Dissertation

1

Investigating
the
effects
of
processing
conditions

and
material
properties
on
the
particle
size

distributions
of
oil
in
water
emulsions
in
high

shear
rotor-‐stator
emulsifications.

2

Table
of
Contents

1.
Abstract
..............................................................................................................................................
4

2.
Introduction
.......................................................................................................................................
5

2.1
Aims
and
Objectives
.....................................................................................................................
6

2.2
Limitations
...................................................................................................................................
6

2.3
Abbreviations
and
Symbology
.....................................................................................................
6

3.
Literature
Report
...............................................................................................................................
7

3.1
Emulsions
.....................................................................................................................................
7

3.1.1
Types
of
Emulsions
................................................................................................................
8

3.2
Surfactants
.................................................................................................................................
10

3.2.1
Types
of
Surfactants
............................................................................................................
10

3.2.2
Selection
of
Surfactants
......................................................................................................
11

3.3
Techniques
for
Creating
Emulsions
in
Industry
..........................................................................
12

3.3.1
Rotor-‐stator
homogenizers
.................................................................................................
12

3.3.2
Ultrasound
Emulsification
...................................................................................................
13

3.3.3
High
Pressure
Emulsification
...............................................................................................
14

3.4
Interactions
between
droplets
..................................................................................................
15

3.5
Destabilizing
Mechanisms
in
Emulsions
.....................................................................................
16

3.6
Rheological
properties
of
Emulsions
..........................................................................................
18

3.6.1
Viscosity
of
the
continuous
phase
......................................................................................
18

3.6.2
Volume
fraction
of
the
dispersed
phase
.............................................................................
19

3.6.3
Surfactant
Properties
..........................................................................................................
19

3.6.4
Droplet
size
distribution
......................................................................................................
19

4.
Methodology
...................................................................................................................................
20

4.1
Materials
....................................................................................................................................
20

4.2
Equipment
..................................................................................................................................
20

4.2.1
Brookfield
DV-‐II
Pro
Programmable
Viscometer.
...............................................................
20

4.2.2
High
Shear
Rotor
Stator
Mixer
............................................................................................
21

4.2.3
Malvern
Mastersizer
2000
..................................................................................................
21

4.3
Experimental
Procedure
............................................................................................................
22

4.3.1
First
Phase
...........................................................................................................................
22

4.3.2
Second
Phase
......................................................................................................................
22

4.3.3
Third
Phase
.........................................................................................................................
23

5.
Safety
Hazards
.................................................................................................................................
23

6.
Results
..............................................................................................................................................
24

3

6.1
Experimental
Results
.................................................................................................................
24

6.2
Treatment
of
results
..................................................................................................................
26

7.
Discussion
and
conclusion
...............................................................................................................
32

8.
References
.......................................................................................................................................
33

4

1.
Abstract

The
droplet
size
distribution
is
of
prime
importance
in
emulsion
technology
due
to
its
direct
link
with

the
stability
of
emulsions.
The
ability
to
predict
droplet
sizes
at
varying
conditions
that
influence

droplet
sizes
will
save
researchers
time
and
companies
resources
by
avoiding
the
derivation
of

undesired
products.
What
this
study
attempts
to
do
is
relate
three
variables
that
influence
droplet

size
and
condense
them
into
one
variable
known
as
“D”.

Four
oils
were
used
in
this
study;
liquid
paraffin,
rapeseed
oil,
flax
oil
and
groundnut
oil.
The

surfactants
used
in
the
production
of
oil
in
water
emulsions
were
sodium
dodecyl
sulfate
and
tween

80.
The
three
factors
studied
were
the
viscosity
of
the
dispersed
phase,
the
time
spent
mixing
and

the
rotation
speed.
This
variables
were
condensed
by
modifying
power
number.
The
power
number

of
an
impeller
is
a
method
of
relating
the
different
conditions
of
mixing.
Modifying
this
to
take
time

into
account
allows
a
way
of
relating
work
done
on
the
emulsion
as
opposed
to
the
amount
of

power
used.
This
was
then
modified
further
to
take
the
different
viscosities
of
the
oil
into
account

thereby
allowing
a
method
in
which
the
mean
particle
size
can
be
predicted.

Whilst
the
results
were
as
expected,
analysis
proved
difficult
in
that
not
all
variables
could
be

condensed
into
one
variable.
The
rotational
speed
variable
proved
difficult
because
once
the

modified
power
number
was
created
as
the
relationship
with
mean
particle
size
was
not
feasible.

Which
meant
D
was
limited
in
that
rotational
speed
had
to
be
kept
constant.
The
time
and
viscosity

variables
however
proved
easier
to
condense
however
the
values
of
D
only
gave
a
rough
estimate
of

the
predicted
mean
particle
size.

5

2.
Introduction

Emulsion
technology
has
become
a
tool
of
great
importance
in
a
number
of
industries.
The

applications
of
which
can
be
seen
daily
in
areas
as
diverse
as
mayonnaise
used
to
improve
the

quality
of
a
meal
down
to
pesticides
which
repel
unwanted
pests.
The
ever
increasing
applications
of

emulsions
include:
their
use
as
vehicles
for
the
delivery
of
lipid-‐soluble
drugs
in
the
pharmaceutical

industry
[1];
in
road
construction
industry,
Bitumen
emulsions
are
used
to
carry
an
active
material,

mainly
bitumen,
for
road
application
while
avoiding
solvents
[3];
and
finally
in
the
paint
industry,
the

development
of
emulsion
paints
allow
for
the
advantages
of
both
oil
and
water
paints,
while

diminishing
their
disadvantages
[2].
Emulsions
are
also
present
in
nature.
Milk
is
perhaps
one
of
the

most
stable
emulsions
produced
in
nature,
although
it
is
not
well
understood
why
milk
is
produced

in
nature
as
an
emulsion
[3].

Emulsions
are
formed
from
the
mixture
of
two
immiscible
liquids
with
the
help
of
surfactants,
more

commonly
known
as
emulsifiers.
One
liquid
constitutes
the
droplets
which
are
dispersed
into

another
liquid.
These
are
known
respectively
as
the
dispersed
phase
and
the
continuous
phase.
This

dispersion
must
remain
perfectly
stable
and
homogenous
over
a
certain
period
of
time.
This
length

of
time
is
dependent
on
the
intended
application
of
the
emulsion
[3].

Emulsions
are
thermodynamically
unstable
structures
given
kinetic
stability
by
the
material

adsorbed
at
the
interface
[4].
The
mechanisms
by
which
an
emulsified
oil
can
return
to

thermodynamic
stability
include
creaming,
flocculation,
coalescence,
and,
frequently
less

significantly,
disproportionation
[5].
Creaming
occurs
because
of
the
density
difference
between
the

dispersed
phase
and
the
continuous
phase
and
leads
to
a
bulk
separation
under
gravity
[5].
During

flocculation
several
droplets
aggregate
to
form
a
cluster
(floc)
but
each
droplet
remains
intact
[5].

Coalescence
is
similar
to
flocculation
in
that
it
requires
droplet–droplet
contact
but
in
this
case
the

contents
of
the
individual
droplets
merge
and
the
Laplace
pressure
forces
the
doublet
to
rapidly
take

on
a
spherical
shape
[5].

When
emulsions
are
prepared,
be
it
in
industry
or
in
a
laboratory,
one
of
the
aims
of
preparation
is

to
get
the
smallest
possible
droplet
sizes
of
the
dispersed
phase.
Droplet
size
is
among
the
main

factors
that
determine
the
stability
of
an
emulsion.
The
smaller
the
droplet
size,
the
more
stable
the

emulsion
and
vice
versa
as
smaller
droplets
will
coalesce
at
a
much
slower
rate
than
bigger
droplets.

There
are
many
methods
of
making
emulsions;
one
of
the
more
common
methods
of
emulsification

used
in
most
industries
and
the
method
used
in
this
study
is
the
high
shear
rotor
stator
mixer.
The

properties
of
which
is
discussed
in
further
detail
in
chapter
3.
Rotor-‐stator
devices
provide
a
focused

delivery
of
energy,
power
and
shear
to
accelerate
physical
processes
such
as
mixing,
dissolution,
and

emulsification
and
deagglomeration
[6].

6

2.1
Aims
and
Objectives

The
aim
of
this
study
is
to
determine
the
mean
particle
size
of
emulsion
droplets
with
varying

variables
such
as
the
viscosity
of
the
oils
in
the
dispersed
phase,
the
rotational
speed
of
the
rotor

stator
homogenizer
as
well
as
time
spent
homogenizing.
This
will
then
allow
for
the
production
of
a

correlation
graph
of
particle
size
against
an
unknown
variable,
“D”,
which
will
combine
all
variables.

