Jihong Han's lectures > Colloidal dispersions > Flashcards

Colloidal dispersions Flashcards

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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
Shear plane can be pushed further away from the surface due to the adsorption of polymers on to the particles. TRUE OR FALSE?
TRUE
26
What is zeta potential?
Is the potential at the shear plane
27
Zeta potential can be reduced due to the adsorption of polymers. TRUE OR FALSE?
TRUE
28
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?
TRUE
29
Do electrolytes compress the double layer and hence reduce the zeta potential? TRUE OR FALSE?
TRUE
30
What is electrophoresis?
is when charged particles move against a stationary | medium in an electrical field
31
What is microelectrophoresis?
The movement of the particles is observed using a microscope
32
What can the zeta potential be measured by?
electrophoresis
33
What is meant by aggregation?
particles coming together forming groups
34
What is meant by coagulation?
the particles come together forming tight clusters. | Difficult to re-disperse
35
what is meant by flocculation?
there are greater spaces between the particles | grouped together. The particles form a loose structure and are easy to re-disperse
36
What does the DLVO theory suggest?
theory assumes that the potential due to electrical repulsion and van der Waals attraction are additive: VT = VA + VR
37
All particles experience van der waals forces. TRUE OR FALSE?
TRUE
38
What forces causes collections of dispersed particles to aggregate?
Van der waals
39
What two repulsive forces keeps particles separate?
- Electrical repulsion (due to zeta potential) | - Steric protection
40
What is steric protection?
Protective polymer layer on the surface of particles
41
On the total potential of interaction curves what occurs in the primary minimum?
at a small distance from the surface, attraction predominate. So there is a deep well approaching zero distance
42
On the total potential of interaction curves what occurs in the primary maximum?
in the intermediate distance range, repulsive forces predominate. This is the energy barrier that stabilises the dispersions
43
On the total potential of interaction curves what occurs in the secondary minimum?
at a long distance from the surface where repulsive force falls more quickly than attractive force, forming a small (shallow) minimum
44
Where can controlled flocculation occur?
At the secondary minimum
45
An Increase in ionic strength means an increase in electrolytes concentration, and consequently an decrease of the thickness of the doublelayer. TRUE OR FALSE?
TRUE
46
VR will be reduced at a given distance H from the surface of a particle. TRUE OR FALSE?
TRUE
47
An increase in ionic strength results in a lower VR, | and consequently lower VT at a given distance H. TRUE OR FALSE?
TRUE
48
How are lyophilic colloids stabilised?
By a combination of charge interaction and solvation
49
Are lyophilic colloids less or more sensitive to electrolytes compared to lyophobic colloids?
Less sensitive
50
When are lyophilic colloids considered to become lyophobic?
When the macromolecules are dehydrated by the addition of sufficient quantity of solvent such as alcohol and acetone
51
What is coacervation?
The collection of colloid rich layer after the addition of another substance
52
What can be added to lyophobic colloids to make them more stable?
Addition of polymeric materials such as non ionic surface active agents, gum and cellulose derivatives
53
The hydration of the polymeric materials is a main factor to stabilise the colloids. TRUE OR FALSE?
TRUE
54
Sterically stabilised colloidal systems are less sensitive to electrolytes and sometimes are called protective colloids. TRUE OR FALSE?
TRUE
55
Colloidal particles cannot be linked together by polymers leading to flocculation. TRUE OR FALSE?
FALSE
56
What are the three conditions that have to be met for bridge flocculation to occur?
- 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
What are associated colloids?
This is when surfactants associate together to form micelles which falls into size range of colloids.
58
About how many molecules associate together to form micelle?
50-100
59
After the surface is saturated by surfactants, they tend to form micelles to shield the hydrophobic core from the aqueous phase. TRUE OR FALSE?
TRUE
60
What is the critical micelle concentration (CMC)?
Is the concentration at which micelles are first formed
61
The rate of increase in the number of ‘particles’ will change dramatically at CMC. TRUE OR FALSE?
TRUE
62
Where are hydrophobic molecules solubilised in a micelle?
Solubilised in the hydrophobic cores of the micelles
63
What four factors affect the determination of CMC?
- Osmotic pressure - Solubility of poor water soluble drugs - Turbidity - Surface tension
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