emulsion Flashcards

Question

quillaia saponins

Answer 1

- o/w of low viscosity - glycosides form quillaja saponaria - can be employed for oral preparation

Answer 2

- possess emulsifying and antiseptic properties - incompatible with anionic compounds - promote o/w emulsion

Answer 3

quaternary ammonium compounds 1. cetrimide 2. cetyl pyridinium chloride 3. benzalkonium chloride

Answer 4

- cationic at low pH and anionic at high pH - not widely used cause expensive - eg lecithin for IV fat emulsion

Answer 5

- low toxicity and irritancy - less sensitive to pH changes and addition of electrolytes - for external as well as internal preparation

Answer 6

- sorbitan esters and polyoxyethylene sorbitan esters - glycol and glycerol esters - fatty acid polyglycol esters - fatty alcohol polyglycol esters (macrogrol ethers) - higher fatty alcohols

Answer 7

sorbitan esters (Span), polyoxyethylene sorbitan esters (Tween) - blends of sorbitan ester and polyoxyethylene sorbitan ester are usually employed - depending on the HLB of the blend, it may promote the formulation of o/w and w/o emulsion

Answer 8

eg. glyceryl monostearate - promote formation of o/w emulsions - effectiveness enhances by soap of monovalent bases and amine soaps

Answer 9

eg. POE 40 stearate - promote formation of o/w emulsions - effectiveness enhanced by stearyl alcohol

Answer 10

eg. cetomacrogol 1000 - blends to hydrophilic and lipophilic members are usually employed - depending on HLB of blend (o/w or w/o) - cetomacrogol 1000 + cetostearyl alcohol = cetomacrogol emulsifying wax

Answer 11

eg. cetostearyl alcohol | - auxilliary emulsifying agents

Answer 12

more useful as auxiliary emulsifying agents and as thickening agents; generally favour the formation of o/w emulsions

Answer 13

1. natural and synthetic clays (bentonite) 2. natural and synthetic gums (acacia, tragacanth, sodium alginate, carrageenan, locust bean, guar, xanthan, sodium CMC, methyl cellulose) 3. proteins (eg. gelatins, soluble casein)

Answer 14

- bentonite derived from montmorillonite from typical smectite clay - swells in the presence of water but raises the viscosity of medium only at pH6 or higher

Answer 15

- polysaccharides - most commonly used - exhibit incompatibility with certain cations or pH - sodium alginate and sodium CMC are incompatible with acids - methyl cellulose is less soluble in hot water

Answer 16

- less commonly used | - gelatin prepared by partial hydrolysis of collagen

Answer 17

- not major interest to the formulator because limited utility as primary emulsifying agents - solids of mineral origin should be sterilised before used because they may contain tetanus spore

Answer 18

1. non-polar solids: favour the formation of w/o emulsions (eg. carbon, glyceryl tristearate) 2. polar inorganic solids: favor formation of o/w emulsions (eg. heavy metal OH, non swelling clays)

Answer 19

- When oil and water are mixed together, droplets of varying sizes are produced. - A tension exists at the droplet interface because the two immiscible phases tend to have different attractive forces for a molecule at the interface - Such a system is thermodynamically unstable

Answer 20

1. chlolesterol + sodium cetyl sulphate: closely pakced condensed complex (stable) 2. oleyl alcohol + sodium cetyl sulphate: loosely packed condense complex (poor emulsion) 3. cetyl alcohol + sodium oleate: fairly closely packed but no complex formation (fairly poor emulsion)

Answer 21

- applied for ionic surfactants | - electric double layer serves as an electrical barrier to approach droplets

Answer 22

- Gums and waxes are commonly used to increase the viscosity of water and oil respectively. - A more viscous continuous phase generally produces a more stable emulsion.

Answer 23

- The adsorption of surfactants at the oil/water interface gives rise to an interfacial film. - This film experiences two interfacial tensions, one between the film and the aqueous phase and the other between the film and the oil phase. - The film will curve in the direction of the greater interfacial tension. Thus, the disperse phase is on the side of the film with the higher interfacial tension.

Answer 24

- Harkin attempted to explain the type of emulsion formed by soaps, such as sodium oleate (soap of monovalent base) and magnesium oleate (soap of divalent base). - Surfactant molecules (e.g. soaps) will orientate at the oil/water interface such that a tightly packed film is formed. - The relative location of the polar heads of the soap molecules will determine the type of emulsion produced.

