Research on liquid film stability reveals mechanism behind destabilization on solid surfaces

Suraj Borkar
Suraj Borkar (ChemE PhD student)

For his research project titled “A New Perspective on the Stability of Liquid Films on Solid Surfaces”, Suraj Borkar (ChemE PhD student), under the guidance of Professor Arun Ramchandran, set out to better understand the cause of destabilization of films of hydrophobic liquids (for example oil) sandwiched between a liquid medium (like water) and a solid surface. Thin films of oil tend to break up into droplets under such conditions.

“For decades, researchers have accepted that for this thin film of oil to remain stable (i.e. it does not break up into droplets), the film thickness must be large, typically greater than 100 nm,” Borkar explains. “When films are thin (less than 100 nm), intermolecular forces can cause the oil film to become wavy, eventually causing the film to break up into oil droplets.”

While the mechanism behind the destabilization of thin layers was well understood, thicker layers were also observed to destabilize and this process was more mysterious. Classical theories explain that the destabilization occurs as a result of the presence of tiny and unavoidable dirt particles in the oil film. “However, even when researchers took extreme effort to avoid dirt particles, thick films still destabilized. Hence, the origin of instability for thick films has been a mystery until now” says Borkar.

The culmination of his research led to the discovery that the insolubility of the two liquids is not absolutely zero, and that this trace solubility was the cause of the destabilization, causing droplets to eventually form on the solid surface over time.

“We stumbled upon this observation back in 2015 and it took us seven years to thoroughly understand the mechanistic details” says Borkar. “I think the novelty of this research is that dissolved material spontaneously condenses on the solid surface in the form of droplets, without changing any thermodynamic property, such as temperature or pressure, that can lead to oversaturation conditions.”

Borkar says the utility of this discovery has applications in both industrial and commercial settings, for example the extraction of crude oil or the recycling of plastics. “A more niche area of research involves DNA transcription where transcription factors (typically water-soluble proteins) condense on a DNA molecule and commences the process of copying the genetic material in the DNA into a messenger RNA.”

Borkar’s research was published in the September 2021 issue of Nature Communications, a peer-reviewed, open access, scientific journal.