Publications by authors named "Philippe Poulin"

57 Publications

Liquid Crystal-Mediated 3D Printing Process to Fabricate Nano-Ordered Layered Structures.

ACS Appl Mater Interfaces 2021 Jun 10;13(24):28627-28638. Epub 2021 Jun 10.

School of Chemical Engineering, University of New South Wales (UNSW), Sydney 2052, New South Wales, Australia.

The emergence of three-dimensional (3D) printing promises a disruption in the design and on-demand fabrication of smart structures in applications ranging from functional devices to human organs. However, the scale at which 3D printing excels is within macro- and microlevels and principally lacks the spatial ordering of building blocks at nanolevels, which is vital for most multifunctional devices. Herein, we employ liquid crystal (LC) inks to bridge the gap between the nano- and microscales in a single-step 3D printing. The LC ink is prepared from mixtures of LCs of nanocellulose whiskers and large sheets of graphene oxide, which offers a highly ordered laminar organization not inherently present in the source materials. LC-mediated 3D printing imparts the fine-tuning required for the design freedom of architecturally layered systems at the nanoscale with intricate patterns within the 3D-printed constructs. This approach empowered the development of a high-performance humidity sensor composed of self-assembled lamellar organization of NC whiskers. We observed that the NC whiskers that are flat and parallel to each other in the laminar organization allow facile mass transport through the structure, demonstrating a significant improvement in the sensor performance. This work exemplifies how LC ink, implemented in a 3D printing process, can unlock the potential of individual constituents to allow macroscopic printing architectures with nanoscopic arrangements.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsami.1c05025DOI Listing
June 2021

Highly conductive colloidal carbon based suspension for flow-assisted electrochemical systems.

iScience 2021 May 20;24(5):102456. Epub 2021 Apr 20.

Centre de Recherche Paul Pascal, CNRS, Université de Bordeaux, 115 Avenue Schweitzer, 33600, Pessac, France.

Carbon suspension electrodes are promising for flow-assisted electrochemical energy storage systems. They serve as flowable electrodes in electrolyte solutions of flow batteries, or flow capacitors. They can also be used for other applications such as capacitive deionization of water. However, developments of such suspensions remain challenging. The suspensions should combine low viscosity and high electronic conductivity for optimized performances. In this work, we report a flowable aqueous carbon dispersion which exhibits a viscosity of only 2 Pa.s at a shear rate of 5 s for a concentration of particles of 7 wt%. This suspension displays an electronic conductivity of 65 mS/cm, nearly two orders of magnitude greater than previously investigated related materials. The investigated suspensions are stabilized by sodium alginate and arabic gum in the presence of ammonium sulfate. Their use in flowable systems for the storage and discharge of electrical charges is demonstrated.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.isci.2021.102456DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8113993PMC
May 2021

Integration of a soft dielectric composite into a cantilever beam for mechanical energy harvesting, comparison between capacitive and triboelectric transducers.

Sci Rep 2020 Nov 26;10(1):20681. Epub 2020 Nov 26.

MIE Team, Chimie Biologie Et Innovation, ESPCI Paris, PSL University, CNRS, 75005, Paris, France.

Flexible dielectrics that harvest mechanical energy via electrostatic effects are excellent candidates as power sources for wearable electronics or autonomous sensors. The integration of a soft dielectric composite (polydimethylsiloxane PDMS-carbon black CB) into two mechanical energy harvesters is here presented. Both are based on a similar cantilever beam but work on different harvesting principles: variable capacitor and triboelectricity. We show that without an external bias the triboelectric beam harvests a net density power of 0.3 [Formula: see text] under a sinusoidal acceleration of 3.9g at 40 Hz. In a variable capacitor configuration, a bias of 0.15 [Formula: see text] is required to get the same energy harvesting performance under the same working conditions. As variable capacitors' harvesting performance are quadratically dependent on the applied bias, increasing the bias allows the system to harvest energy much more efficiently than the triboelectric one. The present results make CB/PDMS composites promising for autonomous portable multifunctional systems and intelligent sensors.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41598-020-77581-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7692552PMC
November 2020

Common misconceptions, hidden biases and modern challenges of dMRI tractography.

J Neural Eng 2020 02 18;17(1):011001. Epub 2020 Feb 18.

