We all have heard at one point that crystals have an organized arrangement of atoms at the molecular level. Such an arrangement translates into a given pattern, which can be unbelievably orderly and give rise to intricate structures. A remarkable example is the coccolith – a calcium carbonate plate – that comprises the body structure of a single-celled marine algae called Emiliania huxleye coccolithophore. This specimen uses confinement to control the growth of its meticulous skeletons, which often have very remarkable toughness properties. For us scientists, such examples are natural inspirational masterpieces.
Crystals; however, do not always possess such a devilishly organized pattern – at least not at a glance. What about edible crystals, for instance? Yes, we eat crystals too, and on a daily basis! Some of you may be familiar with the rock candy or sugar crystals. If not, then you are missing out, and you should definitely try to grow your own sugar crystal on a stick. The outcome is a wild and fierce structure comprised of large crystals nucleating in all directions. With rock candy crystals in mind, one may really wonder how the coccolithopore algae can “tame” the crystal growth to shape their elaborate shields… A natural wonder!
In my research, I am looking into factors that influence and control crystal growth. Zooming in, my studies focus on understanding the growth of minerals in tiny confined spaces. Why would this matter at all? For starters, chemical reactions occurring in miniscule spaces are essential to gadgets we use today. And such devices have been further and further miniaturized over the years. Preventing their malfunction due to uncontrolled crystal growth in the liquid phase (inside your device) could be one of the outcomes of research like mine. Other fields take advantage from this knowledge as well, including scientists who are studying the growth of bones or even rock deformation leading to earthquakes. It is a beautifully broad and interdisciplinary subject.
On a daily research basis, one of the next mysteries to be solved is how the growth of crystals in tiny spaces differ from those in ‘bulk solutions’ or larger spaces. For the science-passionate people out there, it can be counterintuitive at first, but the growth is often slower in confined spaces (if you are using the same mineral, or ion, concentration with no evaporation, of course). One can say it is somewhat ‘frozen in time’ because it generally takes longer for a stable crystal cluster – or nuclei – to form. This fact, in reality, means that in confined spaces, a crystal will need a longer time to form due to reduced ion mobility. Such a feature allows scientists to control the shape while aggregation is happening because it is somewhat more moldable. Human-controlled crystals with more complex shapes can be then produced. Such process can inspire advanced cements that might be useful for fixing fractured bones, for example. Keep in mind; however, that this is not what happens in regular supersaturated solutions such as the one giving rise to rock sugar candy. Somehow mysterious, isn’t it?
I am excited about the mineral reactivity in confinement, and I hope to pursue further research on this topic. While there are a lot of extremely advanced methods to characterize mineral growth and reactivity on single, isolated mineral surfaces, there are fewer possibilities to study the growth reactions in confinement with the same level of detail. This fact is the basis for much greater learnings – especially considering that confined reactions are important everywhere, from geology to the human body.
Sounds engaging? Get your hands dirty and make your own sugar crystal next. Or for those looking for more of a rock(et) science type of discovery, check out our recent paper: Dziadkowiec, J., et al. (2019). Nucleation in confinement generates long-range repulsion between rough calcite surfaces. Scientific reports, 9(1), 1-15.
I am Joanna Dziadkowiec, and I am a post-doc affiliated with the Njord research group at the University of Oslo and Applied Interface Physics group at Vienna University of Technology. The research work described above is funded by the Research Council of Norway.
WHAT IS IN YOUR SUGAR CANDY?
Text by Fernanda Haffner
Illustration by Marion Couturier