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Colloidal gels made of carbon black particles dispersed in light mineral oil are “rheo-acoustic” materials, i.e., their mechanical and structural properties can be tuned using high-power ultrasound, sound waves with submicrometer amplitude and frequencies larger than 20 kHz. The effects of high-power ultrasound on the carbon black gel are demonstrated using two experiments: rheology coupled to ultrasound to test for the gel mechanical response and a time-resolved ultra-small-angle x-ray scattering experiment (TRUSAXS) coupled to ultrasound to test for structural changes within the gel. We show that high-power ultrasound above a critical amplitude leads to a complex viscoelastic transient response of the gels within a few seconds: a softening of its storage modulus accompanied by a strong overshoot in its loss modulus. Under high-power ultrasound, the gel displays a viscoelastic spectrum with glasslike features and a significant decrease in its yield strain. Those effects are attributed to the formation of intermittent microcracks in the bulk of the gel as evidenced by TRUSAXS. Provided that the shear rate is not large enough to fully fluidize the sample, high-power ultrasound also facilitates the flow of the gel, reducing its yield stress as well as increasing the shear-thinning index, thanks again to the formation of microcracks.

The breakdown and buildup mechanisms in concentrated cellulose nanocrystal (CNC) suspensions under shear and during relaxation upon cessation of shear were accessed by small-angle X-ray and light scattering combined with rheometry. The dynamic structural changes over nanometer to micrometer lengthscales were related to the well-known three-regime rheological behavior. In the shear-thinning regime I, the large liquid crystalline domains were progressively fragmented into micrometer-sized tactoids, with their cholesteric axis aligned perpendicular to the flow direction. The viscosity plateau of regime II was associated to a further disruption into submicrometer-sized elongated tactoids oriented along the velocity direction. At high shear rate, regime III corresponded to the parallel flow of individual CNCs along the velocity direction. Upon cessation of flow, the relaxation process occurred through a three-step buildup mechanisms: i) a fast reassembling of the individual CNCs into a nematic-like organization established up to micrometer lengthscales, ii) a slower formation of oriented large cholesteric domains, and iii) their isotropic redistribution.

International audience; The two ends of rodlike cellulose II nanocrystals (CNC-II) were regioselectively functionalized either with gold nanoparticles or thermosensitive polymer chains. In the first case, after the introduction of sulfur atoms at both ends of the rods, a labelling of CNC-II was carried out using a method based on the in situ nucleation and growth of gold nanoparticles (AuNP) from soluble derivatives. Transmission electron microscopy (TEM) images showed that such a method resulted in the grafting of one monodisperse AuNP at each extremity of the CNC-II, i.e. to the formation of hybrid dumbbell-shaped objects. No AuNP was detected on the lateral surfaces of the CNC-II and almost all observed CNC-II exhibited this dual labelling. This result confirmed with a good statistics when compared to previous works the possibility to derivatize only the two ends of the CNC-II, thanks to the antiparallel arrangement of cellulose chains in these nanoparticles. In the second case, the localized grafting of temperature-sensitive macromolecules onto the ends of the CNC-II was performed using an oxidation reaction followed by a peptide coupling. This end-specific grafting of thermosensitive chains onto CNC-II enhanced their colloidal stability when the temperature was below the lower critical solution temperature (LCST) of the polymer. Above the LCST, the TEM images revealed the formation of a network extending to tens of microns resulting from end-to-end associations of the derivatized rods through attractive interactions between collapsed polymer chains. Rheology experiments further evidenced a temperature-induced sol-gel transition from a liquid-like (sol) behavior below the LCST to solid-like (gel) behavior above the LCST, in agreement with a change from purely repulsive interactions to interconnections via the hydrophobic collapsed chains. Importantly, all results concur with a full reversibility of the phenomena upon cooling and reproducibility when samples were subjected to temperature cycles around the LCST. This work reveals that the dual sitespecific derivatization of CNC-II can provide symmetric hybrid particles with innovative assembling and macroscopic properties that cannot be obtained through homogenous chemical modifications.

International audience; Skim milk filtration is performed either at low or high temperature. However, there is still a lack of knowledge concerning the influence of temperature on membrane fouling. We used in situ small-angle X-ray scattering (SAXS) to study external membrane fouling during crossflow ultrafiltration of milk protein (casein micelle) dispersions at 12 • C and 42 • C. Casein micelle concentration distribution was measured in the concentration polarization layer and the deposit in a three-step filtration experiment that consisted of (i) fouling development step (with applied pressure and average cross-flow velocity fixed at 110 kPa and 3.1 cm s − 1 , respectively), (ii) pressure relaxation step (with pressure reduced to 10 kPa), and (iii) deposit erosion step (with crossflow velocity increased to 15.6 cm s − 1). Despite a higher average filtrate flux obtained at 42 • C, filtration at 42 • C resulted in the formation of a thicker and more concentrated deposit than filtration at 12 • C. At both temperatures studied, subsequent pressure relaxation resulted in deposit swelling, which was more intense in the less-compressed external part of the deposit. Deposit swelling rate was significantly higher at 42 • C than at 12 • C. The swelled deposit obtained at 42 • C was more eroded by the crossflow compared to the poorly swelled deposit obtained at 12 •. This suggests that deposit formation and compression were more reversible at 42 • C than at 12 • C.

