Denis C D Roux | Joseph Fourier University (original) (raw)

Papers by Denis C D Roux

Journal of Fluids Engineering

In this work, the influence of nozzle shape on microfluidic ink jet breakup is investigated. Firs... more In this work, the influence of nozzle shape on microfluidic ink jet breakup is investigated. First, an industrial ink used in continuous inkjet (CIJ) printing devices is selected. Ink rheological properties are measured to ensure an apparent Newtonian behavior and a constant surface tension. Then, breakup lengths and shapes are observed on a wide range of disturbance amplitude for four different nozzles. Later on, ink breakup behaviors are compared to the linear theory. Finally, these results are discussed using numerical simulations to highlight the influence of the velocity profiles at the nozzle outlet. Using such computations, a simple approach is derived to accurately predict the breakup length for industrial CIJ nozzles.

Frontiers in Chemistry

Structurally modified hydroxyl functionalized pyridinium ionic liquids (ILs), liquid at room temp... more Structurally modified hydroxyl functionalized pyridinium ionic liquids (ILs), liquid at room temperature, were synthesized and characterized. Alkylated N-(2-hydroxyethyl)-pyridinium ILs were prepared from alkylpyridines via corresponding bromide salts by N-alkylation (65-93%) and final anion exchange (75-96%). Pyridinium-alkylation strongly influenced the IL physicochemical and electrochemical properties. Experimental values for the ILs physicochemical properties (density, viscosity, conductivity, and thermal decomposition temperature), were in good agreement with corresponding predicted values obtained by theoretical calculations. The pyridinium ILs have electrochemical window of 3.0-5.4 V and were thermally stable up to 405 • C. The IL viscosity and density were measured over a wide temperature range (25-80 • C). Pyridine alkyl-substitution strongly affected the partial positive charge on the nitrogen atom of the pyridinium cations, as shown by charge distribution calculations. Ongoing studies on Mg complexes of the new ILs demonstrate promising properties for high current density electrodeposition of magnesium.

Progress in Colloid & Polymer Science, 1994

ABSTRACT In dilute aqueous solutions of surfactants a succession of phases is generally observed,... more ABSTRACT In dilute aqueous solutions of surfactants a succession of phases is generally observed, namely, solutions of globular then elongated flexible micelles (worm-like micelles) followed by the phases of fluid membranes (successively a lamellar phase and the L3 (sponge) phase). This is well accounted for by the continuous decrease of the spontaneous curvature of the surfactant film upon variation of some control parameter (temperature or concentration of added salt or of cosurfactant). However, a number of experimental facts are still open to question, e.g.: i) The solutions of worm-like micelles undergo a separation in two distinct isotropic phases upon variation of the control parameter; ii) Upon increasing the concentration of aggregates in the micellar phase, a nematic phase is found to exist in a narrow range of the control parameter. For lower and higher values of this parameter the isotropic micellar phase persists; iii) The unexpected evolution of the viscosity of the solutions of worm-like micelles. We argue that these facts can be interpreted assuming that in the course of the continuous decrease of the curvature of the amphiphilic film the cylindrical aggregates (worm-like micelles) form increasingly more connections allowing for favorable regions of smaller curvature.

Europhysics Letters (EPL), 1994

... As illustrative examples, one can mention the sponge (isotropic) to lamellar (smectic) transi... more ... As illustrative examples, one can mention the sponge (isotropic) to lamellar (smectic) transition studied by Milner et al. [2], or the onion (liposome) to lamellar (smectic) transition studied by Diat and Roux[3]. Attention ... Rev. Lett., 62 (1989) 1856. [3] DIAT 0. and ROUX D., J. Phys. ...

Cellulose, 2008

The rheology of cellulose microfibril suspensions from TEMPO-oxidized pulp was investigated. The ... more The rheology of cellulose microfibril suspensions from TEMPO-oxidized pulp was investigated. The suspension showed a pseudo-plastic and thixotropic behavior, slowly evolving with time under a given shear rate. The viscosity was proportional to the concentration up to the critical concentration of 0.23%. Above it, the viscosity followed a power law with exponents from 2 to 6 depending on the shear rate, and the system showed shear thinning behavior and behaved gel-like. Below this concentration, the system was more Newtonian. Birefringence measurement of 0.44% and 0.78% suspension showed that microfibrils alignment saturated at a small shear rate with a Herman's orientation parameter below 0.65 probably due to the interconnection of microfibrils.

