Some of Australia’s most advanced technology has been used to investigate brushes. 

Researchers are using advanced neutron scattering techniques at the Australian Nuclear Science and Technology Organisation (ANSTO) to carry out research on the structure of polymers in complex salt environments that will ultimately provide a way to predict their behaviour for real-world applications.

The project seeks to provide a better understanding of the behaviour of polymer brushes in complex salt and solvent environments. 

Polymer brushes are used in environmentally friendly cleaning products, environmental remediation, minerals processing, biotechnology, sensors, drug delivery, and membranes.

The behaviour of many of these applications is determined largely by the interface between the polymer and the surface substrate and the nanostructure of the brush.

The researchers are particularly interested in stimuli-responsive polymers. For example, the polymer chains are very ‘hairy’ at low temperatures but at high temperature, the brushes collapse onto the surface, with different salts altering the collapse temperature.

The research team has published eleven journal articles so far, including a recent study on polymer responses to confinement in response to temperature and a related study on polymer responses in the presence of mixed electrolytes.

Hayden Robertson, a PhD candidate at the University of Newcastle, was recently awarded the Ezio Rizzardo Polymer Scholarship by the Australian Academy of Technology and Engineering (ATSE) for his research on improving the understanding of stimulus-responsive polymers to make smart interfaces with tunable properties.

“What is important about their behaviour is whether the seaweed-like molecules that are attached to a surface are collapsing or expanding in the presence of different salts or solvents,” Mr Robertson says.

“The behaviour of these polymer brushes in water is pretty well understood, but what we are interested in are the interactions between the polymers in the presence of different ions, a mixture of ions or in different solvents, such as propylene carbonate.

“In nature and industrial settings, you will never have only water, it will be a combination of lots of different ions and solvents. We are trying to understand the myriad interactions that arise in complex environments.”

Although an understanding of specific ion effects dates back to work by Franz Hofmeister in the late 19th century, who figured out there was a specific order to an ion's ability to precipitate out egg white proteins in solution, known as the Hofmeister series, it did not explain behaviour in different, more complex systems.

“We do not have a universal theory to predict how these polymers will respond to different chemical environments. Such a predictive theory is required to advance to applications,” the experts say.

The team will be investigating further with more experiments and other techniques, such as ellipsometry. 

The team is also working with industry partners to use this knowledge in the development of environmentally friendly cleaning agents for household/personal care products, and more water-efficient mineral processing additives for the Australian mining industry.