International audience; The combined effect of shear flow and ultrasound (US) waves on the dynamical structural orientations of cellulosic cholesteric liquid crystals was investigated by time-resolved, in situ small-angle X-ray scattering (SAXS). A dedicated channel-type shear flow/ultrasound cell for SAXS characterization was developed to simultaneously generate a shear flow-induced horizontal stress force and a US-induced vertical acoustic radiation force. The control of the alignment of anisometric cellulose nanocrystals (CNCs), with their director parallel to the ultrasonic wave direction of propagation, was revealed at an unprecedented nanometer scale. Concurrently, the application of shear flow induced a horizontal orientation of CNCs with their directors aligned along the velocity direction. By adjusting the level of simultaneously applied shear flow and US intensity to the CNC suspensions, it was possible to tune the direction and the level of orientation of the CNCs during a period of time. For a specific ratio of the applied shear rate to acoustic power, some transient orientation of the CNCs at an intermediate angle between horizontal and vertical directions was evidenced. Relaxation of these orientations’ phenomena upon cessation of flow and/or US was also highlighted.

This study evidences the adsorption of model nonionic polymers onto aluminogermanate imogolite nanotubes, attractive porous nanofillers with potential molecular loading and release applications. We resolve the underlying mechanisms between nanotubes and polyethylene glycols with different molecular weights by means of nanoisothermal titration calorimetry. The analysis of the results provides a direct thermodynamic characterization, allowing us to propose a detailed description of the energetics involved in the formation of polymer/imogolite complexes. The affinity toward the nanotube surface is enthalpy-driven and strongly depends on the polymer chain length, which significantly affects the polymer configuration and the flow properties of the resulting complexes, probed by small-angle neutron scattering and rheology, respectively. These findings open new avenues for the rational design of these hybrid mixtures for advanced applications.

DNA dynamics and flow properties are of great importance for understanding its functions. DNA is a semiflexible polymer chain characterized by having a large persistence length of around 50 nm and high charge density; DNA chains are interacting efficiently at high concentrations, in dependence of the ionic concentration. In relation with DNA molecular characteristics, it is also known that DNA solutions are able to form liquid crystalline phases over a critical polymer concentration. In this work, the supramolecular organization in calf-thymus DNA solution, with low degree of entanglement, appearing under flow was studied in a wide DNA concentration range from 2 to 10 mg/mL, at a pH of 7.3 and 20 °C. The rheological behavior of the system was studied using steady state flow and oscillatory measurements. Transient regimes were also tested by imposing controlled shear rates on a short time up to steady state. Furthermore, a combination of visual observations and flow birefringence measurements was proposed ...

Concentration profiles and structural organization of different colloidal suspensions in the vicinity of membrane during ultrasonic-assisted ultrafiltration were previously evidenced from non-destructive, real-time, in-situ SAXS measurements (Jin et al., 2014 [11], Jin et al., 2014 [12]). On the basis of these obtained results, this paper explored by numerical calculation, four key factors of the buildup of concentrated polarization layer in such process (matter accumulation, flow property, permeability and osmotic pressure). Two different kind of systems have been studied: anisotropic Laponite clay particles and soft casein micelle particles. For all the systems and filtration conditions investigated, the results have shown that the level of matter accumulated is directly linked to calculated permeation flux and in accordance with the experimental one. The rheological parameters introduced in the calculations have allowed to deduce the charts of yield stress in the concentrated layers and revealed the important role of suspensions flow properties in the mechanisms of filtration involved near the membrane surface. The measured properties of the accumulated layers have been computed with a recent model based upon permeability and osmotic pressure (Bouchoux et al., 2013 [17]). It has been shown good agreement between modeled and experimental values in permeation flux for all the different systems and filtration explored.

The influence of filtration membrane resistance on colloidal filter cake swelling after the filtration pressure release is discussed in frame of filtration-consolidation theory. It is argued that in the case of reversibly compressible filter cake, the solid pressure relaxation can result in filtrate inflow across the membrane with the following absorption by the filter cake part adjacent to the membrane surface. According to the model results, the filtrate inflow and the filter cake swelling rates increase with decreasing of the membrane hydraulic resistance. At low membrane resistance, the swelling can result in the non-monotonous bell-like solid concentration distribution in the filter cake (solid concentration on the cake-membrane surface is lower than the maximal solid concentration). In contrast, the filter cake swelling in the absence of filter inflow across the membrane (or the deposit swelling on the impermeable surface) results in the monotonous decrease of the solid concentration. The non-monotonous solid concentration distribution can facilitate the membrane rinsing and cleaning and lead to the filter cake removal before its complete swelling.

The effect of sonication on a highly concentrated commercial suspension of cellulose nanocrystals (CNCs) and the resulting rheological properties have been investigated. Rheology and structural analysis techniques (atomic force microscopy, small-angle X-ray scattering, transmission electron microscopy and dynamic light scattering) were used to characterize the CNC suspension before and after sonication as a function of concentration. The highly concentrated CNC suspension, which does not contain aggregates, as shown by AFM and TEM imaging, turns from a “gel” form into a “liquid” form after a sonication treatment. The self-organization properties of as-prepared and sonicated suspensions were compared by the determination of their phase diagrams and flow rheology was performed to understand the viscosity behavior as a function of concentration for both systems. Sonication induced a decrease of the inter-particular distance, a strong decrease of the viscosity and remarkable changes in the liquid crystalline behavior, while sonicated and non-sonicated suspensions were stable over time. These effects can be attributed to a decrease in the aspect ratio of the suspended particles, which varies from a high value before sonication due to the presence of elongated bundles to a lower value after sonication that promotes individualization.

