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Presentation by M. Rey at Particle-Based Materials Symposium, Erlangen, 7 October 2022

Drawing of a coffee mug using only coffee. (Image by M. Rey.)
Versatile strategy for homogeneous drying of dispersed particles
Marcel Rey,
Submitted to ISMC 2022
Date: 7 October 2022
Time: 11:20 (CET)

After spilling coffee, a tell-tale stain is left by the drying droplet. This universal phenomenon, known as the “coffee ring effect”, is observed independent of the dispersed material. However, for many technological processes such as coating techniques and ink-jet printing a uniform particle deposition is required and the coffee ring effect is a major drawback.
Here, we present a simple and versatile strategy to achieve homogeneous drying patterns by modifying the surface of the dispersed particles with surface-active polymers. A particle dispersion is mixed with excess surface-active polymers (e.g. polyvinyl alcohol). The polymer partially adsorbs onto the particles and excess polymer is removed by centrifugation and redispersion. While pure particle dispersions form a typical coffee ring, the polymer-modified dispersions dry into a uniform particle deposit. In this talk, I will discuss how the polymer coating prevents accumulation and pinning at the droplet edge and leads to a uniform particle deposition after drying.
It should be highlighted that the presented method is independent of particle shape (e.g. spherical, ellipsoidal or ill-defined particle shapes) and is applicable to a variety of commercial pigment particles (e.g. hematite, goethite or titanium dioxide). Further, the method works for different dispersion media (e.g. aqueous, polar and apolar solvents), demonstrating the practicality of this work for everyday processes.

Vide Ramsten joins the Soft Matter Lab

(Photo by A. Argun.)
Vide Ramsten started his PhD at the Physics Department of the University of Gothenburg on the 3rd of October 2022.

Vide has a double master degree in System, control and mechatronics from Chalmers University of Technology and Engineering Cybernetics from the University of Stuttgart.

In his PhD, Vide will focus his research on the development of and experimental testing with swarm robotics.

Presentation by M. Rey at 51st General Assembly of the German Colloid Society, Berlin, 28 September 2022

Drawing of a coffee mug using only coffee. (Image by M. Rey.)
Versatile strategy for homogeneous drying of dispersed particles
Marcel Rey,
Submitted to ISMC 2022
Date: 28 September 2022
Time: 11:20 (CET)

After spilling coffee, a tell-tale stain is left by the drying droplet. This universal phenomenon, known as the “coffee ring effect”, is observed independent of the dispersed material. However, for many technological processes such as coating techniques and ink-jet printing a uniform particle deposition is required and the coffee ring effect is a major drawback.
Here, we present a simple and versatile strategy to achieve homogeneous drying patterns by modifying the surface of the dispersed particles with surface-active polymers. A particle dispersion is mixed with excess surface-active polymers (e.g. polyvinyl alcohol). The polymer partially adsorbs onto the particles and excess polymer is removed by centrifugation and redispersion. While pure particle dispersions form a typical coffee ring, the polymer-modified dispersions dry into a uniform particle deposit. In this talk, I will discuss how the polymer coating prevents accumulation and pinning at the droplet edge and leads to a uniform particle deposition after drying.
It should be highlighted that the presented method is independent of particle shape (e.g. spherical, ellipsoidal or ill-defined particle shapes) and is applicable to a variety of commercial pigment particles (e.g. hematite, goethite or titanium dioxide). Further, the method works for different dispersion media (e.g. aqueous, polar and apolar solvents), demonstrating the practicality of this work for everyday processes.

Invited Talk by G. Volpe at Adaptivity in Nonlinear Dynamical Systems, Potsdam, 23 September 2022

M. xanthus cell-cell and cell-particle local interactions during cellular aggregation.
Feedback between active matter and its environment
Giovanni Volpe
Invited Talk (Online) at the hybrid Workshop: Adaptivity in Nonlinear Dynamical Systems
Potsdam, Germany
23 September 2022, 9:30 CEST

I will present some examples of how feedback cycles can occur between active matter and its environment. In particular, I’ll show the formation of active molecules and active droploids from passive colloidal building blocks; the emergence of non-Boltzmann statistics and active-depletion forces between plates in an active bath; and the environment topography alters the way to multicellularity in the bacterium Myxococcus xanthus.

