Séminaires

• Jeudi 2 juillet 2026
  Soft Matter and Interfacial Chemistry : where serendipity opens new research opportunities
  Francois Ganachaud

According to MIT, soft matter refers to a wide range of materials, such as polymers, gels, and foams, that can be easily molded, shaped, or changed without requiring intense heat or complicated processes. Whereas physical chemistry is inherent to the domain, original chemistry is, IMHO, also required to conduct new research in this very open and wide field.
In this talk, I will briefly describe various aspects of my work for the last 25 years or so in soft matter chemistry. These span a wide range of objects, mostly elastomers, emulsions, and various colloids (polymers and fillers). I will show, in particular, how single points of experimental curiosity have led to new research topics (the Ouzo effect, bicarbonate at the interface) that are increasingly acknowledged by the community. A few future extensions, where different domains merge unexpectedly (teaser...), will finally be delivered.

• Jeudi 25 juin 2026
  Étude multi-échelle de l’impact du sel sur la stabilité des mousses aqueuses
  Victor Ziapkoff

Nous étudions l’impact d’une concentration en sel proche de celle des océans sur la stabilité des mousses aqueuses, dans des contextes allant de la dépollution à la compréhension de la stabilité de l’écume de mer. À l’échelle de la mousse, nous montrons que l’ajout de sel favorise la coalescence des bulles et déstabilise les mousses. Des mesures de tension de surface réalisées à l’échelle des interfaces air–liquide ne permettent toutefois pas de conclure clairement sur l’origine de cet effet.

L’étude sur des films de savon uniques révèle au contraire un effet stabilisant du sel : des films nanométriques restent stables pendant plusieurs dizaines de secondes en présence de NaCl, alors qu’ils rompent rapidement sans sel. Afin de résoudre cette apparente contradiction, des mesures de diffusion de neutrons ont été réalisées directement au sein des mousses. Elles montrent que le sel conduit à des films plus minces et donc plus fragiles, favorisant la coalescence. Ces résultats soulignent l’importance d’une approche multi-échelle pour comprendre l’effet du sel sur la stabilité des mousses.

• Jeudi 18 juin 2026
  Mechanochemical trapping of LCST-induced phase-separation in thermoresponsive hydrogels
  Diego Ciardi
  Johannes Gutenberg University, Mainz, Germany

Thermoresponsive polymers exhibiting a Lower Critical Solution Temperature (LCST) undergo a coil-to-globule transition above a critical temperature, leading to significant changes in chain hydration and in the optical properties of the solution [1]. When LCST polymers are incorporated into a crosslinked network, the same transition induces a volume phase transition (VPT), causing the hydrogel to shrink. Above the critical temperature, the gel expels water and develops heterogeneous polymer-rich and polymer-poor domains, accompanied by pronounced changes in toughness and optical transparency [2,3]. These transitions are generally considered reversible, with the system returning to its initial state upon cooling.
In this work, we show that such reversibility is not always preserved and strongly depends on the thermal history of the material. Under specific conditions, phase separation can become permanently trapped within the polymer network, even after cooling back to room temperature. We demonstrate that the mechanical forces generated during the VPT can induce covalent bond scission, leading to the formation and recombination of radicals and ultimately to a rearrangement of the polymer network. This rearrangement stabilizes persistently phase-separated domains and results in enhanced mechanical properties.
While force-triggered chemical reactions have been widely explored in different material systems [4–6], here we present a strategy that couples mechano-radical chemistry with phase separation, giving rise to trainable hydrogels whose final properties depend on the applied thermal treatment.
Finally, we investigate the influence of the polymer nature on such phae-separation and discuss possible reasons why persistent phase separation has not been reported previously, despite LCST behavior being known for nearly seventy years. We hope that this work will open new perspectives for the design of adaptive polymer hydrogels with programmable structures and properties.