Spray drying represents a viable alternative for the stabilization of juice and extract of a great diversity of plant in tropical zones, such as jackfruit from Nayarit, Mexico. The jackfruit powder allows physicochemical and microbiological stability for storage, transportation, and marketing. In addition, this allows expansion of consumption and use of these exotic tropical fruits. The aim of this work was to find the best enzymatic hydrolysis and spray drying treatment for obtaining jackfruit pulp and juice in powder without affecting its rheological and physicochemical properties. Jackfruit pulp was treated with three commercial enzymes and their mixtures, and the best treatment was then optimized by Response Surface Methodology. The jackfruit pulp and the hydrolyzed juice were spray dried using maltodextrin as a carrier agent. The best hydrolysis was obtained with Celluzyme(®) and Pectinex Ultra Pulp(®) and the optimal conditions were 1% of enzyme concentration, during 3 h at 37 °C (p = 0.92), that leads reducing sugar of 78.50 ± 1.93 mg mL(−1) and viscosity of 7.94 ± 0.82 cps (94.7% reduction). The enzyme concentration is a direct function of reducing sugars content, while incubation time is an inverse function of viscosity. The spray drying treatment with the highest yield (74%) without affecting rheological and physicochemical properties compared to the fresh hydrolyzed juice was the treatment with 50% (TSS/weight) maltodextrin.

International audience; This study focuses on investigating the phenomena involved in the formation of the concentration polarization and fouling layer during the cross-flow ultrafiltration process of cellulose nanocrystal (CNC) suspensions. Thanks to new cross-flow ultrafiltration cells specially designed, experiments of first time-resolved in situ Small Angle X-ray Scattering (SAXS) and second time-resolved in situ micro Particle Image Velocimetry (micro-PIV) at the vicinity of the membrane surface during filtration were performed. These two methods have given access to the concentration profiles and the velocity field as a function of the distance z from the membrane surface within the concentration polarization layers. The results obtained show an increase in particles concentration related to a decrease in the velocity within the layers formed during the process. This information linked to the rheological behavior of the suspensions permitted access to the calculated stress field within the concentrated layers during the cross-flow ultrafiltration process. Three different areas of shear stress/shear rate behaviors near the membrane surface have been emphasized. The important role of the rheological behavior and interparticle interaction in the dynamic evolution in space and time of the accumulated layers has been highlighted.

International audience; This study focuses on bringing a better understanding of the mechanisms involved in the formation of the concentration polarization and fouling phenomena during the cross-flow ultrafiltration process of colloidal Laponite clay suspensions. New cross-flow ultrafiltration cells were designed to perform firstly time resolved in-situ small angle X-ray scattering (SAXS) and secondly time resolved in-situ micro particle image velocimetry (micro-PIV) at the vicinity of the membrane surface during the filtration. These two methods have allowed to access to the concentration profiles and the velocity field as a function of the distance z from the membrane surface with respectively 20 μm and 30 μm accuracy, within the concentration polarization layers. The results obtained show an increase of the volume fraction related to a decrease of the velocity within the layers formed during the process. The correlation of these results with the rheological behavior of the suspensions permitted to access to the calculated stress field within the concentrated layers during the cross-flow ultrafiltration process. Three different regions near the membrane surface have been emphasized with different shear stress/shear rate behaviors. The important role of the rheological behavior and inter particle interaction in the dynamic evolution in space and time of the accumulated layers has been highlighted.

International audience; The formation of a deposit layer on membrane surfaces is an important problem, particularly in milk filtration. Properties of the deposit and efficiency of deposit removal can be studied using various indirect methods based mainly on average membrane resistance in deposit formation-deposit removal cycles, but their conclusions on deposit reversibility depend on conditions surrounding deposit analysis. Here we present a method for direct characterization of the reversibility of deposit compression via analysis of local solid concentration distribution during deposit formation at constant pressure and cross-flow velocity and deposit removal after pressure relaxation. Two models are proposed for deposit characterization: a model of crossflow filtration with deposit formation to characterize deposit compressibility-permeability from the data on concentration distribution at steady-state of deposit formation, and a model for evaluating deposit swelling kinetics from the data on steady-state compressibility-permeability. The method was applied here for analysis of the deposit formed on the surface of a polymeric ultrafiltration membrane during crossflow filtration of casein micelle suspensions at 25 • C. Local solid concentration distribution in the deposit and concentration polarization layer was probed in situ using small-angle X-ray scattering (SAXS). Experiments were performed in a special-purpose SAXS-filtration cell. It was demonstrated that casein micelle deposits obtained at 1.1 bar transmembrane pressure swell after pressure relaxation. However, swelling rate was significantly lower than that obtained by modeling using deposit compressibility-permeability obtained from the analysis of steady-state concentration distribution. We thus find evidence that casein micelle deposits produced during crossflow membrane filtration undergo compression that is partially irreversible.

Spray drying represents a viable alternative for the stabilization of juice and extract of a great diversity of plant in tropical zones, such as jackfruit from Nayarit, Mexico. The jackfruit powder allows physicochemical and microbiological stability for storage, transportation, and marketing. In addition, this allows expansion of consumption and use of these exotic tropical fruits. The aim of this work was to find the best enzymatic hydrolysis and spray drying treatment for obtaining jackfruit pulp and juice in powder without affecting its rheological and physicochemical properties. Jackfruit pulp was treated with three commercial enzymes and their mixtures, and the best treatment was then optimized by Response Surface Methodology. The jackfruit pulp and the hydrolyzed juice were spray dried using maltodextrin as a carrier agent. The best hydrolysis was obtained with Celluzyme® and Pectinex Ultra Pulp® and the optimal conditions were 1% of enzyme concentration, during 3 h at 37 °C (p = 0.92), that leads reducing sugar of 78.50 ± 1.93 mg mL−1 and viscosity of 7.94 ± 0.82 cps (94.7% reduction). The enzyme concentration is a direct function of reducing sugars content, while incubation time is an inverse function of viscosity. The spray drying treatment with the highest yield (74%) without affecting rheological and physicochemical properties compared to the fresh hydrolyzed juice was the treatment with 50% (TSS/weight) maltodextrin.

