Editorial: Probing out-of-equilibrium soft matter

Irmgard Bischofberger, Ramón Castañeda-Priego, Roberto Cerbino, Luca Cipelletti, Emanuela del Gado, Alberto Fernández-Nieves

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Irmgard Bischofberger, Ramón Castañeda-Priego, Roberto Cerbino, Luca Cipelletti, Emanuela del Gado, et al.. Editorial: Probing out-of-equilibrium soft matter. Frontiers in Physics, 2023, 11, pp.1173632. 10.3389/fphy.2023.1173632. hal-04858567

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OPEN ACCESS

EDITED AND REVIEWED BY
Jasper Van Der Gucht,
Wageningen University and Research,
Netherlands

*CORRESPONDENCE

Irmgard Bischofberger,
IRMgard@mit.edu
Ramón Castañeda-Priego,
ramoncp@fisica.ugto.mx
Roberto Cerbino,
cerbino@gmail.com
Luca Cipelletti,
luca.cipelletti@umontpellier.fr
Emanuela Del Gado,
ed610@georgetown.edu
Alberto Fernandez-Nieves,
alberto.fernandez@physics.gatech.edu

SPECIALTY SECTION

This article was submitted to
Soft Matter Physics,
a section of the journal
Frontiers in Physics

RECEIVED 24 February 2023

ACCEPTED 06 March 2023

PUBLISHED 14 March 2023

CITATION

Bischofberger I, Castañeda-Priego R, Cerbino R, Cipelletti L, Gado ED and Fernandez-Nieves A (2023), Editorial: Probing out-of-equilibrium soft matter. *Front. Phys.* 11:1173632.
doi: 10.3389/fphy.2023.1173632

COPYRIGHT

© 2023 Bischofberger, Castañeda-
Priego, Cerbino, Cipelletti, Gado and
Fernandez-Nieves. This is an open-
access article distributed under the terms
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permitted, provided the original author(s)
and the copyright owner(s) are credited
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which does not comply with these terms.

Editorial: Probing
out-of-equilibrium soft matter

Irmgard Bischofberger¹*, Ramón Castañeda-Priego²*,
Roberto Cerbino³*, Luca Cipelletti⁴,⁵*, Emanuela Del Gado⁶* and
Alberto Fernandez-Nieves⁷*

¹Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA, United States, ²Sciences and Engineering Division, University of Guanajuato, León, Mexico, ³Faculty of Physics, University of Vienna, Vienna, Austria, ⁴L2C, University of Montpellier, Montpellier, France, ⁵Institut Universitaire de France, Paris, France, ⁶Department of Physics, Institute for Soft Matter Synthesis and Metrology, Georgetown University, Washington, DC, United States, ⁷Department of Condensed Matter Physics, ICREA-Institucio Catalana de Recerca i Estudis Avancats, Institute for Complex Systems (UBICS), University of Barcelona, Barcelona, Spain

KEYWORDS

soft matter, biophysics, non-equilibrium, structure, dynamics, rheology, microrheology

Editorial on the Research Topic
Probing out-of-equilibrium soft matter

This Research Topic originates from the symposium *Probing Out-of-Equilibrium Soft Matter* that was held on October 22-23, 2021 at the University of Fribourg (Switzerland) to celebrate and honor the career of Véronique Trappe (https://orcid.org/0000-0002-0301-258X). The symposium assembled leading scientists in the rapidly growing field of non-equilibrium soft matter physics, a field to which V. Trappe has made key contributions that have changed the view of many [1-6]. While the equilibrium behaviour of soft matter is amply studied and understood, novel tools are needed to capture the complexity of out-of-equilibrium soft materials. A particular challenge is getting access to and understanding the fast processes occurring at the nano- and micro-scale of the elementary constituents, while simultaneously capturing the slower evolution of bulk properties in non-equilibrium conditions. To take on this task, new theoretical, numerical and experimental methodologies need to be developed that enable the investigation of the structure, dynamics, thermodynamics, and rheology of out-of-equilibrium soft matter. Adopting a comprehensive view that covers fundamental topics as well as research focusing on processes and issues faced in applications, this Research Topic aims to showcase some of the latest advancements and innovations in the field.

Living and active materials are intrinsically non-equilibrium systems due to metabolic activity and/or energy consumption. Using newly developed fabrication and image processing tools, Chang et al. probe the effect of surface curvature on the proliferation of Madin-Darby Canine Kidney (MDCK) epithelial cells. They show that proliferation is insensitive to changes in curvature, and that the main mechanism of cell proliferation control is contact inhibition. Sheung et al. use a combination of light sheet microscopy, particle tracking, and differential dynamic microscopy to elucidate anomalous and advective transport in actomyosin-microtubule biomimetic composites. A complex interplay between increasing activity and confinement as the
actomyosin fraction increases governs the transport properties of
these active cytoskeletal systems.

