‘Molecular dynamics simulations of nanobubbles and nanodrops’
In this thesis phenomena related to the stability and the growth/dissolution of nanobbubles and nanodrops, are explained.
‘By using molecular dynamics (MD) simulations we tried to better understand, for example, why very small but stable bubbles do exist,’ says Shantanu Maheshwari. ‘Some stay stable even for days, though the pressure in these small bubbles is very large.’
However, Shantanu was most (pleasantly) surprised on his findings in order to explain the stability of multiple surface nanobubbles. Here, some experiments showed that surface nanobubbles don’t always remain stable, despite macroscopic theories suggesting otherwise.
‘The one bubble seems to grow at the expense of the other, which is contrary to macroscopic theoretical arguments,’ Shantanu says. ‘We showed that the gas-solid interaction energy, plays a crucial role in the stability of surface nanobubbles. This wasn’t considered in any macroscopic theory before. It led to a nice publication in ACS Nano Journal.’
First, in this PhD work, the stability of a single surface nanobubble on a heterogeneous surface was addressed, by systematically performing MD simulations. Shantanu: ‘We showed that dissolution of surface nanobubbles exhibit "stick-jump" motion of the contact line, similar to the dissolution of surface nanodrops.’
Further, the dynamics of formation of a vapour nanobubble around a heated nanoparticle was studied.
The conditions required to nucleate a vapour nanobubble, in terms of the nanoparticle temperature and the temperature "far away" from the nanoparticle surface, were investigated. ‘A prediction for the nucleation conditions was made, by using heat balance arguments with additional assumptions,’ Shantanu explains his method of working.
Next he moved on from nanobubbles to nanodrops. ‘We performed simulations of a nanodrop on curved surfaces, to estimate the magnitude of line tension, to study the effect of surface curvature on the line tension of nanodrops,’ he says.
Shantanu: ‘During the PhD project, my view on the topic and on scientific progress, broadened considerably. I also learnt to work simultaneously on multiple problems. In this way the chance on actual progress increases.’
‘Also, I learnt to sit back and talk about the topics in research with my colleagues, and be open to their ideas. In that sense I matured as well. I find it rewarding to see that some experimentalists can benefit from our simulation work. Simulations can contribute to better understanding of the phenomena under research, designing and performing novel experiments from there.’
After his PhD Defence, Shantanu prefers a job in industry, for example at Shell Bangalore Research Centre.
‘Here a lot of interesting research programs are carried out,’ he says. ‘As an experienced person on molecular dynamic simulations, I can be of added value, for example on clarifying various catalysis reactions. Although academic research is more fundamentally driven, I don’t expect essential differences in working on such topics and subjects of research within industry.’