Sherbrooke Connectivity Imaging Laboratory (SCIL), Université de Sherbrooke, Sherbrooke, Canada. 2500, boul. de l'Université, Sherbrooke (Québec), J1K 2R1, Sherbrooke, Canada. Author to whom any correspondence should be addressed.

The human brain is a complex and organized network, where the connection between regions is not achieved with single axons crisscrossing each other but rather millions of densely packed and well-ordered axons. Reconstruction from diffusion MRI tractography is only an attempt to capture the full complexity of this network, at the macroscale. This review provides an overview of the misconceptions, biases and pitfalls present in structural white matter bundle and connectome reconstruction using tractography. The goal is not to discourage readers, but rather to inform them of the limitations present in the methods used by researchers in the field in order to focus on what they can do and promote proper interpretations of their results. It also provides a list of open problems that could be solved in future research projects for the next generation of PhD students.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1088/1741-2552/ab6aadDOI Listing
February 2020

Tractostorm: The what, why, and how of tractography dissection reproducibility.

Hum Brain Mapp 2020 05 10;41(7):1859-1874. Epub 2020 Jan 10.

Sherbrooke Connectivity Imaging Laboratory (SCIL), Université de Sherbrooke, Sherbrooke, Canada.

Investigative studies of white matter (WM) brain structures using diffusion MRI (dMRI) tractography frequently require manual WM bundle segmentation, often called "virtual dissection." Human errors and personal decisions make these manual segmentations hard to reproduce, which have not yet been quantified by the dMRI community. It is our opinion that if the field of dMRI tractography wants to be taken seriously as a widespread clinical tool, it is imperative to harmonize WM bundle segmentations and develop protocols aimed to be used in clinical settings. The EADC-ADNI Harmonized Hippocampal Protocol achieved such standardization through a series of steps that must be reproduced for every WM bundle. This article is an observation of the problematic. A specific bundle segmentation protocol was used in order to provide a real-life example, but the contribution of this article is to discuss the need for reproducibility and standardized protocol, as for any measurement tool. This study required the participation of 11 experts and 13 nonexperts in neuroanatomy and "virtual dissection" across various laboratories and hospitals. Intra-rater agreement (Dice score) was approximately 0.77, while inter-rater was approximately 0.65. The protocol provided to participants was not necessarily optimal, but its design mimics, in essence, what will be required in future protocols. Reporting tractometry results such as average fractional anisotropy, volume or streamline count of a particular bundle without a sufficient reproducibility score could make the analysis and interpretations more difficult. Coordinated efforts by the diffusion MRI tractography community are needed to quantify and account for reproducibility of WM bundle extraction protocols in this era of open and collaborative science.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/hbm.24917DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7267902PMC
May 2020

Shape memory nanocomposite fibers for untethered high-energy microengines.

Science 2019 07;365(6449):155-158

Université de Bordeaux, CNRS, Centre de Recherche Paul Pascal, UMR5031, 33600 Pessac, France.

Classic rotating engines are powerful and broadly used but are of complex design and difficult to miniaturize. It has long remained challenging to make large-stroke, high-speed, high-energy microengines that are simple and robust. We show that torsionally stiffened shape memory nanocomposite fibers can be transformed upon insertion of twist to store and provide fast and high-energy rotations. The twisted shape memory nanocomposite fibers combine high torque with large angles of rotation, delivering a gravimetric work capacity that is 60 times higher than that of natural skeletal muscles. The temperature that triggers fiber rotation can be tuned. This temperature memory effect provides an additional advantage over conventional engines by allowing for the tunability of the operation temperature and a stepwise release of stored energy.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1126/science.aaw3722DOI Listing
July 2019

Tractography and machine learning: Current state and open challenges.

Magn Reson Imaging 2019 12 9;64:37-48. Epub 2019 May 9.

Department of Computer Science, Université de Sherbrooke, Sherbrooke, Québec, Canada.

Supervised machine learning (ML) algorithms have recently been proposed as an alternative to traditional tractography methods in order to address some of their weaknesses. They can be path-based and local-model-free, and easily incorporate anatomical priors to make contextual and non-local decisions that should help the tracking process. ML-based techniques have thus shown promising reconstructions of larger spatial extent of existing white matter bundles, promising reconstructions of less false positives, and promising robustness to known position and shape biases of current tractography techniques. But as of today, none of these ML-based methods have shown conclusive performances or have been adopted as a de facto solution to tractography. One reason for this might be the lack of well-defined and extensive frameworks to train, evaluate, and compare these methods. In this paper, we describe several datasets and evaluation tools that contain useful features for ML algorithms, along with the various methods proposed in the recent years. We then discuss the strategies that are used to evaluate and compare those methods, as well as their shortcomings. Finally, we describe the particular needs of ML tractography methods and discuss tangible solutions for future works.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.mri.2019.04.013DOI Listing
December 2019

Engineering polymer MEMS using combined microfluidic pervaporation and micro-molding.

