Emulsions Flashcards
emulsions are ____ in ___ dispersions
liquid in liquid
true or false
emulsions are thermodynamically stable
FALSE
like suspensions, they’re thermodynamically unstable
how are emulsions stabilized?
by an emulsifying agent - lowers interfacial tension
range of droplet size diameter for emulsions
1-100 micrometers
how can delayed onset be achieved for emulsions?
for ex:
oil soluble drug in an o/w emulsion
the drug will be in the center oil phase. takes time to pass the outer water phase and get into the GI fluid
emulsions are made by _____ equipment that is capable of….
high energy ( ie - homogenizer, blender)
breaking the dispersed phase into very tiny droplets
the addition of _____ makes the emulsion stable
emulsifying agent (emulsifier)
true or false
emulsifying agents are surfactants
TRUE
for an emulsifying agent/surfactant, what way will the hydrophilic head face and the lipophilic tail face BEFORE cmc is reached?
hydrophilic head will face water and lipophilic tail will face air (relatively lipophilic)
**O/W emulsions are formed with what kind of emulsifier?
A HYDROPHILIC EMULSIFIER (with high HLB)
true or false
a high HLB means a lipophilic surfactant
FALSE
high HLB means hydrophilic surfactant
what is the most common emulsion type and is preferred for oral products?
O/W emulsions
bc oily feel in the mouth is objectionable
when are O/W emulsions used as external products?
when a non-greasy feeling and easy to remove/wash is desired
name a food that is an O/W emulsion
mayo
true or false
o/w emulsions are made with hydrophilic emulsifiers
TRUE
true or false
W/O emulsions are formed if a lipophilic emulsifier with a low HLB is used
TRUE
when are w/o emulsions used as external products rather than o/w emulsions?
when emollient, lubricating, or protective properties are desired
true or false
many ointments are emulsions with o/w emulsions
FALSE
W/O - it’s greasy
differentiate between the type of emulsion: cream vs butter
butter is w/o (more greasy!)
cream is o/w
butter is mostly fat or water
fat (W/O emulsion)
HLB of egg yolk
10 - so hydrophilic
that why it’s emulsifer for mayo which is a o/w emulsion
4 ways that we can distinguish types of emulsions and figure out what they are
-feel on the skin
-dye solubility test
-conductivity test
-dilution test
explain the dye solubility test to determine the type of emulsion
a water soluble dye (like methylene blue/brilliant blue) can be dusted on the emulsion
if only the internal drug gets blue - you know that it’s w/o
if the external medium becomes blue, it’s o/w
explain the conductivity test to distinguish the types of emulsions
electrodes are placed in the emulsion
o/w WILL carry a current and w/o will not
explain the dilution test for distinguishing the types of emulsions
O/W emulsions can be diluted with water – will dilute nicely
If you add extra water to a W/O emulsion, it will make phase separation!!
W/O emulsions can be diluted with oil
name a LIPOPHILIC dye that can be used in the dye solubility test to distinguish the types of emulsions
Sudan IV
will stain LIPIDS clear red
emulsifying agents will _____ at the interface between the 2 phases and do what?
ADSORB
REDUCE THE INTERFACIAL TENSION
Name 2 types of emulsifying agents
ionic emulsifiers and non-ionic emulsifiers
when IONIC emulsifers are placed in an o/w emulsion, what will happen?
a charged layer will be formed around the oil droplet
this will create an electrostatic repulsion and will reduce the tendency of adjacent particles to coalesce (join together)
explain how non-ionic emulsifiers work and name 3
there are repulsive effects in the continuous phase due to the long chains
they can also increase the viscosity by forming multimolecular films. they are generally high in MW, and thus can increase the viscosity of the continuous phase and reduce the mobility of the dispersed particles, stabilizing them
acacia, tragacanth, cellulose
emulsifying agents should be adsorbed _____ around the _____ and wetted by _____
QUICKLY around the dispersed phase droplets and wetted by both WATER AND OIL
true or false
an emulsifier film should be formed RAPIDLY during the emulsification process
true
an emulsifer film must be _____
explain
elastic – enough so they can bounce off each other and don’t aggregate
name the 2 types of films that can be formed and which emulsifying agent does what
monomolecular film (ionic)
multimolecular film (non-ionic)
emulsifiers reduce the interfacial tension below…..
10 dynes/cm
true or false
emulsifiers decrease the viscosity of the emulsion
FALSE
increase
emulsifiers must be effective at what concentration
LOW, non-toxic concentrations
name 6 hydrophilic emulsifying agents
what kind of emulsions do they form?
acacia
tragacanth
pectin
microcrystalline cellulose
glyceryl monostearate
bentonite
O/W EMULSIONS —— EMULSIFYING AGENT MATCHES WITH THE EXTERNAL MEDIUM!!!!
Name 6 lipophilic emulsifying agents and what type of emulsions they can make
cholesterol
wool fat
carbon black
talc
calcium palmitate
some spans (sorbitan esters)
W/O EMULSIONS — EMULSIFYING AGENT GOES WITH EXTERNAL PHASE
True or false
hydrophilic emulsifying agents favor to create an O/W emulsion
TRUE
true or false
the higher the HLB of an emulsifier, the more lipophilic it is
FALSE - more hydrophilic
which have higher HLB - spans or tweens?
