Some pictures from the 2019 group hike to several caves near Muggendorf in the Franconian Switzerland.

At the end of the Mehlbeerensteig.
Exploration of the Kammerfelsen
Dripstone in the Doktorshöhle.

Fractional crystallization is crystal formation out of chemical mixtures or solutions. In this process, the growing crystal typically has a different composition than the fluid. This makes fractional crystallization an important method for separating or purifying substances based on differences in solubility. In geology, fractional crystallization is operating within the Earth’s crust and mantle during the formation of igneous rocks.

The simplest case of fractional crystallization in simulation is the crystallization of hard spheres. Praveen Bommineni, MAP student Nydia Varela-Rosales and Marco Klement in the group of Michael Engel now calculated the crystallization behavior of mixtures of hard spheres as a function of size-dispersity (composition) and packing fraction (density). The work was achieved using advanced statistical sampling to speed up simulation and access long times required for observing the crystallization phenomenon. The crystals discovered have relevance for the behavior of nanoparticles, micelles, and the structure of alloys and the elements.

Crystallization from size-disperse mixture of spheres.

Complex Crystals from Size-Disperse Spheres
P.K. Bommineni, N.R. Varela-Rosales, M. Klement, M. Engel
Physical Review Letters 122, 128005 (2019)

After two years of construction and several more years of planning, the new Interdisciplinary Center for Nanostructured Films (IZNF) is now ready for research groups. Our group moved in today!

The new lab is in the heart of the Technical Faculty of FAU next door to our experimental collaborators.

Streetview of our new building IZNF at Cauerstraße 3.
Alberto Leonardi and Chrameh Mbah testing the new workplace.

In a joint collaboration combining experiment (synthesis and self-assembly), analysis (electron microscopy including tomography), and simulation (molecular dynamics and free energy calculations), a team from FAU involving Junwei Wang and Chrameh Mbah reported magic number colloidal clusters:

“Clusters in systems as diverse as metal atoms, virus proteins, noble gases, and nucleons have properties that depend sensitively on the number of constituent particles. Certain numbers are termed ‘magic’ because they grant the system with closed shells and exceptional stability. To this point, magic number clusters have been exclusively found with attractive interactions as present between atoms. Here we show that magic number clusters exist in a confined soft matter system with negligible interactions. Colloidal particles in an emulsion droplet spontaneously organize into a series of clusters with precisely defined shell structures. Crucially, free energy calculations demonstrate that colloidal clusters with magic numbers possess higher thermodynamic stability than those off magic numbers. A complex kinetic pathway is responsible for the efficiency of this system in finding its minimum free energy configuration. Targeting similar magic number states is a strategy towards unique configurations in finite self-organizing systems across the scales.”

Read about it here:

Magic Number Colloidal Clusters as Minimum Free Energy Structures
J. Wang, C.F. Mbah, T. Przybilla, B.A. Zubiri, E. Spiecker, M. Engel, N. Vogel
Nature Communications 9, 5259 (2018)

A paper involving Michael Engel with coauthors Joshua Anderson and Sharon Glotzer from University of Michigan, Masaharu Isobe from Nagoya Institute of Technology, Etienne Bernard then from Massachusetts Institute of Technology, and Werner Krauth from École Normale Supérieure has been chosen as a Milestone Paper “that made significant contributions to their field” among all articles published in the journal Physical Review E in 2013.

Hard-disk equation of state: First-order liquid-hexatic transition in two dimensions with three simulation methods
Michael Engel, Joshua A. Anderson, Sharon C. Glotzer, Masaharu Isobe, Etienne P. Bernard, and Werner Krauth
Phys. Rev. E 87, 042134 (2013)

Several members of the lab traveled to present and promote their newest research results at conferences throughout Germany:

In a recent ACS Nano publication, Alberto Leonardi proposes an etching synthesis method for controlling the shape of core-shell nanocrystals:

“The application of nanocrystals as heterogeneous catalysts and plasmonic nanoparticles requires fine control of their shape and chemical composition. A promising idea to achieve synergistic effects is to combine two distinct chemical and/or physical functionalities in bimetallic core@shell nanocrystals. Although techniques for the synthesis of single-component nanocrystals with spherical or anisotropic shape are well-established, new methods are sought to tailor multicomponent nanocrystals. Here, we probe etching in a controlled redox environment as a synthesis technique for multicomponent nanocrystals. Our Monte Carlo computer simulations demonstrate the appearance of characteristic non-equilibrium intermediate microstructures that are further thermodynamically tested and analyzed with molecular dynamics. Convex platelet, concave polyhedron, pod, cage, and strutted-cage shapes are obtained at room temperature with fully coherent structure exposing crystallographic facets and chemical elements along distinct particle crystallographic directions. We observe that structural and dynamic properties are markedly modified compared to the untreated compact nanocrystal.”

Read about it here:

Particle Shape Control via Etching of Core-Shell Nanocrystals
A. Leonardi, M. Engel
ACS Nano 12, 9186-9195 (2018)

Artistic visualization of core-shell nanocrystal etching. Image credit: Alberto Leonardi.

The MSS Institute organized a trip to Fränkische Schweiz that consisted of a canoe/kayak ride down the river Wiesent from Wiesental and a short hike up the hill where we had a beautiful view and lunch under a big Tilia tree.

We all arrived back at the rental station without getting too (but still a little bit) wet.
View from Gasthaus zum Pfaffenstein in Moritz.

Michael Engel presented the opening lecture at the ICMS conference “Quasicrystals: pattern formation and aperiodic order” in Edinburgh. This conference brought together four different research communities to advance the understanding of quasicrystals and aperiodic order: (i) quasicrystals in materials science, (ii) quasicrystals in soft matter, (iii) quasicrystals in partial differential equations and (iv) quasicrystals in aperiodic tilings.