Category Materials Colloquium

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Tuning polymer dispersity by photoinduced ATRP: monomodal distributions with ppm copper concentration

Richard Whitfield (Polymeric Materials – D-MATL)

Unlike natural biopolymers, such as DNA and proteins, synthetic polymers have a distribution of different molecular weight species. This distribution is measured by a dispersity value and has a significant influence on polymer properties. It is therefore highly beneficial to develop strategies to systematically tune the dispersity, however, current methods are limited to bimodal molecular weight distributions, adulterated polymer chains, or low end‐group fidelity and rely on feeding reagents, flow‐based, or multicomponent systems. To overcome these limitations, we have developed a simple batch system whereby photo-induced atom transfer radical polymerisation is exploited as a convenient and versatile technique to control the dispersity of both homopolymers and block copolymers. By varying the concentration of the copper complex, a wide range of monomodal molecular weight distributions can be obtained. In all cases, high end‐group fidelity was confirmed by MALDI‐ToF‐MS and exemplified by efficient block copolymer formation. Importantly, our approach utilises ppm levels of copper (as low as 4 ppm), can be tolerant to oxygen and exhibits perfect temporal control, representing a major step forward in tuning polymer dispersity for various applications.

Can 2-D Materials Save Moore’s Law?

Mathieu Luisier (Integrated Systems Laboratory – D-ITET)

Since the first experimental demonstration of a monolayer MoS 2 transistor in 2011, transition metal dichalcogenides (TMDs) have received a wide attention from the scientific community as potential replacement for Silicon FinFETs at the end of the semiconductor roadmap. As graphene, TMDs exhibit excellent electrostatic properties due to their 2-D nature, but contrary to it, they are characterized by large band gaps, while keeping decent mobilities. However, so far, no transistor based on a TMD channel could outperform the Si technology. While this limitation can be partly attributed to technical issues, the TMD bandstructure also explains this behavior: electrons/holes are not fast enough to allow for large ON-state currents. Through density functional theory (DFT), the existence of more than 1,800 2-D materials was recently predicted. Among them there might be components with better transport properties than TMDs. We therefore selected 100 monolayers out of this database, combined DFT and quantum transport to simulate their “current vs. voltage” characteristics, and identified 13 candidates with both n- and p-type ON-state currents larger than what Si FinFETs are expected to deliver in the future. In this talk, I will present the results of this study.

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Zoom: https://ethz.zoom.us/j/63151988666

From binary lipid-water phase diagrams to lipid nanoparticle-based mRNA
COVID-19 vaccines

Peter Walde (Laboratory for Multifunctional Materials – D-MATL)

The aim of the talk is to emphasize that basic research on the aggregation behavior of amphiphilic lipids in aqueous solution and on the controlled formation of lipid vesicles (liposomes) for drug delivery applications was essential for the successful development of lipid nanoparticle-based mRNA COVID-19 vaccines.

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Zoom: https://ethz.zoom.us/j/64504425191

Fuel cells, batteries, electrolyzers, etc.: some insights from a materials science point of view

Lorenz Gubler (Electrochemistry Laboratory – PSI)

Electrochemical storage & conversion technologies are expected to play a pivotal role in the energy transition and defossilization of our economy. In addition to batteries used for grid-scale energy storage and electromobility, electrochemical conversion devices using or producing hydrogen, i.e. fuel cells and electrolyzers, can contribute to reducing the carbon footprint of the transport sector and chemical industry. In this seminar, we will be looking at the state-of-the-art of these devices, and highlight selected challenges regarding the choice of cell materials and components. Examples from the research on these topics will be shown to illustrate current limitations of the technology and future prospects.

Do soft solids have strain-dependent surface tension?

Nicolas Bain (Soft and Living Materials – D-MATL)

Despite its importance in any adhesion and wetting phenomena, there is a fundamental property that is not yet understood in soft solids: surface elasticity. Also called the Shuttleworth effect, surface elasticity can be boiled down to one question. Does stretching the surface of a soft solid change its surface tension? In 2017, Xu et. al designed an experiment in which the opening angle of a wetting ridge was a proxy to evidence a dramatic increase of surface tension with stretch. In 2019, however, Masurel et al. claimed that the coupling between nonlinear mechanics and the singular nature of the wetting ridge suffice to explain the behavior of the opening angle observed by Xu et al, without invoking the Shuttleworth effect. The question, therefore, remains open. This presentation will focus on an experimental setup with no geometric singularity, that leaves no doubt on the existence or absence of surface elasticity in soft solids, hopefully closing this long-lasting controversy.

Q. Xu, K. E. Jensen, R. Boltyanskiy, R. Sarfati, R. W. Style, and E. R. Dufresne, Nature communications 8, 1 (2017).
R. Masurel, M. Roché, L. Limat, I. Ionescu, and J. Dervaux, Physical review letters 122, 248004 (2019).

