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Cohen-Addad S.,CNRS Nanosciences Institute of Paris | Hohler R.,University Paris Est Creteil
Current Opinion in Colloid and Interface Science | Year: 2014

We review the state of the art in foam and highly concentrated emulsion rheology, with an emphasis on progress made over the last five years. Since the structures and physico-chemical processes relevant for foams and emulsions are closely analogous, comparing the knowledge recently gained in these two neighboring fields brings fresh insight. In this spirit, we review how the macroscopic mechanical response arises from a coupling between interfacial energy and long range molecular interactions, entropic effects, interfacial rheology, and dynamics at the droplet or bubble scale. We present experiments and models concerning elasticity, osmotic pressure, yielding and flow behavior. © 2014 Elsevier Ltd.


Cohen-Addad S.,CNRS Nanosciences Institute of Paris | Cohen-Addad S.,University Paris Est Creteil | Hohler R.,CNRS Nanosciences Institute of Paris | Hohler R.,University Paris Est Creteil | Pitois O.,ParisTech National School of Bridges and Roads
Annual Review of Fluid Mechanics | Year: 2013

Aqueous foams are complex fluids composed of gas bubbles tightly packed in a surfactant solution. Even though they generally consist only of Newtonian fluids, foam flow obeys nonlinear laws. This can result from nonaffine deformations of the disordered bubble packing as well as from a coupling between the surface flow in the surfactant monolayers and the bulk liquid flow in the films, channels, and nodes. A similar coupling governs the permeation of liquid through the bubble packing that is observed when foams drain due to gravity. We review the experimental state of the art as well as recent models that describe the interplay of the processes at multiple length scales involved in foam drainage and rheology. Copyright © 2013 by Annual Reviews. All rights reserved.


Fainstein A.,Bariloche Atomic Center | Lanzillotti-Kimura N.D.,Bariloche Atomic Center | Jusserand B.,CNRS Nanosciences Institute of Paris | Perrin B.,CNRS Nanosciences Institute of Paris
Physical Review Letters | Year: 2013

We show that distributed Bragg reflector GaAs/AlAs vertical cavities designed to confine photons are automatically optimal to confine phonons of the same wavelength, strongly enhancing their interaction. We study the impulsive generation of intense coherent and monochromatic acoustic phonons by following the time evolution of the elastic strain in picosecond-laser experiments. Efficient optical detection is assured by the strong phonon backaction on the high-Q optical cavity mode. Large optomechanical factors are reported (∼THz/nm range). Pillar cavities based in these structures are predicted to display picogram effective masses, almost perfect sound extraction, and threshold powers for the stimulated emission of phonons in the range μW-mW, opening the way for the demonstration of phonon "lasing" by parametric instability in these devices. © 2013 American Physical Society.


Akamatsu S.,CNRS Nanosciences Institute of Paris | Plapp M.,Ecole Polytechnique - Palaiseau
Current Opinion in Solid State and Materials Science | Year: 2016

Recent advances in the understanding of eutectic and peritectic two-phase pattern formation under purely diffusive transport are reviewed. The parallel progress of two key techniques, namely, in situ experimentation with model, low-melting transparent and metallic alloys in thin and bulk samples, and numerical phase-field simulations, is highlighted. Experiments and simulations are interpreted in the light of the theory of non-equilibrium pattern formation phenomena. Focus is put on microstructure selection and morphological transitions, multiscale patterns in ternary alloys, and the influence of crystallographic effects on pattern formation. Open problems, for example on crystallographic effects, irregular eutectics, and peritectic solidification, are outlined. © 2015 Elsevier Ltd. All rights reserved.


Bureau L.,CNRS Nanosciences Institute of Paris
Physical Review Letters | Year: 2010

We probe the rheology of the model liquid octamethylcyclotetrasiloxane (OMCTS) confined into molecularly thin films, using a unique surface force apparatus allowing us to explore a large range of shear rates and confinement. We thus show that OMCTS under increasing confinement exhibits the viscosity enhancement and the nonlinear flow properties characteristic of a sheared supercooled liquid approaching its glass transition. Besides, we study the drainage of confined OMCTS via the propagation of "squeeze-out" fronts. The hydrodynamic model proposed by Becker and Mugele to describe such front dynamics leads to a conclusion in apparent contradiction with the dynamical slowdown evidenced by rheology measurements, which suggests that front propagation is not controlled by large scale flow in the confined films. © 2010 The American Physical Society.


