emulsions/dvlo theory Flashcards
what 3 factors does the degree of steric effects depend on
-non ionic surfactant chain length
-number of chains per unit area of -interacting surface
chain/solvent interactions
types of emulsions
o/w
w/o
w/o/w
o/w/o
what is an emulsion
dispersion of a liquid in another liquid which are immiscible
basic types of emulsifiers and examples
(-)anionic- sodium dodecyl sulphate
(+)cationic- cetrimide
non ionic- cetostearly alcohol
what do emulsifying agents do
stabilises emulsions and prevents liquids from separating
describe surfactants as emulsifying agents
accumulate at water oil interface, forms interfacial barrier, not very good, charged molecules repel
why are mixed emulsifiers better than surfactants
mix of hydrophilic and lipophilic amphiphiles, denser interfacial film, v good for stabilising emulsions, mostly used in creams
what is amphiphilic
both hydrophobic and hydrophilic
polymers and proteins as emulsifying agents
amphiphilic, adsorb at interface, good emulsifying agents, can bridge between droplets to connect multiple oil droplets so also acts as flocculating agents
example of a natural emulsifier in food
lecithin (egg yolk) (phospholipid)
what are creams
emulsions which one phase is semisolid/wax
signs of instability in emulsions
creaming- disperse phase droplets increase in size and collect near the surface
cracking- phase separation, disperse phase forms large globules or a separate layer on surface
emulsions are unstable and cant be reformed by shaking so what to do
stabilise using a good emulsifying agent to prevent coalescence of oil particles in liquid emulsions/creams
what is coalescence of droplets
droplets increasing in size
factors that cause emulsions to crack
incompatible chemicals- opposite charged surface active agents (cationic to anionic), addition of electrolytes
bacterial growth- protein and non ionic emulsifying agents are good growth medium
temperature changes- freezing disrupts interfacial film and heating denatures protein emulsifying agents and solubility changes in non ionic ones
physical processes that cause instability
flocculation of oil droplets- loosely held together by interactive forces of attraction/repulsion, can be redispersed but can coalesce into bigger droplets
phase inversion- (ow into wo) caused by excess amounts of disperse phase
creaming- emulsion creams on standing for long time, disperse phase rises/sinks
how to keep globules suspended
reduce globule size of dispersed phase, decrease density difference between two phases, increase viscosity of continuous phase
how to reduce microbial growth in emulsions as the water vehicle in liquids/semisolids support microbial growth and contamination
sterilise by filtration/autoclaving, preservatives, fridge storage
how to choose a preservative to prevent microbial growth
base on delivery route, stability of shelf life, non toxic, compatible with excipients, effective against wide spectrum of organisms, optimum pH
3 types of emulsion applications
intravenous- total parental nutrition (TPN) (administration of fats), fat absorbed from GI tract circulates as chylomicrons
oral
intramuscular- w/o for sustained release
examples of acceptable excipients for emulsions
oil phase- soya bean oil, medium chain triglycerides
emulsifiers- phospholipids, egg yolk
some hydrophilic pluronics
emulsions for drug delivery
hydrophobic oil and soluble drug- dissolved in oil then emulsified
surface active drugs- adsorb at interface
3 types of formulations of self emulsifying microemulsions classified by how it disperses in vitro
lipid+drug
SEDDS= self emulsifying drug delivery system= drug+lipid+ssurfactant
SMEDDS= self microemulsifying drug delivery system+ drug+lipid+surfactant+cosurfactant/solvent
what does SEDDS and SMEDDS stand for
self emulsifying drug delivery system
self microemulsifying drug delivery system
2 classifications of self emulsifying microemulsions
liquid lipidic- liquid at room temp, final dosage form fills soft gelatin capsule
semi solid lipidic- semi solid at room temp, final dosage form is capsule/pellet/tablet
what excipients are used in self emulsifying emulsions
lipids- mono/di/triglycerides
-castor oil, sesame oil, peceol
emulsifiers- polyglycolised oils- labrasol, labrafil
-polyglycolised solids- gelucire 44
non ionic surfactants- tween 80, span 80
fatty acids- oleic acid, capric acid
co solvents- glycerol, peg 400
what do co-solvents do
aid dispersion and solvation
what do non ionic surfactants do
aid solubilisation
types of in vitro test
-measurement of emulsion droplet size
-phase diagram
-visual dispersion test
-digestion assay
-dissolution