Microsyst Nanoeng 2018 2;4:15. Epub 2018 Jul 2.

2Centre National de Recherche Scientifique, University of Bordeaux, Solvay, LOF, UMR 5258, 33600 Pessac, France.

In view of the extensive increase of flexible devices and wearable electronics, the development of polymer micro-electro-mechanical systems (MEMS) is becoming more and more important since their potential to meet the multiple needs for sensing applications in flexible electronics is now clearly established. Nevertheless, polymer micromachining for MEMS applications is not yet as mature as its silicon counterpart, and innovative microfabrication techniques are still expected. We show in the present work an emerging and versatile microfabrication method to produce arbitrary organic, spatially resolved micro-structures, starting from dilute inks, and with possibly a large choice of materials. This approach consists in extending classical microfluidic pervaporation combined with MIcro-Molding In Capillaries. To illustrate the potential of this technique, bilayer polymer double-clamped resonators with integrated piezoresistive readout have been fabricated, characterized, and applied to humidity sensing. The present work opens new opportunities for the conception and integration of polymers in MEMS.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41378-018-0017-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6220165PMC
July 2018

Integrated Electromechanical Transduction Schemes for Polymer MEMS Sensors.

Micromachines (Basel) 2018 Apr 24;9(5). Epub 2018 Apr 24.

Laboratoire IMS, University Bordeaux, UMR 5218, ENSCBP, 16 Avenue Pey Berland, 33607 Pessac Cedex, France.

Polymer Micro ElectroMechanical Systems (MEMS) have the potential to constitute a powerful alternative to silicon-based MEMS devices for sensing applications. Although the use of commercial photoresists as structural material in polymer MEMS has been widely reported, the integration of functional polymer materials as electromechanical transducers has not yet received the same amount of interest. In this context, we report on the design and fabrication of different electromechanical schemes based on polymeric materials ensuring different transduction functions. Piezoresistive transduction made of carbon nanotube-based nanocomposites with a gauge factor of 200 was embedded within U-shaped polymeric cantilevers operating either in static or dynamic modes. Flexible resonators with integrated piezoelectric transduction were also realized and used as efficient viscosity sensors. Finally, piezoelectric-based organic field effect transistor (OFET) electromechanical transduction exhibiting a record sensitivity of over 600 was integrated into polymer cantilevers and used as highly sensitive strain and humidity sensors. Such advances in integrated electromechanical transduction schemes should favor the development of novel all-polymer MEMS devices for flexible and wearable applications in the future.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3390/mi9050197DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6187334PMC
April 2018

How to achieve a successful biaxial marriage.

Authors:
Philippe Poulin

Science 2018 05;360(6390):712-713

Centre de Recherche Paul Pascal - CNRS, University of Bordeaux, Avenue Schweitzer, 33600 Pessac, France.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1126/science.aat7399DOI Listing
May 2018

Shear Rheology Control of Wrinkles and Patterns in Graphene Oxide Films.

Langmuir 2018 03 23;34(9):2996-3002. Epub 2018 Feb 23.

Centre de Recherche Paul Pascal, CNRS, 33600 Pessac , France.

Drying graphene oxide (GO) films are subject to extensive wrinkling, which largely affects their final properties. Wrinkles were shown to be suitable in biotechnological applications; however, they negatively affect the electronic properties of the films. Here, we report on wrinkle tuning and patterning of GO films under stress-controlled conditions during drying. GO flakes assemble at an air-solvent interface; the assembly forms a skin at the surface and may bend due to volume shrinkage while drying. We applied a modification of evaporative lithography to spatially define the evaporative stress field. Wrinkle alignment is achieved over cm areas. The wavelength (i.e., wrinkle spacing) is controlled in the μm range by the film thickness and GO concentration. Furthermore, we propose the use of nanoparticles to control capillary forces to suppress wrinkling. An example of a controlled pattern is given to elucidate the potential of the technique. The results are discussed in terms of classical elasticity theory. Wrinkling is the result of bending of the wet solid skin layer assembled on a highly elastic GO dispersion. Wavelength selection is the result of energy minimization between the bending of the skin and the elastic deformation of the GO supporting dispersion. The results strongly suggest the possibility to tune wrinkles and patterns by simple physicochemical routes.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.langmuir.7b04281DOI Listing
March 2018

A conductive hydrogel based on alginate and carbon nanotubes for probing microbial electroactivity.

