Colloids

Question 1

Define disperse systems and their 2 main components

Answer 1

a system in which one substance is dispersed or distributed as particles throughout another phase

1. Disperse phase
2. Dispersion medium continuous phase)

Question 2

Which dispersion is not considered a colloidal dispersion

Answer 2

gas in gas dispersion (molecular dispersion)

Question 3

What are the particle sizes of each type of dispersion

Answer 3

Molecular dispersion: less than 1nm (true dispersion)
Colloidal dispersion: 1nm - 1microm (1000nm)
Fine and coarse dispersion: greater than 1microm

Question 4

What is the difference between true solutions and colloidal dispersions

Answer 4

Colloidal dispersions have larger particle size
True solutions don’t scatter light and appear clear while colloidal dispersions scatter light and appear opaque

Question 5

What are 3 main types of colloidal systems

Answer 5

Lyophobic: “solvent hating” the degree of attraction is small or non-existent
- unstable, particles aggregating

Lyophilic: “solvent loving” the disperse interacts nice with the dispersion medium
- stable

Association colloids:
Contain both lyophobic and strongly lyophilic groups

Question 6

Characteristics of lyophobic and lyophilic colloids

Answer 6

Lyophobic:
- Irreversible
- Do not form spontaneously
- Delta H, Delta G is +
- Delta S is negative??
- Surface free energy NOT lowered by solvation
- Makes the reverse spontaneous
- High sedimentation

Lyophilic:
- Reversible
- Form spontaneously
- Delta H, Delta G is -
- Delta S is positive
- Surface free energy lowered by solvation
- Low sedimentation

Question 7

What are 2 methods to prepare lyophobic colloids

Answer 7

Dispersion: grinding in a mortar, colloid mills, ultrasonic generators

Condensation: physical and chemical

Question 8

What are types of lyophilic systems

Answer 8

True solutions
- Water soluble polymers, acacia, povidone, protein solutions

Gelled Solutions
- High concentration of polymers
- gelatin or starch –> set to gels on cooling
- methylcellulose –> gels on heating

Particulate dispersions
- Contain solid particles, such as bentonite or microcrystalline cellulose

Question 9

Why is particle size important in dispersion stability

Answer 9

-Influence on sedimentation rate
- Increase in surface free energy and aggregation tendancy

Question 10

What are 2 ways to decrease surface free nergy to improve physical stability of the dispersion?
What is the equation

Answer 10

Surface free energy (delta F) = interfacial tension x surface area

By decreasing both values.
To keep the particles small with large surface area the main choice is decreasing the interfacial tension

Question 11

What are the 2 kinetic properties of colloidal particles. Define them

Answer 11

Brownian motion:
results from random collisions of colloidal particles with molecules of the dispersion medium

Diffusion:
colloid particles spontaneously diffuse from a high to low concentration

Question 12

What 2 values can decrease sedimentation when increased

Answer 12

Density of dispersion medium
Viscosity of dispersion medium

Question 13

Describe the Tyndall effect

Answer 13

A laser directed at a colloidal sol will be scattered or absorbed, appearing turbid.
The particle size + concentration is directly proportional to the degree of light scattering

Question 14

What type of microscopy can you see colloidal particles in

Answer 14

Electron microscopy

Question 15

What causes the electrical double layer and its role.

Answer 15

• The charge on the particle surface will attract oppositely charged ions to achieve electrical neutrality

It determines the distance between particles in the dispersion (which affects stability)

Question 16

Define shear plane and zeta potential

Answer 16

Shear plane is the boundary after the tightly bound layer that marks the mobile portion of the double layer

• potential measure at shear plane is called zeta potential

Question 17

How does electrical potential change as we move away from the partcile

Answer 17

Zeta potential decreases from the surface potential to the stern potential and decays slowly

Question 18

How does the Debye length influence the interaction between lyophobic particles

Answer 18

Debye length is the length of the double layer and 2 of them indicate the distance between particle

Question 19

*****Define Deflocculated and Flocculated particles and the zeta potential in each systems

Answer 19

Flocculated (colloidly unstable, pharm. stable)
- Particles remain dispersed loose aggregations (easy to redisperse)
- attractive forces
- low zeta potential
- faster sedimentation
- clumps
- no caking

Deflocculated (colloidly stable)
- Particles are dispersed (difficult redispersion)
- repulsive forces
- High zeta potential
- slower sedimentation
- no clumps
- Caking

Question 20

How can you lower the zeta potential

Answer 20

By adding counter ions

Question 21

Which can be redispersed and which cannot
Flocculation, Aggregation, Coagulant

Answer 21

Flocculation: a loose aggregation
Aggregation: particles associate, but can be overcome by vigorous shaking
Coagulant cannot be redispersed, irreversible

Question 22

What are examples of flocculating agents and their mechanism of action

Answer 22

Electrolytes: decrease zeta potential
Lyophilic macromolecules: protective colloid effect

Question 23

What are protective colloids?

Answer 23

When lyophilic macromolecules are added to lyophobic colloids
- they absorb onto other particle surfaces preventing close contact of particle and therefore preventing coagulation (stable)

Question 24

What provides the stability for lyophobic systems? what about lyophilic?

Answer 24

Lyophobic:
- stabilized by the electrical double layer
- Affected by electrolytes

Lyophilic
- Combination of electrical double layer and solvation
- Unaffected by small amounts of electrolytes (can become lyophobic with large amounts of electrolytes)
(if hydration or polymer increases, flocculation or coagulation occurs)

Question 25

Define coacervation

Answer 25

• precipitation of particles from solution/dispersion with the addition of electrolytes of non-solvents
• drug is replaced in dispersion medium by the electrolyte
• aka salting out

Question 26

Define Micro encapsulation

Answer 26

coating of drug particles with polymers to provide slow release of drug

Question 27

What are the 4 traditional lyophobic systems

Answer 27

Aurothioglucose
Iron dextran injection
Colloidal silver
Colloidal Sulfar topical preparation

Question 28

What are some traditional lyophilic systems

Answer 28

Protein formulations
- Insulin
- Antibody
- Albumin
- Clotting factors
- Cytokines