disperse
system, then L/L  1 mJ/m2, then total surface
energy  0.3J.
Dynamic stability 
2. Physical nature of the
interfacial film
(a) Mechanical stability –
with strong lateral
intermolecular forces
and high film elasticity
(b) Liquid–crystal
formation – with a
high-viscosity region
and a steric barrier to
stabilize of emulsion
3. Existence of an electrical or steric barrier to
coalescence on the dispersed droplets
(a) Electrical barrier –-potential
of ionics:
-potential , stability
(b) Steric barrier
4. Viscosity of the outer phase - diffusion coefficient
of droplets:
D=kT/6a
 - viscosity of the outer phase
a – the radius of the droplets
, D, stability
5. Size distribution of droplets
larger particle have less interfacial surface per unit
volume than smaller droplets, so they are
thermodynamically more stable than smaller ones.
emulsion with uniform size distribution is more
stable.
§4. Emulsifying agent and HLB value
HLB method which was advanced by Griffin in
1949, is the most frequently used method in
the selection of emulsifying agents.
1.HLB value – Hydrophilic-Lipophilic Balance
HLB = Hydrophilic portion/Lipophilic portion
= 0 ~ 40
Paraffin ~ 0, sodium dodecyl sulfate ~ 40
HLB value < 10 lipophilic
HLB value >10 hydrophilic
HLB value for typical nonionic surfactants structures
2. HLB value
1~3
3~6
7~9
8 ~ 18
13 ~15
15 ~18
&
application
anti-foaming agent
w/o emulsifying agents
wetting agents
o/w emulsifying agents
detergents
solubilizing agents
3. Estimate of HLB value
(1)Nonionics:
HLB = mass fraction of hydrophilic group20
(a) Fatty acid of many polyhydric alcohols(多元醇)
HLB = 20(1-S/A)
S – saponification number(皂化值) of the ester;
A – acid number(酸值) of the fatty acid in the ester.
e.g. C17H35COOCH2CH(OH)CH2OH
S=161, A=198, then HLB = 3.7
(b) Nonionics of POE & polyol
HLB = (E + P)/5
E – the weight percentage of oxyethylene content
P – the weight percentage of polyol content
e.g. C16H33(OC2H4)10OH
E = (44  10+17)/(44  10+17+225) = 67.0%;P = 0
HLB = (E+P)/5 = 67.0/5 = 0.67  20 = 13.4
(c) Logarithm: HLB=7+11.7ln(MW/MO)
MW or MO- molecular weight of hydro- or lipo-philic
group: MW=441, MO=225, then HLB=14.9
(2) Ionic surfactants –
group numbers could
be calculated based
upon group
contribution accord-ing
to the formula:
HLB = 7 + (group
numbers)
e.g.C12H25SO4Na
HLB=7+38.70.47512=40
e.g. C16H33(OC2H4)10OH
HLB=7+0.33 10+0.50.475 16=3.20
(3) Mensuration
(a) behavior in water
no dispersibility
poor dispersion
milky dispersion after
vigorous agitation
stable milky dispersion
(upper end almost translucent)
from translucent to clear
clear solution
HLB Range
1–4
3–6
6–8
8 – 10
10 – 13
13 +
(b) Cloud point – POE nonionics 1% aq.
TP , HLB, TP>100ºC, HLB>15,
TP  HLB
(4) HLB of a mixyure
HLBmix= fiHLBi =fAHLBA+(1-fA)HLBB
fi – the weight fraction of surfactant i in mixture
4. Emulsifying agents
(1) Synthetical surfactants
(a) Anionics – HLB > 8 , o/w type
(b) Nonionics – HLB < 18, o/w or w/o type
(c) Cationics - a few
(2) Natural surfactants – lecithin(卵磷脂),
cholesterin(胆甾醇) etc
(3) Polymeric emulsifying agents
(4) Powder emulsifying agents
5. Application - selection of surfactants using HLB
value as emulsifying agents
(1) Optimal HLB value for emulsification
(A)Using the data handbook
(a) HLB value for emulsification of some oils
(b) Mixture of oils
HLBmix= Fj HLBj= FAHLBA+(1-FA)HLBB
Fj ,HLBj – weight fraction and HLB of j oil.
