disperse systems

Question 1

what is a colloid

Answer 1

a disperse system where one phase is in the form of tiny particles/droplets

Question 2

what type of colloid is an emulsion

Answer 2

liquid in liquid

Question 3

what type of colloid is a suspension

Answer 3

solid in liquid

Question 4

name two types of colloids

Answer 4

emulsion- liquid in liquid
suspension- solid in liquid

Question 5

why use disperse systems

Answer 5

single phases may not be able to provide all the formulation requirements

Question 6

what is an emulsion

Answer 6

liquid medicine where one insoluble liquid is suspended as microscopic droplets in another liquid, usually oil and water=immiscible so 2 separate phases formed, molecular film of emulsifier at interface

Question 7

what occurs at the interface of oil and water in emulsions

Answer 7

molecular film of emulsifier

Question 8

types of emulsions

Answer 8

oil in water
water in oil
water oil water
oil water oil

Question 9

why do emulsions need emulsifiers

Answer 9

stability

Question 10

how are emulsions produced

Answer 10

homogenisation

Question 11

what are suspensions

Answer 11

liquid medicine where insoluble solid (drug) is dispersed as fine particles in liquid

Question 12

what is a vehicle

Answer 12

liquid which particles are suspended in

Question 13

difference between emulsion ad suspension

Answer 13

emulsion is only 2 immiscible liquids, suspension can be any phase

Question 14

describe what an emulsion and suspension look like under microscopes

Answer 14

emulsion- circles, molecular film at interface

suspension- irregular particles

Question 15

physical signs of instability

Answer 15

separation and caking

Question 16

what is separation and describe what it looks like

Answer 16

particles fall due to difference in density, redisperse by shaking

looks like a gradient

Question 17

what is caking and describe what it looks like

Answer 17

high density sediment of particles, difficult to redisperse

solid layer at bottom

Question 18

ways to keep particles suspended/prevent sedimentation

Answer 18

reduce particle size, density match with vehicle, increase viscosity of vehicle

Question 19

what can be used to increase viscosity

Answer 19

thickening agents

entangling soluble polymers- long chains entangle

charge dispersal

pvp, gelatin, cellulose ethers (carboxymethyl), natural polysaccharides (xanthax gum, starch)

Question 20

what is charge dispersal

Answer 20

small plate like charged particles dispersed in liquid which thicken the viscosity, particles repel due to charge so liquid resists movement

Question 21

name some substances that can be used to do charge dispersal

Answer 21

carbomer, bentonite, colloidal silicon dioxide

Question 22

what are flocs

Answer 22

loose weakly bonded particle aggregates

Question 23

how to keep suspension particles suspended

Answer 23

flocculation

add surfactant to adsorbs surface charge or add soluble polymer to adsorb to polymer, shaking bottle will break up the flocs and redisperse to make a uniform suspension

Question 24

how does caking form

Answer 24

particles repel each other then fall into a dense cake, weight of particle presses down on particles below them then theyre forced to aggregate

Question 25

why can flocculated structures be redispersed

Answer 25

flocculated structure is very porous so it doesnt cake (when it settles theres still lots of gaps)

Question 26

what is ostwald ripening

Answer 26

smaller particles have greater solubility than large particles, dissolved molecules crystallise on surface of larger particles so the lattice and size increases

particle size/distribution changes due to temperature fluctuations

Question 27

what can increase the rate of ostwald ripening and why

Answer 27

surfactants because they increase solubility

Question 28

how to prevent caking

Answer 28

flocculation