Previous investigations were conducted on two concentrations of DNA solution: 4 mg/mL, for which it has been shown that no supramolecular organization is induced under flow at low shear rates, and 10 mg/mL, in which a liquid crystalline-type texture is formed under flow at low shear rates, attesting to an orientation of pre-organized chains. Rheological experiments are discussed and their results supported by small-angle X-ray scattering (SAXS) and flow birefringence visualization experiments. Scattering from polyelectrolytes has a characteristic signal, which is here observed in SAXS, showing a strong correlation peak between charged chains in water, for both concentrations. This peak is weaker in the presence of 0.01 M NaCl and suppressed in salt excess at 0.1 M NaCl. No plateau in the &sigma, ( &gamma, ˙ ) plot was observed in analysis of rheological experiments on low DNA concentration (4 mg/mL). As typically observed in polyelectrolyte systems both the dynamic moduli and shear viscosity were higher in water as electrostatic forces dominate, than in the presence of salt, especially at low shear rates. The rheological results for concentrations of 0.01 M NaCl are lower than in water as expected due to partial screening of electrostatic repulsions. Rheological data for concentrations of 0.1 M NaCl are unexpected. Electrostatic forces are partially screened in the low salt concentration, leading to a drop in the rheological values. For high salt concentration there are no longer interchain repulsions and so steric interactions dominate within the entangled network leading to the subsequent increase in rheological parameters. Regardless of the solvent, at high shear rates the solutions are birefringent. In the 10 mg/mL case, under flow, textures are formed at relatively low shear rate before all the chains align going to a pseudonematic liquid crystalline phase at high shear rate. The electrostatic repulsion between semi-rigid chains induces a correlation between the chains leading to an electrostatic pseudo-gel in water and loosely in 0.01 M NaCl at low stress applied. To the best of our knowledge, this is the first time that such behavior is observed. In 0.1 M NaCl, DNA behavior resembles the corresponding neutral polymer as expected for polyelectrolyte in salt excess, exhibiting a yield stress. When texture appears in water and in 0.01 M NaCl, a critical transition is observed in rheological curves, where the viscosity decreases sharply at a given critical shear stress corresponding to a plateau in the &sigma, ˙ ) plot also observed in creep transient experiment.

International audience; In this paper, the disintegration of starch (waxy and standard starch) granules into nanosized particles under the sole effect of high power ultrasonication treatment in water/isopropanol is investigated, by using wide methods of analysis. The present work aims at a fully characterization of the starch nanoparticles produced by ultrasonication, in terms of size, morphology and structural properties, and the proposition of a possible mechanism explaining the top-down generation of starch nanoparticles (SNPs) via high intensity ultrasonication. Dynamic light scattering measurements have indicated a leveling of the particle size to about 40 nm after 75 min of ultrasonication. The WAXD, DSC and Raman have revealed the amorphous character of the SNPs. FE-SEM. AFM observations have confirmed the size measured by DLS and suggested that SNPs exhibited 2D morphology of platelet-like shapes. This morphology is further supported by SAXS. On the basis of data collected from the different characterization techniques, a possible mechanism explaining the disintegration process of starch granules into NPs is proposed.

The hydrophilic nature of nanofibrillated cellulose (NFC) impedes its easy incorporation in hydrophobic thermoplastic matrices. This introduces difficulties in composites compounding and achieving the sufficient NFC dispersion within the matrix. The use of matrix in latex form increases the range of applied plastics. However, poor NFC/matrix interfacial adhesion may still result in lower performance composites. The use of ionic interactions is aimed at providing strong interactions at the NFC/matrix interface after film casting and simultaneously the composite homogeneity. In this work, cationic and anionic latexes of poly[styrene- co -(2-ethylhexyl acrylate)] were synthesized via miniemulsion polymerization. The composites were produced by incorporating 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized NFC (up to 5 wt.%) into the latexes, followed by film casting of the ensuing formulations. NFC/latex interactions were examined in terms of the NFC dispersion in the matrix and the ensuing composite mechanical properties. Both elastic modulus and ultimate strength increased for the composites comparing to the neat matrices. The use of cationic latex produced non-stable aqueous dispersions and non-homogeneous composite films, deduced from scanning electron microscopy and tensile experiments. On the contrary, stable aqueous dispersions and homogeneous composites were prepared using anionic latex. X-ray photoelectron spectroscopy revealed differences in chemical composition of the composite top and bottom surfaces.

This study investigates for the first time the behaviors of starch and cellulose nanocrystals (SNC and CNC) suspensions which are simultaneously subjected to pressure, shear flow and ultrasound (US) during cross-flow ultrafiltration. This multi-forces process was characterized from macro-scales to nano-scales, with a custom designed “SAXS Cross-Flow US-coupled Filtration Cell”. In addition, rheological behaviors of SNC samples at different concentrations/temperatures have been investigated. In both cases (ultrafiltration of SNC and CNC suspensions), better performances were observed with US. The in-situ SAXS measurements revealed that for SNC suspensions, no structure change occurred at the length scales range from 10 to 60 nm in this multi-forces process, while CNC particles exhibited an ordered arrangement within the concentrated layer during the same process. SNC particles accumulated on the membrane surface forming a “fragile” concentrated layer which was removed very quickly by subsequent applied US. In contrary, the CNC particles accumulation was very severe, the additional ultrasonic force led to a disruption but not a totally removal of the CNC concentrated layer.

