See 2018

WETTING AND DEWETTING EFFECTS OF BUBBLES, DROPLETS AND SOLIDS

In this thesis wetting interactions of auxiliary body phase with many types of patterned substrates and with various other interactions are investigated. ‘Overall Young’s Law and Young-Laplace equation were always observed,’ says Ivan Dević. ‘However, with increasing complexity of patterns, various side-effects occur.’ 

In this thesis, pure theoretical considerations in combination with numerical experiments were central. ‘My work is part of a national NWO program in which the three Dutch technical universities participate in the Center for Multiscale Catalytic Energy Conversion,’ Ivan says. ‘Extended knowledge of bubbles and droplets on catalytic surfaces is very desirable, as in daily practice reaction surfaces are never completely homogeneous.’

Deformations in interface shapes were studied, for example by decorating flat surfaces with microcaps. Analysis of equilibrium shapes revealed that the droplet position - whether it is on the microcap, the flat substrate or at the microcap rim - is only dictated by values of surface tensions present in the system, and are completely independent of the droplet size.

Already in the first stages of his PhD research project, Ivan obtained nice results, which were published in renowned journals. ‘The first publication was a big step,’ he says. ‘Three publications were published in 2016 and 2017. One is underway still, hopefully to appear very soon now.’

Results

In the fourth chapter, Ivan showed that, under certain conditions, droplets will either completely wet the elliptical patch, or it will start spreading on the lyophobic part of the substrate, although there is a finite amount of the lyophilic patch available to the droplet.

‘In the next phase of research, we introduced external body forces to the droplet,’ Ivan says. ‘We were able to present a full thermo-dynamical calculation of equilibrium shapes. Qualitative difference between my present work and current literature, is that we included contact energy into our calculations.’

Solid state wetting

Ivan feels most proud on developing a numerical code for simulating the process of solid-state dewetting.

‘Applying theory and simulation techniques to this new area of research, was an idea in which I had complete “creative” freedom,’ he says. ‘Also I discovered, and pointed out, the gap of knowledge that conventional literature not yet covered. The atom migration in solids during deformations, for example above 800 centigrade, proved quite similar energetically to droplets and bubbles.’

When researching the effect of substrate physical singularities on the solid dynamics, Ivan concluded that the contact line behaviour shines light on a lot of novel qualitative properties of solid-state dewetting.

In the last chapter he introduced chemical patterning to the solid-state dewetting research. While this induces many complex contact line behaviours, it clearly showed that the solid-state dewetting is completely a contact line driven problem. Future career

Ivan prefers to go and work in industry, after his PhD Defense. ‘I like to return to my home town, Split in Croatia,’ he says.

 ‘I would like to develop some more skills, making it possible for me to work in the automobile or IT sector. In Split business opportunities are present, to perform research on further developments in electronic cars. It would be great if I can use my expertise in physics of fluids here. The automotive industry appeals to me. As a boy already I was fond of the romantic sounds of the Formula I. And for me Michael Schumacher was a hero, and Ross Brawn is someone who was more of an inspiration.’