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Jihong Han's lectures > Colloidal dispersions > Flashcards

Colloidal dispersions Flashcards

1
Q

What is the dispersed phase?

A

The particles that are dispersed

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2
Q

What is the continuous phase?

A

The medium that are the particles are dispersed

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3
Q

What is colloidal dispersions?

A

Disperse systems with particle sizes between 1 and 1000nm

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4
Q

What is coarse dispersions?

A

Particles greater than 1000nm

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5
Q

When the particle size is reduced the total surface area is increased. TRUE OR FALSE?

A

TRUE

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6
Q

Interfacial energy will increase as a result of the increased surface area, the colloidal particles tend to aggregate due to the high interfacial energy. TRUE OR FALSE?

A

TRUE

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7
Q

What is the difference between lyophobic and lyophilic?

A

lyophobic- Materials that do not allow water

lyophilic - Can mix with liquids

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8
Q

What are the features for lyophobic colloids?

A
  • Thermodynamically unstable
  • Not re-dispersible after dried

-Dispersion process does not
occur automatically; need work

-Interaction between particles
and medium weak

-Sensitive to the addition of
electrolytes, resulting in
flocculation or aggregation

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9
Q

What are the features for lyophilic colloids?

A

-Thermodynamically stable

-Redispersible after dried (if
media is added again)

-Dispersion process occurs
automatically after solvent is
added

-Strong interaction between
particle and medium, due to
solvation, hydration

-Not sensitive to electrolytes.
Can be salted out at high
concentrations of electrolytes

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10
Q

Lyophilic colloids – the dispersion process is spontaneous upon the addition of the continuous phase. TRUE OR FALSE?

A

TRUE

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11
Q

Lyophobic colloids - work is needed to break down the

disperse phase. TRUE R FALSE?

A

TRUE

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12
Q

What is brownian motion?

A

colloidal particles are in random collisions with the molecules of the dispersion medium, resulting in the irregular motion of the colloidal particles

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13
Q

What method can be used for the preparation of lyophobic colloids?

A

The condensation method

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14
Q

The larger the particles, the weaker the brownian motion. TRUE OR FALSE?

A

TRUE

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15
Q

Is the movement of particles a result of brownian motion?

A

TRUE

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16
Q

Larger particles settle faster. The rate is directly

proportional to the square of radius. TRUE OR FALSE?

A

TRUE

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17
Q

Stoke’s law does not apply to spherical particles. TRUE OR FALSE?

A

TRUE

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18
Q

Brownian motion disrupts the sedimentation process. TRUE OR FALSE?

A

TRUE

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19
Q

Sedimentation rate is not directly proportional to the

density difference between particle and medium. TRUE OR FALSE?

A

FALSE

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20
Q

High viscosity slows down the sedimentation. TRUE OR FALSE?

A

TRUE

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21
Q

What method can be used to improve stability in a solution for example?

A

Increasing viscosity to slow down sedimentation

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22
Q

What is the Tyndall effect?

A

when a beam of light pass through a colloidal dispersion, a visible bright cone can be seen from the
side

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23
Q

Why can colloidal particles acquire charge?

A
  • Ion dissolution
  • Ionisation
  • Ion adsorption, mostly negatively charged
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24
Q

What is Shear plane?

A

the boundary between the moving particle and the surrounding medium

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25
Q

Shear plane can be pushed further away from the surface due to the adsorption of polymers on to the particles. TRUE OR FALSE?

A

TRUE

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26
Q

What is zeta potential?

A

Is the potential at the shear plane

27
Q

Zeta potential can be reduced due to the adsorption of polymers. TRUE OR FALSE?

28
Q

Counter ions are attracted toward the surface. The closer to the surface, the higher the concentration of the counter ion; the further away from the surface, the lower the concentration of the counter ion, until it becomes electrically neutral. Is this statement TRUE OR FALSE?

29
Q

Do electrolytes compress the double layer and hence reduce the zeta potential? TRUE OR FALSE?

30
Q

What is electrophoresis?

A

is when charged particles move against a stationary

medium in an electrical field

31
Q

What is microelectrophoresis?