Soft Matter 2018 Feb;14(8):1434-1441

Laboratoire Colloïdes et Matériaux Divisés, CNRS UMR 8231, Chemistry Biology & Innovation, ESPCI Paris, PSL Research University, 10 rue Vauquelin, 75005 Paris, France.

Some bacteria can act as catalysts to oxidize (or reduce) organic or inorganic matter with the potential of generating electrical current. Despite their high value for sustainable energy, organic compound production and bioremediation, a tool to probe the natural biodiversity and to select most efficient microbes is still lacking. Compartmentalized cell culture is an ideal strategy for achieving such a goal but the appropriate compartment allowing cell growth and electron exchange must be tailored. Here, we develop a conductive composite hydrogel made of a double network of alginate and carbon nanotubes. Homogeneous mixing of carbon nanotubes within the polyelectrolyte is obtained by a surfactant assisted dispersion followed by a desorption step for triggering electrical conductivity. Dripping the mixture in a gelling bath through simple extrusion or a double one allows the formation of either plain hydrogel beads or liquid core hydrogel capsules. The process is shown to be compatible with the bacterial culture (Geobacter sulfurreducens). Bacteria can indeed colonize the outer wall of plain beads or the inner wall of the conductive capsules' shell that function as an anode from which electrons produced by the cells are collected.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c7sm01929gDOI Listing
February 2018

Giant Electrostriction of Soft Nanocomposites Based on Liquid Crystalline Graphene.

ACS Nano 2018 02 26;12(2):1688-1695. Epub 2018 Jan 26.

Centre de Recherche Paul Pascal, CNRS, Université de Bordeaux , 115 Avenue Schweitzer, 33600 Pessac, France.

High electromechanical coupling is critical to perform effective conversion between mechanical and electrical energy for various applications of electrostrictive polymers. Herein, a giant electrostriction effect is reported in liquid crystalline graphene-doped dielectric elastomers. The materials are formulated by a phase-transfer method which allows the solubilization of graphenic monolayers in nonpolar solvents. Dielectric spectroscopy is combined with tensile test devices to measure the true electrostriction coefficients with differentiating the Maxwell stress effect. Because of their liquid crystal structure, the resultant composites show an ultralarge electrostriction coefficient (∼10 m/V at 0.1 Hz) coupled with good reproducibility during cycles at high deformation rates. This work offers a promising pathway to design high-performance electrostrictive polymer composites as well as to provide insights into mechanisms of true electrostriction in electrically heterogeneous systems. The use of obtained materials as a supersensitive capacitive sensor is demonstrated.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsnano.7b08332DOI Listing
February 2018

Carbon nanotube fiber mats for microbial fuel cell electrodes.

Bioresour Technol 2017 Nov 1;243:1227-1231. Epub 2017 Jul 1.

Centre de Recherche Paul Pascal, Université de Bordeaux, 115, Av. Dr. Albert Schweitzer, 33600 Pessac, France.

Novel carbon nanotube based electrodes of microbial fuel cells (MFC) have been developed. MFC is a promising technology for the wastewater treatment and the production of electrical energy from redox reactions of natural substrates. Performances of such bio-electrochemical systems depend critically on the structure and properties of the electrodes. The presently developed materials are made by weaving fibers solely comprised of carbon nanotubes. They exhibit a large scale porosity controlled by the weaving process. This porosity allows an easy colonization by electroactive bacteria. In addition, the fibers display a nanostructuration that promotes excellent growth and adhesion of the bacteria at the surface of the electrodes. This unique combination of large scale porosity and nanostructuration allows the present electrodes to perform better than carbon reference. When used as anode in a bioelectrochemical reactor in presence of Geobacter sulfurreducens bacteria, the present electrodes show a maximal current density of about 7.5mA/cm.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.biortech.2017.06.170DOI Listing
November 2017

Giant Electrostrictive Response and Piezoresistivity of Emulsion Templated Nanocomposites.

