Disperse Systems - Surfactants and Suspending Agents

Question 1

Surface tension

Answer 1

Water molecules attract each other hydrogen bond pulling away from air

Question 2

Surfactant

Answer 2

• Surface active agent
• Amphatic molecule that consists of a hydrophilic head and a hydrophobic tail
• Accumulate at interfaces
• molecule that self assembles

Question 3

Surfactant uses

Answer 3

• In emulsions and solution
• aggregated suracant used in drug delivery vehicles
• Solublises insoluable drugs

Question 4

Surfacant in oil-water interface

Answer 4

• Adsobption at lower interfacial tension
• Maintain dispersion of oil in to small droplets
• Maintains particles in a dispersed state

Question 5

Ionic surfacant

Answer 5

• Anatonic (dissacosiation at high pH)
• Catatonic (dissacosiation at low pH)

Question 6

Non ionic surfacant

Answer 6

• less toxic and irritant compared to ionic surfacant

Question 7

Anionic

Answer 7

• Negatively charged surfacant with positive counter ion
• Freely soluable in water
• Forms self emulsifying base with Fatty alcohols

Question 8

Cationic

Answer 8

• Positively charged surfacant and negatively charged counterion
• Freely soluable in water
• Has antimicrobial properties

Question 9

Non Ionic

Answer 9

• uncharged
• alkyl chain linked to polyoxyethylene glycol
• Spans - Sorbitan fatty acid esters

Question 10

Zwitterion

Answer 10

• 2 charges overall neutral

Question 11

Co surfacants

Answer 11

• Achieve low interfacial tension, 2nd co surfacant added
• Usually short alcohols or amines
• Helps form and stablise micelles
• Enables interface to become more fluid
• Form efficiently packed film cover whole droplet

Question 12

Micelles

Answer 12

• Non-ionic surfactants dissolved in water
• Colloidal spherical nanoparticles
• 100 sufcants into single entity
• Dynamic break up and reform - slow
• Indavidual monommer leave and reform - fast

Question 13

Formation of micelles

Answer 13

• 60 randomly positioned molecules of polysorbate 80 cluster to form
• undergo reconstructing to yeild final equalibrium
• hydrogen bonding which causes flickering clusters and highly ordered water molecules ‘cages’

Question 14

Critical packing parameter

Answer 14

V/lca
v = volume
lc = Extended chain length
a = cross sectional area

Question 15

Dispersion of lipid in water

Answer 15

Each lipid molecule forces surounding water molecules to become ordered

Question 16

Cluster of lipid molecule

Answer 16

Only lipid potion at edge of cluster are ordered few molecule order increase entropy

Question 17

Micelles in water

Answer 17

All hydrophobic groups are sequested from water no highy ordred shells of water so high entropy

Question 18

Water with hydrophilic head group

Answer 18

• Head group repel eachother when bought close together stops growth of micelle
• Strong repulsion in ionic smaller micelles
• weaker repulsion in non-ionic larger micelles

Question 19

Critical micelle concentration
(CMC)

Answer 19

• The surfacant concentration at which micelles are formed
• Determined by measuring the surface tension at diffrent surfacants

Question 20

Surface tension and CMC

Answer 20

Above CMC the surface tension of the solution is constent

Question 21

Osmotic pressure and CMC

Answer 21

• Dependant on the number of molecules of water rate slowly decreases after CMC

Question 22

Conductivity and CMC

Answer 22

• At CMC theres an abrubt decrease of the current carrier anions to decrease

Question 23

Light scattering and CMC

Answer 23

• Sharp increase from CMC point from free surfacant to micelle only occur at micelle formation

Question 24

Drug solubility and CMC

Answer 24

• Micelles enable drug solubility after CMC point

Question 25

Purpose of micelle

Answer 25

• Enables material that were insoluable in water to become soluable by incorperating into a micelle

Question 26

Suspending agent

Answer 26

• Reduce rate of settling of suspened active ingreedients
• Redily resuspended before use
• Increase viscosity of suspension

Question 27

Ideal quality of suspending agent

Answer 27

• 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