Baresch D.,CNRS Nanosciences Institute of Paris | Thomas J.-L.,CNRS Nanosciences Institute of Paris | Marchiano R.,CNRS Nanosciences Institute of Paris
Physical Review Letters | Year: 2016

We demonstrate the trapping of elastic particles by the large gradient force of a single acoustical beam in three dimensions. Acoustical tweezers can push, pull and accurately control both the position and the forces exerted on a unique particle. Forces in excess of 1 micronewton were exerted on polystyrene beads in the submillimeter range. A beam intensity less than 50 W/cm2 was required, ensuring damage-free trapping conditions. The large spectrum of frequencies covered by coherent ultrasonic sources provides a wide variety of manipulation possibilities from macroscopic to microscopic length scales. Our observations could open the way to important applications, in particular, in biology and biophysics at the cellular scale and for the design of acoustical machines in microfluidic environments. © 2016 American Physical Society.


Prevot G.,CNRS Nanosciences Institute of Paris
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

We have studied the Ostwald ripening of three-dimensional islands on a homogeneous surface with an original off-lattice kinetic Monte Carlo algorithm. In this algorithm, adatom trajectories are highly simplified, while still ensuring that the adatom fluxes between islands are exactly described. From the simulations, we obtained the evolution of the island size distribution over a large time range. The simulations obtained are compared with the results of numerical integration of rate equations derived from a mean-field approximation. Both results indicate that the equilibrium radius of the islands follows a power-law behavior in the limit of a very dilute phase, with an exponent close to 1/4. A general, excellent agreement is obtained, showing the validity of our approach, whereas the validity of the mean-field approximation is discussed for a very small mean island size, or for a large fraction of the surface covered by the islands. © 2011 American Physical Society.


Malham I.B.,CNRS Nanosciences Institute of Paris | Bureau L.,CNRS Nanosciences Institute of Paris
Langmuir | Year: 2010

We probe, using the surface forces apparatus, the thermal response of poly(N-isopropylacrylamide) (PNIPAM) brushes of various grafting densities, grown from plasma-activated mica by means of surface-initiated polymerization. We thus show that dense thermoresponsive brushes collapse gradually as temperature is increased and that grafting density greatly affects their ability to swell: the swelling ratio of the brushes, which characterizes the thickness variation between the swollen and the collapsed state, is found to decrease from ∼7 to ∼3 as the number of grafted chains per unit area increases. Such a result, obtained with an unprecedented resolution in grafting density, provides qualitative support to calculations by Mendez et al. [Macromolecules 2005, 38, 174]. We further show that, in contrast to swelling, adhesion between two PNIPAM brushes appears to be rather insensitive to their molecular structure. © 2009 American Chemical Society.


Goniakowski J.,CNRS Nanosciences Institute of Paris | Noguera C.,CNRS Nanosciences Institute of Paris
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

Relying on classical electrostatics, we extend the understanding of the electrostatic forces responsible for polarity to nano-objects. We show that while no actual divergence of the electrostatic potential occurs in polar nano-objects, beyond a critical object size, the divergent behavior of the potential differences as a function of size induces polar instability analogous to that at semi-infinite surfaces. We highlight several new and generic properties of polar nano-objects: (1) the dependence of the instability behavior on object dimensionality; (2) the driving role of the smallest structural parameter, not necessarily the thickness; (3) the inhomogeneity of the electrostatic potential within a polar termination and its divergent behavior as a function of the termination size; and (4) the polar character of symmetric stoichiometric objects with a vanishing total dipole moment. We give simple analytical arguments in order to build a generic framework, valid independent of the precise object dimensionality, structure, and ionocovalent characteristics. © 2011 American Physical Society.


Bou-Malham I.,CNRS Nanosciences Institute of Paris | Bureau L.,CNRS Nanosciences Institute of Paris
Soft Matter | Year: 2010

Ionic liquids have remarkable physico-chemical properties that make them highly attractive as new solvents or electrolytes in applications ranging from solar cells to MEMS lubrication, in which their flow properties in the vicinity of solid surfaces are crucial. We have performed a study of the nanorheology of two ionic liquids confined in molecularly thin films which shows how surface charges drastically affect their molecular structure and flow properties. © 2010 The Royal Society of Chemistry.

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