Rheology and plasticity

  1. Solutions of thermoresponsive tubes : jamming of cylindrical objects
  2. Fluidisation d'un solide granulaire

Solutions of thermoresponsive tubes : jamming of cylindrical objects

Contact : A. Saint-Jalmes 

In collaboration with INRA at Nantes, we have studied solutions of hydroxystearic acids, associated with alkanolamine counterions. It turns out that - with alkanolamine - the 12-hydroxystearic acid can be solubilized : it self-organizes in long (10 microns) multi-wall tubes. 
These supramolecular structures also reversibly evolve with temperature : under heating, the tubes first grow in diameter (up to Tmax), then they shrink, before finally vanishing and forming small micelles above a temperature Tmelting.

 

changes at the supramolecular scale and effect on rheology

caption : changes in the supramolecular structures and effect on rheology : (left) shifting from a viscous fluid to a yield stress fluid, by changing the concentration or the temperature ; as a consequence of the tubular shape of the supramolecular structures, the critical packing phi* for jamming is strongly reduced when compared to the critical packing of spheres (phircp).
(right) temperature-dependence of the viscosity at three different shear rates.  one recovers the effects of the tube diameter changes and of the  ‘tube’ – ‘micelle’ transition : the viscosity goes through a maximum at Tmax before collapsing above Tmelting

on these systems, we have first studied in details the bulk and interfacial viscoelasticity. Depending on the temperature and concentration, we have shown that these solutions can have unusual rheological properties, ranging from a Newtonian behavior to a yield stress fluid, together with shear-thinning and thermal-thickening behavior. 

Such complex macroscopic behaviors can indeed be correlated to the diversity of the structures at the supramolecular scale. These studies also allows us to study the jamming transition by two routes (temperature and concentration) for non-spherical objects.

More recently, we have fully determined the structural phase diagram of these chemical systems, providing us with a complete understanding, at the microscopic scale, of how the tubes evolve with temperature, and for the different alkanolamine counterions. 
 

Références

  • “Yielding and flow of solutions of thermoresponsive surfactant tubes: tuning macroscopic rheology by supramolecular assemblies”  A.L. Fameau and A. Saint-Jalmes. Soft Matter, 10, 3622  (2014). DOI : 10.1039/c3sm53001a

 

  • Morphological Transition in Fatty Acid Self-Assemblies: A Process Driven by the Interplay between the Chain-Melting and Surface-Melting Process of the Hydrogen Bonds Anne-Laure Fameau, Fabrice Cousin, Arnaud Saint-Jalmes. Langmuir, 33, 12943 (2017). DOI: 10.1021/acs.langmuir.7b02651

Fluidisation d'un solide granulaire

Dans le cadre d'une collaboration avec Eric Clément du PMMH (ESPCI, Paris), nous avons étudié l'influence d'un bruit mécanique sur la réponse en fluage d'un milieu granulaire.

Nous avons montré expérimentalement la fluidification d'un solide granulaire en présence d'oscillations de faibles amplitudes de la contrainte imposée. 

Nous avons donné une interprétation théorique originale de la suppression du seuil d'un fluide à seuil en présence de fluctuations basée sur un phénomène de ratcheting se révélant  sur les temps longs.

Figure Creep

Références :

A. Pons, T. Darnige, J. Crassous, E. Clément, A. Amon "Spatial repartition of local plastic processes in different creep regimes in a granular material", EPL 113, 28001 (2016).

A. Pons, A. Amon, T. Darnige, J. Crassous, E. Clément, "Mechanical fluctuations suppress the threshold of soft-glassy solids: The secular drift scenario", Phys. Rev. E 92, 020201(R) (2015).

A. Amon, V. B. Nguyen, A. Bruand, J. Crassous, E. Clément, "Hot Spots in an Athermal System", Phys. Rev. Lett. 108, 135502 (2012).