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Pharmacy (year one) > Interfacial phenomena > Flashcards

Interfacial phenomena Flashcards

1
Q

What is an interface?

A

The boundary between two phases

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2
Q

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

A

False - they differ

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3
Q

What is surface tension?

A

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

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4
Q

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

A

increase

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5
Q

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

A

False

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6
Q

What factors does surface tension depend on?

A

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

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7
Q

Does temperature influence surface tension?

A

Yes

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8
Q

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

A

decrease

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9
Q

Why does surface tension decrease as temperature increases?

A

Because there is less cohesion between liquid molecules

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10
Q

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

A

high

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11
Q

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

A

low

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12
Q

What is used to determine whether spreading will occur?

A

Spreading coefficient

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13
Q

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

A

adhesion

cohesion

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14
Q

What is the works of cohesion Wa/a?

A

The work necessary to pull apart a column of liquid

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15
Q

What is the works of adhesion Wa/b?

A

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

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16
Q

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

A

False - only when it is positive

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17
Q

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

A

disintegration

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18
Q

What is the contact angle used to determine?

A 
the spreading coefficient (S)
adhesion tension (AT)
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19
Q

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

A

less

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20
Q

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

A

no spreading

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21
Q

How does the contact angle help in formulations?

A

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

22
Q

What is wetting?

A

The ability for a liquid to maintain contact with solid surface

23
Q

What is used to measure the wetting of a solid?

A

Spreading coefficient

24
Q

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

A

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

25
Q

Polymers’ surface tension is related to their_________

A

molecular weight

26
Q

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

A

Polymers

27
Q

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

A

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

28
Q

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

A

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”

29
Q

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

A

True

30
Q

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

A

True

31
Q

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

A

True

32
Q

What is drug absorption in suppositories influenced by?

A

particle size
aqueous solubility
interfacial tension

33
Q

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

A

surface tension

34
Q

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

A

high

35
Q

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

A

False

36
Q

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

A

True

37
Q

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

A

keratin

stratum corneum

38
Q

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

A

stratum corneum

39
Q

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

A

ionic

40
Q

How is adsorption different to absorption?

A

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

41
Q

What are the two types of adsorption?

A

Physical

Chemical/chemisorption

42
Q

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

A

vdW

43
Q

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

A

stronger

44
Q

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

A

False - just before cmc

45
Q

What does the Freundlich model describe?

A

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

46
Q

What does the Languir model describe?

A

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

47
Q

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

A

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

48
Q

Adsorption is proportional to the solubility. True or false?

A

False - inversely proportional as bonds are necessary for solubility

49
Q

Is adsorption an exothermic or endothermic reaction?

A

Exothermic

50
Q

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

A

True

51
Q

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

A

True

52
Q

What are the applications of adsorption?

A

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

Pharmacy (year one) (60 decks)

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