‫‪University of Babylon - College of Engineering‬‬
‫‪Chemical Engineering‬‬
‫‪The second stage‬‬
‫‪Physical Chemistry‬‬
‫‪Report Title:‬‬
‫‪Colloids‬‬
‫اعـــداد الـــطـــالب ‪:‬‬
‫حيدرمصباحم–محيدرممعبدمالكريم‬
‫داللمرعدم–مرسلمجناحم‬
‫رقيةمرائدم–مزهراءمحسن‬
‫زهراءمشويقم–مزيدمفهد‬
‫سارةمنعميم–مجسادمجامس‬
‫‪1‬‬
Introduction :
Colloids are a unique class of mixtures in which one substance is finely dispersed
within another without dissolving completely. Unlike true solutions, where solute
particles are molecularly dissolved, colloidal particles range in size between 1 and
1000 nanometers. They remain evenly distributed throughout the medium due to
Brownian motion and intermolecular forces, preventing them from settling under the
influence of gravity.
Colloids exist in various forms, including sols (solid in liquid), gels (semi-solid
structures), emulsions (liquid in liquid), foams (gas in liquid or solid), and aerosols
(solid or liquid in gas). These systems are essential in everyday life, with examples
such as milk, mayonnaise, fog, jelly, and even blood.
The significance of colloids extends across multiple scientific and industrial fields. In
medicine, colloidal drug delivery systems enhance bioavailability and targeted
treatment. In environmental science, colloidal suspensions influence water
purification and soil stability. Industrial applications range from food production and
cosmetics to paints, inks, and synthetic materials.
Understanding colloidal behavior, stability, and interaction with different substances
is fundamental in developing advanced materials and improving existing
technologies. Scientists continue to explore new applications for colloids, making
them a critical area of study in chemistry, physics, and engineering.
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Colloids:
A colloid is a type of mixture where tiny particles of one substance are evenly
dispersed throughout another substance. These particles are larger than those in a
solution but smaller than those in a suspension. Colloidal particles typically range in
size from 1 to 1000 nanometers (nm) and do not settle out over time due to their
small size and interactions with the dispersing medium.
Key Characteristics of Colloids :
1. Heterogeneous Mixture : Colloids consist of two phases:
➢ Dispersed Phase – The substance present in small particles (milk fat in milk).
➢ Dispersion Medium : The substance in which the dispersed phase is spread
(water in milk).
2. Tyndall Effect : Colloids scatter light when a beam passes through them, making the
path of the light visible. This does not occur in true solutions.
3. Stability : Colloidal particles do not settle under gravity due to Brownian motion
(random movement of particles).
4. Size of Particles : Between 1 nm to 1000 nm.
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Types of Colloidal systems :
Colloidal systems are classified based on the phases of the dispersed phase and the
dispersion medium. There are eight main types of colloidal systems:
Dispersed
Phase
Dispersion
Medium
Type of
Colloid
Example
Solid
Gas
Solid Aerosol
Smoke, dust in air
Solid
Liquid
Sol
Paint, ink, gold sol
Solid
Solid
Solid Sol
Colored glass, gemstones
Liquid
Gas
Liquid Aerosol Fog, mist, cloud
Liquid
Liquid
Emulsion
Milk, mayonnaise
Liquid
Solid
Gel
Jelly, cheese, butter
Gas
Liquid
Foam
Whipped cream, shaving
foam
Gas
Solid
Solid Foam
Pumice, Styrofoam
An easy way of determining whether a mixture is colloidal or not is through use of the
Tyndall Effect. When light is shined through a true solution, the light passes cleanly
through the solution, however when light is passed through a colloidal solution, the
substance in the dispersed phases scatters the light in all directions, making it readily
seen.
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Lyophilic and lyophobic sols or colloids :
1. Lyophilic Sols (Liquid-Loving Sols) :
➢ Definition: These are colloidal solutions in which the dispersed phase has a
strong attraction (affinity) for the dispersion medium (solvent).
➢ Formation: They form easily when the dispersed substance is mixed with the
dispersion medium.
➢ Stability: They are highly stable due to strong solvation (hydration in water).
➢ Reversibility: These sols can be easily reformed by adding the dispersion
medium if they are dried or removed.
➢ Examples: Gum, gelatin, starch, proteins, and rubber sols.
2. Lyophobic Sols (Liquid-Fearing Sols) :
➢ Definition: These are colloidal solutions in which the dispersed phase has little
to no attraction for the dispersion medium.
➢ Formation: They do not form easily and require special techniques like
electrical dispersion or chemical reactions.
➢ Stability: Less stable, and they tend to coagulate (settle) easily.
➢ Reversibility: They are irreversible; once coagulated, they cannot be easily
reformed.
➢ Examples: Metal sols (gold sol, silver sol), sulfur sol, Fe(OH)₃ sol.
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Characteristics of Lyophilic and Lyophobic Sols :
Colloidal solutions (sols) are dispersed systems consisting of fine particles (typically 1-100
nm) suspended in a continuous medium. They are classified into two main types:
Lyophilic sols (solvent-attracting colloids) - Lyophobic sols (solvent-repelling colloids)
This classification is based on the interaction between dispersed particles and the solvent.
1. Characteristics Lyophilic Sols :
➢ Easy Formation: They readily form when the dispersed substance is mixed with the
solvent.
➢ High Stability: Particles do not settle easily due to strong interactions with the
solvent
➢ Increased Viscosity: Their viscosity is higher than that of the pure solvent.