Thereby
allowing
for
the
prediction
of
the
mean
particle
once
the
D
value
is
replicated
using
any

various
combination
of
the
aforementioned
variables.

2.2
Limitations

Due
to
time
constraints,
only
four
oils
were
studied
thereby
limiting
the
research
involved
in

determining
the
effect
of
the
viscosity
of
the
oils
on
the
mean
particle
size.
The
mixer
used
in
this

study
does
not
take
into
account
the
varying
viscosity
of
the
materials,
therefore
the
power

determined
is
an
estimate.

2.3
Abbreviations
and
Symbology

Abbreviations
Meaning

RPM

Revolutions
Per
Minute

SMC

Spindle
Multiplier
Constant

TK

Viscometer
Torque
Constant

SDS

Sodium
Dodecyl
Sulfate

OSC

Oil
Soluble
Content

WSC
Water
Soluble
Content

HLB
Hydrophilic
Lipophilic
Balance

SOP
Standard
Operating
Procedure(s)

cP

Centipoise

f
Volume
fraction

η
Viscosity

φ
volume
fraction
of
the
dispersed
phase

7

3.
Literature
Report

This
section
of
the
study
shall
focus
extensively
on
emulsions
and
surfactants.
This
will
include
the

different
types
of
emulsions,
interactions
between
droplets
and
the
destabilizing
mechanisms
that

take
place
in
the
breakdown
of
emulsion
systems.
The
nature
and
types
of
surfactants
shall
also
be

covered
and
their
roles
in
the
production
and
stabilisation
of
emulsion.
In
addition
to
that,
the

factors
that
come
into
play
when
selecting
of
surfactants
will
be
studies.
Methods
in
which

emulsions
are
created
shall
be
highlighted
as
well
as
the
effect
of
certain
conditions
on
the
rheology

of
the
emulsion.

3.1
Emulsions

An
emulsion
is
a
heterogeneous
system
consisting
of
at
least
one
immiscible
liquid
intimately

dispersed
in
another
in
the
form
of
droplets,
whose
diameter,
in
general
exceed
0.1
µm
[2].

The

phase
which
is
present
in
the
form
of
finely
divided
droplets
is
called
the
dispersed
or
internal
phase;

the
phase
which
forms
the
matrix
in
which
these
droplets
are
suspended
is
called
the
continuous
or

external
phase
[2].
Emulsions
can
be
classified
in
order
of
droplet
size.
Droplet
sizes
which
exceed
1

µm
are
considered
to
be
macro
emulsions,
those
between
100
nm
and
1
µm
are
classed
as
mini

emulsions
whilst
those
between
10
nm
and
100
nm
are
nano
emulsions.
For
the
purpose
of
this

study
only
macro
emulsions
will
be
discussed.

Figure
1
showing
the
interface
between
two
immiscible
liquids

When
two
immiscible
liquids
are
placed
in
contact,
an
interface
is
created
as
a
result
[2].
The

interfacial
free
energy
is
the
minimum
amount
of
work
required
to
create
an
interface
and
is
a

measure
of
the
interfacial
tension
between
two
liquids
[9].
The
interfacial
tension
is
also
a
measure

of
the
difference
in
nature
of
the
two
phases
meeting
at
the
interface,
the
greater
the
dissimilarity,

the
greater
the
interfacial
tension
[9].

Due
to
the
large
area
of
interface
between
the
two
phases

that
must
be
created
and
maintained,
emulsions
are
thermodynamically
unstable
[8].

8

Figure
2
showing
emulsion
formation
and
break
down
[10]

The
change
in
free
energy
in
going
from
state
I
to
state
II
is
made
from
two
contributions:
A
positive

surface
energy
term
and
a
positive
entropy
term
due
to
an
increase
in
the
number
of
droplets
[10].

The
surface
energy
term
is
the
change
in
surface
area
(ΔA)
multiplied
by
the
interfacial
tension
( 𝛶)

[10].

∆𝐺!"#$
= ∆𝐴𝛶 − 𝑇∆𝑆!"#$

Equation
1

When
an
emulsion
if
formed,
with
the
exception
of
micro
emulsions,
ΔAΥ
is
much
positive
and
much

greater
than
-‐TΔSconf

which
means
that
ΔGform

is
in
turn
positive,
therefore
the
formation
of

emulsions
is
nonspontaneous
and
the
system
is
thermodynamically
unstable
[10].
This
is
due
to
the

formation
of
droplets
which
leads
to
an
increase
in
the
surface
area
which
in
turn
increases
ΔAΥ.

3.1.1
Types
of
Emulsions

Based
on
the
dispersion
of
water
or
oil
in
continuous
phase
and
on
the
number
of
phases
present
in

the
system,
macro
emulsions
can
be
subdivided
into
two
categories
[11].
These
are
single
emulsions

and
Double
(or
multiple)
emulsions.

In
the
case
of
simple
emulsions,
droplets
of
one
liquid
phase
are
dispersed
in
another
immiscible

liquid
phase
[12].
Simple
emulsions
could
be
of
two
types;
water-‐in-‐oil
emulsions,
and
oil
in-‐water

emulsions,
known
respectively
as
W/O
and
O/W
emulsions
[12].
Double
emulsions,
as
the
name

indicates
is
one
in
which
both
types
of
emulsions
exist
simultaneously
[2].
Termed
'emulsions
of

emulsions',
the
droplets
of
the
dispersed
phase
themselves
contain
even
smaller
dispersed
droplets

[15].

Two
main
types
of
double
emulsions
can
be
distinguished:
water-‐in-‐oil-‐in-‐water
(W/O/W)

emulsions,
in
which
a
W/O
emulsion
is
dispersed
as
droplets
in
an
aqueous
phase,
and
oil-‐in-‐water-‐
in-‐oil
(O/W/O)
emulsions,
in
which
an
O/W
emulsion
is
dispersed
in
an
oil
phase
[13].
The
type
of

emulsion
formed
is
usually
determined
by
the
surfactants
added
to
the
system.
Illustrations
of
both

simple
and
double
emulsions
are
shown
in
figures
3
and
4.

Figure
3
showing
simple
emulsions

9

Figure
4
showing
double
emulsions

Simple
emulsions
can
be
classified
into
three
groups
depending
on
the
volume
fraction
of
the

dispersed
phase
[14].
These
are
low
dispersed
phase
ratio,
medium
dispersed
phase
ratio
and
high

dispersed
phase
ratio.
Emulsions
in
which
the
disperse
phase
accounts
for
30%
or
less
of
the
total

volume
of
the
emulsion
are
classified
as
low
dispersed
phase
ratio,
whilst
medium
dispersed
phase

ratio
is
in
the
range
of
30%
and
70%,
finally
emulsions
in
which
the
disperse
phase
accounts
for
more

than
70%
of
the
emulsion
volume
are
classified
as
high
disperse
phase
ratio
[14].

Double
emulsions
contain
more
interfaces
and
are
even
more
thermodynamically
unstable
than

single
emulsions
[13].
Double
emulsions
are
prepared
in
a
two-‐step
emulsification
process
using
two

surfactants;
a
hydrophobic
one
designed
to
stabilize
the
interface
of
the
W/O
internal
emulsion
and

a
hydrophilic
one
for
the
external
interface
of
the
oil
globules
(for
W/O/W
emulsions)
[13].
The

primary
W/O
emulsion
is
prepared
under
high-‐shear
conditions
to
obtain
small
droplets
while
the

secondary
emulsification
step
is
carried
out
with
less
shear
to
avoid
rupture
of
the
internal
droplets

[15].
The
applications
of
double
emulsions
are
limited
due
to
problems
with
manufacture
and

control
among
others.
For
example,
they
consist
of
relatively
large
droplets
that
coalesce
either

quiescently
or
due
to
commonly
encountered
processing
regimes
(e.g.,
shear,
sterilization),
and
have

a
strong
tendency
to
release
entrapped
compounds
in
an
uncontrolled
manner
[16].
Usage
of

double
emulsions
for
food
applications
is
further
limited
by
the
lack
of
suitable
food-‐grade

emulsifiers
and
stabilizers
for
the
inner
and
outer
emulsions
[17].
However,
double
emulsions
have

been
used
in
cosmetics
and
pharmaceuticals
for
applications
such
as
drug
controlled
release
and

targeted
delivery
[18].

