Transcript Microemulsions

Emulsions and Microemulsions
Emulsion:
A dispersion of droplets of one liquid
in another, immiscible liquid
• Macroemulsions (d > 1000 nm)
• Miniemulsions (100 nm < d < 1000 nm)
• Microemulsions ( 10 nm < d < 100 nm)
Oil and Water do not mix !!
What we need for making
macroemulsions ?
• Emulsifier: May make it easier to form a
macroemulsion and provide stability against
aggregation, e.g. surfactants or polymers
Some special effects of
surfactants
• Decrease of surface tension
• „Control“ of the type of emulsion
• Droplet stabilization
Decrease of surface tension
• Decrease of the energy input !
„Control“ of the type of emulsion
• HLB - value
(Hydrophilic-Lipophilic-Balance)
• HLB = 20 M hydrophilic part / M total
 For nonionic surfactants only !!
Droplet stabilization
• Electrostatic stabilization
• Steric stabilization
How one can come to small droplets ?
• Macroemulsions (d > 1000nm)
Mechanism of emulsification:
- adsorption
(increase of the surfactant concentration)
- spreading
How one can come to smaller droplets ?
• Miniemulsions (100 nm < d < 1000nm)
- increase of the surfactant concentration
- increase of the energy input !!
(e.g. ultrasound treatment)
- addition of hydrophobic agents
(supress of „Ostwald ripening“)
Laplace pressure ( pLaplace)
•  pLaplace = 2  / r
 - surface tension
r– radius of the droplet
How one can come to much smaller droplets ?
• Microemulsions ( 10 < d < 100 nm)
- Thermodynamically stable dispersion of
one liquid phase into another, stabilized
by an interfacial film.
Microemulsions
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Isotropic, optically clear
Thermodynamically stable
Newtonian-flow behaviour
Low surface tension
Reversible temperature behaviour
Droplet size between 10 and 100 nm
(o/w ; w/o ; bicontinuous)
Microemulsions are
thermodynamically stable !
Ho – Spontaneous Curvature
of the surfactant film
• The most essential parameter
of the system !!
Microemulsions
(ternary systems)
 water, oil, surfactant
Microemulsions
(quaternary systems)
 water, oil, surfactant
and co-surfactant
Polymer induced cluster formation
w/o - microemulsion
+ water soluble polymer
Polyelectrolyte-modified microemulsions
 Oppositely
charged PEL can
be incorporated !!
 PEL increase the
stability of the
surfactant film !!
Fields of application
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Microemulsions as nanosize reactor
Microemulsions in separation processes
Microemulsions as drug delivery systems
Microemulsions in enhanced oil recovery
w/o Microemulsion I
w/o Microemulsion II
containing
e.g. 1mM BaCl2
Precipitation
containing
e.g. 1mM Na2SO4
Mix Microemulsion I and II
Collision and
coalescence of droplets
BaSO4 nanoparticle
formation!
Polyelectrolyte-modified microemulsions
as nanoreactors ?
• PEL can control the
particle growing
process ???
• PEL can stabilize
nanoparticles
during the process
of redispersion ???
Isolation of polymer-stabilized nanoparticles
(patent: WO2004/056928AS)
Nanoparticle formation in w/o microemulsions
Solvent evaporation
Redispersion of the polymer-stabilizied
nanoparticles