W5 Disperse systems- Surfactants and Suspending Agents

Question 1

What does surfactant stand for?

Answer 1

A Surface Active Agent

Question 2

What is a surfactant?

Answer 2

A surfactant molecule is:
* An amphiphilic/amphipathic molecule that consists of a distinct hydrophobic and hydrophilic region
* A molecule that accumulates at interfaces
* A molecule that aggregates or self-assembles

Question 3

What type of surfactant is polysorbate?

Answer 3

non-ionic

Question 4

Which vitamins are not water soluble?

Answer 4

Vitamin D

Question 5

What is an example of an application of micelles?

Answer 5

Micellar cleansing water.

Question 6

What are everyday applications of surfactants?
Some everyday examples?

Answer 6

They are widely used in detergent, agrochemical, pesticide, paint, food and also in the pharmaceutical industry
e.g. paint, dettol

Question 7

What are pharmaceutical applications of surfactants

Answer 7

They are present in suspensions and emulsions
Aggregated surfactants can be used as drug delivery vehicles e.g. micelles and vesicles to solubilise insoluble drugs
e.g. Aveeno, E45, Pfizer vaccine

Question 8

What do surfactants do?

Answer 8

• Adsorption at the oil-water interface lowers interfacial tension
• Aids the dispersal of the oil into droplets of a small size
• Maintains the particles in a dispersed state

Question 9

What are the types of surfactants?

Answer 9

IONIC: Anionic (dissociate at high pH) and cationic (dissociate at low pH)

NON-IONIC: Widely used, less toxic and irritant than ionic surfactants

MIXTURES:
Produce more stable emulsions

Question 10

What is an example of a negatively charged surfactant? (Anionic)
sds..
What are its properties?

Answer 10

Sodium dodecyl sulfate (SDS)
- freely soluble in water
- forms self-emulsifying bases with fatty alcohols
- detergent in medicated shampoos
- skin cleanser in topical applications

Question 11

What is an example of a positively charged surfactant? (cationic)
CpCL..
bnzko..

Answer 11

Cetylpyridnium chloride (quaternary ammonium)
- Freely soluble in water
- Has antimicrobial activity- cleaning of wounds, contaminated utensils preservative
- Enhance transdermal drug delivery preparations

Or benzalkonium, methylbenzethonium

Question 12

Structure of micelles?

Answer 12

Colloidal, spherical or near spherical nanoparticles
Loose aggregates of 50-100 surfactant molecules into a single entity
Size = 5-10nm

Question 13

Micelle formation in water

Answer 13

Water
* Extensively hydrogen bonded
* “Flickering clusters”
* Highly ordered water molecules form “cages” around the hydrophobic alkyl chains

Question 14

Thermodynamics of micelle formation in
water (equation)

Answer 14

ΔG = ΔH - TΔSwhere:
* G = free energy; H = enthalpy; T = temperature; S = entropy
The higher the entropy change, the
more favourable the reaction, because
the lower the free energy
Micelle formation results in an increase in entropy because water molecules regain their freedom upon micellization
(i.e. loss of the cage structure)

Question 14

Thermodynamics of micelle formation in
water (equation)

Answer 14

ΔG = ΔH - TΔSwhere:
* G = free energy; H = enthalpy; T = temperature; S = entropy
The higher the entropy change, the
more favourable the reaction, because
the lower the free energy
Micelle formation results in an increase in entropy because water molecules regain their freedom upon micellization
(i.e. loss of the cage structure)

Question 15

What is the critical micelle concentration (CMC)

Answer 15

• The surfactant concentration at and above which micelles are formed
• Determined by measuring the surface tension at different
  [surfactants]