M7 Emulsions pt 2

Question 1

What is the relationship between surfactant concentration and interfacial tension?

Answer 1

As we increase surfactant concentration, we decrease interfacial tension – up to a point, which is the CMC of the surfactant

Question 2

what is interfacial tension

Answer 2

force that resist it from breaking up into smaller particules is interfacial tension

Question 3

What is the relationship between the location of the surfactant monomers and interfacial tension?

Answer 3

Monomeric surfactant molecules accumulating at the surface and interface decrease surface/interfacial tension

* air considered hydrophobic -> will go to surface and orient which will dec interfacial tension

Question 4

Explain the log concentration of surfactant vs. interfacial tension curve.

Answer 4

A: interfacial tension

B: log concentration of surfactant

C: critical micellar concentration

D: surfactant molecules without full coverage of surface

E: surface adsorption of monomeric surfactant molecules with full coverage of surface

F. air/oil – water interface G. micelle formation

Question 5

What happens to surfaceant molecules in dilute dispersions vs more saturated

Answer 5

dilute: surfaceants orient themselves at oil.water interface
- as conc of surfactnat inc surface alyer will becomes saturated
- once saturated further increases will no longer affect interfacial tension or stability of system
- surfacnts mols will start forming mmicelles

Question 6

What is the effect of micellization on interfacial tension?

Answer 6

Micelles formation after the CMC is reached does not influence interfacial tension

Question 7

what is CNC

Answer 7

point at which michelle formation begins

• depends on structural characteristics to depends on surfactant

Question 8

what happens to tendency to form michelles as the legnth of hydrocarbon chain inc

Answer 8

• increases the tendency to form micelles

Question 9

micelle formation of non ionic surfactants vs ionic

Answer 9

ionic surfactants -> get repulsion between adjacent charged head groups that opposes michelle formation

*non ionic surfactants for micheles art conc << ionic ones

Question 10

what does a higher CMC mean

Answer 10

• more monomers can go to interface ( more efficient)

*low CMC wll form micelles before oil ro water droplets are coated -> less efficient

Question 11

What is meant by surface excess concentration of surfactant in the Gibbs equation?

Answer 11

• Γ = surface excess surfactant concentration
  
  • portion of surfactant occupying the interface and contributes to lowering the interfacial tension

Question 12

calc Q 32

Question 13

when do you get mixed micelles

Answer 13

* some micelles ahve toils pointed out others with heads pointed out

If a blend of surfactants is used in the preparation of an emulsion → formation of mixed micelles

Question 14

what is aggregation number

Answer 14

number of surfactant molecules that form one micelle

Question 15

what are association colloids

Answer 15

micelles

Question 16

what forms of surfactants are found below CMC and Above CMC

Answer 16

Below CMC: monomers
Above CMC: micelles

Question 17

what does each varaible mean

Answer 17

• Γ: surface excess or surfactnat (surfactant mol at surface)
  
  • moles/Cm²
• R: universal gas cosntant (8.314 x 107 erg/mole/K aka g cm²/s²
• T: abolute temp in K
• ∆γ: change in surface tension of mixture with change in surfactant conc
  
  • dynes/cm OR g cm /s²
• C: concentration of surfactant in liq bulk
  
  • unitless bc log

Question 18

What is HLB

Answer 18

Hydrophile - Lipophile Balance

describing the hydrophilic-hydrophobic characteristics

ie. solubility of surfactants

the HLB scale ranges from1-20 (in some special cases up to 50)

Question 19

HLB of something Lipophilic? Hydrophilic

Answer 19

HLB 0-10 = lipophilic

HLB: 10-20 = hydrophilic

Question 20

What type of emulsion is formed when a surfactant of HLB=14 is used?

Answer 20

• o/w

*Hlb over 10 - hydrophilic

Question 21

What type of emulsion is formed when a surfactant of HLB=5 is used?

Answer 21

w/o

Question 22

Using the Tables below, select a pair of emulsifiers to prepare 100 g of an w/o emulsion containing 50g olive oil and 10g beeswax requiring a total of 7% w/w surfactant concentration

Answer 22

Question 23

What emulsifying agents form monomolecular film around the disperse phase?