References
1. Halperin, A., Kröger, M. & Winnik, F. M. Poly(N-isopropylacrylamide) Phase Diagrams : Fifty Years of Research. Angew. Chem. Int. Ed. 54, 15342–15367 (2015).
2. Guo, H., Sanson, N., Hourdet, D. & Marcellan, A. Thermoresponsive Toughening with Crack Bifurcation in Phase-Separated Hydrogels under Isochoric Conditions. Adv. Mater. 28, 5857–5864 (2016).
3. Guo, H. et al. Thermoresponsive Toughening in LCST-Type Hydrogels with Opposite Topology : From Structure to Fracture Properties. Macromolecules 49, 4295–4306 (2016).
4. Wang, Z. et al. Toughening hydrogels through force-triggered chemical reactions that lengthen polymer strands. Science 374, 193–196 (2021).
5. Takahiro, M., Kawakami, R., Namba, R., Nakajima, T. & Gong, J. P. Mechanoresponsive self-growing hydrogels inspired by muscle training. Science 363, 504–508 (2019).
6. Ramirez, A. L. B. et al. Mechanochemical strengthening of a synthetic polymer in response to typically destructive shear forces. Nat. Chem. 5, 757–761 (2013).

• Jeudi 11 juin 2026
  Mechanics of Cavitation in Soft Elastic Solids
  Franck Vernerey
  University of Colorado

When polymers are confined to small dimensions, cavitation often becomes the dominant route to failure. A familiar example is the debonding of pressure-sensitive adhesives, where cavities nucleate, grow, and organize into complex patterns that ultimately control adhesion and failure. Similar mechanisms arise in thin elastomeric layers, soft interfaces, and biological tissues under confinement. Understanding why cavities nucleate, grow, and self-organize into patterns requires a multiscale description that links molecular-scale physics to macroscopic failure.
To understand how molecular-scale physics influences cavitation, we first discuss how variations in polymer network architecture influence fracture in elastomers and lead to the emergence of a material length scale, a.k.a, the fracto-cohesive length, which governs defect tolerance and bridges molecular-scale dissipation and continuum fracture. Building on this perspective, we then examine the role of this length scale in cavitation and find that cavitation emerges from a competition between nucleation and growth. Geometry and confinement strongly influence this competition, giving rise to collective cavity patterns that can dramatically alter the mechanical response and failure of soft elastic layers.
Thus, cavitation provides an example of a cascading multiscale process, where polymer-network structure gives rise to an emergent fracture length scale, which shapes cavity interactions and pattern formation, ultimately controlling the macroscopic failure of confined soft solids.

• Jeudi 4 juin 2026
  Rheofluidics : single-drop oscillatory rheology with microfluidics
  Matteo Milani
  PMMH

The measurement of frequency-dependent viscoelastic moduli is of paramount importance in many fields, from material science to biology, and is typically accomplished in bulk materials using commercial rheometers. The trend towards miniaturization in the biotechnology, manufacturing and chemical processing industries has motivated the extension of viscoelastic measurements to microscopic objects with well-defined shape and size such as droplets, vesicles, microcapsules, or even single cells. For instance, local mechanical probes such as AFM nanoindentation can be used to probe single-cell stiffness, and micropipette aspiration probes the interfacial properties of droplets and vesicles [1,2]. Despite their versatility, these techniques are characterized by complex deformation geometries and a relatively low throughput, which makes them unfit to sample highly heterogeneous populations such as those typical of biological samples. To this end, novel microfluidic approaches have been recently developed to measure the stiffness of cells and droplets flowing through narrow channels. These approaches are well-suited for applications requiring a high throughput, but they lack the fine control of stress and strain required by quantitative mechanical measurements. Here, we present a novel technique called Rheofluidics, which combines the high throughput of microfluidics with the versatility of traditional rheological probes. Like a stress-controlled rheometer, Rheofluidics measures the time-dependent deformation of droplets subject to a well-defined hydrodynamic stress, whose time evolution is controlled by the shape of the microfluidic channel in which the droplets are flowing. To validate this approach and to demonstrate the power of this technique, we study the linear and nonlinear rheology of oil droplets, hydrogel beads and lipid vesicles, extracting their viscoelastic properties with a throughput more than 1000 times higher than that of standard rheology.

