Disperse Systems

Question 1

What is happening to water molecules for surface tension?

Answer 1

Are attracted to each other, with hydrogen bonds. They are also pulling away from the air.

Question 2

What are the problems involving surface tension in pharmaceutics?

Answer 2

Displace water molecules
Wetting process hindered if surface tension too high
Need to add surfactant molecules to replace some of the water molecules in the surface.

Question 3

What is a surfactant?

Answer 3

Surface active agent

Question 4

What type of molecule is a surfactant?

Answer 4

Amphiphilic and amphipathic molecule that consists of a distinct hydrophobic and hydrophilic region.

Question 5

What are the two types of surfactants?

Answer 5

Ionic surfactants
-an ionic dissociate at a high pH
-cationic dissociate at low pH
Non ionic surfactants

Question 6

What are co-surfactants used for?

Answer 6

To achieve a very low interfacial tension, by incorporating a second amphiphile.

Question 7

What is the structure of micelles?

Answer 7

Oil inside, water outside.

Question 8

Micelles formation in water is…

Answer 8

Dispersion of lipids in water
Water surrounds the tail
Cluster of lipid molecules
Micelles cluster

Question 9

What side does a reaction favour in thermodynamics?

Answer 9

Lowest free energy state

Question 10

What are suspending agents used for?

Answer 10

Reduce the rate of settling of suspended active ingredients
Increases viscosity of the suspension

Question 11

what are non-ionic surfactants used for?

Answer 11

widely used, less toxic and irritant than ionic surfactants

Question 12

what do mixtures of surfactants produce?

Answer 12

more sable emulsions

Question 13

how does lowering the interfacial tension help the adsorption of the oil-water interface?

Answer 13

aids the dispersal of the oil into droplets of a small size
maintains the particles in a dispersed state

Question 14

what are anionic surfactants?

Answer 14

negatively charged surfactants, positive counterion

Question 15

what are cationic urfactants?

Answer 15

positively charged surfactants, negative counterions

Question 16

what are zwitterions?

Answer 16

two charges, overall neutral

Question 17

what are some naturally occuring surfactants?

Answer 17

bile salts
lecithin
synovial fluid
lugns surfactant

Question 18

what are the characteristics of co-surfactants?

Answer 18

usually short chain alcohols or amines ranging from C4 to C10
helps in the formation and satabilisation of micelles/ microemulsions
increases feklxi bility and fluidity at the interface

Question 19

what is the rapid process involving micelles?

Answer 19

individual monomers may enter or leave the micelles

Question 20

what is the slow process involving micelles?

Answer 20

micelles are constantly breaking down and reforming

Question 21

what is the self- assembly of surfactants?

Answer 21

60 randomly positioned molecules of polysorbate 80 first aggregate into small clusters, which the come together to form a single micelle
the micelle then undergoes restructuring to yield its final euilibrium

Question 22

what happens when the head groups of micelles come too close together?

Answer 22

start to repel each other
which stops the micelles from growing

Question 23

what type of repulsion do ionic micelles have?

Answer 23

strong repulsion which becomes a smaller micelle

Question 24

what type of repulsion do non-ionic micelles have ?

Answer 24

less strong repulsion which becomes a larger micelle

Question 25

what is the critical micelle concentration (CMC)?

Answer 25

the surfactant concentration at and above which micelles are formed
detrmined by measuring thensurface tension at different [surfatants]

Question 26

what is the surface tension like above the CMC?

Answer 26

constant

Question 27

what does the osmotic pressure in water depend on after CMC?

Answer 27

number of molecules present in water

Question 28

what are the sites of possible solubilisation?

Answer 28

a) hydocarbon core
b) core/mantle region
c) head group (mantle) region
d) surface adsorption

Question 29

what are suspending agents used for?

Answer 29

to reduce the rate of settling of suspended active ingredients
increases the viscosity of the suspension
drugs can be readily and uniformly resuspended before use

Question 30

what are the characteristics of an ideal suspending agent?

Answer 30

Readily and uniformly incorporated into formulation
* Readily dispersed in water without special techniques
* Ensure the formation of a loosely packed system which does not cake
* Does not influence the dissolution rate or absorption rate of the drug
* Be inert, non-toxic and free from incompatibilities