Presentation by M. Rey at ISMC 2022, Poznan, 23 September 2022

Drawing of a coffee mug using only coffee. (Image by M. Rey.)
Versatile strategy for homogeneous drying of dispersed particles
Marcel Rey, Johannes Walter, Johannes Harrer, Carmen Morcillo Perez, Salvatore Chiera, Sharanya Nair, Maret Ickler, Alesa Fuchs, Mark Michaud, Maximilian J. Uttinger, Andrew B. Schofield, Job H. J. Thijssen, Monica Distaso, Wolfgang Peukert, Nicolas Vogel
Submitted to ISMC 2022
Date: 23 September 2022
Time: 12:10 (CET)

After spilling coffee, a tell-tale stain is left by the drying droplet. This universal phenomenon, known as the “coffee ring effect”, is observed independent of the dispersed material. However, for many technological processes such as coating techniques and ink-jet printing a uniform particle deposition is required and the coffee ring effect is a major drawback.
Here, we present a simple and versatile strategy to achieve homogeneous drying patterns by modifying the surface of the dispersed particles with surface-active polymers. A particle dispersion is mixed with excess surface-active polymers (e.g. polyvinyl alcohol). The polymer partially adsorbs onto the particles and excess polymer is removed by centrifugation and redispersion. While pure particle dispersions form a typical coffee ring, the polymer-modified dispersions dry into a uniform particle deposit. In this talk, I will discuss how the polymer coating prevents accumulation and pinning at the droplet edge and leads to a uniform particle deposition after drying.
It should be highlighted that the presented method is independent of particle shape (e.g. spherical, ellipsoidal or ill-defined particle shapes) and is applicable to a variety of commercial pigment particles (e.g. hematite, goethite or titanium dioxide). Further, the method works for different dispersion media (e.g. aqueous, polar and apolar solvents), demonstrating the practicality of this work for everyday processes.

Presentation by G. Wang at ISMC 2022, Poznan, 20 September 2022

Recognize and selectively trap chiral particles by critical Casimir force. (Image by G. Wang.)
Nanopositioning and nanoalignment of microparticles on patterned surfaces
Gan Wang, Piotr Nowakowski, Nima Farahmand, Benjamin Midtvedt, Falko Schmidt, Mikael Käll, Svyatoslav Kondrat, Sigfried Dietrich and Giovanni Volpe
Date: 20 September 2022
Time: 14:10 (CEST）

Direct manipulation of objects in a solution can provide opportunities to investigate material properties and construct microscopic devices. However, currently available methods, such as optical tweezers and thermal tweezers, have several limitations especially to control the orientation and alignment of particles near surfaces. Here, we experimentally demonstrate that by exploiting the critical Casimir effect, emerging in the presence of a critical binary liquid, microparticles (diameter d≈2µm) can be trapped with nanometer precision. We investigated the motion of SiO2 microscopic disks above nanopatterned surfaces coated with a thin gold film immersed inside a critical mixture. By adjusting the adsorption preference of the gold film to one of the two components of the mixture liquid, we can finely tune the balance between the critical Casimir repulsion and attraction generated between different regions of the substrate and the disk. In this way, we can control the configuration of the disk and make it perform some complex motion. Furthermore, we show how this approach can be used to align particles with patterns, e.g., to sort asymmetric particles with respect to their chirality. We foresee this method can be extended to control the movement of small objects of various materials, thereby severing as a platform to study microscale physical and chemical phenomena.

