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

w/o - microemulsionw/o - microemulsion + water soluble polymer+ water soluble polymer

Polymer induced cluster formation

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

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

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