Langmuir 2017 05 25;33(18):4528-4536. Epub 2017 Apr 25.

ESPCI Paris, PSL Research University, CNRS, Laboratoire Sciences et Ingénierie de la Matière Molle, UMR 7615, 10 rue Vauquelin, 75231 Paris cedex 05, France.

Using an emulsion road and optimizing the dispersion process, we prepare polymer carbone nanotubes (CNT) and polymer reduced graphene oxide (rGO) composites. The introduction of conductive nanoparticles into polymer matrices modifies the electronic properties of the material. We show that these materials exhibit giant electrostriction coefficients in the intermediate filler concentration (below 1 wt %). This makes them very promising for applications such as capacitive sensors and actuators. In addition, the values of the piezoresistivity measured in the high filler concentration situation are at least an order of magnitude greater than the one reported in the literature. This opens the way to use these materials for stress or strain sensor applications considering their giant responses to mechanical deformations.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.langmuir.6b04185DOI Listing
May 2017

Advances in Subcritical Hydro-/Solvothermal Processing of Graphene Materials.

Adv Mater 2017 Jun 28;29(22). Epub 2017 Feb 28.

CNRS, Univ. Bordeaux, ICMCB, UPR9048, F-33600, Pessac, France.

Many promising graphene-based materials are kept away from mainstream applications due to problems of scalability and environmental concerns in their processing. Hydro-/solvothermal techniques overwhelmingly satisfy both the aforementioned criteria, and have matured as alternatives to wet-chemical methods with advances made over the past few decades. The insolubility of graphene in many solvents poses considerable difficulties in their processing. In this context hydro-/solvothermal techniques present an ideal opportunity for processing of graphenic materials with their versatility in manipulating the physical and thermodynamic properties of the solvent. The flexibility in hydro-/solvothermal techniques for manipulation of solvent composition, temperature and pressure provides numerous handles to manipulate graphene-based materials during synthesis. This review provides a comprehensive look at the subcritical hydro-/solvothermal synthesis of graphene-based functional materials and their applications. Several key synthetic strategies governing the morphology and properties of the products such as temperature, pressure, and solvent effects are elaborated. Advances in the synthesis, doping, and functionalization of graphene in hydro-/solvothermal media are highlighted together with our perspectives in the field.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/adma.201605473DOI Listing
June 2017

Simultaneous Graphite Exfoliation and N Doping in Supercritical Ammonia.

ACS Appl Mater Interfaces 2016 Nov 3;8(45):30964-30971. Epub 2016 Nov 3.

Department of Advanced Materials, Hannam University , Daejeon 305-811, South Korea.

We report the exfoliation of graphite and simultaneous N doping of graphene by two methods: supercritical ammonia treatment and liquid-phase exfoliation with NHOH. While the supercritical ammonia allowed N doping at a level of 6.4 atom % in 2 h, the liquid-phase exfoliation with NHOH allowed N doping at a level of 2.7 atom % in 6 h. The N doped graphene obtained via the supercritical ammonia route had few layers (<5) and showed large lateral flake size (∼8 μm) and low defect density (I/I < 0.6) in spite of their high level of N doping. This work is the first demonstration of supercritical ammonia as an exfoliation agent and N doping precursor for graphene. Notably, the N doped graphene showed electrocatalytic activity toward oxygen reduction reaction with high durability and good methanol tolerance compared to those of commercial Pt/C catalyst.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsami.6b10570DOI Listing
November 2016

Superflexibility of graphene oxide.

Proc Natl Acad Sci U S A 2016 10 19;113(40):11088-11093. Epub 2016 Sep 19.

Centre de Recherche Paul Pascal - CNRS, University of Bordeaux, 33600 Pessac, France;

Graphene oxide (GO), the main precursor of graphene-based materials made by solution processing, is known to be very stiff. Indeed, it has a Young's modulus comparable to steel, on the order of 300 GPa. Despite its very high stiffness, we show here that GO is superflexible. We quantitatively measure the GO bending rigidity by characterizing the flattening of thermal undulations in response to shear forces in solution. Characterizations are performed by the combination of synchrotron X-ray diffraction at small angles and in situ rheology (rheo-SAXS) experiments using the high X-ray flux of a synchrotron source. The bending modulus is found to be 1 kT, which is about two orders of magnitude lower than the bending rigidity of neat graphene. This superflexibility compares with the fluidity of self-assembled liquid bilayers. This behavior is discussed by considering the mechanisms at play in bending and stretching deformations of atomic monolayers. The superflexibility of GO is a unique feature to develop bendable electronics after reduction, films, coatings, and fibers. This unique combination of properties of GO allows for flexibility in processing and fabrication coupled with a robustness in the fabricated structure.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1073/pnas.1605121113DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5056031PMC
October 2016

High Yield Synthesis of Aspect Ratio Controlled Graphenic Materials from Anthracite Coal in Supercritical Fluids.