This review covers the preparation, characterization, properties, and applications of methylcelluloses (MC). In particular, the influence of different chemical modifications of cellulose (under both heterogeneous and homogeneous conditions) is discussed in relation to the physical properties (solubility, gelation) of the methylcelluloses. The molecular weight (MW) obtained from the viscosity is presented together with the nuclear magnetic resonance (NMR) analysis required for the determination of the degree of methylation. The influence of the molecular weight on the main physical properties of methylcellulose in aqueous solution is analyzed. The interfacial properties are examined together with thermogelation. The surface tension and adsorption at interfaces are described: surface tension in aqueous solution is independent of molecular weight but the adsorption at the solid interface depends on the MW, the higher the MW the thicker the polymeric layer adsorbed. The two-step mechanism of gelation is confirmed and it is shown that the elastic moduli of high temperature gels are not dependent on the molecular weight but only on polymer concentration. Finally, the main applications of MC are listed showing the broad range of applications of these water soluble cellulose derivatives.

International audience; The structural organization of the concentration polarization layer (CPL) during the cross-flow membrane separation process of anisometric aqueous suspensions of colloidal cellulose nanocrystals and beidellite clay particles has been characterized by in situ time-resolved small-angle X-ray scattering (SAXS). Dedicated cross-flow filtration cells were implemented on the ID02 TRUSAXS beamline at the European Synchrotron Radiation Facility (Grenoble, France). From the analysis of the scattered intensities and structure factors of particles in the CPL, both the concentration profiles ɸ(Δz,Δt) and anisotropic structural organization have been characterized as a function of filtration time (Δt) and distance from the membrane surface (Δz). Remarkably, a coupling between concentration and anisotropy was revealed and modeled using either a simple or stretched exponential trend for rod- or disk-like systems, respectively. Using a simple filtration model, the time evolution of the deposit thickness, membrane resistance and specific resistance of the deposit, deduced from an analysis of the normalized concentration profiles, allowed directly predicting the rapid decay of permeate flux associated to the exponential growth of concentration and anisotropic organization inside the CPL. Ex situ scanning electron microscopy (SEM) observations and wide-angle X-ray diffraction (WAXD) analyses performed on dried deposits parallel and perpendicular to the membrane surface revealed well-defined layered structures from nanometer to micrometer length scales.

This study investigates effects of ultrasound (US) on cross-flow ultrafiltration of skim milk by multi-scale characterization, using a custom designed “SAXS Cross-Flow US-coupled Filtration Cell”. The study of flow properties of casein micelle suspensions shows an evolution of their rheological behavior from Newtonian to shear-thinning until the emergence of yield stress with the increase of concentration (from 27 g L−1 to 216 g L−1). The concentration profiles during cross-flow filtration of skim milk have been revealed for the first time by real-time in-situ Small Angle X-ray Scattering (SAXS) measurement. Without any change of internal structure of casein micelles and membrane selectivity, the applied ultrasound (20 kHz, 2 W cm−2) leads to a significant increase of permeate flux arising from a disruption of concentrated layer. Varying the US intensity from 0.6 W cm−2 to 2.9 W cm−2 does not affect the US enhancement factor, which however depends on the feed concentration. In fact, increase of feed concentration induces the formation of highly cohesive fouling layer during filtration that the applied US could hardly disrupt. Results also suggest that the preventive US application mode is promising since formation of the reversible fouling layer was strongly limited in this mode.

Nanofibrillated cellulose (NFC) aqueous suspensions were produced from once-dried bisulfite softwood pulp using enzymatic or 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation pretreatments, followed by wet grinding, as an ultimate fibrillation technique. Two commercial enzyme solutions: cellulase, with the major activity of endoglucanase and exoglucanase, and monocomponent endoglucanase, were compared to facilitate the nanofibrils isolation from cellulose fibers. The influence of their concentrations, as well as the other processing conditions, was analyzed. The morphology of the produced NFC was characterized using optical microscopy, atomic force microscopy (AFM), field emission gun-scanning electron microscopy (FEG-SEM), and morphological fiber analyzer (MorFi). Nanofibrils with a wide size distribution were produced. The average lateral dimensions of 12 ± 7 nm for the most disintegrated enzymatically hydrolyzed NFC and 4 ± 2 nm for TEMPO-oxidized NFC were determined from the AFM height images. The degree of polymerization (DP) decreased and the crystallinity index (CI) increased with an increase of the concentration of both enzyme solutions. TEMPO-oxidation did not have a significant impact on the cellulose CI; however, the DP was strongly affected. The monocomponent endoglucanase solution was found to have a better effect on the nanofibrils isolation rather than their depolymerization.

International audience; A new coupling of ultrasound device with membrane process has been developed in order to enhance cross-flow ultrafiltration of colloidal suspensions usually involved in several industrial applications included bio and agro industries, water and sludge treatment. In order to reduce mass transfer resistances induced by fouling and concentration polarization, which both are main limitations in membrane separation process continuous ultrasound is applied with the help of a vibrating blade (20 kHz) located in the feed channel all over the membrane surface (8 mm between membrane surface and the blade). Hydrodynamic aspects were also taking into account by the control of the rectangular geometry of the feed channel.Three colloidal suspensions with different kinds of colloidal interaction (attractive, repulsive) were chosen to evaluate the effect of their physico-chemical properties on the filtration.For a 90W power (20.5 W cm(-2)) and a continuous flow rate, permeation fluxes are increased for each studied colloidal suspension, without damaging the membrane. The results show that the flux increase depends on the initial structural properties of filtered dispersion in terms of colloidal interaction and spatial organizations.For instance, a Montmorillonite Wyoming-Na clay suspension was filtered at 1.5 x 10(5) Pa transmembrane pressure. Its permeation flux is increased by a factor 7.1, from 13.6 L m(-2) h(-1) without ultrasound to 97 L m(-2) h(-1) with ultrasound. (C) 2013 Elsevier B.V. All rights reserved.

