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Light-driven microswimmers: pushing, pulling and shaping materials from within

Artificial microswimmers or self-propelled colloidal particle systems are currently a subject of great interest in soft condensed matter for a variety of reasons. First, they present us with model systems to study the collective behavior of their more complex natural counterparts and they represent beautiful examples of out-of-equilibrium systems. Second, they can help us to understand how biofilms form and how bacteria move around in and shape their polymeric habitat.

One class of these artificial model systems moves actively by consuming chemical energy from its local environment. In this talk, I will introduce a novel self-propelled particle system in which we control the energy consumption by light and how we can reversibly switch the swimming direction between both sides of the particle in-situ using photocatalytic effects. Moreover, I will discuss the broad implications of reversing the swimming direction in combination with the propulsion strength of an individual swimmer in the collective behavior of both active systems and mixtures of active and passive particles. A few perspectives will be given on how these pushers and pullers may shape materials from within.

Overview D-MATL Seminar

Magnetic correlations in artificial spin systems

In physics, frustration refers to a situation in which not all interactions can be satisfied simultaneously. Frustrated magnetism often occurs in spin systems with competing interactions and leads to a multitude of interesting phenomena such as highly-degenerate ground states and ice-like fluctuations. Artificial spin systems, built from lattices of thermally-fluctuating nanomagnets, can be used to study the effect of frustration on magnetic properties. In this talk, I will discuss how to design and manufacture artificial spin systems, and how to characterise the emergent magnetic correlations and long-range ordered phases using large-scale facilities available at the Paul Scherrer Institute (Villigen, Switzerland).

Overview D-MATL Seminar

Synthesis and characterization of materials: An example

While most polymers belong to the class of organic compounds, a minor fraction of polymers is attributed to inorganic compounds. These include polymers comprising a backbone without carbon atoms and coordination polymers. Such materials can exhibit particular combinations of properties, as will be demonstrated by selected examples.

Overview D-MATL Seminar

Nanoscale mass transport across two-dimensional materials

Two-dimensional (2D) nanoconstrictions enable ballistic permeation of molecules, yielding orders of magnitude higher permeances compared to conventional membranes. Recent advances in synthesis and handling of 2D materials have enabled the study of such constrictions on atomically-thin membranes. Two prominent examples of such membranes, based on graphene and 2D polymers, will be described in terms of fabrication challenges, flow characteristics and technological implications.

Overview D-MATL Seminar

Preparation and applications of dendronized polymer-enzyme conjugates

Enzymes are catalytically active globular proteins, which promote chemical reactions in all living systems and which are used in many industrial processes (e.g. for softening fabrics) in household products (e.g. as additives in laundry detergents), as well as for organic synthesis and analytical applications (e.g. for blood glucose determinations).

For a number of applications enzymes are stabilized through a modification of their surface, or the enzymes are immobilized on a solid support. One recently developed method for the immobilization of enzymes on silicate surfaces is based on the preparation of conjugates between a synthetic dendronized polymer and the enzymes of interest. The principle of this method will be described and illustrated with selected examples.

Overview D-MATL Seminar

Opportunities and challenges in TEM dynamic studies of metals

Since its invention in 1931, the transmission electron microscope has allowed a direct view into matter with an unprecedented spatial resolution, progressing over the decades towards the atomic scale, and nowadays, with the correction of the spherical aberration, a resolution of 50 pm is at reach. Combined with the advent of sample holders based on microchip technology, there is a wealth of new in situ experiments that can now be envisaged, bringing insights into and unveiling microstructural dynamics at the origin of the phenomena observed macroscopically; here I will focus on their impact in metallurgy. In situ experiments have already brought much valuable understanding of the mechanisms occurring in metals : I will review some of these dynamics experiments; starting with the evolution of a metal under ion irradiation, then dislocation–defect mechanisms related to mechanical properties, phase transitions related to the magnetic properties, and finally the biocorrosion mechanisms of a magnesium lean alloy, a material envisaged for temporary implants. Finally, I will present some directions to future experiments we will be able to perform at ETH.

Overview D-MATL Seminar

Nanoscale control of polarization in ultrathin ferroelectric heterostructures

The success of oxide electronics depends on the ability to design functional properties such as ferroelectricity with atomic accuracy. Using laser optics, we enabled for the first time the access to the targeted properties during ultrathin oxide multilayer synthesis, in real time and with monolayer accuracy. Such a direct and in-situ probe of ferroelectric polarization during growth leads us to heterostructures with user-defined polarization sequences – key to a new class of functional ferroic materials.

Overview D-MATL Seminar

Making model soft composites

It is rather difficult to make materials with a very precisely defined microstructure. However, some animals have developed incredibly precise techniques for doing exactly that. The resulting materials can have highly desirable properties, such as toughness or bright colours. I will explain how we are trying to develop similar materials in the lab by growing microscopic inclusions in polymer gels.

Overview D-MATL Seminar