In
addition
to
that,
other
applications
have
included
the
removal
of
toxic

materials
via
entrapment
and
solubility
enhancement
of
poorly-‐soluble
materials
[19].

10

3.2
Surfactants

An
emulsion
is
the
result
of
two
competing
processes,
the
disruption
of
bulk
liquids
to
produce
fine

droplets
and
the
recombination
of
the
droplets
to
give
back
the
bulk
liquids
[7].
An
emulsion
is

thermodynamically
unstable
and
the
latter
process
is
the
natural
one
[7].
The
success
of
emulsion

technology
lies
in
keeping
the
system
in
a
metastable
state
by
opposing
the
recombination
of

droplets
[7].
This
is
where
surfactants
come
into
play.
A
surfactant
used
as
an
emulsifier
has
two

main
functions:
allowing
emulsion
formation
and
providing
stability
to
the
emulsion
once
made
[20].

A
surfactant
(a
contraction
of
the
term
surface-‐active
agent)
is
a
substance
that,
when
present
in
a

system,
has
the
property
of
adsorbing
onto
the
interfaces
of
the
system
and
of
altering
to
a
marked

degree
the
interfacial
tension
of
those
interfaces
[9].
Surfactants
also
play
various
roles
in
addition

to
this.
They
can
increase
resistance
to
deformation
and
in
some
cases,
they
can
facilitate
droplet

break
up
by
means
of
surface
forces
[20].
The
formation
of
a
surfactant
film
around
the
droplets

facilitates
the
process
of
emulsification
[11].
Most
importantly,
they
counteract
the
(re)coalescence

of
newly
formed
droplets
during
emulsification
[20].
Surfactants
have
a
characteristic
molecular

structure
consisting
of
a
structural
group
that
has
very
little
attraction
for
the
aqueous
phase,
known

as
a
hydrophobic
group,
together
with
a
group
that
has
strong
attraction
for
the
aqueous
phase,

called
the
hydrophilic
group
[9].
This
is
known
as
an
amphipathic
structure
[9].
Because
of
its
dual

affinity,
an
amphipathic
molecule
would
be
out
of
place
in
any
solvent,
be
it
polar
or
non-‐polar,
since

there
is
always
one
of
the
groups
which
"does
not
like"
the
solvent
environment
[21].
This
is
why

amphipathic
molecules
exhibit
a
very
strong
tendency
to
migrate
to
interfaces
and
to
orientate
in
a

manner
in
which
the
polar
group
lies
in
water
and
the
non-‐polar
group
in
oil
[21].

3.2.1
Types
of
Surfactants

Different
types
of
surfactants
are
required
under
different
conditions,
namely
the
solvent.
For

example,
in
a
highly
polar
solvent
such
as
water,
the
hydrophobic
group
may
be
a
hydrocarbon
or

fluorocarbon
chain
of
proper
length,
whereas
in
a
less
polar
solvent
only
some
of
these
may
be

suitable
[9].
Therefore,
for
surface
activity
in
a
particular
system
the
surfactant
molecule
must
have

a
chemical
structure
that
is
amphipathic
in
that
solvent
under
the
conditions
of
use
[9].
Surfactants

are
classified
by
the
type
of
hype
of
hydrophilic
group
in
the
molecules.
There
are
four
main
groups

of
classification.

Anionic
surfactants

In
anionic
surfactants,
the
hydrophilic
portion
of
the
molecule
bears
a
negative
charge
[9].
They

dissociate
in
aqueous
solution
to
form
an
amphipathic
anion
and
a
cation,
they
are
the
most

commonly
used
surfactants
[21].
The
oldest
and
best
known
example
of
anionic
surfactants
are
the

soaps
[2].
Common
examples
of
these
include
lauryl
sulfates,
alkylbenzene
sulfonates
and

lignosulfonates.
They
account
for
approximately
half
of
the
world
production
[21].

Cationic
surfactants

In
cationic
surfactants,
the
hydrophilic
portion
bears
a
positive
charge
[9].
They
dissociate
in

aqueous
solution
to
form
an
amphipathic
cation
and
an
anion
[21].
They
are
typically
more

expensive
than
anionic
surfactants
because
of
the
high
pressure
hydrogenation
reaction
carried
out

during
their
synthesis
[21].
As
a
result,
they
are
only
employed
as
bactericides
or
as
positively

charged
substance,
able
to
adsorb
on
negatively
charged
substrates
[21].
Cationic
surfactants
mainly

consist
of
amine
salts
and
quaternary
ammonium
compounds.

11

Amphoteric
(Zwitterionic)
surfactants

In
amphoteric
surfactants,
both
positive
and
negative
charges
may
be
present
in
the
hydrophilic

portion
[9].
They
exhibit
both
anionic
and
cationic
dissociation
in
aqueous
solution
[21].
Amphoteric

surfactants
are
quite
expensive
and
are
therefore
not
practical
for
regular
usage;
as
a
result
their
use

is
limited
to
very
special
applications
such
as
cosmetics
[21].
Examples
of
amphoteric
surfactants

include
betaines
or
sulfobetaines
[21].

Nonionic
surfactants

In
non-‐ionic
surfactants,
the
surface-‐active
portion
bears
no
ionic
charge
[9].
They
do
not
ionize
in

aqueous
solution,
because
their
hydrophilic
group
is
of
a
nondissociable
type,
such
as
alcohol
[21].
In

many
cases,
the
effectiveness
of
the
hydrophobic
and
hydrophilic
portions
of
the
molecule
can
be

modified,
so
they
can,
in
effect,
be
made
to
fit
any
particular
application
[2].
Nonionic
surfactants

account
for
approximately
45%
of
industrial
production
[21].

Figure
5
showing
the
four
main
classes
of
surfactants

Some
relatively
new
types
of
surfactants
have
been
introduced
in
recent
years,
the
most
prominent

of
which
is
the
surface
active
polymers.
These
result
from
the
association
of
one
or
several

macromolecular
structures
exhibiting
hydrophilic
and
lipophilic
characters.
They
are
now
very

commonly
used
in
formulating
products
as
different
as
cosmetics
and
foodstuffs
[21].

3.2.2
Selection
of
Surfactants

When
selecting
surfactants
for
use
in
emulsification,
all
conditions
of
the
system
have
to
be
taken

into
account.
Examples
of
these
are,
stability
of
the
surfactants
under
the
temperature
and
pH

conditions
and
the
type
of
emulsion
which
must
be
produced
as
a
result
among
many
others.
The

selection
of
different
surfactants
in
the
preparation
of
emulsions
is
often
made
on
an
empirical

basis,
one
such
empirical
scale
for
selecting
surfactants
is
the
hydrophilic-‐lipophilic
balance
(HLB)

number
developed
by
Griffin
in
1949
[10].This
scale
is
based
on
the
relative
percentage
of

hydrophilic
to
lipophilic
groups
in
the
surfactant
molecule
[10].
HLB
values
range
from
0
to
20
on
an

arbitrary
scale
[1].
At
the
higher
end
of
the
scale,
the
surfactants
are
hydrophilic,
these
include

solubilising
agents
and
detergents
[1].

12

Surfactants
on
the
higher
end
of
the
scale
are
water
soluble
and
are
used
in
the
production
of
o/w

emulsions.
At
the
lower
end,
the
surfactants
are
hydrophobic,
these
include
antifoaming
agents.

These
are
oil
soluble
and
are
employed
in
the
production
of
w/o
emulsions.

Table
1
showing
the
range
of
HLB
values
required
for
different
purposes

HLB
range
of
value
Use

0
–
2
Antifoaming
agents

2
–
7
w/o
surfactants

8
–
16
o/w
surfactants

12
–
17
Detergents

17
–
19

Solubilising
agents

In
practice,
a
mixture
of
surfactants
of
high
HLB
and
low
HLB
gives
more
stable
emulsions
than
a

single
surfactant
[1].
In
the
experimental
determination
of
optimum
HLB,
creaming
of
the
phases
is

taken
as
a
sign
of
instability,
the
system
with
minimum
creaming
is
deemed
to
be
of
optimal
HLB
[1].

The
HLB
value
of
a
mixture
of
surfactants
can
be
determined
using
equation
1.

