Colloids

Question 1

What are colloids???

Answer 1

Dispersions in which the size of the dispersed particles is within the range of 1 nm to about 1μm.

Question 1

What are the 2 classifications of colloids???

Answer 1

Lyophobic (solvent hating)

Lyophilic (solvent liking)

Question 2

What are types of dispersion methods???

Answer 2

Colloid mills

Ultrasonic treatment

Question 3

What are types of condensation methods???

Answer 3

Colloidal silver iodide

Changing the solvent, for example, sulfur in acetone into water.

Question 4

What are some of the properties of colloids???

Answer 4

Shape and size of colloid particles
e.g. spherical, ellipsoid.

Kinetic properties
e.g. Brownian motion, diffusion, sedimentation.

Optical properties

Electrical properties

Question 5

What are Micelles???

Answer 5

They are colloidal dimensions.

Question 6

What is the formation of Micelles???

Answer 6

A means of shielding the hydrophobic group of the surfactant from the aqueous environment.

Question 7

What are the 2 parts of a Micelles???

Answer 7

Shell/corona

Core

Question 8

What is the shape of Micelles???

Answer 8

They are not static structures.

They are unstable structures with two times, relaxation time (t1 - microseconds) and slow relaxation time (t2 - milliseconds to minutes).

Question 9

What are the roles of Micelles in drug formation???

Answer 9

Solubilization

Hydrolytic degradation may be reduced
Increases stability of drug

Taste masking

Release rates

Immunology

Medical diagnostic imaging

The study of cell membranes and micellar catalysis

Question 10

What are some properties of micelles???

Answer 10

CMC decreases with the addition of electrolytes.

CMC decreases with an increase in the hydrophobic chain length of a surfactant.

CMC tends to decrease with increasing temperature.

Question 11

What is the electrical double layer (EDL)???

Answer 11

A particle surface with a negative charge with a layer of positive ions that are attracted to the surface form the stern layer.

Question 12

What is zeta potential???

Answer 12

The potential at the stern plane (the plane of the closest approach of ions to the particle
surface).

Question 13

What are suspensions???

Answer 13

They are dispersions of an insoluble drug in a aqueous or non aqueous continuous phase.

Question 14

Why is surfactants used as wetting agents???

Answer 14

They can be used to lower S/L interfacial tension which reduces the contact angle.

Question 15

What is some oral uses of wetting agents???

Answer 15

Polysorbates (Tweens)
Sorbitan esters (Spans)

Question 16

What is some external uses of wetting agents???

Answer 16

Sodium lauryl sulphate

Sodium dioctylsulphosphate

Question 17

What is some parenteral uses of wetting agents???

Answer 17

Polysorbates

Polyoxyethylene/polyoxypropylene co-polymers

Question 18

What are hydrophilic colloids???

Answer 18

It’s a multi-molecular coat around the particles.
It accumulates at the surface because its hydrophobic and this build-up reduces S/L interfacial tension.

Also promotes wetting.

Question 19

How can sedimentation be reduced???

Answer 19

Reducing the particle size.

Increasing viscosity of continuous phase.

Decreasing the density diff. between the two phases.

Question 20

What is a Flocculate???

Answer 20

A cluster of particles held together in a loose open structure.

Flocculated systems can be formulated to achieve formulated suspensions to
minimise caking.

Question 21

What are the possible forces interaction between suspended particles???

Answer 21

Electrostatic repulsion.
Van der walls attraction forces.
Short-range attraction forces.
Steric forces.
Solvation forces.

Question 22

What is the DLVO theory???

Answer 22

The theory states that between colloidal particles the only interactions are;
Electrostatic repulsion and Van der waals attraction forces

Question 23

What is electrostatic repulsion???

Answer 23

Charged particles will repel each other because electrical double layers inhibit
close contact, which inhibits flocculation.

Question 24

How do the particles becomes charged???

Answer 24

Ionisation of groups on the surface of the particles.

Adsorbed ions which will confer charge onto the particle surface.

Question 25

Why do particles flocculate???

Answer 25

At a certain distance of separation, an approaching particle become trapped in the 2o
min energy region - flocculated. To move away again enough energy must
be supplied to the system so that the particle can escape the 2o min region
and act as a discrete particle again with no forces of attraction acting on it.

Question 26

What are some examples of flocculating agents???

Answer 26

Electrolytes -
Controls double layer thickness and VR.

Surfactants -
Ionic surfactants controls VR
Non-ionic surfactants cause steric repulsion.

Polymeric agents -
Can bridge particles together or cause steric repulsion.