Accueil > Séminaires

Séminaires

Contact lines on soft solids

Julien Dervaux Laboratoire Matière et Systèmes Complexes, Université Paris Diderot

Mercredi 21 Novembre - Amphi Urbain

 

Elastocapillarity describes the deformations of soft materials by surface tensions and is involved in a broad range of applications, from micro-electromechanical devices to cell patterning on soft surfaces. Within the very rich field of elastocapillarity, studies on the wetting of soft materials by sessile or moving droplets are presently attracting great interest. In contrast with the wetting of liquids on rigid materials, the surface tension of a liquid drop deforms the soft solid at the contact line and leads to the formation of a “ridge”, which in turn drastically affects the static and dynamic wetting properties.

In this talk, I will briefly introduce the linear theory of static elastowetting before presenting experimental and theoretical results beyond the static linear approximation.

First I will show how the viscous dissipation in soft solids controls the velocity of moving contact lines and how this dissipation can be tuned to control the motion of droplets on thin films. Then, I will show that droplets on soft elastomers and gels leave long-lived “footprints” after removal. The observed logarithmic disappearance of these traces is well captured by a poroelastic model and is responsible for a strong time-dependent hysteresis. Finally I will discuss nonlinear effects in elastowetting and highlight a deep connection between elastocapillary ridges in soft materials and topological defects in crystals.

Lubricant-Infused Materials to Combat Marine Biofouling

Ali Miserez School of Materials Science and Engineering and School of Biological Sciences, Nanyang Technological University, Singapore

Jeudi 22 novembre - 14h30 - Amphi Schützenberger

 

Marine biofouling has been a vexing issue for decades1. The large variety of marine organisms (e.g. mussels, barnacles, tubeworms) that can efficiently attach to immersed surfaces such as ship hulls or port infrastructures increase hydrodynamic drag and the weight of ships, or clog critical piping structures. In turn, biofouling results in high cost to the maritime industry and is responsible for increased greenhouse emissions2. It is also directly responsible for the translocation of invasive species.

If one wants to tackle biofouling and develop efficient coatings that deter or minimize fouling, it is critical to understand the fouling process of macro-fouling organisms such as mussels3 or barnacles4 across multiple length scales, from the molecular level of adsorption on solid substrates as done in our lab5 to the meso-scale of adhesion phenomena to field studies. Biofouling also entices captivating questions with regard to mechano-sensing ability of fouling organisms onto solid surfaces.

In this talk, I will present our recent efforts in using the concept of Slippery, Liquid-Infused Porous Surfaces (SLIPS) to combat marine biofouling6, using mussels as a model organism to unveil the multi-scale mechanisms of fouling prevention. I will present recent results showing that slippery surfaces are remarkably effective in preventing marine fouling in both laboratory and field conditions. Detailed investigations across multiple length scales—from the molecular scale characterization of deposited adhesive proteins, to nano-scale contact mechanics, to macro-scale live observations— provides new insights into the physical mechanisms underlying the adhesion prevention. In particular, I will discuss how lubricant-infusion considerably reduces fouling by deceiving the mechano-sensing ability of mussels, therefore deterring secretion of adhesive threads, as well as how the infused lubricant decreases the molecular work of adhesion and macroscopic adhesion.

References

1. Flemming, H.-C., Sriyutha Murthy, P., Venkatesan, R. & Cooksey, K. E. in Springer Series on Biofilm (Springer-Verlag, Berlin, Germany, 2009).

2. Schultz, M. P., Bendick, J. A., Holm, E. R. & Hertel, W. M. Economic Impact of Biofouling on a Naval Surface Ship. Biofouling 27, 87–98, (2011).

3. Waite, J. H. Mussel Adhesion – Essential Footwork. Journal of Experimental Biology 220, 517–530, (2017).

4. Kamino, K. Mini-review : Barnacle Adhesives and Adhesion. Biofouling 29, 735–749, (2013).

5. Petrone, L. et al. Mussel Adhesion is Dictated by Time-Regulated Secretion and Molecular Conformation of Mussel Adhesive Proteins. Nature Communications 6:8737, (2015).

6. Amini, S. et al. Preventing Mussel Adhesion Using Liquid-Infused Materials. Science 357, 668–673, (2017).

Mechanical properties of poorly connected soft solids

Mehdi Bouzid LPTMS, CNRS, Univ. Paris-Sud, Univ. Paris-Saclay

Jeudi 29 novembre 2018 - 14h00 - Amphi Holweck

 

Self-assembly and aggregation of soft condensed matter like proteins, colloids or polymers into poorly connected and weakly elastic solids is very common and ubiquitous in nature. Phase separation, spinodal decomposition as well as externally driven self-assembly or aggregation often lead to gels, which display diverse structures and solid-like mechanical features. The structural complexity of soft gels entails a versatile mechanical response that allows for large deformations, controlled elastic recovery and toughness in the same material. A limit to exploiting the potential of such materials is the insufficient fundamental understanding of the microstructural origin of the bulk mechanical properties. Investigating how the mechanical response depend on the material microstructure will provide a new rationale, which would ultimately lead to several applications, ranging from improving the performance of batteries (colloidal gels), designing smart composites that can prevent the cascade of catastrophic events and can be used in anti-seismic buildings, and many with important biological function, such as new scaffolds for tissue engineering.
In the first part of my talk, I will present a new highly efficient technique to probe the linear mechanical response of soft gels, as well as a minimal constitutive model. Then I’ll focus on the link between the topology of the network and the non-linear rheological response. I will show the relevance of our analysis to understand the mechanics of F-actin cytoskeleton under large deformations. Our study helps to clarify, the mechanism by which mutations cause podocyte dysfunction and progressive kidney disease in humans. Finally, I will present a new mechanism to account for the non-linear elasticity of a very sparsely connected gels : branched actin networks.


Precise Characterization of Polymer Brushes by Quantum Beam

Atsushi Takahara Institute for Materials Chemistry and Engineering, Center for Molecular Systems (CMS), WPI-I2CNER, Research Center for Synchrotron Light Applications, Kyushu University, Japan

Jeudi 15 novembre 2018

Lire la suite

Model Amphiphilic Polymer Conetworks Comprising Star Polymers End-linked via Dynamic Covalent Acylhydrazone Bonds

Costas S. Patrickios Department of Chemistry, University of Cyprus

Lundi 5 novembre 2018

Lire la suite

Physically based modeling of rubber-like materials

Mikhail Itskov LF Kontinuumsmechanik \ Dept. of Continuum Mechanics RWTH Aachen University

Jeudi 13 septembre 2018

Lire la suite