2023 Impact factor 1.8
Soft Matter and Biological Physics

News / Highlights / Colloquium

EPJ E Highlight - Macroscopic and microscopic structures of clay-surfactant mixtures

The mixtures formed between clay and surfactants of different charge, at different osmotic pressures.

As a tribute to the late colloid scientist Isabelle Grillo, two of her principal co-workers have published a summary of some of the ground-breaking work in her PhD thesis.

The premature death of Isabelle Grillo (1972-2019), a distinguished colloid scientist at the Institut Laue-Langevin (ILL), Grenoble, France, left much of the work on clay-surfactant mixtures that she had presented in her PhD thesis still unpublished. This gap has now been filled by two of her former co-workers, Sylvain Prévost of ILL and Thomas Zemb of the Institut de Chimie Separative de Marcoule, Bagnols-sur-Cèze, who have published an extensive overview of this work and her legacy in EPJ E.

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EPJ E Highlight - Investigating the Flow of Fluids with Non-Monotonic, ‘S-shaped’ Rheology

Streamwise banding of a non-monotonic shear thickening fluid in a tube in the direction of flow. The shaded sections (G+) are regions of high viscosity.

Analysis of cornstarch suspensions under different stresses suggests that some fluids with non-monotonic rheology can segregate into regions of high and low viscosity in a capillary tube.

Water and oil, and some other simple fluids, respond in the same way to all levels of shear stress and, as termed Newtonian fluids, their viscosity is constant for all stresses although it will vary with temperature. Other non-Newtonian fluids exhibit much more complex patterns of behaviour under different stresses and pressure gradients. Laurent Talon and Dominique Salin from Université Paris-Sacly, Paris, France have now shown that, under certain circumstances, cornstarch suspensions can display a banding pattern with alternating regions of high and low viscosity. This work has been published in the journal EPJ E.

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EPJ E Highlight - α-SAS: Improving measurements of complex molecular structures

α-SAS for Janus particles. Credit: E M Anitas.

Integrating small-angle neutron scattering with machine learning algorithms could enable more accurate measurements of complex molecular structures.

Small-angle scattering (SAS) is a powerful technique for studying nanoscale samples. So far, however, its use in research has been held back by its inability to operate without some prior knowledge of a sample’s chemical composition. Through new research published in EPJ E, Eugen Anitas at the Bogoliubov Laboratory of Theoretical Physics in Dubna, Russia, presents a more advanced approach, which integrates SAS with machine learning algorithms.

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EPJ E Topical Issue: Festschrift in honor of Philip (Fyl) Pincus

Guest Editors: David Andelman,
Jean-Marc Di Meglio, and Cyrus R. Safinya

This topical issue comprises 49 contributions covering a broad range of topics, which advance the understanding of soft and biological matter systems from physical and chemical aspects. More than 200 scientists globally contributed to this noteworthy Festschrift, which is divided into thematic categories.

The first theme is focused on equilibrium and non-equilibrium soft matter systems, including topics associated with polymers and colloidal systems, in uncharged and charged systems, where Pincus has made lasting contributions. In addition, other contributions are concerned with liquids, flowing and active matter, and granular systems. The second theme groups together many contributions that are focused on biological physics, including properties of the cell cytoskeleton and associated proteins, intrinsically disordered proteins, lipid membranes, membrane-associated proteins, and assembly and interactions of viral capsids with lipids and polymers. A third group of contributions is in the nascent field of biomolecular and biomimetic materials at the crossroads between physics, chemistry, bioengineering, and materials science. Finally, systems dealing with far-from-equilibrium states of matter in biology are addressed by a few contributions focusing on the physical properties of living cells.

All articles of this collection are available here and are freely accessible until 20 August 2024. For further information read the Editorial.

EPJ E Highlight - Tuning the movement of a self-propelled robot to the physics of living matter

The team’s dynamic robot model. Credit: S. Paramanick., EPJ E (2024)

The two-wheeled robot employs a range of complex active dynamics that can be implemented with precise control.

Robots are becoming an increasingly important part of our lives, performing jobs that are too dangerous for humans. This can often involve navigating complex environments, something rigid-bodied autonomous robots find difficult. Such robots faced similar challenges when miniaturised and used to model physics of living matter.

These challenges could be countered by a robot that can move with the mobility of living things and can respond to environmental signals just like a cellular organism. To model such systems experimentally, it is necessary to develop a tunable system that can replicate life-like dynamics.

