Colloidal dispersions A colloid is a mixture that has particles ranging 1 nanometers to 500 nanometers (0.5 µm) in diameter, yet are still able to remain evenly distributed throughout the solution. These are also known as colloidal dispersions because the substances remain dispersed and do not settle to the bottom of the container. In colloids, one substance is evenly dispersed in another. The substance being dispersed is referred to as being in the dispersed phase, while the substance in which it is dispersed is in the Dispersion Medium (continuous phase). B Pharm 4th semester Physical Pharmacy Physical Pharmaceutics

1. Colloidal Dispersions
and
General Characteristics of Colloidal Particles
Size, Shape, Surface area, surface charge
UNIT-I
Lecture-2
ROHIT KUMAR TRIVEDI

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3. Colloid is a heterogeneous dispersion
Colloidal Dispersions
▪ A colloid is a mixture that has particles ranging 1
nanometers to 500 nanometers (0.5 µm) in diameter, yet
are still able to remain evenly distributed throughout the
solution.
▪ These are also known as colloidal dispersions because the
substances remain dispersed and do not settle to the
bottom of the container.
▪ In colloids, one substance is evenly dispersed in another.
▪ The substance being dispersed is referred to as being in the
dispersed phase, while the substance in which it is
dispersed is in the Dispersion Medium (continuous phase).
(1 – 500 nm)

4. General Characteristics of Colloidal Particles
Size, Shape, Surface area, surface charge
Particle Size
▪ It is not possible to see object whose diameter is less than half of the wavelength of light. The lowest
wavelength is about 4 X 10-5 cm (0.4μm)
▪ Hence it is not possible to see particles of size 0.2 μm or less.
▪ Although there are no precise boundaries of size among the particles of molecular, colloidal and coarse
dispersions.
▪ Colloid particles are usually on the order of 1nm to 500nm (0.5 μm) in size.
Colloidal Dispersions

5. General Characteristics of Colloidal Particles
Size, Shape, Surface area, surface charge
Colloidal Dispersions
Shape:

6. ▪ The size of the colloidal particles is of few micrometres (1 nm to 0.5 μm).
▪ They possess enormous surface area when compared to coarser particles.
▪ The larger surface area enhances the solubility of drug particles.
▪ Large surface area increases surface free energy, which makes the system thermodynamically
unstable.
General Characteristics of Colloidal Particles
Size, Shape, Surface area, surface charge
Colloidal Dispersions
Surface Area:

7. ▪ Colloidal particles possess charge on their surfaces.
▪ The reasons for the origin of charge on the particle
surface are as follows:
1. Functional groups present on surface may get ionised
depends upon pH of the medium.
2. Ions present in the medium may get adsorbed onto the
surface of the particle.
▪ The stability of colloids is attributed to surface charge.
▪ The like charges on the particles create repulsion forces.
▪ During particle collisions particles remain as individual
entities and distribute uniformly.
General Characteristics of Colloidal Particles
Size, Shape, Surface area, surface charge
Colloidal Dispersions
Surface Charge:

8. Classification of Colloidal Dispersions
Next Lecture
Colloidal Dispersions

9. Rohit Kumar Trivedi
Assistant Professor, Pharmacy