■ Emergent Mechanics in Synthetic Active Gels

Studies of conventional polymer gels, foams and emulsions, quintessential systems of soft condensed matter physics, have resulted in numerous fundamental advances and countless technological applications. However, the laws of equilibrium statistical mechanics limit the properties of these materials. One of the distinctive property of living systems is to behave out of equilibrium and thereby access emergent properties, out of reach from their passive analogs : this is the so-called field of active matter. More specifically, important success has been obtained regarding the description of the mechanical behavior of cells and tissues, in terms of active gels.
Active gels provide a natural extension to soft-matter physics. Besides their biological importance, such inherently non-equilibrium systems are an inspiration for developing biomimetic active materials from microscopic components that consume energy and act as local stress or strain actuators. While active fluids consisting of small self-propelling particles have been extensively studied, with a special interest in collective motion, their solid counterparts remains largely unexplored, especially in term of model synthetic experimental system.

This project aims at tailoring artificial systems that combine activity, anisotropy, and elastic architecture, and unraveling their emergent behavior, resulting from collective actuation.

Recent developments spearheaded by Dauchot and Coulais in the fields of active matter [1-3] and architected solids [4-6] now provide prototypical systems to explore the new physics arising when activity and elasticity are combined in the bulk of a material. At the micron-scale, colloidal elastic architectures can be self-assembled and doped with activated swimmers. At the centimeter scale, elastic networks with desired response can be suitably designed, 3D printed and actuated by motors. Though these two systems feature starkly different time and length scales, activation and noise processes, they both share the same interplay between elasticity and activity.

At the microscopic level, we will explore this intimate competition at the structural level, using confocal microscopy, to elucidate the microstructure, vibrations, and plasticity of these living solids. At the macroscopic level, we will investigate the non-linear response of these materials, using both micro and macro-rheology, with a special attention paid to their emerging functionalities and morphologies.

1. Briand, G. & Dauchot, O. PRL 117, 098004–5 (2016).
2. Izri, Z., van der Linden, M. N., Michelin, S. & Dauchot, O. PRL 113, 248302 (2014).
3. Bricard, A., Caussin, J.-B., Desreumaux, N., Dauchot, O. & Bartolo, D. Nature 503, 95–98 (2013).
4. Coulais, C., Teomy, E., de Reus, K., Shokef, Y. & van Hecke, M. Nature 535, 529-532 (2016).
5. Florijn, B., Coulais, C. & van Hecke, M. PRL 113 (2014).
6. Coulais, C., Sounas, D. & Alu, A. Nature 542, 461-464 (2017).

Active Matter, Gels, Emergent Mechanics, Collective Actuation

UMR7083
Gulliver

Description of the research Unit/subunit

The research will be conducted under the supervision of Olivier Dauchot, who is leading the EC2M team (Collective Effects in Soft Matter) from the Gulliver Laboratory, headed by Elie Raphaël, and co-supervised by Corentin Coulais from the Soft-Matter Group at the Van der Waals-Zeeman Institute of the University of Amsterdam, headed by Daniel Bonn.

The research conducted at both the Gulliver lab and the WZI Soft-Matter Group deals with structural and dynamical organization of soft matter. While EC2M focuses on collective phenomena, especially in active matter, Corentin Coulais’ group concentrates its activities on the physics of active mechanical meta-materials, namely soft solids combining internal architecture and active processes.
The thesis will thus take place in an exceptional scientific environment, where it will benefit from the joint expertise of Olivier Dauchot and Corentin Coulais. The project will also greatly benefit from close interactions with Alba Marcellan (Gels) in Paris and with Peter Schall (Colloidal Systems) and Edan Lerner (Computational Soft Matter) in Amsterdam.

Name of the supervisor
Olivier Dauchot

Name of the co supervisor
Corentin Coulais

First, the project will benefit from the exceptional inter-sectorial activity, which takes place in the Soft-Matter Lab, at the University of Amsterdam (UvA). The soft matter group routinely fosters collaborations with Unilever, thanks to several IPP programs, funding several PhD and postdoc positions and a weekly seminar attended by several Unilever scientists. In addition, the recent appointment of Krassimir Velikov (Unilever research scientist) as a professor with special appointment at soft matter-UvA provides invaluable opportunities to bring together Unilever interests (design of novel sensory experiences in gel-like food) and more fundamental questions such as the study of active gels.

The research project naturally sits at the crossroad of biophysics, physico-chemistry and mechanical engineering. Biophysics is not only the main source of motivation for studying active gels. It has also inspired most, if not all, experimental systems probing active gels in vitro. Moving towards the development of fully synthetic active gels is where physico-chemistry comes into play. It should also be stressed that, in the cases where the activity takes its root in some form of diffusio-phoresis, there is a natural coupling between active gel physics and nonlinear chemistry. Such coupling, which in biological system is introduced by the signaling pathways, has to our knowledge not been investigated so far in the context of active gels.
The project will be run in collaboration with, and co-supervised by, Corentin Coulais, from the University of Amsterdam. The student will spend at least 30% of his/her time in the Soft Matter Group at the Van der Waals-Zeeman Institute and will benefit from world-class soft matter expertise in both laboratories. Additionally, the University from Amsterdam is welcoming Joint-Doctorate Programs for which doctoral research is carried out under the joint responsibility of the partner universities and the doctoral thesis is prepared and assessed jointly by the partner universities. Collaboration with Francesco Sciortino (simulations of colloidal gels), in Roma, would give a further international twist to the project.

The candidate should be completing a Master’s degree in physics, engineering, chemistry or a related field. He/she has outstanding experimental skills, a strong theoretical/numerical background and a marked taste for combining experiments, numerical simulations and theory. The following areas of expertise are particularly welcomed : colloidal and polymer synthesis, microfluidics, rapid prototyping, micro-fabrication, mechanical testing, control/automation/robotics, image processing, data mining and computer programming (Python, Matlab, or equivalent) as well as theoretical background in (soft) condensed matter, nonlinear physics, statistical physics and mechanics.

The ideal candidate is highly motivated with a go-getter mentality. As he/she will take fully part of collaborative research environment and will be the link between research teams located at two different locations, he/she is also expected to be a team player. Excellent written and oral communication skills in English are essential.