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Zoom: https://ethz.zoom.us/j/66776813667

Interface stability in all-solid-state batteries

Corsin Battaglia (Materials for Energy Conversion – EMPA Dübendorf)

All-solid-state batteries combining an alkali metal anode and a high-voltage cathode have the potential to double the energy density of current-generation rechargeable batteries. However, interface stability remains a major challenge. On the anode side, alkali metal dendrites penetrating into the solid electrolyte limit the maximum plating current density and prevent fast charging, while on the cathode side the limited oxidative stability of solid electrolytes is a major challenge, especially when the battery is charged beyond 4V.
We recently discovered that the critical current density for dendrite formation in the archetypical ceramic solid electrolyte Na-β”-alumina can reach 10 mA/cm2 at room temperature, which is ten times higher than that measured on a garnet-type Li7La3Zr2O12 electrolyte [1]. Further, we demonstrated that above the melting temperature of sodium, a cumulative capacity of >10 Ah of sodium can be plated and stripped at an unprecedented current density of 1000 mA/cm2 without dendrite formation [2] indicating that the alkali metal and not the electrolyte prevent fast charging at room temperature.
We recently also demonstrated the integration of hydroborate electrolytes with a 4 V class cathode through in-situ formation of a passivating interface layer [3]. Combined with their high ionic conductivity >1 mS/cm at room temperature, low gravimetric density 1.2 g/cm3, low toxicity, high thermal and chemical stability, stability vs lithium and sodium metal, soft mechanical properties enabling cold pressing, compatibility with solution infiltration, and potential for low cost, hydroborate electrolytes represent a promising option for a competitive next-generation all-solid-state battery technology [4].
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[1] M.-C. Bay, M. Wang, R. Grissa, M. V. F. Heinz, J. Sakamoto, C. Battaglia, Adv. Energy Mater. 2019, 201902889
[2] D. Landmann, G. Graeber, M. V. F. Heinz, S. Haussener, C. Battaglia, Materials Today Energy 2020, 18,
[3] R. Asakura, D. Reber, L. Duchêne, A. Remhof, H. Hagemann, C. Battaglia, Energy Environ. Science 2020, 13, 5048
[4] L. Duchêne, A. Remhof, H. Hagemann, C. Battaglia, Energy Storage Mater. 2020, 25, 782

Sculpting hydrogels using advective processing

Alexandra Bayles (Soft Materials – D-MATL)

Polymeric hydrogels, water-laden 3D crosslinked networks, find broad application as advanced biomaterials and functional materials due to their biocompatibility, stimuli responsiveness, and affordability. In these materials, the crosslinking density reports material properties such as elasticity, strength, permeability, and swelling propensity. Patterning this critical design parameter across the volume polymerized is an attractive means by which to engineer hydrogel performance. In this talk, we present a novel processing scheme that uses laminar flow to direct the organization of hydrogel crosslinking density across a single sample. Inspired by techniques used to structure polymeric melts, we design custom millifluidic devices that force disparate streams through serpentine splitting, rotation, and recombination elements. These elements multiply the advecting macromer concentration distribution within the cross-sectional area while preserving its relative spacing and orientation. Incorporating advective assembly devices into conventional 3D printing nozzles enables the fabrication of hierarchical, shape-morphing hydrogels. This work exemplifies advective processing’s potential to encode soft material microstructure and subsequently functionality through geometrically dictated, generalizable flows.

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Open Access – funding opportunities and requirements within and outside ETH Zurich

Rainer Rees Mertins (ETH library – Open Access specialist)

The transformation in scholarly publishing is reflected in the increasing importance of open access, which is  becoming the new standard. The rapid growth of Open Access has been fueled by several factors. One of the most important being the requirements of science funders to make publicly funded research results available to the public. Nevertheless, many scientists also support open access publishing because they are skeptical towards the traditional publishers, the facilitated re-use of publications and the higher citation rates of open access publications. The talk will cover background information on open access and its advantages, but will mainly focus on the practical aspects and how ETH members can publish open access either via library funding or as green open access in the Research Collection. The open access requirements of the
most important funders as well as the institutional open access policy will also be covered.

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Materials design for fast charge storage enabled by the mechanistic insights

Maria Lukatskaya (Electrochemical Energy Systems Laboratory – D-MAVT)

As electronic technology advances, the need in safe and long-lasting energy storage devices that occupy minimum volume arises. Short charging times of several seconds to minutes, with energy densities comparable to batteries, can be achieved in pseudocapacitors: a sub-class of supercapacitors, where capacitance is mediated by fast redox reactions and thus enables at least an order of magnitude more energy to be stored than in typical double layer capacitors. However, traditional pseudocapacitive materials are often high in cost and/or suffer from low cycling stability.
In my talk, I will discuss how the key performance metrics of pseudocapacitors – capacitance and charging rates – can be pushed to the limits in the materials that combine good electrical and ionic conductivities (ensuring fast charge transfer and hence charging rates) with high density of redox-active sites. In particular, I will discuss the electrochemistry of 2D transition metal carbides (MXenes) and 2D conductive metal-organic frameworks, with an emphasis on the mechanism of charge storage and electrode design.