Three studies address shear-driven patterning in soft
materials. Applying shear flow during the temperature-induced
gelation of a colloid-polymer mixture which contains
thermosensitive microgel particles, Rel et al. show that they
can tune the morphology of mesoscopic colloidal clusters. Gels
comprised of fibrous, elongated colloid-dense clusters, log-like
flocs that are aligned along the vorticity direction or isotropic
clusters can be produced by controlling the shear. Villa et al.
adapt a previously designed shear cell [7] to perform stress-
controlled rheo-microscopy experiments on commercial
microscopes. This flexible rheo-microscopy setup, compatible
with different imaging methods, allows to perform quantitative
rheology by assessing the microscopic dynamics with particle
tracking and differential dynamic microscopy analysis. Lastly,
Miller et al. introduce a novel approach to assess dynamic
ordering in sheared dense suspensions using a combined
rheometer and laser scanning confocal microscope. The
spatiotemporal dynamics obtained with high spatial and
temporal resolution reveals distinct regimes of ordering
depending on the particle concentration and the applied stress,
which reflect shear-thickening and transiently shear-jammed
states.

Colloidal suspensions are also the focus of Carpineti et al., who study the transient patterns that emerge during Rayleigh-Bénard convection with thermophilic particles. The gravitationally destabilizing temperature gradient induces rotating patterns in the form of traveling waves that eventually disappear as the stabilizing effect of thermophoresis returns the system to a conductive state. Probing the crystallization kinetics of charged temperature-sensitive microgels in deionized conditions, Bocanegra-Flores et al. discover that due to their microgels' low polydispersity and electrostatic charge a liquid-crystal transition occurs for volume fractions of the order of 0.01–0.05, a factor of ten lower than in neutral microgels.

Soft Matter research is increasingly impacted by current
developments in Machine Learning (ML) techniques. Methods
including computer vision, feature engineering, and classification
tasks have been applied to characterize colloidal systems. In
particular, ML methods have proven useful to identify
correlations in non-equilibrium systems such as glasses.
Oyama et al. discuss how deep neural networks can predict
the characteristic local meso-structures of glasses solely from
instantaneous particle configurations, without any information
about the particle dynamics. Finally, the nature of the non-
equilibrium states also depends on how rapidly a material is
quenched to a specific condition. Rouzaire and Levis discuss the
dynamics of the short range noisy Kuramoto model, where spins
are able to rotate with an intrinsic frequency taken from a
quenched Gaussian distribution. By connecting
synchronisation with the so-called topological Berezenskii-

Kosterlitz-Thouless phase transition, the authors investigate
the dynamics of vortices and other topological defects,
shedding light on their long-time super-diffusive behaviour.

The articles of this Research Topic are representative, while non-exhaustive, of a variety of out-of-equilibrium phenomena in Soft Matter that are rapidly emerging among the most fascinating topics in modern multidisciplinary science. Symposia and workshops such as the one that inspired this Research Topic will continue to play an important role in promoting and deepening interactions between researchers with diverse backgrounds. The ability to discuss openly and in depth, so distinctive of Véronique Trappe's way of conducting research, will be key to continue progress in the field.

Author contributions

All authors listed have made a substantial, direct, and intellectual
contribution to the work and approved it for publication.

Funding

The organization of the workshop was possible thanks to funding from the following contributors: Swiss National Science Foundation, University of Fribourg, NCCR Bioinspired Materials Fribourg, Frontiers, Michelin, Villars, Fri-Mousse.

Acknowledgments

The authors thank the participants of the symposium and the
contributors to this Research Topic. AF-N acknowledges support
from MCIN/AEI/10.13039/501100011033/FEDER, UE (Grant No.
PID2021-122369NB-100). LC gratefully acknowledges support from
the Institut Universitaire de France.

Conflict of interest

The authors declare that the research was conducted in the
absence of any commercial or financial relationships that could be
construed as a potential conflict of interest.

Publisher’s note

All claims expressed in this article are solely those of the authors
and do not necessarily represent those of their affiliated
organizations, or those of the publisher, the editors and the
reviewers. Any product that may be evaluated in this article, or
claim that may be made by its manufacturer, is not guaranteed or
endorsed by the publisher.
References

1. Trappe V, Prasad V, Cipelletti L, Segre P, Weitz DA. Jamming phase diagram for attractive particles. *Nature* (2001) 411:772–5. doi:10.1038/35081021

2. Cipelletti L, Bissig H, Trappe V, Ballesta P, Mazoyer S. Time-resolved correlation: A new tool for studying temporally heterogeneous dynamics. *J Condens Matter Phys* (2003) 15:S257–62. doi:10.1088/0953-8984/15/1/334

3. Trappe V, Sandkühler P. Colloidal gels—Low-density disordered solid-like states. *Curr Opin Colloid Interf Sci.* (2004) 8:494–500. doi:10.1016/j.cocis.2004.01.002

4. Cerbino R, Trappe V. Differential dynamic microscopy: Probing wave vector dependent dynamics with a microscope. *Phys Rev Lett* (2008) 100:188102. doi:10.1103/physrevlett.100.188102

5. Bischofberger I, Calzolari DC, De Los Rios P, Jelezarov I, Trappe V. Hydrophobic hydration of poly-N-isopropyl acrylamide: A matter of the mean energetic state of water. *Sci Rep* (2014) 4:4377. doi:10.1038/srep04377

6. Caggioni M, Trappe V, Spicer PT. Variations of the herschel–bulkley exponent reflecting contributions of the viscous continuous phase to the shear rate-dependent stress of soft glassy materials. *J Rheol* (2020) 64:413–22. doi:10.1122/1.5120633

7. Aime S, Ramos L, Fromental JM, Prevot G, Jelinek R, Cipelletti L. A stress-controlled shear cell for small-angle light scattering and microscopy. *Rev Sci Instrum* (2016) 87:123907. doi:10.1063/1.4972253