References
[1] Costa, Kevin D. "Single‐cell elastography : probing for disease with the atomic force microscope." Disease markers 19.2-3 (2004) : 139-154.
[2] Hochmuth, Robert M. "Micropipette aspiration of living cells." Journal of biomechanics 33.1(2000) : 15-22.

• Jeudi 28 mai 2026
  Mechanical behavior of composite textile reinforcements : Complexity, Characterizations and Structural impact
  Samir Allaoui
  Université de Reims

La mise en forme des composites à renforts textiles induit une réorganisation complexe du milieu fibreux, mettant en jeu des déformations et mécanismes physiques multi-échelles dont la compréhension est indispensable pour optimiser les procédés et la qualité des pièces produites. Au cours des dernières décennies, la communauté scientifique de mise en forme a mené d’importants travaux pour caractériser et comprendre ces comportements aux échelles micro (fibre), méso (mèche) et macro (renfort textile). Le peu de normes dédiées à ces essais rend la tâche d’autant plus délicate. Cette présentation propose une synthèse de ces contributions, avec un intérêt particulier pour le frottement, mécanisme fondamental qui sous-tend l’ensemble de ces comportements."

• Jeudi 30 avril 2026
  Probing Schroeder’s Paradox of Polymeric Gels
  Wei Hong
  School of Mechanical Engineering and Mechanics, 
Eastern Institute of Technology, Ningbo, China

Abstract
It has long been recognized that for a swollen polymeric gel, the maximum swelling ratio, or the maximum solvent uptake, is different between a sample immersed in liquid solvent and one in saturated vapor. Such a phenomenon, known as Schroeder’s paradox, is seemingly contradictory to classical thermodynamic expectations, as the two environments – saturated vapor and liquid solvent – are in equilibrium with each other. Over the past century, there has been debates whether it conforms to thermodynamics or is just a non-equilibrium behavior due to kinetics, and various explanations have been proposed but none seemed convincing and universally applicable. In this study, extensive experiments have been systematically conducted, and the possible mechanisms have been ruled out one by one. Although no conclusive argument has yet been reached, several key factors stand out : the topology of polymer network, the state of polymer chains, and the effect of surface, and further theoretical and experimental study is needed to finally identify the dominating one.

Biosketch
Dr. Wei Hong is currently Chair Professor and Dean of the School of Mechanical Engineering and Mechanics at Eastern Institute of Technology (EIT). Wei got both B.S. and M.S. degrees from Tsinghua University, and Ph.D. from Harvard University. Wei was a faculty member at Iowa State University in the US, Hokkaido University in Japan, and later the Southern University of Science and Technology in China. Wei serves as the associate editors of IJSS and Meccanica, and on the editorial boards of various other journals, and has been elected a Fellow of ASME. His recent research focuses on polymer and soft matter physics, adhesion, dielectric breakdown, smart and flexible structures, and surface instabilities.

• Jeudi 26 mars 2026
  Strain-responsive mechanical properties of polymeric materials
  Koichi Mayumi
  The Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan

