Lecture 8: colloidal systems

Question 1

What are the classifications of dispersed systems?

Answer 1

1. Molecular dispersion
2. Colloidal dispersion
3. Coarse dispersion

Question 2

What category of dispersions do micelles fall in?

Answer 2

Colloidal dispersions

Question 3

What are the pharmaceutical uses of colloids and nano drug delivery systems?

Answer 3

1. To increase the dissolution of materials in pharmaceutical applications
2. To enhance the stability of aqueous and oily pharmaceutical preparations
3. To provide a controlled release and targeted delivery of therapeutics 4. To impart unique therapeutical properties to certain drugs

Question 4

What are the types of colloidal systems?

Answer 4

1. Lyophilic colloids
2. Lyophobic colloids
3. Association colloids

Question 5

What kind of particles are present in a lyophilic colloidal suspension?

Answer 5

Particles that are solvated by the dispersion medium
“solvent loving”

Question 6

What kind of particles are present in a lyophobic colloidal suspension?

Answer 6

Particles have little attraction for dispersion medium.

“solvent-hating”

Question 7

What are association colloids?

Answer 7

Dispersions of micelles with aggregates of 50 or more surfactant molecules

Question 8

Of the different types of colloidal systems, which are thermodynamically stable and which are thermodynamically unstable?

Answer 8

Thermodynamically unstable: lyophobic colloids
Thermodynamically stable: lyophilic and association colloids

Question 9

What happens when a beam o light is passed through a colloidal system?

Answer 9

The light gets scattered and a cone shape is formed

Question 10

What is the light scattering effect of colloids used for?

Answer 10

The determination of the size, shape and interactions

Question 11

How does Brownian motion change for particles with different sizes?

Answer 11

Brownian movement is faster for smaller particles.

Question 12

How does Brownian motion change for solutions with different viscosities?

Answer 12

Brownian motion decreases with increasing viscosity of the medium

Question 13

How does diffusion rate change with temperature, particle size and viscosity?

Answer 13

Diffusion increases with temperature while it decreases with increasing particle size and viscosity

Question 14

How does the velocity of sedimentation change with radius of the particle?

Answer 14

The velocity of sedimentation increases with increasing radius

Question 15

How does the velocity of sedimentation change with viscosity of the medium?

Answer 15

The velocity of sedimentation decreases with greater viscosity.

Question 16

What is viscosity?

Answer 16

The resistance to flow of a liquid

Question 17

How does a Newtonian fluid behave with respect to its viscosity and shear stress?

Answer 17

Increasing shear stress has no effect of the viscosity, it remains constant

Question 18

How does a plastic fluid behave with respect to its viscosity and shear stress?

Answer 18

Viscosity decreases with increasing shear rate until a minimum shear rate is reached, after which increasing shear stress has no effect of the viscosity, it remains constant

Question 19

How does a pseudoplastic fluid behave with respect to its viscosity and shear stress?

Answer 19

Viscosity decreases with increasing shear rate

Question 20

How does a dilatant fluid behave with respect to its viscosity and shear stress?

Answer 20

Viscosity increases with increasing shear rate

Question 21

In a solid surface in contact with a solution of ions, what is the rigid layer composed of?

Answer 21

1. The surface of the solid with the adsorbed potential determining ions
2. The counter ions

Question 22

In a solid surface in contact with a solution of ions, what is the diffuse layer composed of?

Answer 22

A combination of ions that have a charge opposite to the charge of the rigid layer

Question 23

In a solid surface in contact with a solution of ions, what is the bulk solution composed of?

Answer 23

It’s a neutral ionic solution

Question 23

In a solid surface in contact with a solution of ions, what is the electrical double layer?

Answer 23

The electrical double layer consists of the rigid and diffuse layer

but in high concentration the electric double layer doesn’t exist??

Question 24

In a solid surface in contact with a solution of ions, what is Nernst potential?

Answer 24

It is the potential at the solid surface
So it’s basically the difference in potential between the actual surface and the electroneutral region of the solution.

Question 24

In a solid surface in contact with a solution of ions, what is zeta potential?

Answer 24

1. It is the electrical potential at the shear plane
2. It is the difference in potential between the surface of the tightly bound layer and the electroneutral region of the solution

Question 25

In a solid surface in contact with a solution of ions, what is the thickness of the electric double layer dependent on?

Answer 25

The type and the concentration of ions in the solution.

Question 26

How does stability change with zeta potential?

Answer 26

Higher (absolute value of) zeta potential = higher stability

Question 27

What happens if the (absolute value of) zeta potential is too low?

Answer 27

The colloidal system will coagulate

Question 28

What happens to zeta potential at different pH?

Answer 28

At extreme pH, the absolute value of zeta potential is very high (which is good)
At the isoelectric point the zeta potential is zero (bad)

Question 29

What are the ways by which flocculation of the colloidal suspension is prevented?

Answer 29

1. Electrostatic stabilisation
2. Steric stabilisation
3. Protective sheath

Question 30

How does electrostatic stabilisation work to reduce flocculation?

Answer 30

1.Provide an electric charge on the dispersed particles (EDL consideration).
2. Aggregation of particles are prevented by electrostatic forces of repulsion.

Question 31

How does steric stabilisation work to reduce flocculation?

Answer 31

1. Surround each particle with a protective sheath.
2. Aggregation of particles prevented by steric hindrance of the adsorbed polymer
3. Water shell bound to the hydrophilic surfaces gives rise to hydration repulsion.

Question 32

How does protective sheath work to reduce flocculation?

Answer 32

1. Hydrophobic colloids could be stabilized by the addition of large amounts of hydrophilic colloid, with the hydrophile being adsorbed on the hydrophobic particles.
2. The hydrophile is the protective colloid

Question 33

What is the gold number?

Answer 33

1. When using a hydrophilic colloid as a protective sheath to stabilise a hydrophobic colloid, the protective property of the hydrophilic colloid is expressed in terms of the gold number
2. It is the minimum weight (mg) of the protective colloid required to prevent a colour change from red to violet in 10 mL of gold solution on the addition of 1 mL of a 10% solution of sodium chloride.