1. Suspensions and Colloids

2. Classes of solutions
True Solutions
(Suspensions)
Colloidal Solutions
Suspensions:
Heterogeneous mixtures
Relatively large particles
e.g. whole blood
many medicines (Shake well before using)

3. Colloids and suspensions are heterogeneous
mixtures

4. Solutions
A solution is a homogenous mixture composed of two or more substances.
A solute is dissolved in another substance, known as a solvent.
Types of solutions:
Solvent is gas (mixture of different gases)
Solvent is liquid
Gas in liquid (water solution of HCl)
Liquid in liquid (H2SO4 in the water)
Solid in liquid (glucose , NaCl in the water)
Solvent is solid – alloys like bronze (Cu and Sn)

5. Solubility The ability of one compound to dissolve in another compound
Miscible liquids - liquid is able to completely dissolve in another liquid (ethanol, water).
The solubility of a given solute in a given solvent typically depends on temperature
Solubility of ionic compounds - there is a limit to how much salt can be dissolved in a given volume of water

6. Solubility

7. Dissolving substances in water
No-electrolytes do not interact with the solvent (oxygen, sucrose).
Electrolytes interact with molecules of the solvent → dissociate, ionize
The ions are then surrounded by solvent molecules (H2O).
Hydrated ions then arise.

8. Colloids Colloids are mixtures of a solvent and suspended particles.
Particles are too small to see but are larger than molecules.
Due to their small size they do not settle out of solution.
There are several types of colloid:
aerosol (gas + liquid or solid, e.g. fog and smoke),
foam (liquid + gas, e.g. whipped cream),
emulsion (liquid + liquid, e.g. milk),
sol (liquid + solid, e.g. paint),
solid foam (solid + gas, e.g. marshmallow),
solid emulsion (solid + liquid, e.g. butter),
solid sol (solid + solid, e.g. pearl, opal).

9. Types of Colloids Dispersed Phase Continuous Name Gas Liquid Foam
Solid
Aerosol
Emulsion
Gel
Sol
Solid sol

10. Properties:
Brownian motion
Tyndall Effect (Reflection and light scattering)
Coagulation peptization
Dialysis

11. PHYSICAL STATE OF INGREDIENTS IN FOOD SYSTEMS
Food Dispersions
1. True solution
2. Colloidal dispersion
3. Emulsion
4. Foam
5. Gel
Dispersions
1. Continuous phase
2. Dispersed phase
May be solid, liquid, or gas.

12. Colloidal Dispersion (SOL)
True Solution
The dispersion of particle < 1 nm in liquid.
Examples: sugar, lactose, minerals, and vitamins.
Colloidal Dispersion (SOL)
Dispersion of particle sizes between nm in liquid.
Common colloids: dispersion of proteins, large molecular salts.
Example: milk.

13. Suspensions and Colloids
Suspensions and colloids are NOT solutions.
Suspensions: The particles are so large that they settle out of the solvent if not constantly stirred.
Colloids: The particle is intermediate in size between those of a suspension and those of a solution.

14. Smog – A Suspension

15. Types of Colloids Examples Dispersing Medium Dispersed Substance
Colloid Type
Fog, aerosol sprays
Gas
Liquid
Aerosol
Smoke, airborne bacteria
Solid
Whipped cream, soap suds
Foam
Milk, mayonnaise
Emulsion
Paint, clays, gelatin
Sol
Marshmallow, Styrofoam
Solid foam
Butter, cheese
Solid emulsion
Ruby glass
Solid sol

16. The Tyndall Effect
Colloids scatter light, making a beam visible. Solutions do not scatter light.
Which glass contains a colloid?
colloid
solution

17. Removal of Colloidal Particles
Colloid particles are too small to be separated by physical means (e.g. filtration).
Colloid particles are coagulated (enlarged) until they can be removed by filtration.
Methods of coagulation:
heating (colloid particles move and are attracted to each other when they collide);
adding an electrolyte (neutralize the surface charges on the colloid particles).
Dialysis: using a semipermeable membranes separate ions from colloidal particles.

18. Hydrophilic & Hydrophobic Colloids
Focus on colloids in water.
“Water loving” colloids: hydrophilic.
“Water hating” colloids: hydrophobic.
Molecules arrange themselves so that hydrophobic portions are oriented towards each other.
If a large hydrophobic macromolecule (giant molecule) needs to exist in water (e.g. in a cell), hydrophobic molecules embed themselves into the macromolecule leaving the hydrophilic ends to interact with water.

19. Hydrophilic and Hydrophobic Colloids
Most dirt stains on people and clothing are oil-based. Soaps are molecules with long hydrophobic tails and hydrophilic heads that remove dirt by stabilizing the colloid in water.
Bile excretes substances like sodium stereate that forms an emulsion with fats in our small intestine.
Emulsifying agents help form an emulsion.

