Colloids 5 W4

Question 1

If particles interact strongly they can…

Answer 1

Sediment irreversibly

Question 2

If particles interact weakly they can…

Answer 2

Flocculate

Question 3

Sediments are…

Answer 3

Dense and compact with low sedimentation volume

Question 4

Flocs are…

Answer 4

Readily re dispersible by shaking and have high sedimentation volume

May appear unsightly

Question 5

DLVO summary

Answer 5

Theory describe the interactions between chargerd particles in a medium

Question 6

Overall energy is …

Answer 6

Sum of attractive (VDW) and repulsive (double layer) interactions

Question 7

3 regions of the potential:separation diagram:

Answer 7

o Primary minimum
o Primary maximum
o Secondary minimum

Question 8

DLVO Theory doesn’t account for

Answer 8

several important interactions that affect pharmaceutical dispersions, especially why polymers are widely used as suspending agents.

Question 9

Adsorbed polymers or colloidal particles can …

Answer 9

exert steric and entropic repulsive forces

Question 10

Overall stability of dispersion can be modified by changing:

Answer 10

o theparticles’surfacepotentialor
o themedium’sionicstrengthor
o addingpolymersorcolloidalparticlestotheparticlesurfaceorthemedium.

Question 11

With dispersed formulations, excipients are used to …

Answer 11

stabilise the dispersed phase, by increasing repulsion between particles or by controlling flocculation

Question 12

Non-ionic surfactant

Answer 12

type of surfactant that does not carry any electrical charge in its hydrophilic (water-attracting) head.

Question 13

Surfactant

Answer 13

short for “surface-active agent”) is a substance that reduces the surface tension between two substances, such as a liquid and a solid or two liquids. Surfactants are able to do this because they have both a hydrophilic (water-attracting) head and a hydrophobic (water-repelling) tail, which enables them to interact with both polar and nonpolar molecules. This unique structure allows surfactants to help mix, spread, and stabilize otherwise immiscible substances, like oil and water.

Question 14

Stable dispersed formulations need to balance :

Answer 14

Toxicity/ionic strength (to control flocculation)

Drug solubility (to maintain chemical stability and avoid otswald ripening)

Flavour, appreance and stability

Question 15

Ostwald ripening

Answer 15

where larger particles or droplets grow at the expense of smaller ones over time. This process is driven by differences in solubility or chemical potential between particles of different sizes. Ostwald ripening is commonly observed in emulsions, alloys, and crystal growth.

Question 16

Mechanism of Ostwald Ripening

Answer 16

1. Solubility and Particle Size: Smaller particles have a higher surface-to-volume ratio, which increases their surface energy and makes them more soluble than larger particles.
2. Dissolution and Re-deposition: Due to this difference in solubility, smaller particles tend to dissolve more readily into the surrounding medium. The dissolved molecules or ions then diffuse through the medium and redeposit onto larger particles or droplets, causing them to grow.
3. Continued Growth of Larger Particles: As smaller particles disappear and larger ones grow, the system becomes increasingly unstable with larger particles dominating over time.