Scientists from
the University of
Bristol have developed a
soap, composed of iron rich salts dissolved in water, that responds to a
magnetic field when placed in solution. The soap’s magnetic properties were
proved with neutrons at the Institut Laue-Langevin (ILL) to result from tiny
iron-rich clumps that sit within the watery solution. The generation of this
property in a fully functional soap could calm concerns over the use of soaps
in oil spill clean ups and revolutionize industrial cleaning products.
Scientists have
long been searching for a way to control soaps (or surfactants as they are
known in industry) once they are in solution to increase their ability to
dissolve oils in water and then remove them from a system. The team at the University of Bristol has previously worked on soaps
sensitive to light; carbon dioxide; or changes in pH, temperature, or pressure.
Their latest work, reported in Angewandte
Chemie, is the world’s first soap sensitive to a magnetic field.
Ionic liquid
surfactants, composed mostly of water with some transition metal complexes
(heavy metals like iron bound to halides such as bromine or chlorine) have been
suggested as potentially controllable by magnets for some time, but it had
always been assumed that their metallic centers were too isolated within the
solution, preventing the long-range interactions required to be magnetically
active.
The team at Bristol, led by Professor
Julian Eastoe, produced their magnetic soap by dissolving iron in a range of
inert surfactant materials composed of chloride and bromide ions, very similar
to those found in everyday mouthwash or fabric conditioner. The addition of the
iron creates metallic centers within the soap particles.
To test its
properties, the team introduced a magnet to a test tube containing their new
soap lying beneath a less dense organic solution. When the magnet was
introduced the iron-rich soap overcame both gravity and surface tension between
the water and oil, to levitate through the organic solvent and reach the source
of the magnetic energy, proving its magnetic properties.
Once the
surfactant was developed and shown to be magnetic, Eastoe’s team took
it to the Institut Laue-Langevin to investigate the science behind its
remarkable property.
When surfactants
are added to water they are known to form tiny clumps (particles called
micelles). Scientists at ILL
used a technique called neutron scattering to confirm that it was this clumping
of the iron-rich surfactant that brought about its magnetic properties.
Isabelle Grillo, PhD,
head of the Chemistry Laboratories at ILL
said: “The particles of surfactant in solution are too small to see using light
but are easily revealed by neutron scattering which we use to investigate the
structure and behavior of all types of materials at the atomic and molecular
scale.”
The potential
applications of magnetic surfactants are huge. Their responsiveness to external
stimuli allows a range of properties, such as their electrical conductivity,
melting point, the size and shape of aggregates, and how readily its dissolves
in water to be altered by a simple magnetic on and off switch. Traditionally
these factors, which are key to the effective application of soaps in a variety
of industrial settings, could only be controlled by adding an electric charge
or changing the pH, temperature, or pressure of the system, all changes that
irreversibly alter the system composition and cost money to remediate.
Its magnetic
properties also makes it easier to round up and remove from a system once it
has been added, suggesting further applications in environmental clean ups and
water treatment. Scientific experiments which require precise control of liquid
droplets could also be made easier with the addition of this surfactant and a
magnetic field.
Eastoe said: “As most
magnets are metals, from a purely scientific point of view these ionic liquid
surfactants are highly unusual, making them a particularly interesting
discovery. From a commercial point of view, though these exact liquids aren’t
yet ready to appear in any household product, by proving that magnetic soaps
can be developed, future work can reproduce the same phenomenon in more
commercially viable liquids for a range of applications from water treatment to
industrial cleaning products.”
