Antoine Legrain

Elastocapillary self-folding of micro-machined structures – capillary origami

Promotion date: November 19.

Promotor: Prof. dr. ir. Leon Abelmann

Assistant Promotor: Dr. Niels Tas

Micro-technology is tied to photo-lithography which consists on applying a mask on a planar surface, silicon wafers, through UV illumination. Machining in three dimensions is nearly impossible, or limited to expensive techniques.

In a two-dimensional flat and organized configuration, one unit can be linked to only four neighbors. Within a cube the number of possible connections with neighbors increase to six. When considering millions of units the difference in interconnections is big. New fabrication paradigms are necessary to overcome these limits.

Origami might be such an innovating concept within micro-technologies. In this thesis capillary forces are used to assemble micro-machined structures - the so-called capillary origami technique.

First, flexible micro-structures were fabricated using traditional fabrication techniques that are fully compatible with any micro-machining process. Droplets of water were then applied to the foldable objects. Through evaporation, the liquid tends to reduce its surface in contact with air, always keeping its spherical shape, and provokes bending. The moving parts meet during folding and adhere thanks to strong forces at this scale. After wetting the structures, and letting the water dry, 3D structures arise at the size of a grain of salt!

Advances with capillary origami are made, for example by designing structures with a central tube through which water could be provided by a pump in order to trigger the folding. Also it was shown that conducting metal lines, running on top of the hinges, could be bent. Also thousands of thin ribbons were folded in one go after immersion in water.

Was the approach of your research original from the beginning?

Actually the project had already started when I arrived, as I took over the work of Joost van Honschoten who passed away in 2011. I was able to fulfill his Veni project. The last two years of my PhD-period were financed additionally. In this project I was to use the same technique as José Bico and his team in Paris on elastocapillary folding, but this time in the micro-scale. The collaboration with Bico started during the last year of my PhD. The Gracias group is very active in the field of self-folding.

At the start of the PhD-project I was allowed to define some new research lines. During this search period, I came into contact with self-folding techniques deployed by American scientists. Their results were promising, and together with colleagues from Paris we started studies into strategies using water only, and construct 3D-structures from there. In the last year of my project, the most salient results were achieved.

Did you collaborate with other researchers on this project?

Within Mesa+ we collaborated theoretically with professor Jacco Snoeijer, allied to the Physics of Complex Fluids Group. In theory and macro-scale applications, we were happy the ESPCI Paris Tech School contributed with their expertise. Cleanroom technician Erwin Berenschot was of great help during this project. 

In what journals did you publish your results?

One article was published in the Journal of Applied Physics. Two others are submitted in peer-reviewed journals; they are currently available on ArXiv. A last article is in preparation with collaborators in Paris. I also published in PLOS 1: an open source journal that is rapidly arising. Further, I was a speaker on the NEMS conference in China.

My work was under attention in the international, national and regional press, as this line of research is very appealing to the public. I experienced this as a nice extra result, making my work and knowledge accessible to the public. For example, Huffington Post asked me to write an article on their well-read blogs pages.

In what way did you develop as a scientist and researcher during your PhD project?

As coming from an engineering background, I was not very used to performing complex experimental research projects. This I learned now in an expertise field that was very different form my original one. Also I learned many cleanroom techniques from scratch, such as microfabrication, which I had never worked on before. Working in a team is also something I learned, from my supervisors and colleagues.

What are your future plans?

I would like to stay in academic research, to further develop my skills, as I like to learn new things every day, and the freedom to give substance to my own line of research. In striving for this, I leave open every possibility. For example a research position in North America would be great.

How do you remember your working period at Mesa+?

The experience and the cleanroom equipment available, is one of the major strong points of Mesa+. The atmosphere of working I appreciated especially. The colleagues were always willing to help, and the scientific staff was supportive all the way through, never pushing me in a preconceived direction.