TWEENS have high HLB values – thus favor o/w emulsions over spans
**span 80 vs span 20
span 80 - has 18 carbons in the fatty acid chain
span 20 - has 12 carbons in the fatty acid chain
ZERO — MEANS NO DOUBLE BONDS IN THE CHAIN
LONGER FATTY ACID CHAIN = MORE HYDROPHOBIC. THUS SPAN 80 IS MORE HYDROPHOBIC THAN SPAN 20**
***SPAN 80 VS TWEEN 80
TWEEN 80 always has much higher HLB bc it has PEG attached which is HYDROPHILIC
EVEN WITH SAME CHAIN LENGTH — TWEEN IS MORE HYDROPHILIC BC HAS PEG AS PART OF THE HEAD
What is “creaming” and in which emulsions does it happen?
upward movement of the dispersed droplets (OIL)
happens in O/W emulsions
associated with physical instability of emulsions
what is sedimentation
the downward movement of dispersed droplets (water)
both creaming and sedimentation pose the risk of what?
coalescence — bc they bring particles together
true or false
creaming or sedimentation always results in the breakdown of the emulsion
FALSE - not necessarily
the dispersed droplets can be re-dispersed with mild agitation (shaking). the droplets still maintain their individuality
when ____ occurs to an emulsion, simple mixing fails to resuspend the globules in the stable emulsified form
BREAKING
why does mixing not fix a emulsion that has broken
bc the film surrounding the particles is destroyed. the oil will coalesce together, and there will be phase separation
TRUE OR FALSE
breaking of an emulsion is irreversible
TRUE
irreversible coalescence of emulsion droplets can be called ___ or ____
breaking or cracking
name and explain 2 ways that emulsions can undergo phase inversion***
-adding an electrolyte (ie - o/w emulsion has sodium stearate (Hydrophilic) as the emulsifier. when calcium chloride is added, CALCIUM STEARATE (lipophilic emulsifier) will be formed — WHICH FAVORS W/O EMULSION!!!)
-changing the phase volume ratio
IE - adding a lot of water to a w/o emulsion will result in phase inversion to o/w emulsion (if more than 70% of the total emulsion volume is added)
name 2 things that can DESTABILIZE emulsions
excessive heat or freezing/thawing
presence of light, air, contaminating microorganisms that decompose emulsifying agents
which particular emulsifiers can microorganisms decompose? what can be done to prevent this?
nonionic and anionic emulsifiers, glycerin, and vegetable gum thickeners
ADD PRESERVATIVES!! Also, make sure they get into the water phase because this is where the bacteria tend to grow
most emulsions exhibit what flow? what is an exception?*****
NON-NEWTONIAN FLOW
EXCEPT extremely dilute ones
internal phase of the emulsion has less than 5% concentration.
what is the flow pattern?
NEWTONIAN – it’s so diluted
behaves like pure water or oil
as mentioned, when the volume of the dispersed phase is less than 5% of the system, the emulsion exhibits newtownian flow.
when will it exhibit pseduoplastic (non-newtonian) flow??
when the dispersed phase volume concentration increases
if increased even MORE—- will ehibit PLASTIC FLOW (have to shake a lot to yield value to flow) and behave like a semisolid
if increased MORE – GREATER THAN 75% — phase inversion will occur and the viscosity changes – possibly newtonian flow
which are generally preferred by the patients - oral emulsions or solutions/suspensions
solutions/suspensions bc they dont have the oily feeling in the mouth
____ emulsions can include TPN
parenteral
for topical emulsions, what is likely the external medium?
oil
true or false
coalescence can be reduced by increasing the droplet size of the dispersed phase
FALSE
true or false
increasing the viscosity of the medium can reduce coalescence
TRUE
decreasing the difference between _________________ can reduce coalescence*****
decreasing the difference between the density of the dispersed phase and the density of the medium
name 2 methods of preparing primary emulsions
continental gum method (dry gum)
english gum method (wet gum)
***primary emulsion ratios
(for both wet and dry gum)
same for both
4 parts oil: 2 parts water: 1 part emulsifier
4mL:2mL:1g
explain the dry gum method of preparing primary emulsion
levigate 1 part of the gum-like emulsifer (acacia) with 4 parts of the oil
then, add the water ALL AT ONCE and triturate until you hear cracking and the mixture is creamy white
ass other ingredients by 1st DISSOLVING THEM IN SMALL AMT WATER and QS water to final volume
explain the english gum/wet gum method of preparing primary emulsion
same 4:2:1 ratio
triturate gum and WATER together to form mucilage (slurry) and add the oil SLOWLY while triturating to form the emulsion
*acacia always forms what kind of emulsion
o/w
rate of sedimentation decreased if the particle size of the dispersed phase _______
decreases
rate of sedimentation increases if the viscosity of the dispersion phase _______
decreases
true or false
irreversible aggregation of emulsions is creaming
FALSE
can be redispersed
breaking and cracking are irreversible
