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Seminars - Summer term 2019

Seminar “Special problems in colloidal physics”

Location: HHU Düsseldorf, Seminarroom 25.32.O2.51
Program:
DateSpeakerTopicTime
Mon 08.04.2019   S. Reigh  Rotational dynamics of diffusiophoretic sphere motor  14:30 s.t.
Thu 02.05.2019   R. Wittmann  Complex fluids in complex confinement  14:30 s.t.
Fri 03.05.2019   A. Sprenger  Self propelled particles in anisotropic environments  14:30 s.t.
Tue 07.05.2019   C. Hoell  Collective orientational ordering in microswimmer suspensions through hydrodynamic interactions  14:30 s.t.
Fri 17.05.2019   S. Babel  Feedback-driven colloids  14:30 s.t.
Mon 20.05.2019   S. Jahanshahi  From microswimmers to microflyers IV  14:30 s.t.
Mon 27.05.2019   S. Mandal  Active hard-sphere glasses  14:30 s.t.
Tue 28.05.2019   S. Goh  A DFT study on the configurational bistability in ferrogels with an anisotropic model  14:30 s.t.
Mon 08.07.2019   A. Ider  Hydrodynamics of a circle microswimmer in a nematic liquid crystal  14:30 s.t.
Prof. Dr. H. Löwen

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Seminar “Special problems in computer simulation of soft matter”

Location: HHU Düsseldorf, Seminarroom 25.32.O2.51
Program:
DateSpeakerTopicTime
Mon 08.04.2019   S. Reigh  Rotational dynamics of diffusiophoretic sphere motor  14:30 s.t.
Mon 15.04.2019   M. Golkia  Mechanical properties of deformed bulk metallic glasses  14:30 s.t.
Fri 17.05.2019   S. Babel  Feedback-driven colloids  14:30 s.t.
Mon 20.05.2019   S. Jahanshahi  From microswimmers to microflyers IV  14:30 s.t.
Mon 27.05.2019   S. Mandal  Active hard-sphere glasses  14:30 s.t.
Tue 28.05.2019   S. Goh  A DFT study on the configurational bistability in ferrogels with an anisotropic model  14:30 s.t.
Mon 08.07.2019   A. Ider  Hydrodynamics of a circle microswimmer in a nematic liquid crystal  14:30 s.t.
Prof. Dr. J. Horbach

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Seminar “Soft Matter”

Location: HHU Düsseldorf, Seminarroom 25.32.O2.51
Program:
DateSpeakerAffiliationTime
Thu 11.04.2019   Ties van der Laar  Wageningen University, The Netherlands  10:30 s.t.
Ties van der Laar: „Sticky, squishy and stuck. A soft matter approach to membrane failure”
Wageningen University, The Netherlands - Seminar@HHUD: 11.4.19 10:30 s.t., Seminarroom 25.32 O2.51

In this talk I will highlight various ways we have used soft matter science to solve problems in membrane technology. We have developed microfluidic tools to study clogging, used colloidal particles to study cake formation and developed sensors to measure very small forces that might play a role in these processes. My focus will be on the colloidal scale and I will highlight two specific examples, one related to clogging and the other related to the colloidal glass transition.

Sticky, squishy and stuck. A soft matter approach to membrane failure
Fri 22.02.2019   Damien Vandembroucq  Paris, France  11:30 s.t.
SPP1594 SpringSchoolTalk: Fracture and plasticity of disordered materials II
Fri 22.02.2019   Yannick Champion  Grenoble, France  9:30 s.t.
SPP1594 SpringSchoolTalk: Statistical and entropic description of metallic glass
Thu 21.02.2019   Jörg Baschnagel  Université de Strasbourg, France  11:15 s.t.
SPP1594 SpringSchoolTalk: Shear stress and shear-stress fluctuations in simulated amorphous systems II
Thu 21.02.2019   Yannick Champion  Grenoble, France  9:30 s.t.
SPP1594 SpringSchoolTalk: Thermal activation of shear band formation in metallic glass
Wed 20.02.2019   Frans Spaepen  Harvard University, USA  9:30 s.t.
SPP1594 SpringSchoolTalk: The Continuous Random Network - a Review
Tue 19.02.2019   Damien Vandembroucq  Paris, France  16:30 s.t.
SPP1594 SpringSchoolTalk: Fracture and plasticity of disordered materials I
Tue 19.02.2019   Frans Spaepen  Harvard University, USA  15:00 s.t.
SPP1594 SpringSchoolTalk: An Overview of the Mechanical Behavior of Metallic Glasses
Tue 19.02.2019   Jörg Baschnagel  Université de Strasbourg, France  13:15 s.t.
SPP1594 SpringSchoolTalk: Shear stress and shear-stress fluctuations in simulated amorphous systems I
Wed 13.02.2019   Carmen Lucía Moraila Martínez  University of Sinaloa, Culiacán, Mexico  14:30 s.t.
Carmen Lucía Moraila Martínez: „Morphological study of drying complex fluids: a low resources technique for dengue virus detection”
University of Sinaloa, Culiacán, Mexico - Seminar@HHUD: 13.2.2019 14:30 s.t., Seminarroom 25.32 O2.51

Drying of colloidal suspensions appears in many applications such as coatings (paints, ink printing, paving), colloidal assembly/templating, discrimination of particles with different size, even medical diagnostics. Complex liquids, suspensions of solid particles, polymeric dispersions, emulsions and simple liquids behave in different way at interfacial regions.

