Emulsions (exam 2) Flashcards
emulsion
mixture of two or more immiscible liquids
in a emulsion, liquids are made miscible by using
emulsifying agents
emulsion is a ________________
the dispersed phase is _________________
dispersion medium is ________________
two phase system
internal phase
external/continuous phase
advantages of emulsions
stable and homogenous
good palatability of distasteful oil
small oil globules more digestible and absorbed
less irritation on skin
liquid emulsions
oral
topical
parenteral
semi solid emulsions
topical
O/W (oil in water) emulsion
internal phase - oil
external phase - water
W/O (water in oil) emulsion
internal phase - aqueous
external phase - oil
emulsifiers favor a particular ________________ and form either _______________ emulsions
emulsion type
w/o or o/w
the phase presenting in the greater concentration tends to be
the external phase
emulsifiers can overcome
an unfavorable phase ratio
the phase that is being added tends to be the
external phase
inversion of emulsions occurs when
emulsion prepared by heating is cooled
volume of internal or external phase changes
emulsions are
physically unstable
creaming
migration of droplets of the internal phase to the top or bottom of the emulsion
flocculation
small spheres of oil stick together to form flocs, but the drops remain separated
coalescence
merging of small droplets into larger droplets
breaking is ______________ combined
coalescence and creaming
breaking
oil separates completely from the water so it floats at top in a single, continuous layer
which processes are reversible?
irreversible?
creaming and flocculation
breaking and sometimes flocculation
Surface tension theory
tendency of liquids to have minimal surface area
if drops come into contact, they join
emulsifiers facilitate the breakup of large globules by
lower the interfacial surface tension
reduce repellant force
diminish liquids attraction for its own molecules
oriented wedge theory
molecular layer of emulsifying agent is curved around a droplet of internal phase based on hydrophilic/hydrophobic parts
plastic or interfacial film theory
emulsifier surrounds the droplets of internal phase as a thin layer or film
prevents contact and join of internal phase
two step process of emulsification
lowering interfacial tension
formation of protective wedge film around droplet
an emulsifier concentrates at
the interface of two immiscible phases
emulsifying agent with relatively strong hydrophilic group produces a
O/W emulsion
emulsifying agent with relatively strong hydrophobic group produces a
W/O emulsion
examples of emulsifiers
surfactants
stabilizers
thickeners
surfactants can function as
solubilizers
wetting agents
flocculating agent
emulsifying agent
anionic surfactants
at pH over 8
soaps and sulfonates
cationic surfactants
at pH 3-7
benzalkonium chloride
nonionic surfactants
at pH 3-10
sorbitan esters
polyoxyethylene derivatives
a surfactant that produces an unstable emulsion (_______________), should be used in combination with a second substance (____________________) which stabilizes the product
primary emulsifier
stabilizer, secondary emulsifier
high molecular weight alcohol stabilizers
sterile alcohol
cetyl alcohol
cholesterol and derivatives
colloidal clays stabilizers
magnesium hydroxide
aluminum hydroxide
bentonite
carbohydrate thickeners
acacia
pectin
tragacanth
agar
microcrystalline cellulose
protein thickeners
gelatin
egg yolk
casein
emulsifier should have HLB value similar to
external or internal phase
hydrophilic emulsifiers (o/w) HLB value
8-18
lipophilic emulsifiers (w/o) HLB value
3-6
methods to prepare emulsions
continental or dry gum method
English or wet gum method
bottle or Forbes bottle method
4:2:1 method
4 parts oil
2 parts water
1 part gum
order of mixing for dry gum method
1 part gum –> 4 parts oil –> 2 parts water
order of mixing for wet gum method
1 part gum –> 2 parts water –> 4 parts oil
Forbes bottle method is used for emulsions of
volatile oils or oils with low viscosity
microemulsions
stable, transparent emulsions
rapid absorption (oral/transdermal)
diameter of droplets is small
most _________ undergo oxidation, so a ___________ is needed
oils
antioxidant or chelating agent
chelating agents
organic compounds that form complexes with metal ions and inactive oxidation process
auxiliary label for emulsions
container must be tightly closed
shake well
antioxidants for aqueous systems
ascorbic acid
sodium bisulfate, metabisulfite
sodium thiosulfate
antioxidants for oil systems
ascorbyl palmitate
butylated hydroxytoluene
tocopherol
sulfur dioxide
chelating agents examples
edetic acid
edetate disodium
calcium disodium edetate
citric acid
emulsions should be protected from
freezing
excessive heat
oral in the fridge
external at room temp
