Researchers have made the first example of a liquid ‘dry emulsion’, using only an ordinary kitchen blender and fine particles of modified silica. The work is an extension of earlier studies with a substance called ‘dry water’, which was first patented in 1968 for cosmetic applications, according to Ben Carter at the UK’s University of Liverpool. ‘While there are no immediately obvious applications for the dry emulsion, the technology could potentially be useful for safely transporting hazardous liquids and emulsions,’ he says, adding that it is also of interest because of its complex structure, which involves the ‘hierarchical encapsulation’ of oil in water in air.
Dry water was ‘rediscovered’ by scientists at the University of Hull in 2006 and Andrew Cooper’s research group at the University of Liverpool recently demonstrated its potential as a storage material for gases, including methane and carbon dioxide. It is made by simply blending hydrophobic silica particles with water to produce a silica-coated dry powder that comprises 95% water.
Carter and colleagues created the dry emulsion in much the same way, by blending an ordinary oilin- water emulsion, similar to that used in food products, such as mayonnaise, with silica particles to form an oil-in-water-in-air emulsion. The oil droplets, ca 2μm in size, are kept stable by a polymer surfactant, and are held within water droplets ca 50μm in size, which are in turn stabilised by a coating of silica particles. Although other so-called dry emulsions are known, this is the first one that remains ‘wholly liquid’, Carter says.
The group has already used the technology in the laboratory to prepare dry liquids of 2M hydrochloric acid and dilute sodium hydroxide, which could potentially offer a safer way of transporting other hazardous chemicals, Carter says. ‘We would only want to go to the trouble [of making a dry emulsion] if the hazardous material in question could not be blended with silica on its own,’ he added, pointing out that loadings are limited to emulsions comprising up to 6% oil.
Unfortunately, the dry emulsion is unlikely to be helpful when it comes to cleaning up oil spills, he says, as ‘the hydrophobic silica cannot stabilise oil-based liquids, it will simply get covered in oil’. The group has tried using lipophobic silica to make dry oils, but without success to date.