Emulsion systems

Question 1

Mixture

Answer 1

material made up of two or more different substances not chemically combined (can easily be separated)

Question 2

Solution

Answer 2

homogeneous mixture of two or more substances in a single phase.

Question 3

Heterogeneous mixture

Answer 3

colloids and suspensions. two or more phases.

Question 4

Homogeneous mixture

Answer 4

uniform distribution of particles in same phase. solutions

Question 5

Colloid

Answer 5

smaller particles (1 nano meter - 1 micro meter) are not filterable. Look homogeneous but scatter light. can be prepared in many different phases

Question 6

Suspensions

Answer 6

larger particles (>0.5 micro meter) are filterable and settle under gravity. Opaque to light, show particles.

Question 7

Tyndall effect

Answer 7

light can’t be seen through solution. larger particles deflect light, colloid scatters light solutions light deflects of big particles

Question 8

Emulsions

Answer 8

colloidal dispersion of immiscible liquid in immiscible liquid or solid.

Question 9

How do emulsions work

Answer 9

fluids are sheared and fragmented to the other phase using a lot of energy to create a metastable state

Question 10

Emulsion parameters

Answer 10

number of phases, droplet size, ratio of internal phase, uniformity factor

Question 11

Simple emulsion

Answer 11

one phase in another. W/O or O/W

Question 12

Multiple emulsion

Answer 12

one phase in another phase in another phase in another… O/W/O or W/O/W… mainly used for controlled release of substances

Question 13

Macro emulsion

Answer 13

conventional emulsion
large droplet size >1000nm
thermodynamically unstable
phase separation occurs over time
kinetically stable
Opaque
conventional shear preparation

Question 14

Micro emulsion

Answer 14

smaller particle size 10-100nm
thermodynamically stable
dynamic systems
low interfacial tension between O+W
low energy to make
transparent

Question 15

Nano emulsion

Answer 15

conventional emulsion (same as macro)
smaller droplet size 20-500nm
transparent, require more energy to prepare

Question 16

Dilute systems

Answer 16

behave as viscous newtonian fluids, no coalescence. <0.01

Question 17

Moderate concentration

Answer 17

if non-coalescing dilute dispersion theories apply <0.2

Question 18

Concentrated system

Answer 18

agents used to prevent coalescing, complex behaviour as viscoelastic solids. >0.2

Question 19

Emulsion examples

Answer 19

mayo, paint, moisturiser, ointments, drug carriers

Question 20

Emulsification

Answer 20

two rough classes of techniques: laminar (gentle stirring) and turbulent (high energy)

Question 21

Turbulent flow emulsification

Answer 21

colloid mill, high shear, high pressure homogeniser. More energy put in = smaller droplets

Question 22

Laminar flow emulsificatoin

Answer 22

temperature quench or PIT (phase inversion temperature). Only works with non-ionic surfactants.

Question 23

PIT

Answer 23

Increases with increasing HLB number. Emulsion is heated to PIT where phases swap then immediate cooling to stabilise the system.

Question 24

Thermodynamics of formation

Answer 24

emulsions are thermodynamically unstable and non-spontaneous as interfacial tensions is much larger than entropy. emulsions want to return to their original state so require stabilisers

Question 25

Kinetic stability

Answer 25

surfactants or polymers create energy barrier so that emulsions do not revert - making them metastable

Question 26

Physics of formation

Answer 26

shearing or stirring of emulsion breaks up droplets into smaller sizes.

Question 27

Droplet size distribution

Answer 27

emulsions are not uniform but become more uniform with more shear

Question 28

Equipment for emulsification

Answer 28

sufficient agitation is required to break up droplets. propellor and turbine (low viscous), ultra sonics/colloid mills/homogenisers (high viscous)

Question 29

Methods of seeing emulsion

Answer 29

laser diffraction, sound waves, nuclear magnetic resonance, microscopy

Question 30

Differentiating O/W W/O

Answer 30

O/W: lighter, disperses in water, conducts electricity, takes up dye.

Question 31

Emulsion breakdown

Answer 31

separation of oil and water back to original phases. Coalescence, ostwald ripening, flocculation, creaming, phase separation

Question 32

Creaming/sedimenting

Answer 32

from external forces, density difference and uniformity factor. prevent with rheology modifier

Question 33

Flocculation

Answer 33

aggregation of droplets into larger groups due to van der waals forces. prevent with high energy barrier

Question 34

Ostwald ripening

Answer 34

small droplets deposit onto large droplets due to high solubility of disperse droplets. prevent with disperse phase components

Question 35

Coalescence

Answer 35

droplets fuse back together from instability of liquid film between droplets. prevent with surfactants

Question 36

Emulsifier

Answer 36

a surface active agent the reduces surface tension with a hydrophilic head and lipophilic tail. differ in W/O or O/W emulsions

Question 37

Stabilisation of emulsions

Answer 37

electrostatic repulsion steric repulsion marangoni gibbs effect thin film stabalisation

Question 38

Marangoni gibbs effect

Answer 38

as droplets come close together they flatten out, thin film of continuous phase between droplets create interfacial tension and prevent drainage of film

Question 39

Interfacial film strengthening

Answer 39

powders with W+O affinity polymers non-ionic surfactants

Question 40

Emulsion stability dependents

Answer 40

concentration/size of emulsifier Size of droplet type of emulsion processing

Question 41

Stability testing

Answer 41

freeze thaw cycle various temperature tests centrifuge visual assessment low shear evaluation rheology humidity...