ACS Nano 2016 05 12;10(5):5293-303. Epub 2016 May 12.

CNRS, University of Bordeaux, ICMCB , UPR 9048, Pessac 33600, France.

This paper rationalizes the green and scalable synthesis of graphenic materials of different aspect ratios using anthracite coal as a single source material under different supercritical environments. Single layer, monodisperse graphene oxide quantum dots (GQDs) are obtained at high yield (55 wt %) from anthracite coal in supercritical water. The obtained GQDs are ∼3 nm in lateral size and display a high fluorescence quantum yield of 28%. They show high cell viability and are readily used for imaging cancer cells. In an analogous experiment, high aspect ratio graphenic materials with ribbon-like morphology (GRs) are synthesized from the same source material in supercritical ethanol at a yield of 6.4 wt %. A thin film of GRs with 68% transparency shows a surface resistance of 9.3 kΩ/sq. This is apparently the demonstration of anthracite coal as a source for electrically conductive graphenic materials.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsnano.6b01298DOI Listing
May 2016

Prospects of Supercritical Fluids in Realizing Graphene-Based Functional Materials.

Adv Mater 2016 Apr 16;28(14):2663-91. Epub 2016 Feb 16.

CNRS, University of Bordeaux, ICMCB, UPR 9048, F-33600, PESSAC, France.

Supercritical-fluids science and technology predate all the approaches that are currently established for graphene production by several decades in advanced materials design. However, it has only recently been proposed as a plausible approach for graphene processing. Since then, supercritical fluids have emerged into contention as an alternative to existing technologies because of their scalability and versatility in processing graphene materials, which include composites, aerogels, and foams. Here, an overview is presented of such materials prepared through supercritical fluids from an advanced materials science standpoint, with a discussion on their fundamental properties and technological applications. The benefits of supercritical-fluid processing over conventional liquid-phase processing are presented. The benefits include not only better performances for advanced applications but also environmental issues associated with the synthesis process. Nevertheless, the limitations of supercritical-fluid processing are also stressed, along with challenges that are still faced toward the achievement of the great expectations from graphene materials.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/adma.201504436DOI Listing
April 2016

Investigation of the dynamics of growth of polymer materials obtained by combined pervaporation and micro-moulding.

Soft Matter 2016 Feb 24;12(6):1810-9. Epub 2015 Dec 24.

CNRS, Solvay, LOF, UMR 5258, Univ. Bordeaux, F-33600 Pessac, France.

We report an extensive study of the concentration process of aqueous polymer solutions confined within microfluidic channels, owing to the pervaporation of water through the matrix of the chip. Concentration of polymer continuously increases up to the formation of a dense material which eventually invades the channel. This technology can be used to fabricate micro-composites of different shapes starting from dilute inks. We use both theory and screening experiments to show that the dynamics of growth can be predicted by simple conservation equations. More precisely, we establish a quantitative prediction of the growth dynamics taking into account deformations of the soft channels of the moulds, and the solvent chemical activity of the polymer solution. The present results based on general transport equations for binary mixtures provide direct guidance for the design of micro-fabricated materials considering their shape, dimensions, time scale of fabrication, and chemical composition. This quantitative framework is indeed essential to engineer integrated polymer-based micro-devices by using combined pervaporation and microfluidic moulding.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c5sm02394gDOI Listing
February 2016

Optical detection of individual ultra-short carbon nanotubes enables their length characterization down to 10 nm.

Sci Rep 2015 Nov 25;5:17093. Epub 2015 Nov 25.

Univ. Bordeaux, LP2N, F-33405 Talence, France.