𝐻𝑙𝑏 = 𝑓 𝑂𝑆𝐶 𝑋 𝐻𝑙𝑏 𝑂𝑆𝐶 + 1 − 𝑓 𝑊𝑆𝐶 𝑋 𝐻𝑙𝑏[𝑊𝑆𝐶]

Equation
1

A
major
disadvantage
of
the
HLB
concept
is
that
it
does
not
take
into
account
the
effect
of

temperature
on
the
surfactants.
With
increasing
temperature,
the
hydration
of
lipophilic
groups

decrease
and
the
surfactant
becomes
less
hydrophilic
thus
decreasing
its
HLB
[30].

3.3 Techniques
for
Creating
Emulsions
in
Industry

In
industry,
there
are
a
number
of
techniques
available
in
order
to
create
different
types
of

emulsions,
some
more
complex
than
others.
The
aim
is
however
always
the
same;
to
achieve
the

smallest
possible
droplet
sizes.
Examples
of
these
techniques
include
rotor-‐stator
devices,
colloid

mills,
high
pressure
systems,
membrane
systems
and
ultrasound
techniques.

3.3.1
Rotor-‐stator
homogenizers

Modern
emulsions
have
been
prepared
on
an
industrial
scale
by
a
variety
of
emulsification

equipment
based
on
a
similar
operating
principle,
agitation.
Rotor-‐stator
homogenization
belongs
in

this
category
[22].

Homogenizers
are
used
to
mechanically
mix
a
plurality
of
liquids
having
no
mutual
compatibility
as
in

the
case
of
water
and
oil
to
thereby
homogenize
them
into
an
emulsion
[23].
In
addition,
they
are

also
used
in
solid-‐liquid
suspensions
and
chemical
reactions.
The
rotor-‐stator
assembly
consists
of
a

rotor
of
two
or
more
blades
and
a
stator
with
either
vertical
or
slant
slots
around
the
wall
of
the

homogenizer
cell.
The
rotor
is
housed
inside
the
stator
[22].

When
two
liquids
are
supplied
to
the
hollow
of
the
rotor
by
a
pump,
the
rotor
starts
to
rotate
in
the

state
where
these
liquids
are
being
supplied.
A
centrifugal
force
is
applied
to
the
liquids,
which
are

ejected
from
the
radial
flow
passages
formed
in
the
rotor
to
enter
the
gap
between
the
rotor
and

stator,
entering
radial
flow
passages
of
the
stator.
The
stator
does
not
rotate
but
remains
stationary,

so
that
when
the
rotor
starts
to
rotate,
a
vortex
flow
is
generated
in
the
liquids
existing
in
the
radial

flow
passages
of
the
rotor
and
the
stator
[23].

Homogenization
intensity
(power)
and
the
residence
time
that
emulsion
droplets
stay
in
the

shearing
field
are
the
primary
parameters
for
controlling
emulsion
droplet
size.
Other
parameters

13

that
might
affect
the
performance
of
rotor-‐stator
homogenization
are
the
viscosity
of
the
two

liquids,
surfactant,
rotor-‐stator
design,
volume
size,
and
volume
ratio
of
the
two
phases
[22].

Figure
6
various
rotors

3.3.2
Ultrasound
Emulsification

The
use
of
mixing
and
shearing
devices
represent
a
simple
way
of
introducing
energy
for
the

formation
of
emulsions,
it
is
however
not
the
only
method
[2].

Under
the
influence
of
ultrasound,
emulsions
can
be
formed.
There
are
two
main
views
as
to
why

emulsions
are
formed
when
irradiated
by
ultrasounds.
Firstly,
there
is
the
view
that
cavitation
may

be
responsible
for
this,
the
other
being
that
capillary
waves
at
the
interface
is
responsible
for
droplet

formation.

There
are
several
possible
mechanisms
of
droplet
formation
and
disruption
under
the
influence
of

ultrasound.
This
can
be
done
by
the
formation
of
droplets
as
a
consequence
of
unstable
oscillations

of
the
interface.
These
capillary
waves
may
occur
and
contribute
to
dispersion,
only
if
the
diameter

of
droplets
to
be
disrupted
is
larger
than
the
wavelength
of
the
capillary
waves.
This
mechanism
has

to
be
taken
into
account
as
one
cause
of
droplet
disruption
in
an
acoustic
field,
but
only
for
a
small

fraction
of
droplets
with
diameters
exactly
in
the
corresponding
range
[25].

Cavitation
occurs
when
a
sound
wave
travels
through
the
liquid
thereby
compressing
and
stretching

it.
When
there
is
insufficient
stretch
or
the
liquid
contains
no
gas,
nothing
happens,
however
if
the

liquid
is
saturated
with
gas,
bubbles
appear.
The
disruption
of
the
liquids
under
the
vibrations
cause

the
formation
of
cavities
[2].

Cavitation
also
occurs
when
the
pressure
amplitude
of
the
applied
sound
source
reaches
a
certain

minimum.
This
is
known
as
the
cavitation
threshold.
In
o/w
system,
the
process
of
emulsification

initiates
when
the
cavitation
threshold
is
attained
[24].

14

One
disadvantage
of
cavitation
is
that
the
intense
agitations
brought
about
has
the
effect
of

increasing
the
number
of
collisions
amongst
dispersed
droplets
thus
increasing
the
possibility
of

coalescence
[2].

Figure
7
showing
an
ultrasonic
homogenizer

3.3.3
High
Pressure
Emulsification

High
pressure
homogenizers
are
one
of
the
most
widely
used
tools
for
the
preparation
of
emulsions

in
industry.
Until
a
few
years
ago,
high-‐pressure
homogenization
of
emulsions
meant
10
to
40
MPa,

but
today,
100
MPa
is
not
unusual
[27].

In
a
high-‐pressure
homogenizer,
the
oil
and
water
mixture
is
subjected
to
intense
turbulent
and

shear
flow
fields.
Turbulence
is
said
to
be
the
predominant
mechanism
even
through
laminar
shear

and
cavitation
may
also
play
an
important
role
in
droplet
formation
of
the
dispersed
phase
[27].

High
pressure
homogenizers
essentially
consist
of
a
high
pressure
pump
and
a
homogenizing
nozzle.

The
pump
is
used
to
compress
the
crude
emulsion
to
the
homogenizing
pressure.
The
pressurized

crude
emulsion
is
depressurized
in
a
homogenizing
nozzle
and
in
doing
so
the
drops
are
disrupted

[26].

The
homogenizing
nozzle
is
decisive
for
the
efficiency
of
disruption
when
producing
emulsions
using

high-‐pressure
homogenizers,
depending
on
the
type
of
nozzle,
the
homogenizer
is
classified
into

either
standard
nozzle,
microfluidizer,
jet
disperser
or
orifice
valve
[26].

15

Figure
8
showing
high
pressure
emulsification
with
different
nozzles

3.4 Interactions
between
droplets

In
Chapter
3.3,
three
of
the
most
common
methods
of
producing
emulsions
in
industry
were

highlighted,
however
this
becomes
moot
if
the
emulsions
are
of
no
use
due
to
their
unstable
nature.

The
stability
of
emulsions
is
largely
dependent
on
the
interaction
of
droplets
in
the
dispersed
phase.

When
two
droplets
approach
one
another,
a
number
of
colloidal
interactions
come
into
play,
the

most
important
being
the
Van
der
Waals,
steric
and
electrostatic
interactions.
The
main
mechanisms

for
emulsion
droplet
stabilization
are
electrostatic
and
steric
interactions
[28].

Van
der
Waals
attraction

There
are
three
different
types
of
van
der
waals
interaction
between
molecules;
dipole
–
dipole,

dipole
-‐
induced
dipole
and
London
dispersion
forces.
Dipole
–
dipole
and
dipole
–
induced
dipole

attractions
tend
to
cancel
one
another,
therefore
the
most
important
are
the
London
dispersion

interactions
that
arise
from
variations
in
charge.
Hamaker
suggests
that
the
sum
of
the
London

dispersion
interaction
between
droplets
results
in
strong
van
der
waals
attractions,
this
increases
as

the
droplets
draw
closer
[10].

In
order
to
counteract
van
der
waals
attraction,
which
will
lead
to
flocculation,
repulsive
forces
have

to
be
introduced.
These
exist
in
the
form
of
electrostatic
and
steric
repulsion
and
is
dependent
on

the
type
of
the
surfactant
used
[10].

Electrostatic
Repulsion

This
occurs
due
to
the
interaction
between
ionic
surfactant
molecules
in
an
emulsion
system.
As

mentioned
in
chapter
3.2,
surfactants
will
exist
at
the
interfaces
between
the
dispersed
and

continuous
phase.
Using
an
o/w
emulsion
as
an
example,
the
surfactant
hydrophobic
group
will

remain
within
the
droplets
whilst
the
hydrophilic
group
will
remain
in
the
aqueous
phase.
This
has

the
effect
of
forming
a
layer
around
the
droplets
as
shown
in
figure
8.
As
droplets
approach
one

another,
repulsive
forces
increase
due
to
the
similar
charge
on
the
hydrophilic
layer.
This
prevents

the
coalescence
of
droplets.

