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 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 Microemulsions as nanosize reactor Microemulsions in separation processes Microemulsions as drug delivery systems Microemulsions in enhanced oil recovery

Mix Microemulsion I and II w/o Microemulsion I w/o Microemulsion II containing e.g. 1mM BaCl2 BaSO4 nanoparticle formation! Precipitation Mix Microemulsion I and II Collision and coalescence of droplets containing e.g. 1mM Na2SO4

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