Important results for campus chemists

Funded by the Engineering and Physical Sciences Research Council (EPSRC), Dr ir Stefan A. F. Bon and Dr David L. Cheung, researchers from Warwick’s chemistry department, found that tiny nanoparticles could be twice as likely to stick to the interface of two non mixing liquids, than previously believed.

Their results were published in the Physical Review Letters under the title “Interaction of nanoparticles with ideal liquid-liquid interfaces” and offer a large variety of practical applications, revolving around the uses of nanoparticles in living cells, polymer composites, and high-tech foams, gels, and paints.

As part of their research, they reviewed molecular simulations of the interaction between a non-charged nanoparticle and an “ideal” liquid-liquid interface.

What they found was that very small nanoparticles (of around one to two nanometres) varied considerably in their simulated ability to stick to such interfaces from what was expected in the standard model.

The researchers realized that it took up to 50 per cent more energy to dislodge the particles from the liquid-liquid interface for the smallest particle sizes.

However as the radius of the particles increased this deviation from the standard model gradually faded out.

Elaborating on the practical aspects of the findings, Dr Bon told the Boar that a small liquid droplet can be coated with nanoparticles, and is then used to fabricate next generation nanocomposite coatings with superior characteristics, such as scratch and fire resistance.

The results of the experiments will also be highly useful in areas such as agriculture or the food industry, and has already lead to a number of collaborative projects with several large international companies, which have an interest in how one can put tiny particles on soft interfaces and invent new types of material.

Nanoparticles are really hard to control, Dr Bon added “Until now theoretical calculations showed that very small particles don’t stick very well, but our work shows that they stick way better than previously thought and that the established theory thus far is only partially correct.”

To illustrate the scale at which the simulations were conducted, he then added “you really have to think on a nanoscale, 1 to 10 nanometres, it’s like taking the side of a 5p coin, assuming it has roughly 1 mm, you then slice it into a million pieces.”

Asked about future research plans, Dr Bon commented that his team will focus on the analysis of particles that are not the same, such as a sphere which on one side is water oriented and on the other oil oriented, often referred to as Janus particles (Greek and Roman mythology): “Synthetically it starts to become possible to make much more complex particles.”

The researchers will also work on ways to build on this newly found natural stickiness of nanoparticles by designing Janus polymer nanoparticles with opposing hydrophobic and hydrophilic surfaces that will bind even more strongly at oil/water liquid interfaces.