Keynote Lecture by G. Volpe at ISMC 2022, Poznan, 20 September 2022

An exemplar of Hexbugs, commercially available toy robots that have been used in the experimental demonstration proposed. (Image from arXiv: 2209.04168)
Playing with Active Matter
Giovanni Volpe
Keynote Lecture at ISMC 2022
Poznan, Poland
20 September 2022, 13:30 CEST

In the last 20 years, active matter has been a very successful research field, bridging the fundamental physics of nonequilibrium thermodynamics with applications in robotics, biology, and medicine. This field deals with active particles, which, differently from passive Brownian particles, can harness energy to generate complex motions and emerging behaviors. Most active-matter experiments are performed with microscopic particles and require advanced microfabrication and microscopy techniques. Here, we propose some macroscopic experiments with active matter employing commercially available toy robots, i.e., the Hexbugs. We demonstrate how they can be easily modified to perform regular and chiral active Brownian motion. We also show that Hexbugs can interact with passive objects present in their environment and, depending on their shape, set them in motion and rotation. Furthermore, we show that, by introducing obstacles in the environment, we can sort the robots based on their motility and chirality. Finally, we demonstrate the emergence of Casimir-like activity-induced attraction between planar objects in the presence of active particles in the environment.

Presentation by J. Pineda at ISMC 2022, Poznan, 19 September 2022

Input graph structure including a redundant number of edges. (Image by J. Pineda.)
Revealing the spatiotemporal fingerprint of microscopic motion using geometric deep learning
Jesús Pineda, Benjamin Midtvedt, Harshith Bachimanchi, Sergio Noé, Daniel Midtvedt, Giovanni Volpe, and Carlo Manzo
Submitted to ISMC 2022
Date: 19 September 2022
Time: 13:40 (CEST)

The characterization of dynamical processes in living systems provides important clues for their mechanistic interpretation and link to biological functions. Thanks to recent advances in microscopy techniques, it is now possible to routinely record the motion of cells, organelles, and individual molecules at multiple spatiotemporal scales in physiological conditions. However, the automated analysis of dynamics occurring in crowded and complex environments still lags behind the acquisition of microscopic image sequences. Here, we present a framework based on geometric deep learning that achieves the accurate estimation of dynamical properties in various biologically-relevant scenarios. This deep-learning approach relies on a graph neural network enhanced by attention-based components. By processing object features with geometric priors, the network is capable of performing multiple tasks, from linking coordinates into trajectories to inferring local and global dynamic properties. We demonstrate the flexibility and reliability of this approach by applying it to real and simulated data corresponding to a broad range of biological experiments.

Presentation by H. Bachimanchi at ISMC 2022, Poznan, 19 September 2022

Plankton tracking with holographic microscope and deep learning. (Image by H. Bachimanchi.)
Quantitative microplankton tracking with holographic microscopy and deep learning
Harshith Bachimanchi, Benjamin Midtvedt, Daniel Midtvedt, Erik Selander, and Giovanni Volpe
Presentation at ISMC 2022
Poznan, Poland
19 September 2022, 12:40 CEST

A droplet of sea water contains an entire ecosytem. There are microscopic plants, the phytoplanktons, which produce oxygen by absorbing carbon dioxide from the atmsphere by the process of photosynthesis. There are microscopic animals, the microzooplankton, which feed on the phytoplankton. In oceanic ecology, phytoplanktons consume around 65 peta grams of carbon annually, producing approximately 50% of oxygen on the Earth. Microzooplankton take on the role of herbivores, and consume about two thirds (40 Pg carbon) of this primary production. Despite their central importance, our understanding of the phytoplankton and microzooplankton in shaping oceanic communities is still much less developed at a single plankton level.
Here, we demonstrate that by combining holographic microscopy with deep learning, we can follow microplanktons through generations, by continuously measuring their three dimensional position and dry mass. The deep learning algorithms circumvent the computationally intensive processing of holographic data, and allow measurements over extended periods of time. This permits us to reliably estimate growth rates, both in terms of dry mass increase and cell divisions, as well as to measure trophic interactions between species such as predation events. We exemplify this by detailed descriptions of microzooplankton feeding events, cell divisions, and long term monitoring of single cells from division to division.

Soft Matter Lab members present at ISMC 2022, Poznan, 19-23 September 2022

The Soft Matter Lab participates to the ISMC 2022 in Poznan, Poland, 19-23 September 2022, with the presentations listed below.