The colloidal stability together with the tunable aggregation and viscoelastic properties of thermoresponsive polymer-grafted cellulose nanocrystals (CNCs) were investigated. TEMPO oxidation of CNCs followed by peptidic coupling in water were used to covalently graft thermosensitive Jeffamine polyetheramine M2005 chains onto the surface of CNCs. The resulting polymer-decorated particles (M2005-g-CNCs) exhibited new colloidal properties, by their ability to perfectly redisperse in water and organic solvents such as toluene, dichloromethane or DMF after freeze-drying. In addition, they presented an enhanced thermal stability when compared to that of sulfated or TEMPO-oxidized CNCs. Dynamic light scattering experiments were used to demonstrate that the thermally induced aggregation of M2005-g-CNCs was fully reversible and reproducible over many temperature cycles and that, most interestingly, the aggregation number could be tuned by varying the ionic strength and/or the pH of the medium, making the suspension multiresponsive. This property arises from the variations of the sign (attractive or repulsive) and the range of the different types (entropic, electrostatic, hydrophobic) of interaction forces between the thermosensitive polymer-decorated nanoparticles. The variation of the viscoelastic properties of M2005-g-CNCs suspensions as a function of temperature, probed by oscillatory rheology measurements of more concentrated suspensions, revealed a reversible temperature-triggered liquid-to-gel transition. Such enhanced functionalities pave the way to the design of advanced CNC-based materials benefiting both from the intrinsic characteristics of these biosourced particles and the new properties imparted by the stimuli-sensitive grafted chains.

Cellulose nanocrystals (CNC) have gained a lot of interest in recent years in the field of composites due to their unique mechanical properties and also because cellulose is the most abundant and renewable polymer in nature. In this work, Pluronic grade triblock copolymer was adsorbed on the surface of CNC in order to improve the thermal stability and also its dispersion from the dried state. The adsorbed cellulose nanocrystals (A-CNC) were characterized to check their thermal, functional and structural properties by thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and atomic force microscopy (AFM). Interestingly, improved thermal stability was observed and also the dispersion of A-CNC in aqueous medium was much better than for unmodified CNC. The aqueous A-CNC suspensions were characterized by small angle X-ray scattering (SAXS) to evaluate the dispersion of the nanoparticles. The flow properties of A-CNC dispersions were also analyzed. Further, A-CNC was used to prepare nanocomposites by melt extrusion using linear low density polyethylene (LLDPE) as matrix. The thermo mechanical and morphological properties of the ensuing nanocomposites were characterized by dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The dispersion state of A-CNC within the polymeric matrix was also characterized by SAXS.

Cellulose nanofibrils (CNFs) are produced and commonly used in the form of aqueous suspensions or gels. A number of studies have focused lately on rheological properties of CNF suspensions, which gives insight into properties of such materials and can reflect their behavior during handling. This Review summarizes the recent progress in rheological studies on CNF aqueous suspensions using rotational rheometry. Here, we discuss linear viscoelastic properties, i.e., frequency-dependent storage and loss moduli; shear flow behavior, i.e., apparent viscosity and shear stress as a function of shear rate; local flow characteristics, etc. In this Review, we point out that the rheological behavior of at least two types of CNF suspensions should be distinguished: (i) ones produced using mechanical fibrillation with or without enzymatic pretreatment (no surface chemical modification), which possess highly flocculated structure, and (ii) ones produced involving chemical modification pretreatments, e.g., carboxylation, carboxymethylation, quaternization, or sulfonation, which possess better colloidal stability and do not evidently flocculate.

We study the transient response to simple shear of aqueous dispersions of Laponite clay particles and poly(ethylene oxide) at concentrations for which shear induces structure in the form of a network of polymer–clay bonds. We examine the effects of shear on the structure at the micrometer length scale. Bulk rheometric measurements give the material’s response to step changes in shear rate. We find that a critical value of the shear rate separates two regions with different rheological behaviors. Static small-angle light scattering shows a corresponding qualitative change in the anisotropy of the dispersion under shear at the micron scale. We interpret our results in terms of the effects of shear on the interactions between clay particles and polymer chains and on the aggregation mechanisms in the dispersion.

The rheological behavior of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized nanofibrillated cellulose (NFC) suspensions at different concentrations were examined using Couette with smooth and serrated surfaces and vane-in-cup geometries. A slippage against the walls of rheometer rotor or/and stator (wall-slip) as well as flow localization within a specific volume of the sample (shear banding) took place. These phenomena were visualized using a technique based on introduction of titanium dioxide pigment into the specific volume of NFC suspension and monitoring its deformation. The flow instabilities appeared more pronounced with an increase of the NFC concentration. It was shown that the use of serrated geometry is necessary to compete with the wall-slip but is not sufficient to prevent it completely. Serrated Couette was found to be the most appropriate geometry (among the tested) to measure the rheological properties of NFC suspensions. Small-angle X-ray scattering was used to provide a supplementary information about the structural organization of NFC suspensions. The statistical average diameter of 4.8 nm was determined from the scattering data for the NFC swollen in water.

Aqueous dispersions of nanometric clay platelets (Laponite) have been dewatered through different techniques: centrifugation, mechanical compression, and osmotic stress (dialysis against a polymer solution). The positional and orientational correlations of the particles have been determined through small-angle neutron scattering. Uniaxial compression experiments produce concentrated dispersions (volume fraction > 0.03) in which the platelets have strong orientational and positional correlations. The orientational correlations cause the platelets to align with their normal along a common axis, which is the axis of compression. The positional correlations cause the platelets to be regularly spaced along this direction, with a spacing that matches the average volume per particle in the dispersion. The swelling law (volume fraction versus separation distance) is one-dimensional, as in a layered system. Changes in the applied osmotic pressure cause the water content of the dispersion to either rise or decrease, with time scales that are controlled by interparticle friction forces and by hydrodynamic drag. At long times, the dispersions approach osmotic equilibrium, which can be defined as the common limit of swelling and deswelling processes. The variation of the equilibrium water content with the applied osmotic pressure has been determined over 1 decade in volume fractions (0.03 < < 0.3) and 3 decades in pressures. This equation of state matches the predictions made from the knowledge of the forces and thermal agitation for all components in the dispersion (particles, ions, and water).