Polymeric materials that exhibit strain-responsive mechanical properties are attracting increasing attention as a class of adaptive and functional materials capable of dynamically adjusting their behavior under external deformation. In such systems, mechanical characteristics such as stiffness, strength, and energy dissipation evolve in response to applied strain, often driven by reversible changes in molecular conformation, network architecture, or intermolecular interactions. Understanding and controlling these strain-coupled processes enable the design of polymers with tunable and programmable mechanical performance, which are promising for applications in soft robotics, flexible electronics, and biomedical devices. In the seminar, I will introduce several topics on the strain-responsive mechanical properties of polymeric materials : (i) tough and elastic polymer gels reinforced by strain-induced crystallization, (ii) shear-induced gelation of polymer/nanoparticle solutions, (iii) fracture of cross-linked epoxy resins with different network structures.
Recently, we have successfully developed tough polymer gels utilizing strain-induced crystallization (SIC) [1-6]. In order to realize SIC in polymer gels, the polymer chain orientation under stretching should be homogeneous. We have discovered that SIC occurs in polymer gels with homogeneous polymer networks and sufficiently high polymer concentrations : slide-ring (SR) hydro gels [1], SR ion gels [2, 3], Tri-branched PEG gels [4], and Tetra-branched PEG gels [5]. From in-situ wide-angle X-ray scattering (WAXS) experiments on the gels under repeated tensile deformation, we found that nanocrystals of PEG in the gels forms at large strains and disappears quickly when applied stress is reduced. The reversible strain-induced crystallization yields the high toughness and elasticity. A similar concept can be applied to bio-based polysaccharide hydrogels to improve their mechanical toughness [7].

References :
[1] Liu C., Morimoto N., Jiang L., Kawahara S., Noritomi T., Yokoyama H., Mayumi K.*, Ito K.* Science 2021, 372, 1078.
[2] Hashimoto K., Shiwaku T., Aoki H., Yokoyama H., Mayumi K.*, Ito K.* Sci. Adv. 2023, 9, eadi8505.
[3] Enoki T., Hashimoto K., Oda T., Ito K., Mayumi K.* Macromolecules 2024, 57, 11498.
[4] Fujiyabu T., Sakumichi N., Katashima T., Liu C., Mayumi K., Chung U. I., Sakai T.* Sci. Adv. 2022, 8, eabk0010.
[5] Hashimoto K., Enoki T., Liu C., Li X., Sakai T., Mayumi K.* Macromolecules 2024, 57, 1461.
[6] Mayumi K.* Polym. J. 2024, 57, 449.
[7] Geonzon, L. C., Chan, J., Kou, H., Hou, L. X., Oda, T., Tuvikene, R., Matsukawa, S., Mayumi, K.*, Chem. Mater., 37, 6991 (2025).

• Jeudi 19 mars 2026

Confined directional drying : free convection, humidity-insensitive evaporation, and the case of nanoparticles
Jean-Baptiste Samon

Confined directional drying refers to a model experiment for the study of mass transport phenomena that occur during the drying of a complex fluid. In such experiments, a dilute complex fluid is confined within a capillary with cross-sectional dimensions < 100 µm. When the air/liquid meniscus remains trapped at the outlet of the capillary, solvent evaporation induces a flow that continuously accumulates the non-volatile solute at the tip of the cell.

In this presentation, I will focus on three different aspects of such experiments : (i) the role of free convection on the concentration process in the case of a dilute solution/dispersion, (ii) the impact of the solute concentration on the driving force of evaporation which can lead to humidity-insensitive evaporation in the case of polymer solutions, and (iii) the case of a dispersion of nanoparticles. For this last point, we have developed PDMS microfludic chips for confined directional drying experiments, and we have exploited hydrophilic fillers naturally present in the PDMS matrix to measure the water potential and thus obtain a quantitative description of the process.

