Research

Franquin_labyrintheWithin the InFluX lab, our research activities are focused on the fundamental understanding of the mechanics of soft matter, of slender objects, i.e., plates, rods, ribbons, shells and their application to the Biomechanics of living organisms. Our strategy to tackle a research problem is based on controlled desktop experiments, supported by a theoretical analysis using scaling laws and dimensional analysis, able to predict the result of observations.

I like the idea that Research is a kind of labyrinth, but unlike the labyrinth-jail proposed here by Franquin (excerpt from “idées noires”), researchers build their own labyrinth !


Soft matter rheology

granular_Chain

Giving a clear-cut definition of soft matter is clearly not easy and often a matter of taste. Usually, soft matter is defined either from its internal structure that consists in basic units much larger than atoms, or from its mechanical behavior: the easiness to deform in response to stress, to undergo a glass transition due to collective phenomena and the occurence of nonlinear responses. Considering this definition, soft matter commonly refers to polymers, colloids, surfactants and liquid crystals. Recently, a new class of materials, granular matter, joined the Soft matter family. An analogy between structured fluids subjected to thermal fluctuations and granular assemblies emerged. For example, several authors suggests analogy, still actively debated, between jamming in granular matter and glass transition. Our works in this very active research field aim to understand the influence of connectivity on the mechanical response of materials. Two approaches were followed, first the study of confined chains in polymer films through dewetting instability. More recently, we start a study of granular chains assemblies.

Recent works

  • Physics of Granular assemblies
    D. Dumont, P. Rambach, T. Salez (ESPCI), P. Damman
  • Nano-rheology of of star chains from dewetting in polymer thin films
    A. Lechantre, S. Gabriele, P. Damman

Mechanics of slender structures

cropped-copy-cropped-IMG_3354-crop_DxOb.jpgSoft elastic structures, i.e., involving at least one very small dimension, are prone to undergo mechanical instability. Plates or rods subjected to external compression forces undergo a buckling instability. However, by confining a plate in a curtain or a twisted ribbon morphology or by gluing it on top of a deformable foundation, the buckling no longer appears. Instead, the growth of regular wrinkles is observed due to these geometric or energetic constraints. Our research aims to understand the basic ingredients necessary for the formation of these patterns from a combination of geometry and energy minimisation coupled to nonlinearities.

General presentation on elastic instabilities (Physics Seminar, UMONS 2013, in French):
 https://www.youtube.com/watch?v=iXJnSdgfzY8

Recent works

  • Formation of facets in twisted ribbons
    H. Phan Dimh, V. Démery (ESPCI), F. Brau, B. Davidovitch (UMass), P. Damman
    twisted_ribbonSheets subjected to external forces store the exerted work in elastic deformations that underlie wrinkled and crumpled states. When the forces are compressive, the exerted work is stored as bending energy. However, when compression results from geometrical constraints, the final shape may involve a complex combination of bending and stretching energies. For instance, confining a thin sheet in 3D sphere or in a twisted ribbon is often described as an assembly of flat polygonal facets delimitated by ridges where stretching and bending predominate.
  • Period-doubling bifurcation in wrinkling instability
    F. Brau, H. vandeparre, A. Sabbah, C. poulard (UPsud), A. Boudaoud (ENS-Lyon), P. Damman
  • What do determine the shape of Curtains ?
    H. Vandeparre, M. Pinuera (ESPCI), F. Brau, J. Bico, B. Roman (ESPCI), P. Reis (MIT), C. Gay (MSC), W. Bao, C.N. Lau (UCRiverside), P. Damman

Biomechanics

cameleon

In this new research activity, we apply our knowledge in elasticity and fluid flow to understand the structure and function of biological systems, animals and plants. Our works aim to contribute to answer fundamental questions for living world, such as: How do mechanics  determine the feeding and drinking strategy of animals ? How do elastic instability explain the various shapes of plants ?

General presentation about prey capture by chameleons (Physics Seminar, UMONS 2016, in French): www.youtube.com/watch?v=GNgq5MUWW2w

Recent works

  • How do small animals, bees, bats, capture viscous nectars ?
    A. Lechantre, P. Damman
    avoir-une-rucheFlower nectar is used by some insects, birds and mammals as energy resources. For highly viscous nectars, bees and some bats have developed a specific capture’s method with the tongue based on viscous dipping. They dive their structured tongue into the fluid and drag the nectar during its withdrawal. From the design of physical models, we are trying to understand the influence of these hairy structures on this process.
  • Viscous adhesion in prey capture
    M. Houze, P. Damman
  • The sticky tongue of the Chameleon
    F. Brau, D. Lanterbecq, L. Zgikh, V. Bels (MHN Paris), P. Damman