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: Occam's razor redux: A simple mathematical approach to designing mechanical invisibility cloaks

Related Stories

The trillion-frame-per-second camera

Apr 29, 2015

When a crystal lattice is excited by a laser pulse, waves of jostling atoms can travel through the material at close to one sixth the speed of light, or approximately 28,000 miles/second. Scientists now have ...

Quantum Criticality in life's proteins (Update)

Apr 15, 2015

(Phys.org)—Stuart Kauffman, from the University of Calgary, and several of his colleagues have recently published a paper on the Arxiv server titled 'Quantum Criticality at the Origins of Life'. The id ...

First NSLS-II X-ray images hint at science to come

Apr 09, 2015

In another "first" at the National Synchrotron Light Source II (NSLS-II) at Brookhaven National Laboratory, a group working at the Hard X-Ray Nanoprobe has taken the facility's inaugural x-ray images. Their ...

Sun experiences seasonal changes, new research finds

Apr 07, 2015

The Sun undergoes a type of seasonal variability with its activity waxing and waning over the course of nearly two years, according to a new study by a team of researchers led by the National Center for Atmospheric ...

QUANT F car will be shown next month in Geneva

Feb 12, 2015

nanoFlowcell AG will show its QUANT F car at the 2015 Geneva Motor Show. This is an electric auto in the style of an "e-sports saloon," a large sports saloon for four, with a range of 800 km (497 miles). ...

Recommended for you

Efimov state in the helium trimer observed

Apr 30, 2015

A quantum state predicted by the Russian theoretician Vitaly Efimov 40 years ago has been discovered by physicists of the Goethe University in a molecule consisting of three helium atoms. The molecule is ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.