Materials Colloquium 2020 - September, 9th, 16:30

Zoom

Roland Logé (Laboratory of Thermomechanical Metallurgy, Institute of Materials, EPFL)

Laser Powder Bed Fusion (LPBF, also known as SLM, Selective Laser Melting) is a well known Additive Manufacturing technology, among the most studied in literature for metals and alloys. A number of drawbacks however still limit its range of applications, among which : (i) the high level of residual stresses; (ii) the often narrow safe processing window, which does not leave much space for microstructure optimization; (iii) the time consuming search for optimum laser parameters, which is material and machine dependent, and also relates to the part size and shape. To solve some of these issues, we introduce a new hybrid “3D LSP” manufacturing process, combining Laser Shock Peening (LSP) with LPBF. 3D LSP can efficiently strain harden a metal and convert LPBF induced Tensile Residual Stresses into CRS. It opens a range of new possibilities such as increased fatigue life or geometrical accuracy, 3D design of grain structures, and improved processability. We also present a new “translation rule”, which is able to predict optimum LPBF parameters for one material, based on those found for another material, using the concept of normalized enthalpy.

Overview Materials Colloquium 2020

Materials Colloquium 2020 - September, 9th, 16:30

Zoom

Chiara Gattinoni (Materials Theory, D-MATL, ETH Zürich)

A precise understanding of the surface and interface behavior of ferroelectric materials is necessary towards their use in promising applications such as memory storage or catalysis. In this seminar I will focus on the example of lead titanate and bismuth ferrite to describe how structural and electronic properties affect ferroelectricity at the nanoscale. I will show that surfaces and interfaces play a pivotal role in (de)stabilizing the ferroelectric polarization in thin films and nanoparticles. I will then investigate how the special properties of ferroelectric surfaces can be used to create efficient catalytic devices.

Overview Materials Colloquium 2020  

Special Edition of the Materials Colloquium 2020

July, 23rd, 15:00

Zoom

Elsa Olivetti (MIT, Department of Materials Science and Engineering)

Materials have long played a role in transitioning between eras. Now the materials community’s most pressing task is to decarbonize society. For the past several decades, materials science has played a key role in lowering carbon dioxide emissions from the electricity sector through development of renewable energy generation and high performing energy storage technologies. However, outside of the energy sector there remain significant greenhouse gas emissions linked to materials production, particularly in the form of infrastructure and chemicals production. This presentation focuses on the significant challenge of reducing the burden of materials production itself. I will review recent progress in understanding the potential for decarbonization in the materials production sector and describe where and how the material science community can have significant impact.

Overview Materials Colloquium 2020  

Materials Colloquium 2020 - May, 13th, 16:30

Zoom

Shovon Pal (Multifunctional Ferroic Materials)

The goal of observing electrons in motion in real time took a leap forward with the use of short laser pulses. First we use a laser pulse to knock or perturb electrons from their equilibrium position in their respective energy landscape, say for example with optical or infrared energies. This pump pulse will then be followed quickly by a terahertz laser probe that reveals the status of the hole that electron leaves behind or even the various scattering routes that the electrons take while relaxing back. If we do this repeatedly for a couple of times, we can find out exactly how the electron is moving and what it is getting up to. In my talk, I will use this simple ideology on materials with fundamentally different band structures and show what we can learn.

Overview Materials Colloquium 2020

 

Materials Colloquium 2020 - April, 22nd, 16:30

Zoom

Sandra Skjærvø (Mesoscopic Systems)

Artificial spin systems are arrays of nanomagnets that are fabricated through state-of-the-art lithography techniques. The nanomagnets interact through dipolar coupling and, depending on the arrangement of the nanomagnets, the system can order magnetically. With X-ray Photon Correlation Spectroscopy, we aim to understand the evolution of the magnetic order in an artificial spin system with square geometry through the known antiferromagnetic phase transition. Below the phase transition at T_N, the system is in a single-domain antiferromagnetic ground state. Upon heating, slow fluctuations in the system lead to striking speckle patterns with distinct features and long life times. The small size and rectangular shape of the array of nanomagnets provides a possible explanation for the distinctness of the speckle patterns, with stripe-like domains nucleating at and propagating from the edges of the array, in line with previous observations.