Ultrashort single-walled carbon nanotubes, i.e. with length below ~30 nm, display length-dependent physical, chemical and biological properties that are attractive for the development of novel nanodevices and nanomaterials. Whether fundamental or applicative, such developments require that ultrashort nanotube lengths can be routinely and reliably characterized with high statistical data for high-quality sample production. However, no methods currently fulfill these requirements. Here, we demonstrate that photothermal microscopy achieves fast and reliable optical single nanotube analysis down to ~10 nm lengths. Compared to atomic force microscopy, this method provides ultrashort nanotubes length distribution with high statistics, and neither requires specific sample preparation nor tip-dependent image analysis.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/srep17093DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4658524PMC
November 2015

Graphene liquid crystal retarded percolation for new high-k materials.

Nat Commun 2015 Nov 16;6:8700. Epub 2015 Nov 16.

Centre de Recherche Paul Pascal, CNRS, Université de Bordeaux, 115 Avenue Schweitzer, 33600 Pessac, France.

Graphene flakes with giant shape anisotropy are extensively used to establish connectedness electrical percolation in various heterogeneous systems. However, the percolation behaviour of graphene flakes has been recently predicted to be far more complicated than generally anticipated on the basis of excluded volume arguments. Here we confirm experimentally that graphene flakes self-assemble into nematic liquid crystals below the onset of percolation. The competition of percolation and liquid crystal transition provides a new route towards high-k materials. Indeed, near-percolated liquid-crystalline graphene-based composites display unprecedented dielectric properties with a dielectric constant improved by 260-fold increase as compared with the polymer matrix, while maintaining the loss tangent as low as 0.4. This performance is shown to depend on the structure of monodomains of graphene liquid-crystalline phases. Insights into how the liquid crystal phase transition interferes with percolation transition and thus alters the dielectric constant are discussed.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/ncomms9700DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4660061PMC
November 2015

Within-brain classification for brain tumor segmentation.

Int J Comput Assist Radiol Surg 2016 May 3;11(5):777-88. Epub 2015 Nov 3.

Université de Sherbrooke, 2500 Boul. de l'Université, Sherbrooke, QC, J1K 2R1, Canada.

Purpose: In this paper, we investigate a framework for interactive brain tumor segmentation which, at its core, treats the problem of interactive brain tumor segmentation as a machine learning problem.

Methods: This method has an advantage over typical machine learning methods for this task where generalization is made across brains. The problem with these methods is that they need to deal with intensity bias correction and other MRI-specific noise. In this paper, we avoid these issues by approaching the problem as one of within brain generalization. Specifically, we propose a semi-automatic method that segments a brain tumor by training and generalizing within that brain only, based on some minimum user interaction.

Conclusion: We investigate how adding spatial feature coordinates (i.e., i, j, k) to the intensity features can significantly improve the performance of different classification methods such as SVM, kNN and random forests. This would only be possible within an interactive framework. We also investigate the use of a more appropriate kernel and the adaptation of hyper-parameters specifically for each brain.

Results: As a result of these experiments, we obtain an interactive method whose results reported on the MICCAI-BRATS 2013 dataset are the second most accurate compared to published methods, while using significantly less memory and processing power than most state-of-the-art methods.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1007/s11548-015-1311-1DOI Listing
May 2016

Giant Permittivity Polymer Nanocomposites Obtained by Curing a Direct Emulsion.

Langmuir 2015 Nov 27;31(44):12231-9. Epub 2015 Oct 27.

Centre de Recherches Paul Pascal, Université Bordeaux 1 , 115 Avenue Schweitzer, Pessac 33600, France.

Near-percolated CNT-polymer composites are promising high-permittivity materials. The main challenge in the field consists of finding compromises that allow high permittivity and low losses in frequency ranges of interest. Using an emulsion approach and optimizing the size of the droplets and the curing procedure, we obtain unprecedented performances and measure giant permittivity larger than 20,000 at 100 Hz along with a conductivity below 10(-4) S/m.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.langmuir.5b02318DOI Listing
November 2015

Multiscale electrochemistry of hydrogels embedding conductive nanotubes.

Chem Sci 2015 Jul 8;6(7):3900-3905. Epub 2015 Apr 8.

Sorbonne Paris Cité , Paris Diderot University , Interfaces , Traitements , Organisation et Dynamique des Systèmes (ITODYS) , CNRS-UMR 7086 , 15 rue J. A. de Baif , 75013 Paris , France . Email: ; ; Tel: +33 157277217.