20. Hydrophilic and Hydrophobic Colloids
Sodium stearate has a long hydrophobic tail (CH3(CH2)16-) and a small hydrophobic head (-CO2-Na+).
The hydrophobic tail can be absorbed into the oil drop, leaving the hydrophilic head on the surface.
The hydrophilic heads then interact with the water and the oil drop is stabilized in water.

21. Particle Sizes Become Larger
Solutions Colloidal Dispersions Suspensions
All particles are on Particles of at least one Particles of at least
the order of atoms, component are large one component
ions, or small clusters of atoms, ions, may be individually
molecules (0.1-1 nm) or small molecules, or seen with a low-
are very large ions or power microscope
molecules ( nm) (over 1000 nm)
Most stable to gravity Less stable to gravity Unstable to gravity
Most homogeneous Also homogeneous, Homogeneous only
but borderline if well stirred

22. Solutions Colloidal Dispersions Suspensions
Transparent (but Often translucent or Often opaque but,
often colored) opaque, but may be may appear translucent transparent
No Tyndall effect Tyndall effect Not applicable
(suspensions cannot be transparent)
No Brownian Brownian movement Particles separate unless
movement system is stirred
Cannot be separated Cannot be separated Can be separated by
by filtration by filtration filtration
Homogeneous ———— to ———— Heterogeneous ——>

23. Properties of colloid solutions
Colloids are everywhere
In the human body
Washing powder, soup, tooth paste, etc.
Many foods ( yogurt, butter, milk)
Nanotechnologies are based on chemistry of colloids

24. Heterogenous (rough) dispersion
Suspension - heterogeneous fluid containing solid particles that are sufficiently large for sedimentation.
Particle size is > 1 mm
Dispersion is made by mechanical agitation (sand in the water).
Aerosol - a suspension of liquid droplets or a suspension of fine solid particles in a gas.
Example : smoke, air pollution, smog etc.

25. Heterogenous (rough) dispersion
Emulsion - a mixture of two or more immiscible liquids
one liquid (the dispersed phase) is dispersed in the other (the continuous phase).
Prepared by shaking – oil/water (milk), water/ oil (butter).

26. Emulsions
Stable coloidal system in which both phases are liquids (water and oil)
Miscible liquid form a solution
Lyophobic colloids form an emulsion
Emulsifying agent – substance require to form a stable emulsion
Emulsifyin agent is surface-active, i.e.it reduce the surface tension (soap, many other detergents.

27. STABILITY OF A FOOD DISPERSION
1. Dispersed particle size
2. Viscosity of continuous phase
3. Dispersed phase concentration
4. Density difference between 2 phases

28. Emulsions
Liquid/liquid systems of 2 immiscible substances are called emulsion. Substances or particle size = microns.
Examples: butter (w/o), margarine (w/o), mayonnaise (o/w), salad dressing (o/w), milk (o/w), cream (o/w), and chip-dip (o/w).
Oil
Oil
Oil
H O
H O 2
Oil 2
Oil
Oil
Oil
H O
H O 2
Oil 2
Oil
Oil
Water
Oil
Oil/Water
Water/Oil

30. Types of Emulsion mm Water Oil Oil-in-water emulsion
Water-in-oil emulsion

31. Multiple Emulsions mm Water Oil Water-in-oil-in-water emulsion
Oil-in-water-in-oil emulsion

34. Emulsion Size
< 0.5 mm mm
1.5-3 mm
>3 mm

35. Number Distributions 0.5-1.5 mm < 0.5 mm 1.5-3 mm >3 mm
Very few large droplets contain most of the oil
Number mm
< 0.5 mm
1.5-3 mm
>3 mm

36. Chemical Composition
Interfacial layer. Essential to stabilizing the emulsion
Oil Phase. Limited effects on the properties of the emulsion
Aqueous Phase. Aqueous chemical reactions affect the interface and hence emulsion stability

39. Emulsion Destabilization
Creaming
Flocculation
Coalescence
Combined methods

40. DESTABILIZATION OF THE DISPERSION
Oil
Oil
Oil
Oil
Oil
Oil
Oil
Oil
Oil
Oil
Oil
Oil
Oil
Oil
Oil
Water
Oil
Oil
Oil
Oil
Oil
Oil
Oil
Oil
Oil
Oil
Oil
Aggregation
Water
Oil
Oil separation
from water
Water

41. Creaming Buoyancy (Archimedes) Friction (Stokes-Einstein)
h Continuous phase viscosity
Dr density difference
g Acceleration due to gravity
d droplet diameter
v droplet terminal velocity
vs Stokes velocity

42. Flocculation and Coalescence
Collision and
sticking (reaction)
Stir or change chemical conditions
FLOCCULATION
Rehomogenization
Film rupture
COALESCENCE

43. Rheology of Flocculated Emulsions
Flocculation leads to an increase in viscosity
Water is trapped within the floc and must flow with the floc
Effective volume fraction increased rg

