A University of Bristol team has dissolved iron in liquid surfactant to create a soap that can be controlled by magnets. The discovery could be used to create cleaning products that can be more easily removed after application and used in the improved recovery of oil spills at sea. 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 to result from tiny iron-rich clumps that sit within the watery solution. The generation of this property in a fully functional soap could reduce environmental concerns over the use of soaps (lingering soap residue) in oil-spill clean ups and revolutionize industrial cleaning products.
Soap is not simply soap. Technically the better term is surfactant. Surfactants are compounds that lower the surface tension of a liquid, the interfacial tension between two liquids, or that between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsifiers, foaming agents, and dispersants. The surfactant helps remove the undesirable compound (such as oil) by separating it from the overall liquid or surface.
Scientists have long been searching for a way to control surfactants once they are in solution to increase their ability to dissolve oils in water and then remove them from a system. This is due to the concern that the surfactant itself may cause lingering environmental effects as well as to improve removal of the oil contaminant.
The team at the University of Bristol have previously worked on soaps sensitive to light, carbon dioxide or changes in pH, temperature or pressure. Their latest breakthrough, 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 allows the potential magnetic effect.
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.
When surfactants are added to water they are known to form tiny clumps (particles called micelles). Scientists at Institut Laue-Langevin used a technique called neutron scattering to confirm that it was this clumping of the iron-rich surfactant that brought about its magnetic properties.
Dr Isabelle Grillo, head of the Chemistry Laboratories at the Institut 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 behaviour of all types of materials at the atomic and molecular scale."
The magnetic soap 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 applications in environmental clean ups and water treatment.
Peter Dowding an industrial chemist, not involved in the research said: "Any systems which act only when responding to an outside stimulus that has no effect on its composition is a major breakthrough as you can create products which only work when they are needed to. Also the ability to remove the surfactant after it has been added widens the potential applications to environmentally sensitive areas like oil spill clean ups where in the past concerns have been raised."
For further information: http://www.bristol.ac.uk/news/2012/8179.html