Scientists working on engendering simple soap with new properties may have uncovered vast new potential for advanced cleaning.
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 removed after application and used in the recovery of oil spills at sea.
Rather than 'soap', the substance should more correctly be called a surfactant, which is a contraction of surface acting agent. These chemicals are characterised by having two groups which are knitted together, but those two groups have totally opposite tendencies. One of the groups is strongly hydrophobic and the other is strongly hydrophilic; it is this schizophrenia, or tension, in the molecule that explains all of the properties of soaps and surfactants and the action of detergents.
If you have ever tried to wash grease from a pan without using a detergent you will appreciate the role of the surfactant - or washing-up liquid. Surfactants have a pre-programmed chemical structure which means that one end of the molecule sticks to the oil, but the other still resides in the water. It becomes possible through the action of detergents to lift the oil from the plate. Soaps and surfactants are molecules with dual properties - almost a dual personality. One is oily and one is watery.
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. 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 is the world's first soap sensitive to a magnetic field.
In keeping with many game-changing inventions, the development of the magnetic soap did not derive from some insightful market knowledge but good old-fashioned scientific curiosity. "In all honesty it is not designed for anything," admits Professor Julian Eastoe, leader of the Bristol University team that developed the product, says. "It was really to establish the proof of principle of whether it would be possible to have these kinds of chemicals that you could control by magnetic field.
"Surfactants are very good at their job. They are a highly evolved chemical species and are superb at cleaning, but then they suffer from limitations and you can't really control when they work or where they work."
With that in mind, Eastoe has been researching over recent years how to take these commodity chemicals and add an extra function that gives a level of control over when and where they act. The first systems he looked at were temperature- or pH-responsive surfactants. Then he moved on to soaps and surfactants that could be activated by light. "We learnt a lot from these studies about how to design molecules for these kinds of special properties," he explains. "We came to the magnetic surfactants because we couldn't find anything in literature about surfactants of soaps that were magnetic so we wondered if it was possible. It was scientific curiosity."
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 centres were too isolated within the solution, preventing the long-range interactions required to be magnetically active.
The magnetic soap was produced 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 centres within the soap particles.
"The compounds that we have made are quite cheap really," Eastoe adds. "You could probably make surfactants that are magnetic and act better than the ones that we developed, but they might be more expensive and therefore the opportunity that they would be taken up for any product or process would be limited. The challenge really was to make the chemicals from readily available materials and the oily part of the molecules that we have made is essentially the chemical brothers of commodity chemicals. It is not true to say that they are exactly the same as you find in your washing up bottles or your fabric conditioner bottles but they are the sisters and brothers of those molecules.
"For the purposes of research you have to work with purified materials rather than commodity chemicals," explains Eastoe. "So one element of the chemicals, the oily part, is essentially just normal surfactants that you would find anywhere. The other part contains a very common iron salt: so it has got ions of iron. The challenge was how could we put together common chemicals, which do not cost an arm and a leg, while maintaining the magnetic property? In coming to those chemicals there were some failures along the way. We had to use our chemical intuition and sometimes it didn't serve us too well. We had to go back then to the chemical drawing board and try a few others and these ones, that have been published recently, were very successful and also met the criteria of being cheap and readily available."
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 it was taken to the Institut Laue-Langevin (ILL), the world's flagship centre for neutron science, and home to the world's most intense neutron source, to investigate the science behind its remarkable property.
When surfactants are added to water they are known to form tiny clumps, or 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.
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 it dissolves in water, to be altered by a simple magnetic 'on/off' switch.
Traditionally, these factors, which are crucial 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 make 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 that require precise control of liquid droplets could also be made easier with this surfactant and a magnetic field.
The research was undertaken without a commercial proposition in mind, but since Eastoe published his research industry has looked at the properties of his product with interest. "We have been contacted by a number of companies with diverse interests ranging from environmental clean-up, oil recovery and chemical delivery, so there has been a considerable interest industrially," he says.
"I was contacted just yesterday by a company that make cement, a Canadian guy, and he seemed to think that surfactants could help in improving the homogeneity in cement. He said that in setting cement there are domains that form and then weaken the cement. I don't know the answer to that, but it is interesting to see if we can help there."
One further use suggested for the surfactant is the clean-up of sea-birds that have been caught in oil spills. The current procedure is just using standard dispersants or soap surfactants. They remove the oil, but also strip the birds of their essential oils. "Someone from the RSPB in the UK contacted me because he thought that there was scope for this technology to provide a responsive and milder cleaning regime for these birds," Eastoe adds. "We are already working on that to see how these soaps work. We have made emulsion and we are now trying to find out whether we can use these magnetic emulsions with the magnetic field to extract the emulsion from feathers - an experiment that I never thought I would be doing."
The next step for Eastoe and his team is further understanding and development with the properties of surfactants. "I don't just work on the magnetic soaps," he says. "There are a lot of things that we do. The business is to try to improve the existing chemicals for optimising the process that they are used in and also exploring different areas."
Controlling carbon dioxide
One very interesting area of research is the opportunity to have soaps that are working in liquid or super critical carbon dioxide as that has major implications in oil and gas recovery. The carbon dioxide is used as a pumping fluid, but it suffers a number of limitations because it has a low viscosity and it will linger around inclusions or find the path of least resistance when pumped underground. By adding soaps and surfactants you can modify the properties of the carbon dioxide so that it is more appropriate for efficient oil and gas recovery.
"We are considering having an added layer of control, which is where we can also have magnetic interactions where it might be possible to use that to help direct the fluids as they are being pumped underground or being recovered even," Eastoe explains. "So, yes, we are looking at, on one level, rather crazy ideas, but that is the job of a scientist."
There is an interesting statistic. If you can increase the viscosity of CO2 by 10 per cent you can double the capacity of a well that is operating under these enhanced oil recovery conditions. But it is very difficult to do as very few compounds are soluble in CO2. It's not like water and it's not like oil. It's like a solvent from a different planet. Virtually nothing we know dissolves in carbon dioxide. Therefore, you don't stand a chance of increasing its viscosity.
"One of the things that I do work on is just that – working for the improvement of soaps and surfactants as additives to carbon dioxide. That itself is a challenge. Now we are looking and thinking about having these being magnetic and light responsive as well."
Given the cost of extracting oil from unresponsive or near depleted wells, allied with the value of that locked-in oil, makes this a quest that will certainly see a huge pot of gold if it can be achieved.