44. Creaming & Slight Flocculation
Flocs have larger effective size
Smaller Dr
Tend to cream much faster

45. Creaming & Extreme Flocculation
Heavily flocculated emulsions form a network
Solid-like properties (gel)
Do not cream (may collapse after lag period)

48. Emulsion Viscosity Dispersed phase volume fraction
Viscosity of emulsion
Emulsion droplets disrupt streamlines and require more effort to get the same flow rate
Continuous phase viscosity

51. Emulsions and Emulsifier
Go to Slide Show mode, click the red button and enjoy!

52. Emulsions We will examine an oil-in-water emulsion
These are common in food systems and include things like mayonnaise
Here is our prototypical system with two oil droplets dispersed in water

53. Emulsions (Oil in water, O/W)
Oil droplets want
to coalesce--this
reduces
surface tension
oil

54. Emulsions (Oil in water, O/W)

55. Emulsions (Oil in water, O/W)
Separates and floats to top because oil
is less dense than water

56. Emulsions (Oil in water, O/W)
To prevent phase
separation we need
an emulsifier
oil

58. Emulsions (Oil in water, O/W)
What happens to this
picture when we add
emulsifiers?

59. Emulsions (Oil in water, O/W)
This system is stabilized
due to a lowering of
surface tension by the
emulsifier.
oil

60. Emulsions (Oil in water, O/W)
Now the water sees only the polar emulsifier heads (which, by the way, it likes)
The oil droplets can see only the nonpolar emulsifier tails (for all it knows it is surrounded by oil)
Everybody is happy and there is no driving force for separation of the phases

64. Emulsifiers Emulsifiers have the following general molecular features
head
Polar head, likes water
Non-polar tail, likes oil

65. EMULSIFIER Mayonnaise Emulsifier Margarine Water Oil Hydrophilic group
Hydrophobic
group
Oil
Water

67. CHEMICAL STRUCTURE OF EMULSIFIERS
Phospholipids (Lecithin) O CH 2
O C (CH 2 ) 16 CH 3 O CH O
CH O C (CH 3 2 ) 14 CH 3 CH + 3
N CH 2 CH 2
O P O CH 2
Hydrophobic CH O 3 - (
fat-soluble)
Hydrophilic (water-soluble)
Mono-
Glycerides (mono-
stearate) O CH 2
O C (CH 2 ) 16 CH 3
HO CH
Hydrophobic
HO CH 2
Hydrophilic
Di-glycerides (
di-stearate) O CH 2
O C (CH 2 ) 16 CH 3 O
CH O C (CH 2 ) 16 CH 3
HO CH 2
Hydrophobic
Hydrophilic

68. Span 60 (sorbitan mono-stearate)
C CH CH 2
O C (CH ) 16 CH 3
C CH C H OH HO
O CH
Hydrophobic
Hydrophilic
Tween 60 (polyoxyalkylene sorbitan mono-stearate)
Hydrophobic
Hydrophilic

75. SOME DESIRABLE CHARACTERISTICS OF FOOD EMULSIFIERS
Ability to reduce interfacial tension below 10 dynes/cm
Ability to be rapidly absorbed at the interface
Ability to function effectively at low concentrations
Resistance to chemical change
Lack of odor, color, and toxicity
Economical

78. FOAM Gas is dispersed in liquid or semi-liquid.
Dispersed-phase: gas
Continuous-phase: liquid
It requires a 3rd component possessing protective or stabilizing properties to maintain the dispersion.
Example: whipped topping

79. The important foam stability factors are:
1. Surface tension
2. Concentration of separate phase
3. Presence of foaming agent to lower surface tension
4. Viscosity of liquid - the higher the viscosity, the more stable the foam.
5. Presence and thickness of adsorption layer (a 3rd stabilizing material).

80. GEL semi-solid state with 2 continuous phases.
Continuous phase of interconnected particles and/or macro-molecules intermingled with a continuous phase of liquid phase such as water.
Examples: jello, jam

81. FOOD DISPERSIONS Dispersed Continuous Name of Examples
Phase Phase Dispersion
Solid (S) Liquid (L) Solution, Colloidal dispersion Milk
Liquid (L) Liquid (L) Emulsion French dressing
Gas (G) Liquid (L) Foam Whipped topping
Gas (G) Solid (S) Solid Foam Foam candy
Solid (S) Gas (G) Solid Aerosol Smoke for flavoring food

82. Foams
Concentrated
Dilute

83. Dilute Foams Somewhat similar to emulsions Various modes of formation
Large (~mm) spherical bubbles
Very fast creaming
Ostwald ripening

84. Concentrated Foams Distorted non-spherical gas cells
Very high volume fraction, often >99%

85. Foam Drainage Water drains from foam under gravity
As water leaves, faces of film are brought closer together