Current-driven magnetic domain-wall logic

Zhaochu Luo (Mesoscopic Systems – D-MATL)

Development of complementary metal–oxide–semiconductor (CMOS) logic is expected to approach its fundamental limit as the scaling down of the CMOS technology is reaching an end. As a route to extend the technology roadmap beyond traditional CMOS logic, novel spin-based logic architectures are being developed to provide nonvolatile data retention, near-zero leakage, and scalability. In particular, architectures based on magnetic domain walls (DWs) take the advantage of the fast motion, high density, non-volatility and flexible design of DWs to process and store information. Such schemes have so far relied on DW manipulation and clocking using an external magnetic field, which hinders their implementation in dense, large-scale chips. Here we demonstrate a method for performing all-electric logic operations and cascading using DW racetracks. Our concept for the magnetic DW logic is based on current-induced DW motion in magnetic nanowires with tunable magnetic anisotropy and chiral interactions. Our work provides a viable platform for scalable all-electric magnetic logic, which could be used for memory-in-logic applications.

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Straining films: a versatile design tool for ferroic materials

Kathrin Dörr (Martin Luther University Halle, Germany)

There is nearly no strain-free thin film on a substrate, and such films are a foundation of modern technologies. Therefore, it has been learned long ago how to exploit film stress / strain for designing electronic properties of common semiconductors. For ferroic (magnetic or ferroelectric) materials like oxides and polymers, strain can be an efficient design tool, too. However, many strain-driven phenomena are yet to be discovered and modelled, because these materials have a more complex structure and physics background. In this talk, recently established approaches to apply different kinds of film strain in ferroic materials are introduced. These include tip-induced nano-strain in force microscopy, electric strain control with piezoelectric substrates, “strain doping“ with helium atoms and “symmetry strain“ transfer at oxide interfaces. The usefulness of such tools for straining films will be shown in examples for controlling crystal symmetries, domain configurations, and switching times – or simply for measuring strain-dependent properties.

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The assembly of non-equilibrium biologically-inspired materials

Michael Murrell (Laboratory of Living Matter, Yale University)

Incorporating growth, adaptation and responsiveness to external cues remain as grand challenges in materials engineering and design. In living cells, the cell cytoskeleton is a dynamic protein-based polymeric scaffolding material, driven from thermodynamic equilibrium through the enzymatic consumption of chemical energy. This consumption in turn leads to time-irreversibility in molecular interactions and the breaking of detailed balance. Through the extent that detailed balance is broken, the cytoskeleton can grow, remodel itself, and adapt to both internal and external mechanical loads – essential processes for controlling the physical behaviors of the cell such as cell division or cell migration. Here, we reconstitute the cell cytoskeleton in vitro, and experimentally control the breaking of detailed balance on the microscopic scale to outline large-scale non-equilibrium dynamical and material phase transitions and characterize the emergence of novel material properties. In doing so, we learn how material properties relate to the physical behaviors of the cell and also identify a framework for how to encode novel capabilities into the engineering of non-equilibrium “active” materials.

Nanomechanics in lean Mg alloys: a length scale appraisal

Indranil Basu (Laboratory of Metal Physics and Technology, DMATL)

Most conventional metallic materials display a trade-off effect associated with their strength-ductility values, often highlighted by the well-known banana-shaped variation of strength vs. ductility. A major challenge, therefore, is to engineer novel microstructures in metallic materials that can successfully evade this inverse strength-ductility relationship. In this regard, one of the most potent design aspect pertains to exploiting the local scale compositional fluctuations and microstructural heterogeneities across different length scales, wherein different phases or grain orientations display varying elastic stiffness and strain accommodation mechanisms.
Magnesium (Mg) alloys with attractive weight-saving properties have seen an increased demand in various applications such as automotive, aerospace, biomedical and communications industries. However, the prospect of developing low cost, lean high strength-high ductility Mg alloys though highly lucrative still remains an elusive problem owing to the strong mechanical anisotropy displayed by Mg that often renders it unsuitable of commercial processing. In this work, it is shown that by intelligent alloying methodologies and processing conditions, nanoscale heterogeneities arising from local scale compositional fluctuations are able to drive synergistic strengthening and ductility response in Mg alloys. The findings throw light to a paradigm shift in the role of Mg as an emerging class of structural materials.

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