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Pharmacy Y2- Exam 1 > Colloids > Flashcards

Colloids Flashcards

1
Q

What are colloids?

A

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

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2
Q

What is an example of a colloid?

A

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

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3
Q

What is solution?

A

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

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4
Q

What are the size of molecules in colliods?

A

0.1 to 10 micrometres

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5
Q

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

A

The DLVO theory

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6
Q

What happens when something is suspended into an aqueuous medium?

A

A particle will almost certainly have a charge in its surface

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7
Q

What happens to a charged particle?

A
  • 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
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8
Q

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

A

it decreases

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9
Q

what are the 2 ways particles are stabilised?

A
  • steric stabilisation

- elecrostatic stabilisation

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10
Q

what does steric stabilisation mean?

A

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

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11
Q

what is electro static stabilisation (zeta-potential)?

A

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

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12
Q

what does the zeta potential govern?

A

the electrokinetic behaviour of the particles such as electrophoresis and sedimentation

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13
Q

what is the zeta potential dependant on?

A

-stern potential and ionic strength medium

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14
Q

what is zeta potential?

A

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

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15
Q

what is the stern potential?

A

the potential with the fixed layer

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16
Q

what is the stern potential dependant of?

A

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

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17
Q

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

A

settle faster

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18
Q

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

A

settle slower

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19
Q

what is the effect of reducing particle size?

A
  • will increase diffusion
  • reduce sedimentation
  • effect dissolution behaviour
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20
Q

what is the effect of increasing viscosity?

A
  • reduce diffusion
  • reduce sedimentation
  • overall effects are dependant on particle size
21
Q

what is the effect of increasing density of the medium?

A
  • no effect
  • reduce sedimentation
  • beneficial for most pharmaceutical suspensions
22
Q

Is deflocculation reversible or irreversible?

A

irreversible

23
Q

Is flocculation reversible or irreversible?

A

reversible

24
Q

What is a surfactant?

A

Are surface active agents

25
Q

What is an amphiphile?

A

Something that is happy to be in both water and oil

26
Q

What is the structure of a surfactant?

A

Tail: lipophilic and head: hydrophilic

27
Q

Where do you find surfactants?

A

Chocolate, washing up liquid ,ice cream, beer

28
Q

What happens to surface tension when surfactants are added?

A

They are lowered

29
Q

What do surfactants do to a liquid?

A

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

30
Q

What is surface tension?

A

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

31
Q

What happens at the surface during surface tension?

A

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

32
Q

What is waters surface tension?

A

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

33
Q

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

A

Decreases surface tension

34
Q

When do micelles form?

A

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

35
Q

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

A

Critical micelle concentration this depends on both the surfactant and medium

36
Q

What factors affects Critical micelle concentration (CMC)?

A
  • 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
37
Q

What are the pharmaceutical uses for surfactants?

A
  • to aid solubilisation
  • as emulsifers
  • as antibacterial cleaning agents
  • as penetration enhancers
  • as penetration enhancers
  • as drug delivery vehicles
38
Q

What is an emulsion?

A

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

39
Q

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

A

By doing a conductivity test

40
Q

Why are emulsions inherently unstable ?

A

Due to high interfacial tension

41
Q

What are the size of emulsion droplets?

A

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

42
Q

How does the conductivity test work?

A

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

43
Q

How does the dye solublity test work?

A

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

44
Q

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

A

Reduce it so its unstable

45
Q

What are some types of emulsifying agents?

A
  • surfancants
  • interfacial complexes
  • hydrophilic colloids
  • solid particles
46
Q

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

A
  • 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
47
Q

Why are all surfactnats not good emulsifyers?

A

Headgroup is critical

48
Q

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

A

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

49
Q

How may instablitiy manifest itself in an emulsion?

A
  • flocculation
  • coalescene
  • phase inversion
  • creaming
  • cracking

Pharmacy Y2- Exam 1 (13 decks)

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