Emulsions are a part of everyday life—from detergents that break up oil and wash it away, to sauces like mayonnaise that combine fats and water. Dispersing these non-mixing liquids usually requires surfactants, which are chemicals that bridge the divide and allow small droplets of one liquid to stay suspended within the other.
However, surfactants may not perform well under the harsh conditions of industrial chemistry—such as in enhanced oil recovery, where remnant oil is flushed out by high-temperature brine. In some cases, the high temperatures and brine salinities of oil reservoirs can cause problems such as aggregation, precipitation and phase separation.
To broaden the use of emulsions in industrial applications, co-corresponding authors Vivek Arjunan Vasantha and Nanji Hadia and their colleagues at A*STAR’s Institute of Chemical and Engineering Science (ICES) turned to ‘Pickering emulsions,’ where nanoparticles take the place of surfactants to stabilize small droplets. Pickering emulsions are kinetically stabilized by nanoparticles at the liquid-liquid interface, overcoming instability issues associated with high temperatures and salinity.
In this proof-of-concept study, Vasantha used simple chemistry to bond brine-soluble zwitterions—molecules with negatively and positively charged fragments—with oil-soluble styrene monomers. Subsequently, when these hybrids were combined with unmodified styrene monomers using a one-step emulsion copolymerization, they self-assembled into small spherical polystyrene nanoparticles covered in a mesh of zwitterions.
“These zwitterionic nanoparticles can be made with one-step copolymerization, removing the need for complex manufacturing and purification processes,” said Ludger Stubbs, a Senior Research Scientist at ICES and a co-author on the study. In addition to being simple to manufacture, the zwitterionic nanoparticles remained stable in industrial salt concentrations and at elevated temperatures.
“Microscope images showed that the nanoparticles indeed formed a rigid, protective barrier between oil and brine, making this the first time such stable emulsions have been prepared using zwitterionic nanoparticles without further chemical additives,” Hadia explained.
Moving forward, the researchers hope to create nanoparticles that are highly responsive to their chemical environments, resulting in smart nanofluids that can form or break emulsions on demand. Such nanofluids would have significant technological applications, from biological environments to oilfield deployment, enhancing the capabilities of industrial chemistry.
The A*STAR researchers contributing to this research are from the Institute of Chemical and Engineering Sciences (ICES).