Disperse Systems (emulsions )

Question 1

emulsion

Answer 1

a mixture of two immiscible (unmixable) liquids, typically consisting of one liquid dispersed in the form of small droplets within another liquid.

Question 2

examples of emulsions in everyday life

Answer 2

creams
lotions
milk
mayonnaise
toothpaste

Question 3

examples of pharmaceutical emulsions

Answer 3

Lotions, creams, ointments, vitamin drops

Question 4

the two immiscible phases present in an emulsion

Answer 4

the dispersed phase(internal phase)
the continuous phase(external phase)

The dispersed phase, comprising small droplets, is dispersed within the continuous phase. In oil-in-water (O/W) emulsions, water is the continuous phase, and oil droplets are dispersed. In water-in-oil (W/O) emulsions, it is the opposite, with oil as the continuous phase and water droplets dispersed within it.

Question 5

in an emulsion where one phase is dispersed in the other, is the emulsion stable?

Answer 5

no, because the dispersed droplets would eventually seperate from the continuous phase to reform the intial immiscible state

Question 6

interface tension

Answer 6

a term used to describe the force acting at the interface between two immiscible phases, such as between two liquids or between a liquid and a gas.

It is the tendency of the interface to minimize its area, and it arises due to the difference in cohesive forces between molecules in the two phases.

Question 7

state two functions of the interface tension

Answer 7

prevents the complete mixing of immiscible liquids. It creates a barrier that resists the penetration of one liquid into the other, maintaining the distinct separation of phases

influences the formation of droplets when one immiscible liquid is dispersed into another. It determines the size and shape of the droplets, with higher tension leading to smaller, more spherical droplets.

Question 8

how are emulsions stabilized

Answer 8

via the addition of a surfactant or an emulsifying agent

Question 9

function of an emulsifying agent or surfactant

Answer 9

To lower interfacial tension and stabilise emulsion

Question 10

is an emulsifying agent the same as a surfactant

Answer 10

no

all emulsifying agents are surfactants, but not all surfactants are emulsifying agents. Emulsifying agents are a subset of surfactants that are specifically chosen for their ability to stabilize emulsions

Question 11

surfactant

Answer 11

a broad category of compounds that have both hydrophilic (water-attracting) and hydrophobic (water-repelling) parts in their molecular structure.

This dual nature allows surfactants to reduce the surface tension between immiscible phases, such as oil and water. Surfactants can act as emulsifying agents when used to stabilize emulsions by preventing the coalescence of dispersed droplets.

Question 12

if an emulsifying agent is not added to an emulsion what happens

Answer 12

the dispersion is unstable and the globules undergocoalescence to form two separate layers of water and oil

Question 13

state some properties an emulsifying agent must possess

Answer 13

Be non-toxic.
Must not interfere with the stability and efficacy of the API.
Be compatible with other ingredients in the formulation.
Be stable to microorganisms.
Possess little or no odour, taste or colour.
Maintain stability of the emulsion for intended shelf-life.
Molecule has 2 parts: hydrophilic and hydrophobic

Question 14

how does an emulsifying agent work

Answer 14

Forms a coherent film around the globules of the dispersed phaseand prevent the coalescence of the droplets.

Question 15

when is it necessary for antioxidants to be added to emulsions

Answer 15

enhances stability by preventing autoxidation of the oil and rancidity/and or destruction of any sensitive components like vitamins, present in the emulsion

Question 16

primary emulsion

Answer 16

The primary emulsion refers to the initial emulsion formed when two immiscible liquids are mixed.

In the context of O/W emulsions, it is the initial mixture where water is the continuous phase and oil is dispersed. For W/O emulsions, it is the initial mixture where oil is the continuous phase and water is dispersed. The primary emulsion is formed by combining the two phases along with an emulsifying agent.

Question 17

secondary emulsion

Answer 17

Secondary emulsions can be formed by taking the primary emulsion and further emulsifying it with additional ingredients

This additional emulsification process can result in the creation of finer droplets within the primary emulsion. Secondary emulsions can have different properties, such as improved stability or altered texture, compared to the primary emulsion.

Question 18

what could be the essence of secondary emulsions pharmaceutically(in terms of drug release)

Answer 18

By forming secondary emulsions with specific characteristics, pharmaceutical scientists can design controlled release systems. This allows for the gradual release of drugs over time, providing sustained therapeutic effects

Question 19

which phase is the emulsifier typically more soluble in

Answer 19

the external/continuous phase

this is the bancroft rule

Question 20

some differences btn o/w and w/o emulsions

Answer 20

Water soluble drugs are more quickly released from o/w emulsions while Oil soluble drugs are more quickly released from w/o emulsions

Preferred for internal use as bitter taste of oils can be masked while w/o preferred for external use

Question 21

coarse emulsions
fine emulsions
microemulsions

Answer 21

mainly large droplets 10 μm to 100 μm

mainly small droplets 0.1 μm to 10 μm

very small droplets 10 to 100 nm

Question 22

how does droplet size affect emulsion stability

Answer 22

the smaller the droplet size the higher the emulsion stability

Question 23

HLB in the context of emulsion agents stands for?

Answer 23

Hydrophilic-Lipophilic Balance

Question 24

the usual HLB range of emulsifying agents

Answer 24

0 to 20

Question 25

Materials that are highly polar or hydrophilic have higher HLBs than materials that are less polar or lipophilic, true or false?

Answer 25

true

Question 26

why might we be required to do if a surfactant with the desired HLB value is not available?

Answer 26

it may be necessary to mix two surfactants, then we calculate the HLB of the surfactant mixture using the formula

HLBmix = fA x HLBA + (1-fA) x HLBB

Question 27

w/o emulsion can be diluted with water and vice versa, what is this based on

Answer 27

the solubility of the external phase of the emulsion

Question 28

is oil a good conductor of electricity?

Answer 28

no, oil is a non conductor

Question 29

name an example of a test used to determine whether emulsions are o/w or w/o

Answer 29

fluorescent test

Oils give fluorescence under UV light, while water does not.Therefore, o/w emulsion shows a spotty pattern while w/oemulsion fluoresces

Question 30

creaming
sedimentation

Answer 30

the upward movent of dispersed droplets in an emulsion

the downwards movement of dispersed droplets in an emulsion

Question 31

Aggregation or flocculation

Answer 31

dispersed droplets come together but do not fuse in an emulsion

Question 32

colascence

Answer 32

the complete fusion of droplets in an emulsion

Question 34

is a creamy emulsion likely to coalasce?
give a reason for your answer

Answer 34

yes, because of the close proximity of the droptlets at the top of the emulsion

Question 35

how to decrease the chance of creaming

Answer 35

decrease droplet size
decrease density difference between the phases
increase viscosity

Question 36

are colascence and breaking reversible?

Answer 36

no they are not

Question 37

causes of breaking

Answer 37

Addition of a chemical that is incompatible with the emulsifying agent
Bacterial growth – may destroy the emulsifying agent. Temperature changes, such as heating or freezing.

Question 38

is breaking the same as coalascence

Answer 38

no
breaking is a broader term that describes the overall instability of the emulsion, leading to phase separation. Coalescence is a specific process within this instability, involving the merging of individual droplets. Coalescence contributes to the overall breaking of the emulsion by reducing its stability and promoting the formation of larger droplets or distinct phases.