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Flashcards in methods of formulation 1 Deck (30):
1

what is the size difference between colloid and coarse dispersions?

colloid: 1nm - 1um
coarse: >1um

2

what property must a colloid have in order for it to be classified as a colloid?

it must NOT settle under gravity

3

what properties do lyophilic sols exhibit?

high viscosity
asymmetrical particles
stable in presence of electrolytes

4

what properties do lyophobic sols exhibit?

low viscosity
symmetrical particles
unstable in presence of electrolytes

5

How are lyophilic sols formed?

by surfactants forming into micelles

6

How are lyophobic sols formed?

by dispersions of oil in water

7

Lyophilic colloids form spontaneously, but how do you form lyophobic colloids?

by dispersion (breakdown of coarse materials by colloid mills or by ultrasonic treatment) or by condensation (rapid production of a supersaturated solution by lowering temp)

8

What 3 ways can be used to purify colloids?

- dialysis
- electrodialysis (electrodecantation)
- ultrafiltration

9

Other than spherical, what shape can colloidal particles be?

prolate ellipsoids (rugby ball shape)
oblate ellipsoids (discus shape)

10

Below what size will particles sediment?

0.5um (any lower, and they have to be sedimented by centrifugation)

11

What is the difference between coagulation and flocculation?

Coagulation: irreversible aggregation
Flocculation: reversible aggregation

12

How are gels formed?

by aggregation of colloidal sol particles

13

A gel rich in liquid is called a ...

jelly

14

A gel with no liquid is called a ...

zerogel e.g. sheet gelatin, tragacanth flakes

15

What are gels from lyophobic sols made from and what is their structure?

- clays (e.g. bentonite)
- the face of the particle is -ve and the edge is +ve so the structure is a 'card floc' shape

16

Lyophobic gels show thixotropy, what is this?

gel-sol-gel due to the weak forces holding the particles together
shaking the gel --> sol
upon standing --> gel again

17

What are the 2 types of gels from lyophilic sols?

type I: irreversible, covalent bonds, have a cross linking agent, swell in water but don't dissolve due to the cross links
type II: reversible, weak H bonds, thixotropy, form micelles (the higher the temp, the more micelles)

18

What is the relation between CMC and length of hydrophobic chains?

CMC decreases with increasing lengths of hydrophobic chains

19

How many surfactants make up a micelle and what is the diameter of a micelle?

50-100
diameter = 2.5nm

20

what is a suspension and what is it used for?

coarse dispersion of insoluble particles >1um
- for the admin of poorly soluble drugs

21

What 3 things should suspensions show?

- shouldn't settle too quickly
- shouldn't aggregate and should be easily re-suspended
- viscosity should allow for pouring/admin through a syringe needle

22

are emulsions stable?

no - only if globules retain initial character and remain uniformly distributed

23

what is separation of an emulsion called?

cracking/breaking

24

what is creaming?

when disperse phase in emulsions sinks or floats due to density differences between the 2 phases

25

How can you increase emulsion stability?

- reduce globule size
- decreased density differences
- increase viscosity of continuous phase

26

What is a foam?

FGS

27

What is an aerosol?

liquids/solids in a gas
- If liquid e.g. mist, fog
- if solid e.g. smoke

28

What is the ideal aerosol particle size for inhalers?

1-5um
>10 = particles deposited in mouth/throat
<0.5um = particles exhaled

29

Are foams stable?

no - due to tendency of liquid film to drain and thin/rupture

30

What is the difference between a foam breaker and a foam inhibitor?

both to prevent foams being formed as they are unstable
foam breaker: basically surfactants, causing rupture
foam inhibitor: adsorb at the air/water interface, disrupting the foam e.g. silicone