Dr Mok Flashcards
what is a solution?
dissolved solute in a solvent
what is a disperse system?
when one phase is distributed through another
what is a colloidal dispersion?
two phase sytem of matter <1 micrometer
what effect do colloids have?
scatter light (tyndall effect)
molecules are in motion (brownian motion)
adsorption
can be charged (electrophoresis)
stable at rest (thixotropy)
in what forms can disperse and continuous phase colloids be in?
liquid
solid
gas
what are the types of colloids?
lyophobic (solvent hating)
lyophilic (solvent loving)
what is a sol?
colloidal suspension of small solid particles in a continuous liquid medium
what is a gel?
colloidal suspension in which the liquid medium has become viscous enough to act as a solid
what is a two phase gel system?
lyophobic
what is a one phase gel system?
lyophilic
what do gel formulations contain?
gelling agents
humectants
preservatives
water
what are foams?
gases dispersed in a liquid/ solid
what are emulsions?
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
what are suspensions?
course dispersion in which insoluble particles >1 micrometer are dispersed in a liquid medium which is usually aqueous
what is surface tension?
when water molecules are attracted to each other
what is a surfactant?
amphipathic/amphiphillic molecule that consists of a distinct hydrophobic and hydrophilic region
what do surfactants used to help?
adsorption at the oil water interphase as it lowers interfacial tension
what are the two types of ionic surfactants?
anionic (dissociate at high pH ,SDS)
cationic (dissociate at low pH, quaterny ammonium)
why are non-ionic surfactants used ?
less toxic and irritant than ionic surfactants
how does mixing surfactants affect stability?
more stable emulsions
what other classification can surfactants be other than ionic or non ionic?
zwitterionic
what are cosurfactants used for?
help to achieve low interfacial tension
what are co surfactants usually made from?
short chain alcohols
what are the cosurfactant and surfactant mixture able to form?
an efficiently packed film, covering the whole droplet
what are micelles?
colloidal spherical nanoparticles that can be made from ionic or nonionic surfactants.
how are micelles formed?
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
what is the critical micelle concentration (cmc)?
the surfactant concentration at and above which micelles are formed
what are suspending agents used for?
reduce the rate of settling of suspended active ingredients
what is the stokes-einsten equation used for?
diffusion coefficient D
what is ficks first law used for?
brownian motion and diffusion
when particles diffuse from high conc to low conc
what is sedimentation (V) used for?
to see the rate of sedimentation from gravity and drag
what are the ffactors influencing rheology of suspensions?
high volume fractions
particle size
distribution
particle shape
electrostatic interactions
steric hinderance
how can we prevent sedimentation?
smaller particles
decrease density difference
increase viscosity in continuous phase
what are the two layers in the electrical double layer of ions?
stern laer
diffuse layer (zeta potential)
what are the factors affecting zeta potential?
ion concentration and pH of continuous phase
what is the DVLO graph used for?
quantative approach to the stability of lyophobic systems
what is the y and x axis of the DVLO graph?
x is distance
y is attraction
why do you want Vmax to be as big as possible?
to reduce frequency of particles coming too close together
what does high energy repulsion mean?
particles will remain dispersed
what is the difference between particles of suspensions and emulsions?
suspensions have macro particles
emulsions have microparticles
what is phase inversion?
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
what is creaming due to?
density difference between oil and water
the oil droplets tend to concentrate at the top of the emulsion
what is flocculation?
when two or more emulsion droplets aggregate withot losing their individual identity
when does coalescence occur?
when two or more droplets collide and form one larger droplet and is irreversible
what is otwald ripening?
when collisions between two droplets may cause one bigger and one smaller droplet
what is entropic effect (steric)?
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
what are osmotic forces (solvation)?
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
what are the four types of forces?
van der waals, electrostatic repulsion, steric and solvation
what are the four reactions of chemical degradation?
hydrolysis
oxidation
photodegradation
polymerisation
what are the stages of kinetics in chemical degradation?
zero
first
pseudo zero
second
pseudo first
what is stability?
the capacity of a product to remain within specifications to ensure potency, quality or potency
what other types of degradation are there, other than chemical degradation?
physical and microbial degradation
what is the allowable degradation percentage after 5 years?
5%
