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Pharmaceutics > Preformulation - Surfactants > Flashcards

Preformulation - Surfactants Flashcards

1
Q

What is a surfactant?

A

Surface + active + agent

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2
Q

What is an interface?

A

Boundary between 2 phases

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3
Q

What is a surface?

A

Boundary between 2 phases, one of which is a gas

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4
Q

Is a surface an interface?

A

YES

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5
Q

Are all interfaces surfaces?

A

NO

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6
Q

What is surface energy?

A

Potential energy per unit SA

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7
Q

What do surfactants do?

A

Reduce surface tension

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8
Q

Describe surface tension

A

Apparent “film” on liquid surface that resists puncture

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9
Q

What interface is surface tension?

A

Liquid-gas interface

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10
Q

What does liquid acquire?

A

Minimal SA

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11
Q

Describe surface energy

A

Intermolecular bonding stabilises molecules + lowers their energy

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12
Q

What does surface energy do?

A

Net inward force exerted on “like” molecules on liquid by bulk

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13
Q

What do surface molecules not have?

A

No “like” neighbours above surface for bonding

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14
Q

What is surface tension?

A

Energy required to expand surface of a liquid by a unit area

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15
Q

For most liquids, what happens to surface tension as temperature increases?

A

Decreases

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16
Q

How do you measure surface tension?

A

Ring/plate placed in H2O till breaks water surface

Attached to hook that measures force

17
Q

What is the contact angle?

A

Angle liquid makes contact with surface

18
Q

What is the contact angle an indicator of?

A

Solid surface wettability

19
Q

What does it mean if there is a smaller contact angle?

A

More wetter surface by liquid

20
Q

What is wettability?

A

Tendency of liquid to adhere to solid surface

21
Q

What is amphiphilic?

A

Has both hydrophilic + hydrophobic portions in same molecule

eg. surfactants

22
Q

What is the contact angle equation?

A

ɣsg - ɣsl - ɣlg COSθ

ɣsg = solid + gas
ɣsl = solid + liquid
ɣlg = liquid + gas
23
Q

What are the uses of surfactants?

A 
Detergents
Emulsifying agent
Solubilising agent
Wetting agent 
Foaming agent
Flocculating agent
24
Q

What does the hydrophilic part do?

A

Interact with H2O surface

25
Q

What does the hydrophobic part do?

A

Try to get away

26
Q

What happens when a liquid’s surface is saturated with surfactant molecules?

A

Excess surfactant molecules sink below liquid surface + self-aggregate into micelles

27
Q

What is the Critical Micelle Conc (CMC)?

A

Minimum surfactant conc at which micelles begin to form

28
Q

What happens to the CMC if there is a larger surfactant molecule?

A

Lower it is

29
Q

What is Traube’s Rule?

A

Molar conc of surfactants needed to achieve a certain surface tension decrease by 3 fold with each -CH2 unit within the homologous series

Pharmaceutics (21 decks)

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