Overview Materials Colloquium 2020

Materials Colloquium 2020 - April, 1st, 16:30

Zoom

Yaroslav Romanyuk (EMPA Dübendorf)

Thin-film solar cells belong to the so-called second generation of solar cells, whereby a thin semiconductor absorber layer of 1…5 microns is used to fully absorb incoming sunlight. The talk will describe current status and research challenges for three thin-film technologies based on Cu(InGa)Se2, CdTe and organometal lead halide perovskites, which have demonstrated power conversion efficiencies in the 22-25% range. All technologies are being actively investigated at the Laboratory for Thin Films and Photovoltaics at Empa: https://www.empa.ch/web/s207

Overview Materials Colloquium 2020

Yinyin Bao (D-CHAB)

Additive manufacturing (commonly called 3D printing) has attracted great attention due to its powerful ability to create complex 3D geometries with precise microarchitectures. In combination with medical imaging techniques, it might provide enormous opportunities to design customized drug formulations and biomedical devices.1 Among the existing 3D printing techniques, digital light processing (DLP) emerged with high resolution and surface quality, desktop size, designable materials and relatively low cost, which is based on a localized light-initiated photopolymerization process, taking place in a bath containing liquid (macro)monomers and photoinitiators. However, the lack of biocompatible and biodegradable materials suitable for DLP limits their application in the biomedical area, especially for the manufacture of elastic personalized devices.2 As a typical elastic implant, airway stents are designed to simulate the airway anatomy providing palliation of symptoms in patients suffering from central airway obstruction.3 However, the clinical use of commercial one-size-fits-all stents is often constrained by the geometrical mismatching to the complex tracheabronchial anatomy of individual patients,4 this could be changed by personalized 3D printing. We aim at the development of biodegradable polymeric materials for DLP 3D printing with highly tunable mechanical properties, towards the manufacture of personalized airway stents. This work opens new perspectives for developing precise personalized medical devices with biodegradability as well as high mechanical properties by 3D printing.
References
1. Zhao, H.; Yang, F.; Fu J.; Gao, Q.; Liu, A.; Sun, M.; He, Y. ACS Biomater. Sci. Eng. 2017, 3, 3083.
2. Zhang, J.; Xiao, P. Polym. Chem., 2018, 9, 1530.
3. Lee P.; Kupeli E.; Mehta A. C. Clin. Chest Med. 2010, 31, 141.
4. Dutau, H.; Musani, A. I.; Laroumagne, S.; Darwiche, K.; Freitag L.; Astoul P. Respiration 2015, 90, 512.

Overview Materials Colloquium 2020

Guido Panzarasa (Soft and Living Materials)

Living systems can grow bottom-up a huge variety of materials with the highest degree of sophistication and an overall efficiency that remains largely unparalleled by artificial fabrication techniques. Moreover, living materials are adaptive i.e. are able to exist and perform autonomously under dissipative conditions. These features are possible thanks to the ability to control complex reactions networks, carefully organized in spatio-temporal sequences. Filling the gap between state-of-the-art stimuli-responsive materials and living materials requires to combine materials science with systems chemistry. In this way, chemical curiosities such as clock and oscillating reactions become versatile tools to program in time the autonomous and transient self-assembly of organic as well as inorganic building blocks. The design of such ad hoc reaction networks is at the core of my current research efforts. I will show how to “clock” molecules, polymers and metal cations into different structures (from nanoparticles to gels), without the need for external control, and how this approach can pave the way to the development of (almost) living artificial materials.

References:

1. Panzarasa*, A. Osypova, A. Sicher, A. Bruinink, E. R. Dufresne, Controlled formation of chitosan particles by a clock reaction Soft Matter 2018, 14, 6415–6418 DOI: 10.1039/C8SM01060A
2. Panzarasa*, Eric R. Dufresne, Impact of in situ acid generation and iodine sequestration on the chlorite-iodide clock reaction Chaos 2019, 29, 071102 (5 pp) DOI: 10.1063/1.5108791
3. Panzarasa*, T. Sai, A. L. Torzynski, K. Smith-Mannschott, E. R. Dufresne, Supramolecular assembly by time-programmed acid autocatalysis Mol. Syst. Des. Eng. 2020 DOI: 10.1039/c9me00139e
4. Panzarasa*, A. L. Torzynski, T. Sai, K. Smith-Mannschott, E. R. Dufresne, Transient supramolecular assembly of a functional perylene diimide controlled by a programmable pH cycle Soft Matter 2020, 16, 591-594 DOI: 10.1039/C9SM02026H
5. C. C. M. Sproncken, B. Gumí-Audenis, G. Panzarasa, I. K. Voets, Two-stage polyelectrolyte assembly orchestrated by a clock reaction ChemSystemsChem 2020 (accepted)

Overview Materials Colloquium 2020