The formation of stains at the periphery of drying drops of any colloidal dispersion is known as the "coffee stain" effect or "coffee ring" effect. The mechanism for particle deposition by drop drying and the study of the morphology of the deposits left, have been widely studied. The first study proposing a physical model was published by Deegan et al. [1] They demonstrated that there were two conditions necessaries for ring-like deposits apparition: contact line pinning and evaporation from the edge of the drop.

Controlling the distribution of solute during drying is vital in many industrial and scientific processes. The "coffee ring" effect is used for an innovative approach for medical diagnostics. It is based on the comparison of the patterns of dried drops of biological liquids of people with different diseases with regard to people in healthy conditions.

In the field of medicine, one of the great challenges for health in the world is the diagnosis of diseases in an economic way, particularly in countries with low resources. Therefore, the development of techniques that require a minimum use of energy and resources become a necessity.

Recently, it has been found that different diseases (such as HIV, tuberculosis or malaria) can be diagnosed using techniques of biological fluids evaporation. During the drying of a biological fluid an evaporative flow occurs that carries the particles (bacteria, cells, etc.) to the interface and, in the wedge formed by the triple line, a particle segregation by size is presented. This segregation occurs only under certain conditions in which the wetting properties of the surface and particles, electrical charge, particle concentration, play a very important role. In the present work, we propose an indirect, rapid and low resources technique for Dengue virus detection by the drying of a blood micro-drop and the subsequent study of drying morphology.

Reference

  1. Deegan et al., Nature 389, 827–829 (1997)
Morphological study of drying complex fluids: a low resources technique for dengue virus detection
Tue 12.02.2019   Lorenzo Caprini  Gran Sasso Science Institute, L´ Aquila, Italy  14:30 s.t.
Activity-induced delocalization and freezing for self-propelled particles
Wed 05.12.2018   David Fairhurst  School of Science and Technology, Nottingham Trent University, Nottingham, United Kingdom  10:15 s.t.
David Fairhurst: „The Jellycopter: stable levitation using a magnetic stirrer”
School of Science and Technology, Nottingham Trent University, Nottingham, United Kingdom - Seminar@HHUD: 5.12.18 10:15 s.t., Seminarroom

In laboratories around the world, scientists use magnetic stirrers to mix solutions and dissolve powders. It is well known that at high drive rates the stir bar jumps around erratically with poor mixing, leading to its nick-name 'flea'. Investigating this behaviour, we discovered a state in which the flea levitates stably above the base of the vessel, supported by magnetic repulsion between flea and drive magnet. The vertical motion is oscillatory and the angular motion a superposition of rotation and oscillation. By solving the coupled vertical and angular equations of motion, we characterised the flea's behaviour in terms of two dimensionless quantities: (i) the normalized drive speed and (ii) the ratio of magnetic to viscous forces. However, Earnshaw's theorem states that levitation via any arrangement of static magnets is only possible with additional stabilising forces. In our system, we find that these forces arise from the flea's oscillations which pump fluid radially outwards, and are only present for a narrow range of Reynold's numbers. At slower, creeping flow speeds, only viscous forces are present, whereas at higher speeds, the flow reverses direction and the flea is no longer stable. We also use both the levitating and non-levitating states to measure rheological properties of the system.

The Jellycopter: stable levitation using a magnetic stirrer
Thu 15.11.2018   J. Kolker  TU Dortmund  14:30 s.t.
Lattice models for activ particles
Mon 01.10.2018   Alexandra Zampetaki  Universität Hamburg  14:30 s.t.
Alexandra Zampetaki: „Tunable interactions and structures through different 1D substrates”
Universität Hamburg - Seminar@HHUD: 1.10.18 14:30 s.t., Seminarroom 25.32 O2.51

This talk is divided into two parts. In the first part I will present some highlights of our research on systems of helically confined charges. The confinement of identical charged particles on a helical substrate induces an effective oscillatory two-body potential with geometrically tunable features. Such an unconventional potential affects significantly the equilibrium and dynamics of the constrained particles, allowing among others for a deformation of the vibrational band structure and an intriguing bending response, both controlled by the geometry.

