Interfacial phenomena

Question 1

What is an interface?

Answer 1

The boundary between two phases

Question 2

At the interface, the characteristics are the same as those at the bulk. True or false?

Answer 2

False - they differ

Question 3

What is surface tension?

Answer 3

The property of the surface of a liquid that allows it to resist an external force, due to the cohesive nature of the water molecules

Question 4

When equilibrium is reached, forces are equal on each side and there is an ________ in surface area of the interface

Answer 4

increase

Question 5

Surface area depends on the area of the film. True or false?

Answer 5

False

Question 6

What factors does surface tension depend on?

Answer 6

chemical nature of film
change in area (initial compared to at equilibrium)
length of film

Question 7

Does temperature influence surface tension?

Answer 7

Yes

Question 8

As temperature increases, the majority of liquids see a _______ in surface tension

Answer 8

decrease

Question 9

Why does surface tension decrease as temperature increases?

Answer 9

Because there is less cohesion between liquid molecules

Question 10

In liquid/liquid systems, when there is no spreading - it shows there is ____ interfacial tension between the two liquids

Answer 10

high

Question 11

In liquid/liquid systems, when there is spreading - it shows there is a ____ interfacial tension between two liquids

Answer 11

low

Question 12

What is used to determine whether spreading will occur?

Answer 12

Spreading coefficient

Question 13

The spreading coefficient is the difference between the works of _______ and _______

Answer 13

adhesion

cohesion

Question 14

What is the works of cohesion Wa/a?

Answer 14

The work necessary to pull apart a column of liquid

Question 15

What is the works of adhesion Wa/b?

Answer 15

The work necessary to separate two immiscible liquids to form two liquid/gas interfaces

Question 16

Spreading only occurs when the spreading coefficient is negative. True or false?

Answer 16

False - only when it is positive

Question 17

Behaviour of a liquid in contact with a solid is important in the _______ of a tablet

Answer 17

disintegration

Question 18

What is the contact angle used to determine?

Answer 18

the spreading coefficient (S)
adhesion tension (AT)

Question 19

Spreading takes place when the contact angle is ____ than 90 degress

Answer 19

less

Question 20

What happens if the contact angle is more than 90 degrees?

Answer 20

no spreading

Question 21

How does the contact angle help in formulations?

Answer 21

Because if you have a contact angle of more than 90 degrees, you’ll know you need to add something to the solution so the solid can be in contact with water i.e. a surfactant

Question 22

What is wetting?

Answer 22

The ability for a liquid to maintain contact with solid surface

Question 23

What is used to measure the wetting of a solid?

Answer 23

Spreading coefficient

Question 24

Why do hydrophobic drugs require addition of wetting agents such as surfactants?

Answer 24

Because they are needed to lower the surface tension between the solid drug and the vehicle to favour the dispersion of the solid.

Question 25

Polymers' surface tension is related to their_________

Answer 25

molecular weight

Question 26

_______ can be used as binding agents to increase the tablets compaction, contribute to the formation of a hydrated layer over the solid

Answer 26

Polymers

Question 27

In terms of moisture penetrability, what does it mean if a polymer has a high interfacial tension?

Answer 27

It will results in hard and thick polymer layers and therefore poor moisture penetrability

Question 28

Why is it important to control he surface tension of a tablet product?

Answer 28

Because you need to achieve a presentable product for the patient - a high surface tension will result in a hindered wetting process and a low surface tension will result in an "orange peel"

Question 29

Emulsions have a vast interfacial area between dispersed phase and continuous phase. True or false?

Answer 29

True

Question 30

Microemulsions have little/no surface tension. True or false?

Answer 30

True

Question 31

In emulsions, surfactants are used to control/reduce surface tension. True or false?

Answer 31

True

Question 32

What is drug absorption in suppositories influenced by?

Answer 32

particle size aqueous solubility interfacial tension

Question 33

The distribution behaviour in a suppository base is dependent on the _________ of the drug

Answer 33

surface tension

Question 34

Drugs with a ____ surface tension have lower affinity to the lipophilic suppository base and will partition into the rectal fluid easily

Answer 34

high

Question 35

All parts of the skin show the same spreading/wetting. True or false?

Answer 35

False

Question 36

The skin has a high surface tension. True or false?

Answer 36

True

Question 37

Surfactants in transdermal delivery systems are used to interact with ________, ________ and its extracellular matrix

Answer 37

keratin | stratum corneum

Question 38

Reducing surface tension in transdermal delivery systems helps to drug to penetrate through ________

Answer 38

stratum corneum

Question 39

Ibuprofen is a self penetration enhancer. It behaves as an ______ surfactant

Answer 39

ionic

Question 40

How is adsorption different to absorption?

Answer 40

Adsorption is the accumulation of molecules at the interface whereas absorption is the penetration of one compound through the body of a second

Question 41

What are the two types of adsorption?

Answer 41

Physical | Chemical/chemisorption

Question 42

In physical adsorption, the adsorbate is bound to the surface through weak _____ forces

Answer 42

vdW

Question 43

In chemisorption, the adsorbate is bound through _______ valence forces and involves an ion exchange process

Answer 43

stronger

Question 44

You can calculate the surface occupied by each molecule just after cmc has been reached. True or false?

Answer 44

False - just before cmc

Question 45

What does the Freundlich model describe?

Answer 45

adsorption of molecule at relatively high concentration of solute and the adsorbate forms multilayers

Question 46

What does the Languir model describe?

Answer 46

The adsorption of molecules at a relatively low concentration of solute and the adsorbate forms a monolayer

Question 47

What are the four factors that affect the adsorption in S/L systems?

Answer 47

Solubility of the adsorbate pH of solution Temperature Surface area of adsorbant

Question 48

Adsorption is proportional to the solubility. True or false?

Answer 48

False - inversely proportional as bonds are necessary for solubility

Question 49

Is adsorption an exothermic or endothermic reaction?

Answer 49

Exothermic

Question 50

An increase of temperature limits the extent of adsorption. True or false?

Answer 50

True

Question 51

A large surface area leads to a large extent of adsorption. True or false?

Answer 51

True

Question 52

What are the applications of adsorption?

Answer 52

Adsorption of poisons/toxins - activated charcoal Taste masking Haemoperfusion - to treat severe overdose Analysis - TLC uses adsorption