16

Figure
9
Surfactant
layer
formed
around
a
droplet

Steric
Repulsion

This
is
produced
by
using
nonionic
surfactants.
The
thick
tails
of
the
surfactant
in
the
continuous

phase
promote
repulsion
between
droplets
as
a
result
of
unfavourable
mixing
of
the
tails
and

volume
restrictions
upon
approach
[10].

3.5 Destabilizing
Mechanisms
in
Emulsions

Due
to
the
metastable
nature
of
emulsions,
the
return
to
thermodynamic
stability
is
inevitable.
This

occurs
in
a
certain
order
in
which
the
dispersed
droplets
return
to
their
original
phase
and
the
two

separate
phases
are
visible
to
the
naked
eyes.
The
steps
by
which
the
emulsion
returns
to

thermodynamic
stability
are
creaming
and
sedimentation,
flocculation,
Ostwald
ripening,

coalescence
and
phase
inversion.

Creaming
and
Sedimentation

Creaming
is
the
separation
of
an
emulsion
into
a
concentrated
and
a
dilute
fraction,
by
centrifuging,

gravity
or
conceivably
spontaneously.
The
concentrated
fraction
(cream)
is
rich
in
the
disperse
phase

but
not
necessarily
near
100
percent.
Similarly
the
dilute
fraction
(serum)
is
usually
turbid
with
the

remaining
droplets
of
the
disperse
phase
[29].
Although
creaming
may
be
undesirable
in
a
number

of
cases,
it
does
not
represent
a
breaking
of
the
emulsions
[2].
The
droplets
remain
intact,
only
their

position
changes.

The
difference
between
creaming
and
sedimentation
lies
in
the
fact
that
in
creaming
,
droplets
in
the

disperse
phase
has
a
lower
density
than
the
continuous
phase
thereby
causing
the
droplets
to
rise

whilst
the
opposite
is
true
in
sedimentation.

Stokes’
law
suggests
that
the
creaming
rate
will
depend
on
the
density
difference
and
the
square
of

the
droplet
radius
[29].
This
is
given
by:

𝑢 =
!!!! !!!!!
!!!

Equation
2

Where
U
is
the
rate
of
creaming
(sedimentation),
g
is
the
acceleration
of
gravity,
r
the
droplet
radius,

d1
is
the
density
of
the
droplet,
d2
the
density
of
the
continuous
phase
and
η2
is
the
viscosity
of
the

continuous
phase
[2].
From
stokes’
equation,
the
conditions
that
increase
the
rate
of
creaming
are

large
droplet
radius,
a
high
density
difference
between
the
droplet
and
the
continuous
phase
and
a

low
viscosity
of
the
continuous
phase.

17

The
impression
of
stokes’
equation
is
that
it
determines
the
rate
of
creaming
in
an
emulsion,

however
Greenwald
has
indicated
that
it
only
indicates
the
rate
of
creaming
for
a
single
droplet
in

the
system
[2].

Flocculation

Flocculation
refers
to
aggregation
of
the
droplets
into
larger
units
(flocs).
Each
droplet
retains
its
size

and
integrity.
It
is
the
results
of
van
der
waals
attraction
and
occurs
when
there
is
not
sufficient

repulsion
to
keep
the
droplets
apart
to
a
distance
in
which
van
der
waals
attraction
is
weak
[10].

Ostwald
ripening

Ostwald
ripening
is
the
process
by
which
the
Gibbs
free
energy
of
a
two
phase
system
(such
as
an

emulsion)
can
be
decreased
via
a
decrease
in
the
total
interfacial
area
thus
allowing
for

thermodynamic
equilibrium
[31].

This
occurs
as
a
result
of
the
difference
in
solubility
between
the
small
and
large
droplets.
The

smaller
droplets
have
higher
Laplace
pressure
and
higher
solubility
than
the
larger
ones.
With
time,

the
smaller
droplets
disappear
and
their
molecules
diffuse
to
the
bulk
and
become
deposited
on
the

larger
droplets.
The
droplet
size
distribution
shifts
to
larger
values
[10].

Coalescence

At
this
stage,
each
floc
combines
to
form
a
single
droplet.
It
is
an
irreversible
process
that
leads
to
a

decrease
in
the
number
of
droplets
[2].
This
occurs
by
the
process
of
thinning
and
disruption
of
the

liquid
film
between
the
droplets
with
the
result
of
fusion
of
two
or
more
droplets
into
larger
ones.

The
driving
force
for
coalescence
is
the
film
fluctuations
which
results
in
close
approach
of
the

droplets
whereby
strong
van
der
Waals
forces
prevent
their
separation
[10].

Phase
inversion

This
refers
to
the
process
whereby
there
will
be
an
exchange
between
the
disperse
phase
and
the

medium.
For
example,
an
O/W
emulsion
may
with
time
or
change
of
conditions
invert
to
a
W/O

emulsion.
Phase
inversion
of
emulsions
can
be
one
of
two
types:
transitional
inversion
induced
by

changing
the
facers
that
affect
the
HLB
of
the
system,
for
example,
temperature
and/or
electrolyte

concentration
and
catastrophic
inversion,
which
is
induced
by
increasing
the
volume
fraction
of
the

disperse
phase
[10].

18

Figure
10
showing
the
different
destabilizing
mechanisms

3.6 Rheological
properties
of
Emulsions

Rheology
is
the
science
of
deformation
and
flow
of
matter,
and
its
study
has
contributed
towards

clarifying
ideas
concerning
the
nature
of
emulsion
systems.
It
is
a
subject
of
tremendous

technological
importance
in
many
industries
as
the
suitability
of
the
final
products
is
to
a
large

extent
judged
by
their
rheological
properties
[30].

The
viscosity
of
a
liquid
is
defined
as
the
shearing
stress
exerted
across
an
area
when
there
is
unit

velocity
gradient
normal
to
the
area.
In
most
liquids,
shearing
stress
is
proportional
to
the
change
in

shear
with
time.
This
means
the
viscosity
is
independent
of
the
rate
of
shear;
the
liquid
is

Newtonian.
Most
emulsions
however
exhibit
Non-‐Newtonian
properties
as
viscosity
is
a
function
of

the
rate
of
shear
[2].

The
rheological
properties
of
an
emulsion
is
dependent
on
droplet
interaction
which

in
turn
is

dependent
on
factors
such
as
volume
fraction
of
the
dispersed
phase,
viscosity
of
the
continuous

phase,
droplet
size
distribution
and
the
surfactant
properties
among
others
[32].
For
the
purpose
of

this
study
only
the
four
factors
mentioned
shall
be
considered.

3.6.1
Viscosity
of
the
continuous
phase

All
treatments
of
emulsion
viscosity
consider
the
viscosity
of
the
continuous
(η0)
phase
to
have
a

direct
effect
on
the
final
viscosity
of
the
emulsion.
This
is
best
illustrated
in
equation
three

𝜂 = 𝜂!(𝑥)

Equation
3

19

Where
x
represents
the
sum
of
all
other
factors
that
affect
the
viscosity
of
the
emulsion.
In
many

emulsions
the
surfactant
is
dissolved
in
the
continuous
phase
hence
η0
is
usually
referred
to
as
the

viscosity
of
the
solution
rather
than
that
of
the
liquid
in
the
continuous
phase
[2].

3.6.2
Volume
fraction
of
the
dispersed
phase

The
disperse
phase
fraction
is
directly
related
to
the
dispersion
rheology
because
an
increase
in
the

volume
fraction
means
an
increase
in
the
frequency
of
droplet
interaction
and
vice
versa
[32].
An

equation
relating
the
viscosity
of
the
dispersed
phase
with
that
of
the
continuous
phase
and
the

volume
fraction
was
developed
by
Albert
Einstein
[2].

𝜂 = 𝜂!(1 + 2.5𝜙)

Equation
4

Where
φ
is
the
volume
fraction
of
the
dispersed
phase.
The
applications
of
Equation
4
are
however

extremely
limited
in
that
it
only
applies
to
volume
fractions
of
0.02
or
less.
There
have
been

numerous
modifications
to
this
equation
in
order
to
increase
its
application
[2].