In the second part of my talk I will discuss our very recent results regarding the dynamics of polar active matter in the presence of a moving periodic substrate. It turns out that by suitably tuning the parameters of such a substrate we can control the dynamics of polar active particles, achieving a macroscopic directed transport in the opposite direction to that of the substrate‘s motion.

Tunable interactions and structures through different 1D substrates
Mon 17.09.2018   René Wittmann  University of Fribourg, Switzerland  14:30 s.t.
Single-particle distributions in density functional theory
Mon 03.09.2018   Shang Yik Reigh  Max-Planck-Institute for Intelligent Systems, Stuttgart, Germany  14:30 s.t.
Shang Yik Reigh: „Chemically powered micro- and nano-motors by diffusiophoresis”
Max-Planck-Institute for Intelligent Systems, Stuttgart, Germany - Seminar@HHUD: 3.9.18 14:30 s.t., Seminarroom 25.32 O2.51

Molecular motors such as kinesins and dyneins in cell walk along microtubules or actin filaments and transport cargos such as lipid or proteins. The motors accomplish their goals by converting chemical energy to mechanical work. Mimicking the biological motors, man have made artificial motors in a laboratory. The synthetic motors may self-propel in solution with various propulsion sources such as chemicals, heat, electric fields, etc, communicate with each other, and work together to accomplish a common goal. To achieve self-propulsion and efficient swimming, the motors should overcome strong thermal fluctuations from solvent, which induce Brownian motions, and also the regime of low-Reynolds-number fluid attributed to their tiny sizes, where fluid viscosity is dominant over inertia. Here, I would like to address basic principles and underlying physics in motors motions by diffusiophoresis, where chemical and hydrodynamic interactions are coupled, by using continuum theory and microscopic particlebased simulations. I will start with the Janus motor, a spherical particle with a half coated by the catalytic and the other half by the non-catalytic part, and extend the theory to the dimer motors and the dynamics of two separated particles. The theory, simulations, and experiments are compared and the results promise to provide a proper understanding of the nature of self-propelling motors, flow fields, hydrodynamic interactions, and hopefully emergent collective behaviors of many motors.

References

  1. P. H. Colberg, S. Y. Reigh, B. Robertson, and R. Kapral, Acc. Chem. Res. 47 3504 (2014)
  2. S. Y. Reigh and R. Kapral, Soft Matter 11 3149 (2015)
  3. S. Y. Reigh, M.-J. Huang, J. Schofield and R. Kapral, Phil. Trans. R. Soc. A 374 20160140 (2016)
  4. S. Y. Reigh, P. Chuphal, S. Thakur, and R. Kapral, Soft Matter 14 6043 (2018)
Chemically powered micro- and nano-motors by diffusiophoresis
Thu 09.08.2018   Pinaki Chaudhuri  The Institute of Mathematical Sciences, Chennai, India  14:30 s.t.
Thermal and allied transport in glass forming materials
Wed 08.08.2018   Dennis Schubert  Universität Hannover  14:30 s.t.
Integrable Structures in the Hofstadter model
Fri 27.07.2018   Francisca Guzmán Lastra  Universidad Mayor, Santiago de Chile, Chile  11:00 s.t.
Surfing on bacterial carpets
Prof. Dr. Egelhaaf, Prof. Dr. Horbach, Prof. Dr. Löwen

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Colloquia

Location: HHU Düsseldorf, Lecture Hall 5J (Building 25.31 Level 00)
Program:
DateSpeakerAffiliationTime
Thu 27.06.2019   Prof. Dr. Rosch  Universität zu Köln  16:30 s.t.
t.b.a.
Thu 16.05.2019   Prof. Dr. P. Brouwers  Freie Universität Berlin  16:30 s.t.
t.b.a.
Thu 09.05.2019   Prof. Dr. S. Herminghaus  Georg-August-Universität Göttingen  16:30 s.t.
t.b.a.
Thu 31.01.2019   Prof. Dr. Robert Evans  HH Wills Physics Laboratory, University of Bristol, United Kingdom  16:30 s.t.
Prof. Dr. Robert Evans: „Understanding the structure of simple and complex liquids: what we know that Mr. Kirkwood did not know.”
HH Wills Physics Laboratory, University of Bristol, United Kingdom - Seminar@HHUD: 31.01.2019 16:30 s.t., Lecture hall 25.31 O0.5J

The great L.D. Landau argued that there is no theory of liquids; he did not write about liquids in his famous books. J.G. Kirkwood took a different track. This talk will address basic questions on what distinguishes a liquid from a gas or from a crystalline solid and how the form of the pair correlation function g(r) reflects the nature of the ordering.