• Jeudi 26 février 2026

Polylactide Stereocomplexation : Controlled Crystallization and Functionality in Soft Polymeric Materials
Mohammad Raef
Basque Center for Macromolecular Design and Engineering (POLYMAT) and the University of the Basque Country EHU

Polylactide (PLA) stereocomplexation provides a robust route to engineer polymer properties through stereoselective interactions, controlled crystallization, and hierarchical self-assembly. The association of enantiomeric poly(L-lactide) and poly(D-lactide) chains leads to stereocomplex crystals with a distinct triclinic structure, high packing density, and melting temperatures approximately 50 K higher than those of conventional PLA homocrystals. These characteristics position stereocomplexed PLA as a model soft-matter system, in which molecular structure and chain dynamics directly translate into macroscopic performance.
In this seminar, stereocomplexation is discussed as a kinetically governed crystallization process competing with homocrystallization, rather than as a purely thermodynamic outcome. The influence of molecular weight, chain entanglements, processing history, shear fields, thermal protocols, and interfacial interactions on stereocomplex formation is examined. Particular attention is given to how copolymerization, selective nucleation, and multifunctional fillers reshape the crystallization landscape, enabling stereocomplex formation in high-molecular-weight and processing-relevant systems. Beyond enhanced thermal stability, stereocomplex domains act as physical crosslinks and volume-excluding phases that strongly affect chain mobility, mechanical reinforcement, degradation kinetics, and transport phenomena. These effects open extended application potential for stereocomplexed PLA in areas requiring dimensional stability, heat resistance, controlled degradability, and multifunctionality, including advanced packaging, biomedical devices, sustainable composites, and functional soft materials. More broadly, stereocomplexation offers design principles relevant to soft matter science, linking confinement, interfacial crystallization, and multiscale structure–property relationships. By framing PLA stereocomplexation as a tunable platform for controlled crystallization, this seminar highlights its relevance beyond biodegradable polymers, with implications for the rational design of high-performance and sustainable polymeric materials.

• Jeudi 18 decembre 2025

Theory of brittle-to-tough transition in polymer materials
Didier Long
INSA Lyon

Polymer materials of different types break under applied strain with the remarkable feature that the fracture energy can increase by several orders of magnitudes when the rupture behavior changes from brittle to ductile. We show that this brittle-to-ductile transition in these different materials is underpinned by a phase transition regarding rupture mechanisms on a network that has been discovered recently [Fusco et al J. Stat. Phys. 2019]. The key ingredient of this theory is the distribution of the local stress rupture thresholds of the sites. If this distribution is narrow, a crack propagates as soon a cavity appears as a result of stress concentration in the vicinity of the crack tip. Then, a negligible damage 𝛟 at break is observed. Above a critical a value of the disorder, cracks do not propagate in an initial stage because they are blocked by stronger sites. Eventually, once the sample has been weakened by a sufficiently large accumulation of small damage, one of the cracks propagates and final rupture takes place. In this case, the sample accumulates a very large fraction of damage smaller than but of order 1 before catastrophic failure takes place [1]. We show how the theoretical network model of Fusco et al can be transposed to real materials by studying in detail breaking mechanisms in three different polymer materials : 1) neat glassy polymers, for which the brittle-to-ductile transition is induced by increasing the temperature ; 2) high impact glassy polymers toughened with rubbery inclusions ; 3) interpenetrated hydrogels. In these three different systems a brittle-to-ductile transition is observed beyond which impact or tear energy increases by up to 2 or 3 orders of magnitudes. Our transposition of the network theoretical model to these systems allow to describe each specific failure mechanism and to explain quantitatively these effects, which has eluded research for many decades [2].

[1] C. Fusco, D. R. Long, and L. Vanel, Brittle-to quasibrittle transition in creep rupture of 2d disordered elastic materials, J. Stat. Mech. : Theory and Experiment, 053301 (2019). DOI10.1088/1742-5468/ab11de

[2] C. Fusco, T. Lamy, L. Vanel and D.R. Long, Theory of brittle-to-tough transition in polymer materials, submitted (2025)

• Jeudi 4 decembre 2025

Structure-Properties Relationships of Fatty Acid-Polymeric and Protein Self-Assemblies
Maëva Almeida
Internal SIMM seminar

• Jeudi 26 novembre 2025

Functional Polyelectrolyte Dispersants : Mechanistic Insights and Applications in Printed and Coated Materials
Jérôme Claverie
Université de Sherbrooke, Canada