In this study, thermogelation of methylcelluloses is investigated in relation to the molar mass and concentration in aqueous medium. A large hysteresis between heating and cooling ramps was observed whatever the conditions. The heating process in particular was studied to analyze the two steps of gelation using rheometry. At low temperature, in the sol state, viscosity depends on the concentration and molar mass. Over 30°C a gel-like behavior was observed including two steps (the second step is a strong gel with phase separation) having storage moduli that are nearly independent of polymer molar mass but are directly related to polymer concentration.

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This paper aims to illustrate the interest of ultrasound technology as an efficient technique for both heat and mass transfer intensification. It is demonstrated that the use of ultrasound results in an increase of heat exchanger performances and in a possible fouling monitoring in heat exchangers. Mass transfer intensification was observed in the case of cross-flow ultrafiltration. It is shown that the enhancement of the membrane separation process strongly depends on the physico-chemical properties of the filtered suspensions.

The rheological properties of enzymatically hydrolyzed and TEMPO-oxidized microfibrillated/nanofibrillated cellulose (MFC/NFC) aqueous suspensions were investigated in oscillation and steady-flow modes and were compared with the morphology of the studied materials. The flow instabilities, which introduce an error in the rheological measurements, were discovered during flow measurements. A wall-slip (interfacial slippage on the edge of geometry tools and suspension) was detected at low shear rates for two types of NFC suspensions while applying cone-plate geometry. A roughening of the tool surfaces was performed to overcome the aforementioned problem. Applying to TEMPO-oxidized NFC, a stronger suspension response was detected at low shear rates with higher values of measured shear stress. However, a shear banding (localization of shear within a sample volume) became more pronounced. The use of serrated tools for enzymatically hydrolyzed NFC produced lower shear stress at the moderate shear rates, which was influenced by water release from the suspension.

Effects of ultrasound (US) on the structural organization within concentrated particle layers during cross-flow ultrafiltration of Laponite dispersions have been characterized for the first time by in-situ time-resolved small-angle X-ray scattering (SAXS). A novel ‘SAXS Cross-Flow US-coupled Filtration Cell’ has been developed to, on one hand, apply ultrasonic waves close to the flat membrane by embedding in the feed compartment a thin titanium vibrating blade connected to a 20 kHz ultrasonic generator and on the other hand, to monitor in-situ the colloidal organization of the concentrated layer by SAXS. Thanks to this cell, concentration profiles have been measured as a function of the distance z from the membrane surface with a 20 µm accuracy and simultaneously linked to the permeate flux, cross-flux and transmembrane pressure. In-situ ultrasonication leads to a significant increase of permeate flux arising from the break-up of the concentrated layer. Results also suggest that ultrasonication could be considered as an additional force of an effective range on the order of micrometers or smaller. It is capable to completely remove the particles from the membrane surface when the feed dispersions are dense and aggregated, and is more efficient than classical procedures based on an increase of the cross-flow flux.

The sound attenuation in the THz region is studied down to T 16 K in glassy glycerol by inelastic x-ray scattering. At striking variance with the decrease found below 100 K in the GHz data, the attenuation in the THz range does not show any T dependence. This result (i) indicates the presence of two different attenuation mechanisms, active, respectively, in the high- and low-frequency limits, (ii) demonstrates the nondynamic origin of the attenuation of THz sound waves, and confirms a similar conclusion obtained in SiO2 glass by molecular dynamics, and (iii) supports the low-frequency attenuation mechanism proposed by Fabian and Allen [ Phys. Rev. Lett. 82, 1478 (1999)].

The gelation of methylcellulose in water has been studied by X-ray photon correlation spectroscopy, electrophoresis and rheological measurements by looking into the dynamics of silica nanoparticles as tracers in the polymer matrix. The temperature and scattering vector dependence of the structural relaxation time is investigated at the nanometric length scale during the formation of the strong gel state. We find a stress-dominated dynamics on approaching the gel state, characterized by a hyper-diffusive motion of the silica particles. These results support the idea of a unifying scenario for the dynamics of complex out of equilibrium soft materials.

The characteristic length scales of the structure and fractal behavior of a thixotropic colloidal suspension of synthetic clay were studied by using a combination of small-angle neutron and x-ray scattering and static light scattering. At the same time, macroscopic mechanical behavior at rest was characterized by means of rheometric measurements. Two characteristic length scales were detected in these yield stress suspensions of discotic texture. The first, measuring several tens of nanometres, is linked to a fractal dimension of 3. The second, of the order of 1 mm, is linked to a fractal behavior of dimension D that increases with the particle volume fraction. Consequently, it is suggested that the structure of the dispersions at rest is composed of subunits measuring a few tens of nanometers that combine to form dense aggregates measuring about 1 mm. At larger length scales, these micrometer-sized aggregates are rearranged to form a continuous three-dimensional isotropic structure that has a fractal behavior of dimension D, which gives the gels their texture. The increase of this fractal dimension with the particle volume fraction, the ionic strength, and the gelation time is correlated to a hardening of the mechanical properties of the gels at rest. The gel state is reached above a volume fraction f v for a given ionic strength and gelation time. In the gel phase, a critical volume fraction f vc separates two domains. Gels belonging to the domain f v,f v,f vc have a fractal behavior of dimension D5160.05, suggesting an alignment of the micrometer-sized aggregates that leads to the formation of a mechanically weak fibrous structure. Gels belonging f v.f vc have a fractal dimension D51.860.01, corresponding to a mechanically stronger structure consisting of zones of high and lower particle density. A scaling law enabled these fractal dimensions to be correlated with the effect of the volume fraction on the yield stress. In contrast to what is commonly assumed in relation to clay suspensions, it is suggested here that it is the large length scales, of the order of 1 mm, associated with a fractal arrangement that governs the macroscopic mechanical behavior.