(B) Mensuration and check
e.g. using the Span-series (HLBSpen-60=4.3) and
Tween-series (HLBTween-80=15), the optimal HLB
value for emulsification
(2) Optimal emulsifying agents
– two principles
(a) The structure of
hydrophobic groups
of emulsifying agents
is close to the oils
(b) The synergistic effect
6. Phase Inversion Temperature (相转变温度PIT)
(1) Disadvantage of HLB method
(a) Surfactants with same HLB value could possess
different emulsifying ability
(b) It makes no allowance for the change in HLB
value with change in the conditions for
emulsification (temperature, nature of oil & water
phase). E.g. POE T, HLB
(2) PIT – the temperature when the POE is used to
emulsifying agents from o/w emulsion inversion to
w/o
(3) Mensuration of PIT – emulsion : 3-5% emulsifying
agents and o:w volume ratio =1
(4) Emulsion stability
(a) o/w type : PIT – TS =20-60ºC
TS – storage temperature (储藏温度)of emulsion
(b) w/o type : TS – PIT = 10-40ºC
(c) Preparing temperature of emulsificatopn by the PIT
 Preparation at a temperature 2-4ºC below the PIT
to obtain a very fine average particles size
 Cooled down to storage temperature( for o/w) to
increases it stability
(5) Factors affecting PIT
(a) PIT  HLB selection of emulsion PIT according
to their HLB value
(b) Hydrophility of POE , PIT
(c) Distribution of POE , PIT, o/w stability
(d) Addition of electrolyte in water phase, PIT
(e) In oil phase
 addition of nonpolar organics e.g. paraffin
PIT 
addition of polar organics
e.g.
long chain, PIT 
short chain, PIT
Mixture of oils
PITmix= i PITi = A PITA + (1- A) PITB
i – volume fraction of i oil; PITi – PIT of i oil in
this emulsifying system
7. Preparation method of emulsion
(1)
(a)
(b)
(c)
(d)
Addition of emulsifying agents
in water phase
in oil phase
nascent soap(初生皂法)
mixed films (respectively addition of hydrophilic
surfactants in water and hydrophobic surfactants
in oil phase)
(e) alternately addition of oil and water
(2) Oil-Water mixing
(a) The addition of water to oil - to obtain a very fine
average particles size and stable o/w emulsion
(b) The addition of oil to water
(3) Methods of emulsification
(a) Direct emulsification – 70 - 75ºC
(b) Phase inversion emulsification
(4) Equipment of emulsification
(a) Simple agitating - impulse type (推进式), turbo
type(涡轮式)
(b) Homogenizer – high pressure 6.89-34.47 Mpa
(c) Colloid mill (胶体磨) – rotor(转子) and stator(定
子), rotate speed = 1000-20000 rpm ，high
shearing force (高切力)
§5. instability of emulsion and demulsification
1.
(1)
(2)
(3)
(4)
Inversion of emulsion – o/w  w/o
Phase volume ratio
Polyvalent ions
Temperature T>PIT
Addition of electrolytes
o/w  w/o
e.g. Inversion of o/w to w/o
by an interface film of sodium
cetyl sulfate (十六烷基硫酸钠)
and cholesterol (胆固醇)upon
addition of polyvalent cations
2. The creaming(分层),
flocculation(絮凝),and
coalescence(聚结) – the
reversible prelude of
emulsion breaking
(a) Creaming – difference
in gravitational
(b) Flocculation - attractive
force between droplets
(c) Coalescence – irreversible
- breaking, phase separation
3. Emulsion breaking(破乳) – to break the
interface films
(1) Methods
(a) Physical method
 Heating
 Electrical precipitation
 Ultrasonic
(b) Chemical method
 De-emulsifying agent
 Inorganic acid
 Polyvalent ion to inversion
(2) Mechanism
(a) Displacing – emulsifying agents are displaced
by de-emulsifying agent
(b) Wetting – powder emulsifying agents
(c) Flocculating – cross-linking agents
(d) Collision - deemulsification
(e) Make the interface film to distortion(变形) and
tendering(变脆)
(3) Factor affecting de-emulsification
(a) pH value – e.g. carboxylate surfactant is
unstable at low pH.
(b) Electrolyte
 Concentration – I , , stability.
 Valenta value – polyvalent ion , stability
(c) Temperature - T, solubility of surfactants,
intensity of film
(d) Phase volume ratio – volume fraction > 74.02%
(h) Stirring – Reynolds number (雷诺数) - 3500
§6. Micro-emulsion
Generally : surfactants & cosurfactants and etc
In 1986,the cosurfactant-free microemulsion
have been prepared
• The differentia with macro-emulsion
2. Mechanism of formation
(1) Negative interfacial tension theory – Schulman
and co-workers:  0  spontaneous process
it may be a transient phenomenon(暂时), and at
equilibrium must be zero or slightly positive.
 is macroscopy property and made no sense in
micro-emulsion
oil
(2) 双重膜(duplex film?)
mo
surfactants + co-surfactants
Mixed film
mw
+ auxiliary agent(助剂)
water
If mw  mo, then the films is bended to water phase, w/o
If mw < mo, then the films is bended to oil phase, o/w
(3) Swollen micelles