The local functionalities of biocompatible objects can be characterized under conditions similar to the operating ones, using scanning electrochemical microscopy (SECM). In the case of alginate beads entrapping carbon nanotubes (CNTs), SECM allows evidencing of the local conductivity, organization, and communication between the CNTs. It shows that the CNT network is active enough to allow long range charge evacuation, enabling the use of alginate/CNT beads as soft 3D electrodes. Direct connection or local interrogation by a microelectrode allows visualization of their communication as a network and eventually the study of them individually at the nanoscale.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c5sc00549cDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5707460PMC
July 2015

Effect of the rheological properties of carbon nanotube dispersions on the processing and properties of transparent conductive electrodes.

Langmuir 2015 Jun 20;31(21):5928-34. Epub 2015 May 20.

CNRS, Centre de Recherche Paul Pascal, Université de Bordeaux, 115 Avenue Schweitzer, 33600 Pessac, France.

Transparent conductive films are made from aqueous surfactant stabilized dispersions of carbon nanotubes using an up-scalable rod coating method. The processability of the films is governed by the amount of surfactant which is shown to alter strongly the wetting and viscosity of the ink. The increase of viscosity results from surfactant mediated attractive interactions between the carbon nanotubes. Links between the formulation, ink rheological properties, and electro-optical properties of the films are determined. The provided guidelines are generalized and used to fabricate optimized electrodes using conductive polymers and carbon nanotubes. In these electrodes, the carbon nanotubes act as highly efficient viscosifiers that allow the optimized ink to be homogeneously spread using the rod coating method. From a general point of view and in contrast to previous studies, the CNTs are optimally used in the present approach as conductive additives for viscosity enhancements of electronic inks.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.langmuir.5b00887DOI Listing
June 2015

How polymers lose memory with age.

Soft Matter 2014 Nov;10(44):8985-91

Centre de Recherche Paul Pascal - CNRS, University of Bordeaux, 115 Avenue Schweitzer, 33600 Pessac, France.

Uniquely in the world of materials, polymers deformed at high temperature and subsequently quenched at low temperature, memorize the temperature at which they have been processed. Polymers can even memorize multiple temperatures. This temperature memory is reflected by a maximum of residual stress restored at the temperature of initial processing. It has been speculated that this capability could arise from the presence of dynamical heterogeneities in glassy domains of polymers. Processing the material at a given temperature would result in the selection of certain heterogeneities that participate in the storage of mechanical stress. Because dynamical heterogeneities are associated with particular relaxation times, the temperature memory of polymers should depend on the time, for example, the glass transition temperature depends on the frequency. The first experimental study of temporal effects on the temperature memory of polymers is presently reported. It is found that aging at high temperature shifts the maximum of residual stress towards greater temperatures. The corresponding loss of memory is explained by the relaxation of dynamical heterogeneities with short characteristic times. The present results clarify the origin of the temperature memory and provide insights into their efficient exploitation in applications.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c4sm01320dDOI Listing
November 2014

Materials science. Fibers do the twist.

Science 2014 Feb;343(6173):845-6

Centre de Recherche Paul Pascal, CNRS, Université de Bordeaux, 115 Avenue Schweitzer, 33600 Pessac, France.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1126/science.1250471DOI Listing
February 2014

Carbon nanotubes induced gelation of unmodified hyaluronic acid.

Langmuir 2013 Aug 31;29(32):10247-53. Epub 2013 Jul 31.

Centre de Recherche Paul-Pascal, Université de Bordeaux-CNRS, 115 Avenue Schweitzer, 33600 Pessac, France.

This work reports an experimental study of the kinetics and mechanisms of gelation of carbon nanotubes (CNTs)-hyaluronic acid (HA) mixtures. These materials are of great interest as functional biogels for future medical applications and tissue engineering. We show that CNTs can induce the gelation of noncovalently modified HA in water. This gelation is associated with a dynamical arrest of a liquid crystal phase separation, as shown by small-angle light scattering and polarized optical microscopy. This phenomenon is reminiscent of arrested phase separations in other colloidal systems in the presence of attractive interactions. The gelation time is found to strongly vary with the concentrations of both HA and CNTs. Near-infrared photoluminescence reveals that the CNTs remain individualized both in fluid and in gel states. It is concluded that the attractive forces interplay are likely weak depletion interactions and not strong van der Waals interactions which could promote CNT rebundling, as observed in other biopolymer-CNT mixtures. The present results clarify the remarkable efficiency of CNT at inducing the gelation of HA, by considering that CNTs easily phase separate as liquid crystals because of their giant aspect ratio.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/la4016492DOI Listing
August 2013
-->