How two liquids mix at the surface: an atomic view

Sep 01, 2005
How two liquids mix at the surface: an atomic view

Whenever cream is poured into coffee, these two liquids form a homogeneous mixture, which is difficult to separate again. Other liquids, such as water and oil, do not mix, instead forming emulsions, such as salad dressing.

Image: Schematic representation of atomic-scale demixing observed in BiSn liquid alloy.

In results reported in this week's issue of Physical Review Letters [Phys. Rev. Lett. 95, 106103 (2005)], a collaboration lead by physicists from Harvard University have used x-rays to look at how atoms of two elemental liquids - bismuth and tin - mix together. Despite forming a perfectly miscible alloy in the bulk phase, near the surface the two elements separate into alternating atomic layers.

"The surface demixing is somewhat of a paradox since it occurs due to the strongly enhanced attraction between the atoms of the two components, while for partially miscible mixtures the opposite is true: atoms or molecules are more attracted to their own kind" explains Dr. Oleg Shpyrko, the leading author of the study.

"Surface demixing was predicted in 1950 by Defay and Prigogine, but it eluded experimentalists for more than 50 years: liquids only demix within a nanometer-deep surface region, and there are very few techniques that can probe structure of liquid surfaces on such tiny length scales. As we attempt to understand properties of nanoscale materials where most atoms are near the surface, these and other interfacial effects are expected to play a dominant role."

by Oleg Shpyrko, Argonne National Laboratory
Web address: http://liquids.deas.harvard.edu/oleg/
Email: oshpyrko_AT_anl.gov
Tel: 630-252-7540

Explore further: A 'movie' of ultrafast rotating molecules at a hundred billion per second

Related Stories

Modeling how thin films break up

Jun 19, 2015

Excess surface energy from unsatisfied bonds is a significant driver of dimensional changes in thin-film materials, whether formation of holes, contracting edges, or run-away corners. In general, this break-up ...

The moons of Jupiter

Jun 10, 2015

Jupiter was appropriately named by the Romans, who chose to name it after the king of the gods. In addition to being the largest planet in our Solar System – with two and a half times the mass of all the ...

Recommended for you

To conduct, or to insulate? That is the question

Jul 02, 2015

A new study has discovered mysterious behaviour of a material that acts like an insulator in certain measurements, but simultaneously acts like a conductor in others. In an insulator, electrons are largely stuck in one place, ...

Soundproofing with quantum physics

Jul 02, 2015

Sebastian Huber and his colleagues show that the road from abstract theory to practical applications needn't always be very long. Their mechanical implementation of a quantum mechanical phenomenon could soon ...

Extreme lab at European X-ray laser XFEL is a go

Jul 02, 2015

The Helmholtz Senate has given the green light for the Association's involvement in the Helmholtz International Beamline (HIB), a new kind of experimentation station at the X-ray laser European XFEL in Hamburg, ...

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.