Complexity in nature, whether in chlorophyll or in living organisms, is often derived from a self-assembly and is considered particularly firm. Compact clusters of elemental particles of practical relevance, and can be shown in atomic nucleus, nano particles or viruses. Researchers at Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) have decoded the structure and process behind to form one class of such clusters of orders. Their perceptions have increased understanding of how structures are formed in clusters.
In physics, cluster is defined as the form of independent material in the transformation area between isolated atoms and solid objects or more extensive fluids. Magic magic clusters can be traced back to the work of Eugene Wigner, Maria Göppert-Mayer and Hans Jensen, who used this theory to explain the stability of a nuclear atomic nucleus that won a Nobel prize for physics for their research in 1963. So far , scientists have assumed that the effect is caused solely as a result of the atomic attraction, "said Professor Dr Nicolas Vogel, the Teacher for a Chronicle Synthesis. Our research now proves that particles that do not attract each other also form structures such as these. Our announcement contributes to a greater understanding of how structures are generally formed in clusters. & # 39;
The research has based on interdisciplinary cooperation: Professor Dr Nicolas Vogel, researcher in the Commonwealth Technology Chair, and Professor Dr Michael Engel, researcher at the Multi-Scale Simulation Characterist – from & # 39; The Chemical and Biological Engineering Department – has worked closely with the materials science specialist, Professor Dr. Erdmann Spiecker by the Chair of Materials Science (investigating micro and nanostructures), combining their expertise of different areas. Vogel was responsible for synthesis, Spiecker for structure analysis and Engel for modeling clusters of colloidal polymer balls. The colloidal term of the ancient Greek word is for glue and refers to particles or droplets that are split into a dispersed medium, either solid object , gas or liquid. Our three approaches have been closely linked to this project, & # 39; underlines Professor Engel, they match each other and allow us to have a deep understanding of the basics behind the formation of structures for the first time. & # 39;
Structures are assembled themselves
The first step for researchers in a process that encompassed several stages was the synthesizing of minute colloidal clusters, not more than one tenth of a single hair diameter. First of all, water evaporates from emulsion droplet and the polymer balls are pushed with each other. Over time, they gather stunning clusters increasingly acute and start crystallizing. Unbelievably how many thousands of individual particles independently find an ideal position in an accurate and proportionate structure where each particle is placed in predictable jobs, Professor Vogel.
The researchers discovered more than 25 different coloidal clusters of different shapes and sizes and can define four cluster physiology differently: where evaporation was quicker, bullet clusters were formed, as the droplet interface was moving faster than it could reinforced colloidal particles. If the evaporation rate was reduced, the clusters were predominantly spherical. Spherical clusters have a completely dressed face with only a weak pattern of crystals. Clusters have been formed with ecological proportionality as the evaporation rate decreases further. These clusters have a high degree of symmetry and have a number of two, three or five proportional axis.
The use of high resolution microscopy to show the cluster face provides insufficient proof of these symmetries. Even if the cluster face appears to be very good orders, it is not certain that the particles inside the cluster are arranged as expected. To check this, the researchers used electronic tomography, which is available at the Erlangen Center for Nanoanalysis and Electron Microscopy (CENEM). Individual clusters are bombed with highly energetic electrons from each direction and the images are recorded. Of more than 100 projections, researchers were able to rebuild the three-dimensional structure of the clusters and therefore the pattern of particles within the clusters in a computerized tomography reminder such as that used in medicine.
In the next stage, researchers conducted simulations and accurate numerical calculations. The analyzes proved that clusters that contain numbers of particles matching magic numbers are indeed more stable, as predicted based on the theory. It is known that the icosahedral symmetry found in viruses and high-metal metal clusters, but was not investigated directly. Now, with these results, there is a detailed and systematic understanding of how magic number clusters are formed in the example system that was investigated for the first time, allowing collections on for other natural systems where clusters tend to be formed.
University of Erlangen-Nuremberg. .