When oxide or carbon-based particles are stabilized using polyelectrolytes, a distinct molecular-weight segregation phenomenon occurs whereby only chains within a specific molecular-weight effectively adsorb onto the particle surface. Building on this observation, we designed a series of tailored dispersants optimized for both inorganic oxides and carbon nanomaterials. Using these dispersants, we formulated conductive inks based on carbon nanotubes that remain stable even in low-polarity media such as alkanes.
While dispersants enable robust colloidal stability, they can significantly impede electronic conductivity once embedded in a final coating. To overcome this limitation, we developed ephemeral dispersants—polymeric stabilizers engineered to evaporate under mild conditions upon exposure to a defined stimulus. These materials provide excellent dispersion during processing yet vanish afterward, allowing the efficient printing of carbon nanotubes and graphene with minimal insulating residue.
Finally, we demonstrate the role of dispersants in directing hydrothermal synthesis of inorganic oxides, enabling access to a versatile library of semiconducting particles with enhanced photocatalytic activity.

• Jeudi 20 novembre 2025 - Amphi Charpak

Engineering Plant-based Food Emulsions and Foams : Mayo to Milk
Vivek Sharma
Chemical Engineering, University of Illinois Chicago, IL.

The success and suitability of plant-based emulsions as sustainable, palatable, and healthy substitutes are tied to their ability to emulate the properties, processing, and functionalities of animal-based products. We translate several challenges underlying the design, manufacturing, and consumption of plant-based emulsions into fundamental quests in soft matter physics and rheology. We characterize the ingredient-dependent differences in flow behavior of animal and plant-based emulsions, with milk representing dilute and mayo jammed-dense emulsions, respectively. The presence of macromolecular additives like polysaccharides and proteins in suspending fluid and interfaces of plant-based emulsions makes their response non-Newtonian. The extensional and interfacial flows influence the emulsification, emulsion stability, and shear rheology. At the macroscale level, the extensional rheology response of the emulsions impacts many processing operations and sensory perception of texture, mouthfeel, and apparent thickness, stretchiness, or stringiness. However, there is a clear lack of appropriate extensional rheology characterization techniques, and a limited understanding of macromolecular or drop/particle microphysics that sets the rheological response and processability. We develop experimental protocols for characterizing the influence of ingredients like proteins and polysaccharides on shear rheology and extensionally dominated interfacial flows in pinching necks and draining films. By visualizing and analyzing flows in pinching necks created using dripping, dipping, dripping-onto-substrate (DoS) rheometry, and stretching bridges like in the tack test, we characterize the extensional rheology response relevant for processing and applications. We show that a deeper understanding of ingredient- dependent emulsion rheology, shelf-life, and consumer perception involves a joyous odyssey into the physics and mathematics of self-similarity, finite-time singularity in free-surface flows, colloidal interactions, coalescence and lubrication flows, pinching and spreading kinetics, stretched polymer physics, protein science, and scaling theory or dimensional analysis.

• Jeudi 6 novembre 2025

Polymer Colloids : From Synthesis to Functional Properties
Elise Deniau
IMMM, Le Mans Université

The work presented adresses the field of materials chemistry and physicochemistry, with particular emphasis on the design, characterization and valorization of functional colloids structured at the nanometric scale.
Through an interdisciplinary approach combining controlled polymer syntheses, physical chemistry of interfaces and multi-scale characterizations, this research has led to a better understanding of structure-property-function relationships in a variety of application contexts, such as gas or micropollutant capture, organic electronics, active ingredient release or micro- and nano-plastic degradation.
All this work illustrates the originality of the properties of colloidal systems, while highlighting the potential for innovation offered by mastery of macromolecular architectures. These advances open up promising prospects for the design of new nanomaterials to meet today’s major societal challenges, notably by providing solutions to major environmental issues such as climate change, water pollution and plastic pollution.