How g(r) decays at large r defines crossover lines in the phase diagram. These lines are not phase boundaries but point to i) how repulsive and attractive interparticle forces compete to determine structure and ii) how in experiments and simulations on binary colloidal mixtures with different sizes, the presence of two different length scales leads to a sharp structural crossover line: the three gij(r) decay with a common (short) wavelength on one side and with long wavelength on the other.

For certain one-component models with pair potentials exhibiting two (suitably chosen) competitive length scales, we find a structural crossover line that points, at high packing, to where in the phase diagram quasi-crystals might form.

We reflect upon what is known about the structure of liquids.

Understanding the structure of simple and complex liquids: what we know that Mr. Kirkwood did not know.
Thu 10.01.2019   Prof. Dr. Rodrigo Pereira  Federal University of Rio Grande do Norte/ Natal, Brazil  16:30 s.t.
Prof. Dr. Rodrigo Pereira: „From quantum spin chains to chiral spin liquids”
Federal University of Rio Grande do Norte/ Natal, Brazil - Seminar@HHUD: 10.01.2019 16:30 s.t., Lecture hall 25.31 O0.5J

Chiral spin liquids are highly entangled phases of matter in which interacting spins break time reversal and reflection symmetries, but do not develop conventional magnetic order even at zero temperature. They are expected to exhibit exotic properties following from a spectrum of deconfined fractional excitations, and the first signatures of such properties may have just been observed in recent experiments. In this talk I will explain our current theoretical understanding of chiral spin liquids in terms of effective field theories ranging from strongly coupled gauge theories to coupled-chain constructions based on arrays or junctions of quantum spin chains.

From quantum spin chains to chiral spin liquids
Thu 20.12.2018   Prof. Dr. Stefan U. Egelhaaf  Heinrich-Heine-Universität Düsseldorf  16:30 s.t.
Prof. Dr. Stefan U. Egelhaaf: „Manipulating particles with light – The Nobel Prize in Physics 2018”
Heinrich-Heine-Universität Düsseldorf - Seminar@HHUD: 20.12.2018 16:30 s.t., Lecture hall 25.31 O0.5J

Arthur Ashkin was awarded (a share of) the Nobel Prize in Physics 2018 'for the optical tweezers and their application to biological systems'. I will explain why optical means, so-called optical tweezers, can be used to manipulate small objects, in the range from nanometers to micrometers. This is particularly appealing because the objects can be manipulated without directly interfering with the sample. Optical tweezers are nowadays applied to a broad range of objects, including colloids, biomolecules and living cells. The diversity of systems and questions which can be addressed using optical tweezers will be illustrated with examples. This includes experiments performed in our lab, which are based on optical tweezers but also take this concept a step further.

Manipulating particles with light – The Nobel Prize in Physics 2018
Thu 22.11.2018   Dr. Götz Lehmann  Heinrich-Heine-Universität Düsseldorf  16:30 s.t.
Dr. Götz Lehmann: „Eigenschaften und Anwendungen akustischer Metamaterialien”
Heinrich-Heine-Universität Düsseldorf - Seminar@HHUD: 22.11.2018 16:30 s.t., Lecture hall 25.31 O0.5J

Akustische Metamaterialien bestehen aus „Meta-Atomen”, elementaren Bausteinen, die größer sind als Atome, jedoch kleiner als die Wellenlänge von Schallwellen. Es sind die Struktur dieser Bausteine und ihre geometrische Anordnung, die über die Ausbreitung von Schallwellen in Metamaterialien entscheiden. Auf diese Weise lassen sich akustische Eigenschaften realisieren, die mit gewöhnlichen Materialien unmöglich sind.

Die akustischen Eigenschaften eines Materials sind in der Regel bestimmt durch die Massendichte und den Kompressionsmodul. Es erscheint uns völlig selbstverständlich, dass diese Parameter keine negativen Werte annehmen können. In Metamaterialien besitzt nun einer der Parameter, oder sogar beide, einen Wert kleiner Null. In meinem Vortrag werde ich vorstellen, wie sich effektiv negative Werte für diese beiden Parameter realisieren lassen und welche Konsequenzen dies für die Ausbreitung von Schall hat.

Im zweiten Teil des Vortrages werde ich über mögliche Anwendungen von akustischen Metamaterialien sprechen. Neben extrem dünnen Schallisolierungen lassen sich akustische Superlinsen und Tarnkappen konstruieren. Superlinsen erlauben das Fokussieren von Schallwellen jenseits der Beugungslimits, was gerade im Bereich der Ultraschalldiagnostik Interesse weckt. Mit Hilfe von akustischen Tarnkappen lässt sich die Gegenwart von Objekten vor dem Schallfeld verstecken.

Eigenschaften und Anwendungen akustischer Metamaterialien
WE Physik, Heinrich-Heine-Universität Düsseldorf

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Seminar about Bachelor, Master and other Theses from the Institut for Theoretical Physics II

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Link: Physics Colloquium
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