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Molecular weight, stiffness, temperature, and polymer and ionic concentrations are known to widely influence the viscosity of polymer solutions. Additionally, polymer molecular weight—which is related to its dimensions in solution—is one of its most important characteristics. In this communication, low molecular weight DNA from salmon sperm was purified and then studied in solutions in a wide concentration range (between 0.5 and 1600 mg/mL). The intrinsic viscosity of this low molecular weight DNA sample was firstly determined and the evidence of the overlap concentration was detected around the concentration of 125 mg/mL. The chain characteristics of these short molecules were studied in terms of the influence of their molecular weight on the solution viscosities and on the overlap parameter CDNA[η]. Furthermore, to complete previously reported experimental data, solutions of a large molecular weight DNA from calf-thymus were studied in a high concentration range (up to 40 mg/mL). The rheological behavior is discussed in terms of the generalized master curve obtained from the variation of the specific viscosity at zero shear rate (ηsp,0) as a function of CDNA[η].

International audience; A facile method of using optical trapping to measure cell adhesion forces is presented and applied to the adhesion of Saccharomyces cerevisiae on glass, in contact with solutions of different compositions. Trapping yeast cells with optical tweezers (OT) is not perturbed by cell wall deformation or cell deviation from a spherical shape. The trapping force calibration requires correction not only for the hydrodynamic effect of the neighboring wall but also for spherical aberrations affecting the focal volume and the trap stiffness. Yeast cells trapped for up to 5 h were still able to undergo budding but showed an increase of doubling time. The proportion of adhering cells showed the expected variation according to the solution composition. The detachment force varied in the same way. This observation and the fact that the detachment stress was exerted parallel to the substrate surface point to the role of interactions involving solvated macromolecules. Both the proportion of adhering cells and the removal force showed a distribution which, in our experimental conditions, must be attributed to a heterogeneity of surface properties at the cell level or at the subcellular scale. As compared with magnetic tweezers, atomic force microscopy, and more conventional ways of studying cell adhesion (shear-flow cells), OT present several advantages that are emphasized in this paper.

The linear and nonlinear rheological behaviors of semidilute aqueous solutions of the amphiphile triblock polymer Pluronics P103 in water are reported here. For C surf ⩽ 20 wt%, micelles are spherical at temperatures lower than ca. 27 °C and grow with increasing temperature to form long polymer-like micelles. These polymer-like micelles exhibit strong viscoelasticity and a shear-banding region that shrinks as the cloud point is approached. Master time–temperature–concentration curves were obtained for the dynamic moduli using traditional shifting factors. In the nonlinear regime, P103 polymer-like micellar solutions follow the master dynamic phase diagram proposed by Berret and colleagues, in which the flow curves overlap in the low-shear-rate homogeneous flow region. Within the nonhomogeneous flow region (confirmed by flow birefringence and small-angle light-scattering measurements), oscillations and overshoots are detected at the inception of shear flow, and two main relaxation mechanisms are apparent after cessation of steady shear flow. Evidence for nonequilibrium critical behavior is presented, in which the order parameter is the difference of critical shear rates that limit the span of the plateau stress. Most of the steady-state and transient features of the nonlinear rheology of the P103 polymer-like micelles are reproduced with the Bautista–Manero–Puig (BMP) model, including the predictions of nonequilibrium critical behavior under flow.

Understanding the mechanisms involved in structural development in the vicinity of membrane constitutes a considerable challenge in the improvement of ultrafiltration process in industrial applications. In situ small-angle X-ray scattering (SAXS) performed with custom-made ultrafiltration cell has permitted the structural arrangement to be probed and concentration profiles to be obtained in deposited layers during frontal filtration of casein micelle suspension. SAXS allowed the structure of the accumulated layers of casein micelles between 280 microm and 1 mm from the membrane surface to be followed at length scales from a few nanometers to about 100 nm. These results have been combined with hydrodynamic measurements (permeation flux) and rheological investigations. Under frontal filtration, the time dependence of concentration at different distances from the membrane surface has been obtained. This temporal evolution is marked by an exponential increase of the concentration followed by a slower growth which has been associated with a change in the rheological behavior of the suspension from Newtonian to shear thinning behavior.

International audience; Understanding the mechanisms involved in structural development in the vicinity of membrane constitutes a considerable challenge in the improvement of ultrafiltration process in industrial applications. In situ small-angle X-ray scattering (SAXS) performed with custom-made ultrafiltration cell has permitted the structural arrangement to be probed and concentration profiles to be obtained in deposited layers during frontal filtration of casein micelle suspension. SAXS allowed the structure of the accumulated layers of casein micelles between 280 ím and 1 mm from the membrane surface to be followed at length scales from a few nanometers to about 100 nm. These results have been combined with hydrodynamic measurements (permeation flux) and rheological investigations. Under frontal filtration, the time dependence of concentration at different distances from the membrane surface has been obtained. This temporal evolution is marked by an exponential increase of the concentration followed by a slower growth which has been associated with a change in the rheological behavior of the suspension from Newtonian to shear thinning behavior.