Dr Mok

Question 1

what is a solution?

Answer 1

dissolved solute in a solvent

Question 2

what is a disperse system?

Answer 2

when one phase is distributed through another

Question 3

what is a colloidal dispersion?

Answer 3

two phase sytem of matter <1 micrometer

Question 4

what effect do colloids have?

Answer 4

scatter light (tyndall effect)
molecules are in motion (brownian motion)
adsorption
can be charged (electrophoresis)
stable at rest (thixotropy)

Question 5

in what forms can disperse and continuous phase colloids be in?

Answer 5

liquid
solid
gas

Question 6

what are the types of colloids?

Answer 6

lyophobic (solvent hating)
lyophilic (solvent loving)

Question 7

what is a sol?

Answer 7

colloidal suspension of small solid particles in a continuous liquid medium

Question 8

what is a gel?

Answer 8

colloidal suspension in which the liquid medium has become viscous enough to act as a solid

Question 9

what is a two phase gel system?

Answer 9

lyophobic

Question 10

what is a one phase gel system?

Answer 10

lyophilic

Question 11

what do gel formulations contain?

Answer 11

gelling agents
humectants
preservatives
water

Question 12

what are foams?

Answer 12

gases dispersed in a liquid/ solid

Question 13

what are emulsions?

Answer 13

pseudo stable dispersion of at least two immiscble liquids, one of which is dispersed throughout the other in the form of fine droplets stabilised by an emulsifyer

Question 14

what are suspensions?

Answer 14

course dispersion in which insoluble particles >1 micrometer are dispersed in a liquid medium which is usually aqueous

Question 15

what is surface tension?

Answer 15

when water molecules are attracted to each other

Question 16

what is a surfactant?

Answer 16

amphipathic/amphiphillic molecule that consists of a distinct hydrophobic and hydrophilic region

Question 17

what do surfactants used to help?

Answer 17

adsorption at the oil water interphase as it lowers interfacial tension

Question 18

what are the two types of ionic surfactants?

Answer 18

anionic (dissociate at high pH ,SDS)
cationic (dissociate at low pH, quaterny ammonium)

Question 19

why are non-ionic surfactants used ?

Answer 19

less toxic and irritant than ionic surfactants

Question 20

how does mixing surfactants affect stability?

Answer 20

more stable emulsions

Question 21

what other classification can surfactants be other than ionic or non ionic?

Answer 21

zwitterionic

Question 22

what are cosurfactants used for?

Answer 22

help to achieve low interfacial tension

Question 23

what are co surfactants usually made from?

Answer 23

short chain alcohols

Question 24

what are the cosurfactant and surfactant mixture able to form?

Answer 24

an efficiently packed film, covering the whole droplet

Question 25

what are micelles?

Answer 25

colloidal spherical nanoparticles that can be made from ionic or nonionic surfactants.

Question 26

how are micelles formed?

Answer 26

60 random positioned molecules of polysorbate 80 first ggregate into small clusters which come together to form a micelle. highly orded water molecules form cages around the hydrophobic alkyl chains in a surfactant, lipid portions at the edge of the cluster force orders the water formation, all hydrophobic groups are grouped for a water containing micelle to form

Question 27

what is the critical micelle concentration (cmc)?

Answer 27

the surfactant concentration at and above which micelles are formed

Question 28

what are suspending agents used for?

Answer 28

reduce the rate of settling of suspended active ingredients

Question 29

what is the stokes-einsten equation used for?

Answer 29

diffusion coefficient D

Question 30

what is ficks first law used for?

Answer 30

brownian motion and diffusion when particles diffuse from high conc to low conc

Question 31

what is sedimentation (V) used for?

Answer 31

to see the rate of sedimentation from gravity and drag

Question 32

what are the ffactors influencing rheology of suspensions?

Answer 32

high volume fractions particle size distribution particle shape electrostatic interactions steric hinderance

Question 33

how can we prevent sedimentation?

Answer 33

smaller particles decrease density difference increase viscosity in continuous phase

Question 34

what are the two layers in the electrical double layer of ions?

Answer 34

stern laer diffuse layer (zeta potential)

Question 35

what are the factors affecting zeta potential?

Answer 35

ion concentration and pH of continuous phase

Question 36

what is the DVLO graph used for?

Answer 36

quantative approach to the stability of lyophobic systems

Question 37

what is the y and x axis of the DVLO graph?

Answer 37

x is distance y is attraction

Question 38

why do you want Vmax to be as big as possible?

Answer 38

to reduce frequency of particles coming too close together

Question 39

what does high energy repulsion mean?

Answer 39

particles will remain dispersed

Question 40

what is the difference between particles of suspensions and emulsions?

Answer 40

suspensions have macro particles emulsions have microparticles

Question 41

what is phase inversion?

Answer 41

when oil in water particles come together and the charge of the droplets are reduced then once they are incontact the droplets re-align forming water in oil droplets

Question 42

what is creaming due to?

Answer 42

density difference between oil and water the oil droplets tend to concentrate at the top of the emulsion

Question 43

what is flocculation?

Answer 43

when two or more emulsion droplets aggregate withot losing their individual identity

Question 44

when does coalescence occur?

Answer 44

when two or more droplets collide and form one larger droplet and is irreversible

Question 45

what is otwald ripening?

Answer 45

when collisions between two droplets may cause one bigger and one smaller droplet

Question 46

what is entropic effect (steric)?

Answer 46

when two particles come into close contact, the polymer chains tart to overlap, which leads to a loss in the freedom of the polymer chains, which eventually forces the droplets apart again

Question 47

what are osmotic forces (solvation)?

Answer 47

when two particles come into close contact the polymer chains start to overlap, which induces an osmotic gradient, which leads to water entering the concentrated region in attempt to dilute it and in tur forces the particles apart again

Question 48

what are the four types of forces?

Answer 48

van der waals, electrostatic repulsion, steric and solvation

Question 49

what are the four reactions of chemical degradation?

Answer 49

hydrolysis oxidation photodegradation polymerisation

Question 50

what are the stages of kinetics in chemical degradation?

Answer 50

zero first pseudo zero second pseudo first

Question 51

what is stability?

Answer 51

the capacity of a product to remain within specifications to ensure potency, quality or potency

Question 52

what other types of degradation are there, other than chemical degradation?

Answer 52

physical and microbial degradation

Question 53

what is the allowable degradation percentage after 5 years?

Answer 53

5%