Electric-Field-Induced Phase-Separation of Liquid Mixtures

Aug 09, 2004
Temperature quench of the system

Researches have shown that electric fields can control the phase separation behaviour of mixtures of simple liquids under practical conditions, provided that the fields are non-uniform. This direct control over phase separation behaviour depends on field intensity, with the electrode geometry determining the length-scale of the effect. This phenomenon will find a number of nanotechnological applications, particularly as it benefits from field gradients near small conducting objects.

Ludwik Leibler and colleagues at the City of Paris Industrial Physics and Chemistry Higher Educational Institution (ESPCI) have predicted theoretically and demonstrated experimentally that reversible phase separation can be induced in ordinary liquid mixtures under practical conditions provided non-uniform fields are used.

It is exciting and astonishing that such a simple but fundamental physics has not been explored so far. In some sense this is the simplest electro-optical effect that can exist: it does not require anything from the molecules other than having a modestly different dielectric constant. This is contrast to all other electro-optical effects (e.g. liquid crystals, birefringent molecules, etc.). The results are reported in the 29 July issue of Nature.

They predicted and demonstrated that applying a voltage of 100 V across unevenly spaced electrodes about 50 µm apart, can reversibly induce the demixing of paraffin and silicone oil at about 1 K (and more) above the phase transition temperature of the mixture. When the field gradients are turned off, the mixture becomes homogeneous again.

How the method works
When neutral object (say a colloidal particle) is placed in a field gradient it is attracted towards an electrode. This is due to a well known dielectrophoretic force. Here, this effect is used to separate molecules of liquids with different dielectric constant. When field gradients are high enough, phase separation is induced. A sharp interface, which is a signature of phase separation, is formed even though electric field varies smoothly.

Electric-field-induced phase-separation
Electric-field-induced phase-separation

Similar ideas to those of the paper can be used to compensate gravity effects and produce zero-gravity conditions in mixtures and suspentions; or liquid phase separation can be efficiently induced in a centrifuge.

The effect benefits from decrease of the size of the electrodes (larger fields and and shorter time constants). Hence, it seems ideally suited for microfluidic applications (liquid separation and distillation, light guiding and deflection, etc.) The effect can be also induced by electromagnetic radiation (laser tweezers).

Explore further: Seeking 'absolute zero', copper cube gets chillingly close

add to favorites email to friend print save as pdf

Related Stories

Blades of grass inspire advance in organic solar cells

Sep 30, 2014

Using a bio-mimicking analog of one of nature's most efficient light-harvesting structures, blades of grass, an international research team led by Alejandro Briseno of the University of Massachusetts Amherst ...

Light scattering on dust holds clues to habitability

Sep 25, 2014

We are all made of dust. Dust particles can be found everywhere in space. Disks of dust and debris swirl around and condense to form stars, planets and smaller objects like comets, asteroids and dwarf planets. ...

Magnetic neural control with nanoparticles

Sep 18, 2014

Magnetic nanoparticles don't have to be "one size fits all." Instead, individual magnetic nanoparticles can be tailored in an array of differing sizes and compositions to allow for heating them separately ...

Recommended for you

Backpack physics: Smaller hikers carry heavier loads

11 hours ago

Hikers are generally advised that the weight of the packs they carry should correspond to their own size, with smaller individuals carrying lighter loads. Although petite backpackers might appreciate the ...

Extremely high-resolution magnetic resonance imaging

11 hours ago

For the first time, researchers have succeeded to detect a single hydrogen atom using magnetic resonance imaging, which signifies a huge increase in the technology's spatial resolution. In the future, single-atom ...

'Attosecond' science breakthrough

12 hours ago

Scientists from Queen's University Belfast have been involved in a groundbreaking discovery in the area of experimental physics that has implications for understanding how radiotherapy kills cancer cells, among other things.

User comments : 0