Biomacromolecules, Jan 12, 2015

In the fields of tissue engineering and regenerative medicine, many researchers and companies ali... more In the fields of tissue engineering and regenerative medicine, many researchers and companies alike are investigating the utility of concentrated mesenchymal stem cell suspensions as therapeutic injectables, with the hope of regenerating the damaged tissue site. These cells are seldom used alone, being instead combined with synthetic biomacromolecules, such as branched poly(ethylene glycol) (PEG) polymers, in order to form cross-linked hydrogels postinjection. In this article, we present the results of a detailed experimental and analytical investigation into the impacts of a range of eight-arm PEG polymers, each presenting functional end groups, on the rheological properties of concentrated living cells of mesenchymal origin. Using two-photon confocal microscopy, we confirmed that the aggregates formed by the cells are fractal structures, the dimension of which changed with PEG polymer type addition. From these results and the observed substantial variation in rheological footprint...

Biomacromolecules, 2013

With the rapidly growing interest in the use of mesenchymal stromal cells (MSCs) for cell therapy... more With the rapidly growing interest in the use of mesenchymal stromal cells (MSCs) for cell therapy and regenerative medicine applications, either alone as an injected suspension, or dispersed within injectable hydrogel delivery systems, greater understanding of the structure−functionproperty characteristics of suspensions of adhesion-dependent mesenchymal cells is required. In this paper, we present the results of an experimental study into the flow behavior of concentrated suspensions of living cells of mesenchymal origin (fibroblasts) over a wide range of cell concentrations, with and without the addition of hyaluronic acid (HA), a commonly utilized biomolecule in injectable hydrogel formulations. We characterize the change in the shear viscosity as a function of shear stress and shear rate for cell volume fractions varying from 20 to 60%. We show that high volume fraction suspensions of living mesenchymal cells, known to be capable of homotypic interactions, exhibit highly complex but reproducible rheological footprints, including yield stress, shear thinning and shearinduced fracture behaviors. We show that with the addition of HA, we can significantly modify and tailor the rheology of these cell suspensions at all volume fractions. Using FACS and confocal imaging, we show that the observed effect of HA addition is due to a significantly modulation in the formation of cellular aggregates in these suspensions, and thus the resultant volume spanning network. Considering the aggregates as fractal structures, we show that by taking into account the changes in volume fractions with shear, we are able to plot a master curve for the range of conditions investigated and extract from it the average adhesion force between individual cells, across a population of millions of cells. The outcomes of this study not only provide new insight into the complexity of the flow behaviors of concentrated, adhesive mesenchymal cell suspensions, and their sensitivity to associative biomacromolecule addition, but also a novel, rapid method by which to measure the average adhesion force between individual cells, and the impacts of biomacromolecules on this important parameter.

Journal of Colloid and Interface Science, 2004

The impact of a water droplet on a glass surface is studied experimentally using a high-speed vid... more The impact of a water droplet on a glass surface is studied experimentally using a high-speed video camera which can catch up to 60,000 images per second with an exposure time of 10 µs. A wide range of impact velocities are studied by varying the fall height, showing different spreading regimes. Particular attention is given to the dynamics of the contact angle and its relation to the maximum expanding radius and capillary number. A linear relation between the contact line velocity and the impact velocity is found experimentally. Using acoustic analysis, an evaluation of the pressure at the contact line is given. We also confront predicted and experimental jetting times. This work shows that descriptions of drop impact based purely on conservation of energy are inadequate to describe the dynamics of the event. The different shapes taken by the drops between the initial impact and the maximum radius determine the final outcome.  2004 Elsevier Inc. All rights reserved.

We define a creep-flow–based measurement procedure to allow reliable and reproducible results on ... more We define a creep-flow–based measurement procedure to allow reliable and reproducible results
on aging and yielding materials to be obtained. Investigation of the effects of different parameter such as
the pre-shear time, the recovery time and the applied stress magnitude on the viscoelastic properties of a
lyotropic liquid crystal phase is reported. Cryo-TEM observations indicate the formation of multiconnected
bilayers at rest. Shearing the investigated material shows a propensity to acquire all the macroscopic
properties of “soft jammed systems”. These properties are then interpreted in terms of shear-induced
structural rearrangement on the basis of cryofracture observation obtained at different times after the
preshear imposed.