When
the
volume
fraction
is
below
0.3,
droplets
can
move
freely
past
one
another,
however
as
the

volume
fraction
increases,
this
interaction
increases.
Volume
fractions
above
0.74
will
see
the

droplets
become
tightly
packed
and
the
movement
of
droplets
become
severely
impaired.
The

increase
in
dispersed
phase
volume
fraction
sees
the
rheology
of
a
liquid
consequently
change
from

Newtonian,
to
shear
thinning,
to
a
viscoelastic
type
of
behaviour
[32].

3.6.3
Surfactant
Properties

The
interfacial
rheology
of
the
droplets
can
significantly
influence
droplet
interactions,
which
are

enhanced
by
the
presence
of
a
surfactant.
When
the
concentration
of
surfactant
is
high,
excess

surfactant
molecules
are
formed
in
the
continuous
phase,
this
thereby
influences
the
rheology
of
the

dispersion
by
inducing
depletion
flocculation
[32].

The
presence
of
surfactants
also
leads
to
the
existence
of
an
interfacial
film
which
may
affect

emulsion
viscosity.
This
is
because
of
the
effect
of
the
film
on
the
internal
circulation
of
the
droplet.

In
an
attempt
to
relate
the
viscosity
of
an
emulsion
with
the
concentration
of
the
surfactant
and
the

volume
fraction
of
the
dispersed
phase,
Sherman
empirically
derived
the
equation
[2].

𝑙𝑛𝜂 = 𝑎𝐶𝜙 + 𝑏

Equation
5

Where
C
is
the
concentration
of
the
surfactant
whilst
a
and
b
are
constants
[2].

3.6.4
Droplet
size
distribution

In
an
emulsion
system
with
a
given
dispersed
phase
volume
fraction,
the
smaller
the
droplet
size,

the
greater
the
number
of
droplet
interaction,
therefore
increasing
the
droplet
size
of
a

monodisperse
emulsion
system
increases
the
viscosity
of
the
emulsion
[32].
This
goes
hand
in
hand

with
the
presence
and
concentration
of
a
surfactant
as
that
propagates
the
presence
of
smaller

droplets
[2].

20

4.
Methodology

This
project
is
based
on
experiments
divided
in
three
phases
and
shall
be
explain
in
this
section
in

full
detail.
The
first
phase
involves
the
measurement
of
the
viscosity
of
several
different
oils
and

selection
of
suitable
oils.
The
second
consists
of
making
o/w
emulsions
using
four
of
the
oils
of
which

their
viscosities
have
previously
been
measured
as
well
as
deriving
the
appropriate
combinations
of

chosen
surfactants
that
will
ensure
the
emulsions
remain
stable
enough
to
be
analysed.
Included
in

the
second
phase
is
the
measurement
of
the
densities
of
all
liquid
components
used
in
the

production
of
the
emulsions.
Finally
the
third
involves
the
derivation
of
the
particle
size
distribution

of
the
previously
mentioned
emulsions
and
more
importantly,
the
mean
particle
size.

4.1
Materials

• Liquid
Paraffin

• Rapeseed
Oil

• Flax
Oil

• Groundnut
Oil

• Span
80

• Sodium
Dodecyl
Sulfate

4.2
Equipment

4.2.1
Brookfield
DV-‐II
Pro
Programmable
Viscometer.

This
viscometer
works
by
measuring
torque
whilst
inserted
in
an
aqueous
material.
The
viscosity
of

the
material
is
then
calculated
by
using
the
equation
6.

𝑉𝑖𝑠𝑐𝑜𝑠𝑖𝑡𝑦 𝑐𝑃 =
!!!
!"#
𝑋 𝑆𝑀𝐶 𝑋 𝑇𝐾 𝑋 𝑇𝑜𝑟𝑞𝑢𝑒

Equation
6

This
machine
is
fairly
simple
to
use
as
the
spindle
constant
is
already
given
depending
on
the
choice

of
spindle.
Rotational
speed
is
a
variable
which
can
be
fixed
whilst
torque
is
given
on
a
screen.
The

machine
also
allows
for
the
measurement
of
the
temperature
of
the
chosen
material
using
a
probe.

This
allows
for
continuity
whilst
comparing
the
viscosities
of
different
materials
as
temperature
is

inversely
proportional
to
viscosity.

Figure
11
Brookfield
viscometer
and
a
variety
of
spindles

21

4.2.2
High
Shear
Rotor
Stator
Mixer

This
piece
of
equipment
allows
for
the
emulsification
of
a
mixture
of
liquids.
It
has
a
maximum

rotational
speed
of
10,000
RPM
and
a
minimum
of
a
100
RPM
thereby
allowing
the
effect
of
a
huge

range
of
rotational
speeds
to
be
monitored.

Figure
12
Silverston
high
shear
rotor
stator
mixer

4.2.3
Malvern
Mastersizer
2000

The
Malvern
Mastersizer
works
not
by
measuring
particle
size
but
by
measuring
low
angle
laser
light

scattering
(LALLS)
which
then
allows
for
the
production
of
a
particle
size
distribution
curve.
A
42

element
composite
array
and
two
backscattering
detectors
allow
for
the
collection
of
scattered
light.

Scattered
intensities
can
be
measured
at
a
range
of
scattering
angles
from
0
to
135
degrees
by
the

light
source.
This
is
then
analysed
using
Mie
Theory
(1908).
In
order
to
do
this,
the
real
and

imaginary
index
of
both
the
dispersant
and
sample
is
required.
Figure
13
is
an
example
of
a
resulting

particle
size
distribution
curve.

22

Figure
13
showing
a
standard
particle
size
distribution
curve
4.3
Experimental
Procedure

4.3.1
First
Phase

As
viscosity
was
one
of
the
variables
studied
in
this
project
is
was
imperative
that
the
viscosity
of
the

chosen
oils
were
measured
before
proceeding.
A
100
ml
beaker
was
filled
with
liquid
paraffin
and

spindle
three
was
chosen
as
an
appropriate
spindle.
The
viscometer
was
then
switched
on
and

allowed
to
calibrate.
The
spindle
was
then
attached
to
the
viscometer
and
allowed
to
recalibrate.

The
spindle
was
then
inserted
into
the
beaker
of
paraffin
until
the
mark
on
the
spindle
was
level

with
the
surface
of
the
liquid
paraffin.
The
temperature
probe
was
then
inserted
in
the
beaker
and

the
temperature
taken
down.
The
rotational
speed
was
then
set
to
a
value
of
100
and
the
torque

measured
and
recorded.
This
was
repeated
a
total
of
three
times
in
order
to
improve
the
accuracy
of

the
results.
The
spindle
was
then
wiped
down
with
blue
roll
and
the
same
was
done
for
the
rest
of

the
oils.

4.3.2
Second
Phase

In
order
to
make
a
stock
solution
of
2%
SDS
solution,
a
5
l
beaker
was
filled
with
2940
ml
of
water

and
heated
slowly
to
75o
C
using
a
hot
plate.
60
g
of
SDS
was
measured
out
into
a
500
ml
beaker
on
a

top
pan
balance.
Using
an
overhead
stirrer
to
stir
the
mixture,
the
beaker
of
SDS
solution
was
then

slowly
inserted
into
the
beaker
of
water
using
a
spatula.
The
stirrer
was
stopped
when
all
the
SDS

had
dissolved.
98
ml
of
liquid
paraffin
was
then
measured
out
into
a
beaker
and
using
a
pipette,
2
ml

of
span
80
was
then
introduced
into
the
beaker
filled
with
liquid
paraffin.
A
magnetic
stirrer
was

used
to
stir
the
mixture
until
all
the
span
80
which
had
settled
at
the
bottom
had
dissolved.
In
order

to
create
stable
oil
in
water
emulsions,
an
HLB
value
between
8
and
18
was
required.
However
even

in
that
range,
the
emulsions
had
to
stay
stable
long
enough
for
the
Mastersizer
to
determine
the

particle
size
distribution.
Four
mixtures
of
varying
volumes
of
liquid
paraffin,
liquid
paraffin
doped

with
2%
span
80,
water
and
water
doped
with
2%
SDS
solution
as
shown
in
Table
1
were
then
made.

