emulsions and microemulsions emulsion: a dispersion of droplets of one liquid in another, immiscible...
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Emulsions and Microemulsions
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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)
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Oil and Water do not mix !!
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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
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Some special effects of surfactants
• Decrease of surface tension
• „Control“ of the type of emulsion
• Droplet stabilization
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Decrease of surface tension
• Decrease of the energy input !
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„Control“ of the type of emulsion
• HLB - value
(Hydrophilic-Lipophilic-Balance)
• HLB = 20 M hydrophilic part / M total
For nonionic surfactants only !!
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Droplet stabilization
• Electrostatic stabilization
• Steric stabilization
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How one can come to small droplets ?
• Macroemulsions (d > 1000nm)
Mechanism of emulsification:
- adsorption
(increase of the surfactant concentration)
- spreading
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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“)
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Laplace pressure ( pLaplace)
pLaplace = 2 / r
- surface tension
r– radius of the droplet
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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.
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Microemulsions
• 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)
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Microemulsions are thermodynamically stable !
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Ho – Spontaneous Curvature of the surfactant film
• The most essential parameter
of the system !!
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Microemulsions (ternary systems)
water, oil, surfactant
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Microemulsions (quaternary systems)
water, oil, surfactant
and co-surfactant
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w/o - microemulsionw/o - microemulsion + water soluble polymer+ water soluble polymer
Polymer induced cluster formation
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Polyelectrolyte-modified microemulsions
Oppositely charged PEL can be incorporated !!
PEL increase the stability of the surfactant film !!
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Fields of application
• Microemulsions as nanosize reactor
• Microemulsions in separation processes
• Microemulsions as drug delivery systems
• Microemulsions in enhanced oil recovery
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BaSO4 nanoparticle formation!
Precipitation
w/o Microemulsion I w/o Microemulsion II
containing
e.g. 1mM Na2SO4
containing
e.g. 1mM BaCl2
Mix Microemulsion I and II
Collision and coalescence of droplets
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Polyelectrolyte-modified microemulsions as nanoreactors ?
• PEL can control the particle growing process ???
• PEL can stabilize nanoparticles during the process of redispersion ???
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Isolation of polymer-stabilized nanoparticles
(patent: WO2004/056928AS)
Nanoparticle formation in w/o microemulsions
Solvent evaporation
Redispersion of the polymer-stabilizied nanoparticles