Disperse Systems

Disperse system
The presence of two distinct phases in which one substance (the dispersed phase) is distributed throughout the second substance (the continuous phase)
1 of 37
Surface tension
This arises due to a difference in attractive forces between the bulk and the surface. Molecules at the surface experience an inward attraction, causing the surface to contract
2 of 37
LaPlace pressure
The difference in pressure across a curved surface/interface where the pressure inside is greater than the pressure outside, e.g. in a bubble
3 of 37
Cohesion
Affinity for molecules/phases that are similar
4 of 37
Adhesion
Affinity for molecules/phases that are different
5 of 37
Spreading
Phenomenon at liquid-liquid interface
6 of 37
Wetting
Phenomenon at solid-liquid interface
7 of 37
What happens when adhesion > cohesion?
There is enough affinity for both phases to interact with one another. This creates a film which results in one interface (e.g. milk in a cup of tea) and one value of interfacial tension. Contact angle is smaller
8 of 37
What happens when cohesion > adhesion?
There is low affinity between the two interfaces, and a lot more work needs to be done to overcome the tension so the system is very unstable. This results in one interface but two surfaces. Contact angle is larger
9 of 37
Lyophobic colloids
Low affinity for the continuous phase and form thermodynamically unstable dispersions, i.e. they require energy to form
10 of 37
Lyophilic colloids
High affinity for the continuous phase and form thermodynamically stable dispersions, i.e. their formation is spontaneous
11 of 37
Critical micellar concentration
The concentration at which the surface is saturated and micelles begin to form
12 of 37
Krafft point
The temperature above which the solubility of a surfactant INCREASES sharply. (At temperatures below this point, surfactant molecules precipitate instead of forming micelles)
13 of 37
Cloud point
The temperature above which the solubility of a surfactant DECREASES sharply; this results in a cloudy solution
14 of 37
Dialysis
This allows for the separation of colloidal particles from small molecules/ions. The semi-permeable membrane allows for the diffusion of ions and molecules but not of colloids
15 of 37
Brownian motion
The random movement of particles under thermal agitation (has been observed for particles up to 5 micrometers, anything larger is impacted by gravity so the randomness of movement is then reduced).
16 of 37
Sedimentation
The downward motion under gravitational forces. This is not common in colloids due to their small size unless the gravitational force is increased by ultracentrifugation
17 of 37
Light scattering
A colloid in a dispersion is able to scatter light so if you have a completely clear liquid, shining a light into the solution will scatter the light if there is a colloid present
18 of 37
Ultramicroscopy
Scattered light can be detected by this method. Colloidal particles appear as spots against a dark background
19 of 37
Zeta potential
The potential difference existing between the surface of a solid particle immersed in a conducting liquid (e.g. water) and the bulk of the liquid. It is measured in the "slipping plane"
20 of 37
Coagulation
This is permanent aggregation - a lot of energy is needed to separate the colloids (shaking will not be enough)
21 of 37
Flocculation
Re-dispersion of aggregates is easily achieved by shaking
22 of 37
Suspension
A coarse dispersion in which the internal phase (therapeutically active ingredient) is dispersed uniformly throughout the external phase
23 of 37
Stoke's law
Equation that measures sedimentation rate. It is only valid when the concentration of the dispersed phase is < 2% solids, the dispersed phase is composed of spherical particles of which there is a narrow distribution of size and the solvent is polar
24 of 37
Ostwald ripening
The recrystallisation of smaller particles disappears due to the temperature fluctuations during storage
25 of 37
Diffusible solid
Disperses very easily by shaking the vehicle in a calibrated bottle or by making a paste then increasing the water content. Sedimentation is slow which improves dose uniformity. The dispersed phase is still insoluble in H2O but is easily wetted
26 of 37
Indiffusible solid
Insoluble in water and easily wetted but the suspensions formed are unstable. There is quick sedimentation of the dispersed phase which is a risk for uniformity - requires suspending agent
27 of 37
Emulsion
Requires a dispersed phase, a continuous phase and an emulsifier. The dispersed and continuous phases are always immiscible with one another; they are usually an oil and water phase
28 of 37
Microemulsion
Colloidal solutions that contain oil, water and a very high concentration of surfactant
29 of 37
Emulsifier
They form a film on the surface of oil droplets to increase the affinity between the dispersed phase and the continuous phase. If the film is broken, the contents will "crack" - this is the separation of the two phases
30 of 37
Surfactant
These reduce interfacial tension through electrostatic repulsion if they have charged polar heads
31 of 37
Saponification
The result of the reaction between a triglyceride and a strong base. The product is amphiphilic so it can be used to stabilise and emulsion
32 of 37
Hydrocolloid
They can be used as emulsifiers by forming a multimolecular layer on the dispersed droplets; working by steric repulsion. They have little effect on interfacial tension. They stabilise oil in water emulsions and can also increase viscosity
33 of 37
Bancroft's Rule
The phase in which an emulsifier is most soluble becomes the continuous phase
34 of 37
Hydrophilic Lipophilic Balance
Numerical value of an amphiphilic molecule - if it is too high, it is too soluble in water and if it is too low it is too soluble in oil. Should be between 1 and 50
35 of 37
Sedimentation volume
Volume of the sediment (Vu) divided by volume of the suspension (Vo). Value will be higher for a flocculated suspension
36 of 37
Degree of flocculation
Volume of the sediment (Vu) divided by the volume of the sediment in a deflocculated suspension (V infinity. If the answer is 1, the flocculating agent has not worked
37 of 37

Other cards in this set

Card 2

Front

This arises due to a difference in attractive forces between the bulk and the surface. Molecules at the surface experience an inward attraction, causing the surface to contract

Back

Surface tension

Card 3

Front

The difference in pressure across a curved surface/interface where the pressure inside is greater than the pressure outside, e.g. in a bubble

Back

Preview of the back of card 3

Card 4

Front

Affinity for molecules/phases that are similar

Back

Preview of the back of card 4

Card 5

Front

Affinity for molecules/phases that are different

Back

Preview of the back of card 5
View more cards

Comments

No comments have yet been made

Similar Pharmacy resources:

See all Pharmacy resources »See all Disperse systems resources »