The
HLB
values
of
the
resulting
emulsions
were
determined
using
the
equation
1:

Table
2
HLB
values
of
different
volumes
of
reagents

Oil
+
2%
Span
80

(ml)

Oil
(ml)
Water
+
2%
SDS

(ml)

Water
(ml)
HLB
Value

7.0
3.0
3.0
7.0
15.0

7.5
2.5
2.5
7.5
13.2

8.0
2.0
2.0
8.0
11.4

8.5
1.5
1.5
8.5
9.7

23

Once
the
four
mixtures
were
made,
they
were
allowed
to
homogenise
for
1
minute
each
at
1000

rpm
and
set
aside
for
two
hours
in
order
to
study
the
stability
of
the
resulting
emulsions.
Once
the

most
stable
emulsion
was
selected,
the
combination
of
volumes
of
the
reagents
used
to
make
said

emulsion
was
used
to
make
all
other
emulsions
in
this
study.
Using
the
right
combination
of
volumes

of
reagents,
ten
mixtures
of
liquid
paraffin,
liquid
paraffin
doped
with
2%
span
80,
water
and
water

doped
with
2%
SDS
solution
was
made
in
50
ml
beakers.
The
same
was
done
using
flax
oil,
Rapeseed

oil
and
groundnut
oil.
The
HLB
value
of
9.7
was
found
to
be
the
most
stable
and
was
selected.

Afterwards,
6
beakers
were
weighed
out
using
a
top
pan
balance
accurate
to
three
significant

figures.
1
ml
of
each
oil
was
measured
out
into
each
of
these
beakers
and
weighed
on
the
top

balance.
The
difference
between
the
mass
of
the
beakers
before
the
oil
was
inserted
and
after
the

oil
was
inserted
was
noted
as
the
density
of
each
oil.
The
same
was
then
done
for
the
2%
SDS

solution
in
water
as
well
as
the
surfactant
Span
80.
The
measurements
of
all
densities
were
done
at

room
temperature.

4.3.3
Third
Phase

Using
the
high
shear
homogeniser,
5
emulsions
were
made
using
the
liquid
paraffin
and
water

mixtures
at
1000,
2000,
3000,
4000
and
5000
rpm.
This
done
whilst
keeping
the
time
constant
to

one
minute.
The
other
5
emulsions
were
made
by
keeping
the
rpm
to
a
constant
value
of
3000rpm

but
using
time
as
the
variable.
The
times
used
were
1,
2,
6,
8
and
10
minutes.
Once
the
emulsions

were
made,
they
were
taken
up
to
the
Mastersizer
in
order
to
measure
the
particle
size
and
particle

size
distribution
of
the
emulsions.
The
refractive
indices
of
the
continuous
phase,
liquid
paraffin,
and

the
dispersant,
deionised
water
was
entered
in
order
to
create
a
new
standard
operating
procedure

(SOP).
Once
this
was
done,
using
a
plastic
pipette,
a
few
drops
of
the
sample
to
be
tested
was
added

to
the
unit.
Once
the
obscuration
was
in
the
right
range,
the
Mastersizer
was
allowed
to
start

testing,
running
a
minimum
of
5
different
tests
and
the
average
of
those
taken
and
the
mean

particle
size
recorded.

5.
Safety
Hazards

Threat
to
Safety
Dangers
Precautions
taken

SDS
• Flammable

solid

• Harmful
if

swallowed

• Harmful
if

inhaled

• Causes
serious

eye
damage

• Keep
away

from
heat

• Wear

protective

gloves

• Wear
safety

goggles

• Wear
Mask

24

6.
Results

In
this
section,
the
experimental
results
shall
be
presented
in
various
tables.
These
shall
then
be

treated
to
derive
a
value
of
D.
Following
this
will
be
a
discussion
of
the
results.

6.1
Experimental
Results

Results
of
viscosity
measurement

Table
3
Viscosity
of
different
oils

Oil
Revolutions

per
minute

Torque
1

(%)

Torque
2

(%)

Torque
3

(%)

Average

Torque

(%)

Viscosity

(cP)

Liquid
Paraffin
100
26.3
26.3
26.4
26.3
263

Sesame
Oil
100
12.4
12.6
12.6
12.5
125

Groundnut
Oil
100
14.0
14.1
14.0
14.0
140

Flax
Oil
100
7.5
7.5
7.5
7.5
75

Almond
Oil
100
12.1
12.4
12.3
12.3
123

Olive
Oil
100
13.5
13.7
13.8
13.7
137

Rapeseed
Oil
100
11.4
11.4
11.4
11.4
114

The
four
oils
chosen
were
Liquid
paraffin,
Flax
oil,
Rapeseed
oil,
and
Groundnut
oil
as
they
are
evenly

spread
between
the
range
of
75
and
263
cP.
When
measured,
the
temperature
of
these
oils
were
±

0.1o
C
of
each
other
which
meant
the
effect
of
this
temperature
difference
on
the
viscosities
of
the

oil
would
have
been
small
enough
to
ignore.

Results
of
rotational
speed
and
time
measurement

Tables
4,
6,
8
and
10
present
the
results
of
the
effect
of
rotational
speed
on
mean
particle
size

conducted
at
a
constant
time
of
one
minute
whilst
tables
5,
7,
9
and
11
present
the
results
of
the

effects
of
time
spent
homogenizing
on
mean
particle
size,
this
was
conducted
at
a
constant

rotational
speed
of
3000
RPM.

Liquid
Paraffin

Table
4
showing
the
relationship
between
rotational
speed
and
mean
particle
size

Revolutions
per
minute
Mean
particle
size
(µm)

1000
113.697

2000
63.893

3000
47.855

4000
37.719

5000
28.451

25

Table
5
showing
the
relationship
between
time
and
mean
particle
size

Time
(minutes)
Mean
particle
size
(µm)

1
47.855

2
34.402

6
26.081

8
25.479

10
22.935

Groundnut
Oil

Table
6
showing
the
relationship
between
rotational
speed
and
mean
particle
size

Revolutions
per
minute
Mean
particle
size
(µm)

1000
104.849

2000
54.348

3000
39.923

4000
31.102

5000
23.094

Table
7
showing
the
relationship
between
time
and
mean
particle
size

Time
(minutes)
Mean
particle
size
(µm)

1
39.923

2
34.738

6
24.273

8
22.348

10
21.863

Rapeseed
Oil

Table
8
showing
the
relationship
between
rotational
speed
and
mean
particle
size

Revolutions
per
minute
Mean
particle
size
(µm)

1000
99.676

2000
44.294

3000
24.777

4000
20.738

5000
14.364

Table
9
showing
the
relationship
between
time
and
mean
particle
size

Time
(minutes)
Mean
particle
size
(µm)

1
24.777

2
24.308

6
17.402

8
16.847

10
16.178

26

Flax
Oil

Table
10
showing
the
relationship
between
rotational
speed
and
mean
particle
size

Revolutions
per
minute
Mean
particle
size
(µm)

1000
79.893

2000
38.409

3000
18.746

4000
16.973

5000
15.632

Table
11
showing
the
relationship
between
time
and
mean
particle
size

Time
(minutes)
Mean
particle
size
(µm)

1
18.746

2
17.356

6
14.078

8
13.847

10
13.574

6.2
Treatment
of
results

Power
number
(Np)
can
be
calculated
using
equation
3

𝑁! =
!
!!!!!

Equation
7

Where:

P
is
the
Power
in
Watts,
ρ
is
total
fluid
density
of
the
emulsion
in
kilogram
per
metre
cubed,
n
is

rotational
speed
in
seconds
and
d
is
the
diameter
of
the
stirrer
in
meters.

Table
12
Corresponding
power
at
different
rotational
speeds

Revolutions
per
minute
Revolution
per
second
Power
(Watts)

1000
16.67
125

2000
33.34
250

3000
50.00
375

4000
66.67
500

5000
83.34
625

In
this
study,
the
overall
work
done
on
the
different
systems
is
more
relevant
than
the
rate
at
which

the
work
is
done.
Therefore
in
order
to
take
time
into
account,
the
P
variable
will
be
multiplied
by

time
in
seconds.
The
modified
power
(MNp)
is
no
longer
a
dimensionless
number.
In
order
to

compensate
for
this,
rather
than
having
the
rotational
speed
cubed,
it
will
be
squared
therefore
all

units
will
cancel
out
therefore
making
the
modified
power
a
dimensionless
number.

Modified
power
number
is
calculated
using
equation
8.

𝑀𝑁! =
!"
!!!!!

Equation
8

27

𝑑! =
!! ! !! ! !! ! !! !⋯!(!! ! !!)
!!!!!!⋯!!!