In a new paper in the EPJ E, the authors, including Nitin Kumar from the Indian Institute of Technology Bombay and his co-authors, describe the development of a scheme for generating tunable active dynamics in a self-propelled robotic device. The result is a two-wheeled robot that utilizes a simple differential-drive mechanism, enabling a range of complex active dynamics to be implemented with precise control.

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EPJ E Highlight - Investigating collective motions in schools of zebrafish

Zebrafish display interesting collective dynamics. By Azul - Own work, Copyrighted free use, https://commons.wikimedia.org/w/ index.php?curid=260841

Observations reveal new insights into the evolution of collective motions within schools of zebrafish, and how their complexity and structure vary with density.

Active systems display a wide range of complex and fascinating behaviours, many of which are not yet fully understood. Found on scales ranging from microbes and self-propelling particles to large groups of fish, birds, and mammals, they are made up of many individual parts, which each convert energy from their surroundings into motion.

Through new analysis published in EPJ E, Antonio Romaguera and collaborators at the Rural Federal University of Pernambuco, Brazil, have gained deeper insights into the collective motions of schools of zebrafish: active systems in which multiple fish can collectively move in the same direction. The team’s discoveries could help researchers to better understand the unique properties of active matter, and how complex behaviours emerge and evolve on different scales.

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EPJ E Highlight - Modelling vibration patterns in granular materials

Building statistical models of grain behaviours

The ‘Laguerre ensemble’ statistical model can better describe the vibrational patterns of granular materials at a critical point of transition in their behaviour.

Granular materials are collections of solid particles which can behave in similar ways to both solids and liquids via interactions between grains. Previously, researchers have explored how the behaviours of these materials can be described in the language of statistical mechanics.

Through new research published in EPJ E , Onuttom Narayan at the University of California, together with Harsh Mathur at Case Western Reserve University, show how the characteristic vibrational patterns associated with granular materials at the point where they transition to more solid-like states can be reproduced more accurately. The work could help researchers to gain a deeper understanding of how granular materials behave.

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EPJ E Highlight - Breaking an electrolyte’s charge neutrality

Electrical charge (red) builds up on a varied cross-section channel. Credit: Malgaretti et al. (2024).

Excess charge builds up in salt solutions due to interactions between electrostatic forces and a channel’s varying cross section

Plant vascular circulation, ion channels, our own lymphatic network, and many energy harvesting systems rely on the transport of dissolved salt solutions through tortuous conduits. These solutions, or electrolytes, maintain a positive or negative charge that’s vital to how the system functions. However, this charge balance depends on the properties of the channel that contains the fluid. In a study published in EPJ E, Paolo Malgaretti, of the Helmholtz Institute Erlangen-Nürnberg for Renewable Energy/Forschungszentrum Jülich, Germany, and his colleagues, now derive equations that describe how local electrical charge in electrolytes changes in channels with varying cross sections, at equilibrium. The result could help to predict pathways for charged particles in biological and technological systems.

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EPJ E Colloquium - Convective mixing in porous media: A review of Darcy, pore-scale and Hele-Shaw studies

Solute concentration field of a convective flow in a porous medium

When a porous medium is filled with two fluid layers of different density, with the heavier fluid sitting on top of the lighter one, the system may become unstable. Due to the vertical density contrast, convective finger-like structures can form and accelerate fluid mixing. This configuration is representative of a variety of systems of practical interest, particularly in geophysical processes.

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EPJ E Topical review - Lift at low Reynolds number

In hydrodynamics, a lift phenomenon arises when a force acts on an object perpendicularly to its initial motion. In everyday life, we are familiar with this effect allowing for instance planes to take off or soccer balls to follow bent trajectories. For such big and fast objects, inertia combines with symmetry breaking (wing shape profile or ball rotation) to give rise to lift. However, lift forces are also at play at low Reynolds numbers, i.e. for small objects or slow flows where fluid viscosity dominates over inertia.

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Editors-in-Chief
F. Croccolo, G. Fragneto and H. Stark
We are highly delighted by the quality of the proof. This is exceptional compared to all other journals we have published in until now. Thank you!

Martin M. Müller, Univ. Lorraine, France

ISSN (Print Edition): 2429-5299
ISSN (Electronic Edition): 2725-3090

© EDP Sciences, Società Italiana di Fisica and Springer-Verlag