➢ Resistance to Coagulation: They do not coagulate easily when small amounts of
electrolytes are added.
➢ Intermolecular Forces: They exhibit Van der Waals forces or hydrogen bonding with
the solvent.
Examples: Starch sol in water Protein sols like gelatin
2. Characteristics Lyophobic Sols :
➢ Difficult Formation: They do not form easily and often require dispersing agents.
➢ Low Stability: Particles tend to settle over time due to weak solvent interaction.
➢ Similar Viscosity to Solvent: They do not significantly affect the viscosity of the
medium.
➢ Easily Coagulated: They precipitate when small amounts of electrolytes are added.
➢ Dependence on Surface Charge: Their stability relies on electrostatic charges
surrounding the particles.
Examples: Gold sols - Aluminum hydroxide sols .
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Aggregation methods Colloids :
Colloids are systems consisting of fine particles distributed in a continuous medium, with
unique physical and chemical properties. One of the most important characteristics of
colloids is their ability to cluster and cluster in different structures, which affects their
stability and behavior.
Aggregation methods in colloids are a key factor in controlling their final properties,
determining how fine particles are related to each other to form larger and more stable
structures. Assembly methods are divided into different types affected by multiple
physical and chemical factors, including :
1. Homogeneous aggregation: This type is characterized by the regular distribution and
balance of particles in the colloidal medium without the influence of external forces,
creating stable and harmonious patterns and structures.
2. Heterogeneous assembly: occurs when particles assemble irregularly, often due to
external forces such as gravity or electrostatic forces, resulting in the formation of
inconsistent clusters.
3. Electrical assembly: It depends on the application of an electric field that leads to the
movement and charging of particles, causing them to attract and gather in certain
patterns.
4. Chemical assembly: It occurs through chemical reactions that connect particles, forming
stable structures with certain properties.
These methods play a key role in industrial and research applications, such as
nanomaterial manufacturing and water treatment, making understanding assembly
mechanisms essential to achieving the desired results.
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colloids in dialysis :
The use of colloids in dialysis is an important aspect of medical procedures aimed at
maintaining osmotic balance and blood pressure during the dialysis process. Colloids are
substances that contain large molecules that are unable to pass through cell membranes,
thus remaining in the blood and helping to draw water from the tissues into the
bloodstream.
The importance of using colloids in dialysis includes:
1. Improving osmotic balance: Colloids help draw fluids from the tissues into the blood
vessels, reducing the risk of hypotension during the dialysis session.
2. Maintaining blood volume: Colloids help maintain the normal blood volume during
dialysis, reducing the risk of a sudden drop in blood volume.
3. Reducing protein loss: Albumin, for example, helps minimize the loss of essential
proteins during the dialysis process, which is important for the patient’s health.
4. Preventing hypotension: During dialysis, fluid removal can sometimes cause a drop in
blood pressure. Colloids help keep the blood pressure stable during the procedure.
Common colloid substances used in dialysis include:
➢ Albumin: A natural protein commonly used to maintain blood volume and pressure.
➢ Dextran: A synthetic substance sometimes used in dialysis.
➢ Hydroxyethyl starch (HES): Also used to prevent low blood pressure.
In conclusion, colloids are used in dialysis to provide comfort and safety to the patient and
ensure that the dialysis session progresses smoothly from a physiological standpoint.
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Electrodialysis :
On the other hand, electrodialysis is an advanced technique used to separate ions and
dissolved materials in solutions using an electric field across semi-permeable membranes.
This technology can play a significant role in improving the separation and purification
processes of solutions containing colloids or other contaminated materials.
Separation Mechanism in Electrodialysis:
Electrodialysis relies on the application of an electric field to separate ions in the solution
through selective membranes. This technique is primarily used for water purification and
the removal of salts and heavy metals from solutions. The process involves directing ions
through specialized membranes, where some membranes allow only the passage of
positive ions (cation-exchange membranes), while others allow the passage of negative
ions only (anion-exchange membranes).
How Electrodialysis Affects Colloids:
When a solution containing colloids is subjected to electrodialysis, the process results in
the separation of ions and dissolved materials, which may help in removing impurities
from the solution. For instance, if the solution contains colloids contaminated with salts or
heavy metals, electrodialysis can be used to remove these contaminants from the solution.
Electrodialysis helps improve the purity of solutions containing colloids, as it can reduce
the concentration of contaminating ions in the solution, thus improving the properties of
emulsions. Electrodialysis can also have a significant impact on industries such as
pharmaceuticals, food, and cosmetics, where it is used to remove impurities or modify the
physical properties of solutions.
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Ultrafiltration :
ultrafiltration is a separation process that uses semi permeable membranes to separate
molecules based on their size. Pressure is applied to push the liquid through the
membrane, allowing small particles to pass through while larger molecules are trapped.
ultrafiltration work with colloids
➢ Application of ultrafiltration: When applying ultrafiltration to colloids, membranes
of suitable pores size can be used to separate colloidal particles from liquid.
➢ Molecules smaller than the size of the pores pass through the membrane.
➢ Molecules larger than the size of the pores are trapped on the membrane.
➢ Result: Pure liquid (filter) is obtained containing small molecules, a concentration of
trapped colloidal particles.
Advantages of ultrafiltration:
➢ High efficiency in class.
➢ Low energy consumption.
➢ The possibility of controlling the size of separated particles.
➢ Non-thermal process.
Disadvantages of ultrafiltration:
➢ Possibility of blockage of membranes.
➢ Cost of membranes.
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