Colloids

Question 1

What are colloids?

Answer 1

Is a dispersion of one phase to another continious phase where the dispersed phase is made from particles that are small

Question 2

What is an example of a colloid?

Answer 2

e.g. gas and solid would be pollution and gas and liquid would be aerosols

Question 3

What is solution?

Answer 3

Is a dispersion of molecules if a material in a liquid medium and is clear

Question 4

What are the size of molecules in colliods?

Answer 4

0.1 to 10 micrometres

Question 5

What theory governs the interaction of particles and let us understand the behaviour

Answer 5

The DLVO theory

Question 6

What happens when something is suspended into an aqueuous medium?

Answer 6

A particle will almost certainly have a charge in its surface

Question 7

What happens to a charged particle?

Answer 7

• particle will have charge on surface eg negative.
• this negative charge attracts positive held close to the surface as fixed layer called stern layer
• now on the outside of particle most of the charge on particle has been screened so still negative charge.
• so outside stern layer there is a diffuse layer, an in-balance of ions that balances out charge on the particle so more positive

Question 8

what happens to the electrical potential as the distance from the the particle surface increases?

Answer 8

it decreases

Question 9

what are the 2 ways particles are stabilised?

Answer 9

• steric stabilisation

- elecrostatic stabilisation

Question 10

what does steric stabilisation mean?

Answer 10

the coating of the particle in an polymer which is inert so they don’t interact

Question 11

what is electro static stabilisation (zeta-potential)?

Answer 11

involving the surface charge on the surface of the particles. if zeta potential is great than + or - 30mV means its stable state.

Question 12

what does the zeta potential govern?

Answer 12

the electrokinetic behaviour of the particles such as electrophoresis and sedimentation

Question 13

what is the zeta potential dependant on?

Answer 13

-stern potential and ionic strength medium

Question 14

what is zeta potential?

Answer 14

is the voltage at the edge of the diffuse layer where it meets the surrounding liquid

Question 15

what is the stern potential?

Answer 15

the potential with the fixed layer

Question 16

what is the stern potential dependant of?

Answer 16

particle chemistry and surface charge (pH) and presence of absorbed material

Question 17

what will happen to the rate of sedimentation with a flocculated system?

Answer 17

settle faster

Question 18

what will happen to the rate of sedimentation with a deflocculated system?

Answer 18

settle slower

Question 19

what is the effect of reducing particle size?

Answer 19

• will increase diffusion
• reduce sedimentation
• effect dissolution behaviour

Question 20

what is the effect of increasing viscosity?

Answer 20

• reduce diffusion
• reduce sedimentation
• overall effects are dependant on particle size

Question 21

what is the effect of increasing density of the medium?

Answer 21

• no effect
• reduce sedimentation
• beneficial for most pharmaceutical suspensions

Question 22

Is deflocculation reversible or irreversible?

Answer 22

irreversible

Question 23

Is flocculation reversible or irreversible?

Answer 23

reversible

Question 24

What is a surfactant?

Answer 24

Are surface active agents

Question 25

What is an amphiphile?

Answer 25

Something that is happy to be in both water and oil

Question 26

What is the structure of a surfactant?

Answer 26

Tail: lipophilic and head: hydrophilic

Question 27

Where do you find surfactants?

Answer 27

Chocolate, washing up liquid ,ice cream, beer

Question 28

What happens to surface tension when surfactants are added?

Answer 28

They are lowered

Question 29

What do surfactants do to a liquid?

Answer 29

Interfere with intermolecular bonding of the liquid thats why they are used fo wetting and emulsifying?

Question 30

What is surface tension?

Answer 30

An interface between two things like water and air/oil has cohesive forces act on molecules in bulk of liquid

Question 31

What happens at the surface during surface tension?

Answer 31

Cohesive forces acts to pull molecules into bulk this acts to reduce surface area

Question 32

What is waters surface tension?

Answer 32

72mN/m which is high most others will be lower

Question 33

What happens when the temperature is increased how does this effect surface tension?

Answer 33

Decreases surface tension

Question 34

When do micelles form?

Answer 34

Once added surfactant molecules have formed a complete monolayer at the liquid-air interface, any additional surfactant must remain in solution. These extra surfactant molecules then self-assemble so that their hydrophobic regions are kept from water forming micelles

Question 35

What is the name of the concentratin at which micelles form?

Answer 35

Critical micelle concentration this depends on both the surfactant and medium

Question 36

What factors affects Critical micelle concentration (CMC)?

Answer 36

- increasing in hydrocarbon chain length increases hydrophobicity, decreasing CMC and increasing micellar size for both ionic and non ionic surfactnats - non ionic surfactants have much lower CMCs and higher aggregation numbers - effect of counterion - temp chsnge - effect of addition of electrolytes

Question 37

What are the pharmaceutical uses for surfactants?

Answer 37

- to aid solubilisation - as emulsifers - as antibacterial cleaning agents - as penetration enhancers - as penetration enhancers - as drug delivery vehicles

Question 38

What is an emulsion?

Answer 38

2 immiscible liquids one finely subdivided in the other 2 phases continous and disperse

Question 39

How do you distinguise between 2 main liquids in an emulsion?

Answer 39

By doing a conductivity test

Question 40

Why are emulsions inherently unstable ?

Answer 40

Due to high interfacial tension

Question 41

What are the size of emulsion droplets?

Answer 41

Not unifrom, relatively low number of large droplets and lots of small ones

Question 42

How does the conductivity test work?

Answer 42

If water is the conrinuous phase it will conduct elevtricity through it so the light bulb will light up

Question 43

How does the dye solublity test work?

Answer 43

If the dye is water solube then it will partition into the water phase as either dropelets of change the full solution around the droplets the dye colour

Question 44

What does a high interfacial/surface tension do to the stability?

Answer 44

Reduce it so its unstable

Question 45

What are some types of emulsifying agents?

Answer 45

- surfancants - interfacial complexes - hydrophilic colloids - solid particles

Question 46

What may happen when surfactants accumulate at an interfeace to do with their film formed?

Answer 46

- sufactans such as sodium dodeyl (lauryl) sulphate it has a very high charge on its head group so there will be replusion between neighbouring surfactants. The interface will not be rigid - sodium oleate forms a condensed film and will stay in play as the place and the head group isnt as strong the long tail creates condesed film

Question 47

Why are all surfactnats not good emulsifyers?

Answer 47

Headgroup is critical

Question 48

Why do you use a mixer of surfancants as emulsifyers rather than just one?

Answer 48

Inorder to make interfacial complexes which could be 2 surfactants or a surfactant and a long alcohol to make a better film, film formed makes them more viscous, high flexibility and lower interfacial tension

Question 49

How may instablitiy manifest itself in an emulsion?

Answer 49

- flocculation - coalescene - phase inversion - creaming - cracking