Equation
9

Table
13
showing
the
density
of
each
of
each
component
in
the
resulting
emulsions

Component

Density
(kgm-‐3
)
Volume
in
solution
(m3
)

Liquid
Paraffin
707
9.83

Groundnut
Oil
835
9.83

Rapeseed
Oil
880
9.83

Flax
Oil
911
9.83

SDS

1071
0.03

Span
80
984
0.17

Deionised
Water
1000
9.97

Equation
9
allows
for
the
calculation
of
the
density
of
an
overall
mixture
once
the
densities
and

volumes
of
the
individual
components
are
known.
The
fluid
density
of
all
emulsions
are
presented
in

table
14.

The
diameter
of
the
stirrer
was
found
to
be
0.0185m.

Table
14
showing
the
densities
of
the
emulsions
prepared

Emulsion
Fluid
Density
(kgm-‐3
)

Liquid
Paraffin
in
water
856

Groundnut
Oil
in
water

919

Rapeseed
Oil
in
water
941

Flax
Oil
in
water
956

Using
all
the
information
above,
the
modified
power
number
can
now
be
calculated.
The
modified

power
number
at
different
rotational
speeds
and
the
corresponding
particle
size
are
shown
below.

Tables
15
to
18
presents
the
results
derived
whilst
changing
the
rotational
speed
and
keeping
the

time
spent
homogenizing
at
one
minute.
Tables
19
to
22
present
the
results
derived
whilst
changing

the
time
spent
homogenizing
and
keeping
rotational
speed
at
a
constant
3000
RPM

Liquid
Paraffin

Table
15
Modified
power
number
and
corresponding
mean
particle
size

Modified
Power
Number

Mean
particle
size
(µm)

14250168.15
113.697

7125084.08
63.893

4751956.26
47.855

3563610.83
37.719

2850717.63
28.451

28

Groundnut
Oil

Table
16
Modified
power
number
and
corresponding
mean
particle
size

Modified
Power
Number

Mean
particle
size
(µm)

13435433.62
104.849

6717716.81
54.348

4480269.44
39.923

3359866.09
31.102

2687731.61
23.094

Rapeseed
Oil

Table
17
Modified
power
number
and
corresponding
mean
particle
size

Modified
Power
Number

Mean
particle
size
(µm)

13165588.76
99.676

6582794.38
44.294

4390285.17
24.777

3292384.63
20.738

2633749.69
14.364

Flax
Oil

Table
18
Modified
power
number
and
corresponding
mean
particle
size

Modified
Power
Number

Mean
particle
size
(µm)

12987118.84
79.893

6493559.42
38.409

4330771.40
18.746

3247753.77
16.973

2598047.14
15.632

Figure
14
showing
the
relationship
between
Modified
power
number
and
mean
particle
size

0

20

40

60

80

100

120

0
5000000
10000000
15000000

Mean
partcle
size
(µm)

Modiﬁed
Power
Number

Graph
of
Power
number
against
mean
partcle
size

Liquid
Paraﬃn

Groundnut
Oil

Rapeseed
Oil

Flax
Oil

29

Liquid
Paraffin

Table
19
Modified
power
number
and
corresponding
mean
particle
size

Modified
Power
Number

Mean
particle
size
(µm)

4751956.26
47.855

9503912.53
34.402

28511737.58
26.081

38015650.11
25.479

47519562.63
22.935

Groundnut
Oil

Table
20
Modified
power
number
and
corresponding
mean
particle
size

Modified
Power
Number

Mean
particle
size
(µm)

4480269.44
39.923

8960538.89
34.738

26881616.66
24.273

35842155.55
22.348

44802694.44
21.863

Rapeseed
Oil

Table
21
Modified
power
number
and
corresponding
mean
particle
size

Modified
Power
Number

Mean
particle
size
(µm)

4390285.17
24.777

8780570.35
24.308

26341711.04
17.402

35122281.39
16.847

43902851.74
16.178

Flax
Oil

Table
22
Modified
power
number
and
corresponding
mean
particle
size

Modified
Power
Number

Mean
particle
size
(µm)

4330771.40
18.746

8661542.80
17.356

25984628.41
14.078

34646171.21
13.847

43307714.02
13.574

30

Figure
15
showing
the
relationship
between
Modified
power
number
and
mean
particle
size

As
the
aim
is
to
also
take
the
viscosity
of
the
oil
into
account,
the
modified
power
number
can
be

divided
by
the
viscosities
of
the
different
oils
(in
cP).
This
allows
a
correlation
graph
of
multiple

points
to
be
plotted.
This
variable
shall
be
called
“D”,
units
of
which
shall
be
cP-‐1
.

𝐷 =
!"
!!!!!η

Equation
10

Liquid
Paraffin

Table
23
Modified
power
number
and
corresponding
mean
particle
size

D
(cP-‐1
)
Mean
particle
size
(µm)

18068
47.855

36137
34.402

108410
26.081

144546
25.479

180683
22.935

Groundnut
Oil

Table
24
Modified
power
number
and
corresponding
mean
particle
size

D
(cP-‐1
)

Mean
particle
size
(µm)

32002
39.923

64004
34.738

192012
24.273

256015
22.348

320019
21.863

0

10

20

30

40

50

60

0
10000000
20000000
30000000
40000000
50000000

Mean
Partce
size
(µm)

Modified
Power
Number

Graph
of
Modified
Power
number
against
Mean
Partcle
size

Liquid
Paraffin

Groundnut
Oil

Rapeseed
Oil

Flax
Oil

31

Rapeseed
Oil

Table
25
Modified
power
number
and
corresponding
mean
particle
size

D
(cP-‐1
)
Mean
particle
size
(µm)

38511
24.777

77023
24.308

231068
17.402

308090
16.847

385113
16.178

Flax
Oil

Table
26
Modified
power
number
and
corresponding
mean
particle
size

D
(cP-‐1
)

Mean
particle
size
(µm)

57744
18.746

115487
17.356

346462
14.078

461949
13.847

577436
13.574

Figure
16
Correlation
graph
between
D
and
Mean
particle
size

y
=
31.717e-‐2E-‐06x

R²
=
0.6255

0

10

20

30

40

50

60

0
100000
200000
300000
400000
500000
600000
700000

Mean
partcle
size
(µm)

D
(cP-‐1)

Graph
of
D
against
Mean
Partcle
Size

32

7.
Discussion
and
conclusion

From
the
results
presented
in
chapter
6.1,
a
number
of
relationships
can
be
explained.
Increasing

the
rotational
speed
led
to
a
decrease
in
mean
particle
size,
increasing
the
time
spent
homogenising

also
led
to
a
decrease
in
the
mean
particle
size.
The
explanations
for
these
are
simple,
more
energy

was
spent
homogenising
the
emulsions
which
therefore
led
to
smaller
particle
sizes.
Interestingly,

the
results
also
consistently
showed
that
with
increasing
dispersed
phase
viscosity
came
an

increased
particle
size.
Whilst
calculating
the
modified
power
number
with
increasing
rotational

speed,
a
trend
was
found.
With
increasing
modified
power
number
came
an
increase
in
the
mean

particle
sizes.
The
reason
for
this
was,
although
the
amount
of
energy
expended
was
increased

sequentially,
the
number
of
revolutions
per
second
was
also
increasing
by
the
same
amount
and

additionally
as
this
was
being
squared,
it
meant
the
overall
number
was
reduced.
This
therefore

meant
that
the
modified
power
number
is
limited
to
results
in
which
the
rotational
speed
was
kept

constant
as
increasing
energy
could
not
possibly
lead
to
an
increase
in
the
mean
particle
size.
It
was

therefore
impossible
to
condense
rotational
speed
into
the
variable
D.
Figure
15
however
shows

that
the
expected
trend
when
keeping
rotational
speed
constant
was
followed.
With
increasing

energy
as
a
result
of
increasing
time,
mean
particle
size
was
reduced.
The
attempt
to
take
viscosity

into
account
was
largely
unsuccessful
as
corresponding
mean
particle
size
values
were
far
off
what

was
expected.
However
it
does
hold
up
as
a
means
of
getting
an
estimated
mean
particle
size
once
a

value
of
D
is
derived.
The
ways
in
which
this
study
could
have
been
made
better
and
which
may
have

led
to
the
variable
D
having
a
more
relevant
relationship
with
mean
particle
size
would
have
been
to

use
a
mixer
that
allows
for
the
calculation
of
torque.
This
could
have
then
led
to
more
accurate

calculations
of
power.
Also
with
more
time,
more
oils
could
have
been
studied
which
would
have

increased
the
range
of
emulsions
that
the
variable
D
can
be
used
on.

33

8.
References

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Florence
and
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