A

The movement of the particles is observed using a microscope

32
Q

What can the zeta potential be measured by?

A

electrophoresis

33
Q

What is meant by aggregation?

A

particles coming together forming groups

34
Q

What is meant by coagulation?

A

the particles come together forming tight clusters.

Difficult to re-disperse

35
Q

what is meant by flocculation?

A

there are greater spaces between the particles

grouped together. The particles form a loose structure and are easy to re-disperse

36
Q

What does the DLVO theory suggest?

A

theory assumes that the potential due to electrical repulsion and van der Waals attraction are additive:
VT = VA + VR

37
Q

All particles experience van der waals forces. TRUE OR FALSE?

38
Q

What forces causes collections of dispersed particles to aggregate?

A

Van der waals

39
Q

What two repulsive forces keeps particles separate?

A
  • Electrical repulsion (due to zeta potential)

- Steric protection

40
Q

What is steric protection?

A

Protective polymer layer on the surface of particles

41
Q

On the total potential of interaction curves what occurs in the primary minimum?

A

at a small distance from the surface, attraction predominate. So there is a deep well approaching zero distance

42
Q

On the total potential of interaction curves what occurs in the primary maximum?

A

in the intermediate distance range, repulsive forces predominate. This is the energy barrier that stabilises the dispersions

43
Q

On the total potential of interaction curves what occurs in the secondary minimum?

A

at a long distance from the surface where repulsive force falls more quickly than attractive force, forming a small (shallow) minimum

44
Q

Where can controlled flocculation occur?

A

At the secondary minimum

45
Q

An Increase in ionic strength means an increase in electrolytes concentration, and consequently an decrease of the thickness of the doublelayer. TRUE OR FALSE?

46
Q

VR will be reduced at a given distance H from the surface of a particle. TRUE OR FALSE?

47
Q

An increase in ionic strength results in a lower VR,

and consequently lower VT at a given distance H. TRUE OR FALSE?

48
Q

How are lyophilic colloids stabilised?

A

By a combination of charge interaction and solvation

49
Q

Are lyophilic colloids less or more sensitive to electrolytes compared to lyophobic colloids?

A

Less sensitive

50
Q

When are lyophilic colloids considered to become lyophobic?

A

When the macromolecules are dehydrated by the addition of sufficient quantity of solvent such as alcohol and acetone

51
Q

What is coacervation?

A

The collection of colloid rich layer after the addition of another substance

52
Q

What can be added to lyophobic colloids to make them more stable?

A

Addition of polymeric materials such as non ionic surface active agents, gum and cellulose derivatives

53
Q

The hydration of the polymeric materials is a main factor to stabilise the colloids. TRUE OR FALSE?

54
Q

Sterically stabilised colloidal systems are less sensitive to electrolytes and sometimes are called protective colloids. TRUE OR FALSE?

55
Q

Colloidal particles cannot be linked together by polymers leading to flocculation. TRUE OR FALSE?

56
Q

What are the three conditions that have to be met for bridge flocculation to occur?

A
  • The polymer has two or more segments that can adsorb on to the particles
  • The polymer molecules are long enough to adsorb on to two particles
  • The surface coverage of the particle is low
57
Q

What are associated colloids?

A

This is when surfactants associate together to form micelles which falls into size range of colloids.

58
Q

About how many molecules associate together to form micelle?

59
Q

After the surface is saturated by surfactants, they tend
to form micelles to shield the hydrophobic core from
the aqueous phase. TRUE OR FALSE?

60
Q

What is the critical micelle concentration (CMC)?

A

Is the concentration at which micelles are first formed

61
Q

The rate of increase in the number of ‘particles’ will change dramatically at CMC. TRUE OR FALSE?

62
Q

Where are hydrophobic molecules solubilised in a micelle?

A

Solubilised in the hydrophobic cores of the micelles

63
Q

What four factors affect the determination of CMC?

A
  • Osmotic pressure
  • Solubility of poor water soluble drugs
  • Turbidity
  • Surface tension

Jihong Han's lectures (11 decks)

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