Answer 23

Ionic and non-ionic surfactants

*act by dec interfacial tension

Question 24

What emulsifying agents form multimolecular film around the disperse phase?

Answer 24

Hydrocolloids such as polymers, acacia, gelatin

*sterioc hinderance (forming solid particle film)

Question 26

What emulsifying agents form solid particle film around the disperse phase?

Question 27

How does bentonite exert its emulsifying properties?

Answer 27

It forms a solid particle film on the surface of oil droplets

Question 28

What are the desirable properties of surfactants? non-ionic emulsifiers

Answer 28

\*Depends on the emulsifying ability desired and the toxicity (determines route of administration) of each emulsifying agent. less toxic and less iritant

Question 29

What are the desirable properties of surfactants? ionic emulsifiers

Answer 29

should not be given orally (irritant to GIT) Cationic: toxic at low concentrations ⇒ limited to external use when antiseptic properties are required Anionic: have high pH (alkaline) ⇒ unsuitable for broken skin

Question 30

what is phase inversion? how can it be utilized?

Answer 30

- change in emulsion type w/o -\> o/w ex: during prep of o/w the water phase is poured into oil-\> first add small amount of water to form w/o then subsequent addition of water will form an o/w - this order of addition results in better physical stability of final product

Question 31

List a few frequently used antioxidant.

Answer 31

BHA, BHT, α-tocopherol, alkyl gallates (Propyl Gallate B.P.), ascorbic acid, ascorbyl palmitate

Question 32

What equipment can be used for emulsification?

Answer 32

* Mechanical stirrers (rotating blades) * used for low viscosity prep * large quantities may be mixed * Homogenizers * small inlet orifice and presssure used to nicorporate oil * not suitable for viscosity \> 2000 cP * ultrasonifiers * sonic saves break down emulsified droplets * produces uniform emulsion * gentle -\> powerful * colloid mills (rotor/stator) * common

Question 33

What is creaming?

Answer 33

Emulsion instability caused by flocculation and upward sedimentation of oil droplets reversible process

Question 34

What is coalescence?

Answer 34

- complete fusion of droplets within an emulsion leads to a ↓ number of droplets and ultimately separation of the two immiscible phases – irreversible process

Question 35

how do you determine rate of creaming or rate of sedimentation in an emulsion

Answer 35

Stokes law of sedimentation can be used to calculate sedimentation rate in case of creaming sedimentation rate will be a negative number

Question 36

what kind fo stress conditions are used for assessing emulsion shelf lfie

Answer 36

Aging and temperature increase Centrifugation (to accelerate separation into two layers) Agitation (to reflect conditions of shipping)

Question 37

What is the reason for coalescence and what steps would you take to prevent coalescence in an emulsion?

Answer 37

- can be caused by low zeta potential, high surface free energy or high interfacial tension to mitigate: add protective colloids, optimize carticle size, add more surfactant \*coalesence in w/o emulsions is prevented by presence of long hydrocarbon changs of surfactant molecules that project into oil phase

Question 38

What is the reason for creaming and what steps would you take to prevent this in an emulsion?

Answer 38

- caused by flocculation and upward sedimentation - add more rpotective colloids add more surfactant

Question 39

What is the reason for foaming and what steps would you take to prevent foaming in an emulsion?

Answer 39

too muhc surfactant reduce the surfactant conc

Question 40

What is the reason for microbial growth in an otherwise preserved emulsion and what steps would you take to prevent this in an emulsion?

Answer 40

preservative – surfactant interaction reduced antimicrobial function; add more or different preservative

Question 41

What is the reason for unpleasant taste and what steps would you take to achieve palatability in an emulsion?

Answer 41

- inappropriate amount fo certain excipients: propylene glycol, glycerol, preservatives - lack or inappropriate amount of sweetnener or flavouring agent \*reduce/optimize excipient conc, add more or diff sweetener or flavour

Question 42

how to reduce rate of creaming/sedimentation