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PL1002 > Surface > Flashcards

Surface Flashcards

1
Q

Interfacial Tension

A

Force per unit length that exists at an interface between 2 immiscible liquids or 2 solids or a solid and a liquid

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2
Q

Interface

A

The boundary between 2 phases

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3
Q

Why does interfacial tension exist?

A

Due to molecules at the interface experiencing unequal attractive forces compared to those in the bulk

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4
Q

Emulsion

A

Oil and water are immiscible due to interfacial tension so a surfactant is used to allow them to mix by reducing tension

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5
Q

Surface tension

A

Molecules on the surface of a liquid experience a force inwards towards the bulk as there is no force pulling them up

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6
Q

Tension

A

Force per unit length

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7
Q

Units of tension

A

N/mm or dynes per cm

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8
Q

Tension of water

A

72.8 mN/m

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9
Q

Why does water have a high surface tension?

A

Due to H bonding

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10
Q

What happens to surface tension as temperature increases?

A

As temperature increases, surface tension decreases due to IM forces decreasing

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11
Q

Ring Method

A

Ring held on liquid surface and ring tensiometer measures the force per distance required to remove the ring from the liquid surface. Can be used in surface and interfacial tension with 0 contact angle and no wave motion

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12
Q

Wilhelmy Plate Method

A

Use plate instead of ring with same principles

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13
Q

Capillary Rise Method

A

Measure distance liquid travels up capillary tube - can only be used for surface tension and is more subjective than ring method but cheaper. The diameter of the rube has significant bearing

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14
Q

Spreading co-efficient equation

A

S = γΑ - (γB - γΑ/Β)
γΑ = surface tension of surface being spread on
γB = surface tension of material being spread
γΑ/Β = interfacial tension between the 2 materials

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15
Q

Work of cohesion

A

Work required to break apart the forces within a single liquid

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16
Q

Work of cohesion equation

A

Wc = 2γB
2 times the surface tension of the liquid being broken

17
Q

Work of adhesion equation

A

Wa = γΑ + γB - γΑ/Β

18
Q

Work of adhesion

A

Forces between 2 immiscible liquids

19
Q

Mutual saturation

A

Interfacial tension is reduced and Sfinal is negative

20
Q

What happens to spreading co-efficient as C chain length of an oil increases

A

Spreading co-efficient decreases

21
Q

Wetting

A

Spreading of a liquid on a solid

22
Q

What does higher contact angle mean for spreading?

A

Poorer spreading

23
Q

Young’s equation for contact angle and surface tension

A

Wsl = γLV (1 + cosΘ)

24
Q

Critical surface tension (γc)

A

The minimum surface tension of a liquid required to give you complete wetting.

25
Q

Critical surface tension of solid hydrocarbons

A

Low γc

26
Q

What are surfactants used for?

A

Used to improve wetting or to allow 2 immiscible liquids to mix by reducing interfacial tension

27
Q

What is the HLB?

A

Hydrophilic-Lipophilic balance is the size of the head group to the tail group

28
Q

What are surfactants used for in pharmacy?

A

Control the size of the droplets in eye dropper
Wetting of particles in suspension
Improve drug absoprtion

29
Q

What do surfactants do in water?

A

Reduce surface tension by adsorbing at the interface between air and water

30
Q

How do surfactants work in water?

A

They exchange molecules from the surface to the bulk over and over again. They interfere with H bonding between the H2O molecules at the surface by the head groups being present

31
Q

What happens when the surface of a liquid is saturated with surfactant?

A

The critical micelle concentration is reached

32
Q

What is the average lifespan of a micelle?

A

1/10-2 to 1/10-9 seconds

33
Q

What happens as the surface tension plateaus against surfactant concentration?

A

The CMC is reached

34
Q

What happens to the CMC as the hydrophobic tail length increases?

A

CMC value decreases but after 16-18C CMC does not change due to steric hindrance of the tail

35
Q

What is the aggregation number?

A

The number of surfactants that come together to form a single micelle

36
Q

What happens to CMC as aggregation increases?

A

CMC decreases

PL1002 (6 decks)

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