Answer 25

- This applies to emulsifying agents which are finely divided solids, with the following properties: > Insoluble in both aqueous and oily phases. > Preferentially wetted by one of the phases. > Able to form a thin interfacial film. > Of colloidal size. - Such solid particles are attracted to the interface between the two immiscible liquids. - The angle of contact formed by the solid particle at the interface determines the type of emulsion produced.

Answer 26

This ratio of these two groups affects the water or oil solubility of the surfactant aka the hydrophile-lipophile balance. HLB = weight of hydrophilic grp / MR x 20

Answer 27

``` 4-6: w/o emulsifying 7-9: wetting agents 8-18: o/w emulsifying agents 13-15: detergents 10-18: solubilising agents ```

Answer 28

1. Bancroft Theory 2. Oriented wedge theory 3. Theory based on angle of contact

Answer 29

1. agent in water method 2, agent in oil method 3. Nascent soap method 4. Alternate addition method

Answer 30

- emulsifying agent is incorporated in water and the oil is then added with agitation, producing o/w emulsion directly - for w/o, addition of oil is continued until phase inversion occurs

Answer 31

- emulsfying agent is incorporated in oil, which is then added to water with vigorous agitation forming o/w emulsion - for w/o emulsion, addition of oil phase continues until phase inversion occurs

Answer 32

- suitable for emulsions with soap as the emulsifying agent. - The fatty acid is dissolved in the oil and the base in the water. - The soap is formed in situ as the oil and aqueous phases are brought into contact during mixing and an emulsion is subsequently produced. - Depending on the type of soap, o/w or w/o emulsions are produced.

Answer 33

- This method is particularly suitable for vegetable oils. - The water and oil are added alternately in small amounts to the emulsifying agent.

Answer 34

• Simple stirring • Colloid milling • Vibration and ultrasonification Further homogenization to improve stability

Answer 35

there is no coalescence of disperse phase that ultimately leads to separation of the oil and aqueous phases

Answer 36

creaming, flocculation, coalescence and/or cracking

Answer 37

Under influence of gravity, the globules tend to rise or sediment depending on the differences in specific gravities between the phases. This results in concentration of the disperse phase at the top or bottom of the system which can be readily redispersed on shaking. (reversible)

Answer 38

- applies to an isolated sphere in an infinitely large mass of liquid. - The hindrance to motion depends on the concentration of the droplets of the disperse phase and this in turn depends on the volume fraction of the disperse phase

Answer 39

- increasing radius of droplets !! - decrease viscosity of continuous phase !! - increase difference in densities of disperse phase and continuous phase

Answer 40

- reversible aggregation of droplets of the disperse phase in the form of three-dimensional clusters. - The droplets do not lose their identity entirely as the mechanical or electrical barrier surrounding the droplet is sufficient to prevent droplet coalescence.

Answer 41

- droplets join to form larger drop | - irreversible, leading to decrease in number of droplets and finally cracking

Answer 42

- complete breakdown of emulsion with coalescence of droplets and separation of two phases into two layers - may be due to chemical, physical and biological effects

Answer 43

- strong acids/alkali metal soap - anionic compounds + cationionic surfactants - cationic compounds + anionic surfactants - high concentration of electrolytes + soaps - alcohol + gums

Answer 44

- centrifugation - agitation - freeze-thaw cycle - heating-cooling cycle but if stress is excessive may lead to abnormal processes

Answer 45

- The ratio of the volume of separated phase and the total volume of emulsion is determined. - A stable emulsion should not show any

Answer 46

- The mean size of the globules with time is determined by microscopic examination, electronic particle counting method (e.g. Coulter Counter) or laser diffraction technique. - Emulsions which are less stable show greater increase in the mean globule size with time. This is attributed to coalescence of globules which is a form of emulsion instability

Answer 47

- The emulsion conductivity is dependent on the degree of dispersion. - Reduction in conductivity of o/w emulsions indicates oil droplet aggregation and instability. - Conductivity of w/o emulsion indicates water droplet aggregation and instability. - Measurements are made, with the aid of platinum electrodes, on emulsions stored for short periods of time.

Answer 48

- The emulsion viscosity is affected by the globule size and number. - Hence, changes in emulsion viscosity can be used to indicate emulsion stability. - This is measured using viscometers.

emulsion Flashcards

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