In-situ continuous 1D/2D synchrotron SAXS scans to study the kinematics of plastic instability in SCP

We show in this study the high benefits that can be retrieved from the SAXS technique (Small Angle X-ray Scattering) performed with synchrotron lightsource (beamline cSAXS at PSI-SLS) to follow the initiation and the development of a necking (plastic instability) phenomenon underwent by a semicrystalline polymer under tension. High sensitivity and fast detectors used at this beamline as well as motorized fast displacement systems enable to realize 1D and even 2D scans of the specimen during the test. The integration time (33ms) and read out time (3ms) make a spatial resolution of the scanning of 360microm at the displacement rate of 10mm/s ensured by the displacement OWIS stages. At the same time, the tensile machine proceeds with a displacement rate of 20mm/s which means a negligible displacement of the material points on the specimen during the scan. The methodology to handle the data is quite tedious also not complicated. In order to study quantitatively the microstructure evolution during tension for different material points, a precise calibration procedure has been set up thanks to 3-D stereo Digital Image Correlation (DIC system ARAMIS from GOM instruments). The same tensile tests have been performed under DIC to provide the relationship between the running time of the test, the material points coordinates in the reference frame, their respective eulerian positions according to time and their measured local true strain. This gives rise to the following Fig.1 linking all of these variables. The points give the position of the recorded scans along the specimen (Z screaning). The red lines figure out the trajectory of initial material points and allow to find the patterns taken for a same material points at different times. The blue curves are isostrain curves and allow to find all patterns corresponding to a given strain, although for different material points. This figure is the key to be able now to determine whether or not the microstructure state is only governed by the true strain. As a result of the [0.017-1] nm-1 q-range of our experiments, the microstructure is probed at the length scale of scatterers ranging approximately in the 10-350 nm. Its evolution is monitored through a quantitative observable raised from the SAXS pattern analysis. It is an anisotropy index [1] defined as where correspond to the intensities measured along the horizontal and vertical axis of the image frames, respectively the tensile and transverse directions. The local anisotropy is then measured at different locations for different true strain values ranging from 0 to 2 (about 700% of extension ratio). We cover the range of viscoelasticity followed by a long stage of plastic development and a plastic propagation accompanying the hardening rubbery state. The anisotropy index measured for different material points as a function of true strain produces identical curves (within the uncertainty of the measurements). This new result proves that the microstructure is fully governed by the sole strain. Such results enable to consider that this observable gives a true signature of the kinetics of internal reorganization during the tensile deformation of the polymer. It is worthwhile to mention that next efforts made in the modeling of semicrystalline polymer should pretend to recover such signature. References [1] L. Farge, S. André, F. Meneau, J. Dillet, C. Cunat, A common multiscale feature of the deformation mechanisms of a semi-crystalline polymer, Macromolecules, 46(24), (2013), 9659-9668

Remarkable reversal of electrostatic interaction forces on zwitterionic soft nanointerfaces in a monovalent aqueous electrolyte: an AFM study at the single nanoparticle level

International audienceSoft (nano)colloids are increasingly used in medical applications due to the versatile options they offer in terms of e.g. tunable chemical composition, adaptable physical properties and (bio)functionalization perspectives. Obtaining a clear understanding of the nature of the interaction forces that such particles experience with neighboring charged (bio)surfaces is a mandatory prerequisite to draw a comprehensive and mechanistic picture of their stability and reactivity and to further optimize their current functionalities. In this study, adopting an original strategy for nanoparticle attachment to atomic force microscopy (AFM) tips, we demonstrate that the sign of electrostatic forces between carboxylate-terminated poly(amidoamine) nanodendrimers (∼9 nm in diameter) and planar cysteamine-coated gold surfaces can be tailored under fixed pH conditions upon the sole variation of the monovalent salt concentration in solution. The origin of this unconventional electrostatic force reversal is deciphered upon confrontation between AFM force measurements and mean-field force evaluation performed beyond the Derjaguin approximation by integrating the dendrimer and cysteamine electrostatic properties derived independently from electrokinetic measurements. It is shown that the electrostatic force reversal (i) originates from the zwitterionic character of the nanodendrimer–solution interphase, and (ii) becomes operational under the strict condition that the sub-nanometric separation distance between peripheral carboxylate groups and intraparticulate amines is of the order of the characteristic electric Debye layer thickness. The possibility to mediate – via suitable adjustment of monovalent salt content in solution – both the magnitude and sign of the electrostatic forces acting on soft interfaces with zwitterionic functionality paves the way for the design of innovative strategies to control the stability of nanoparticles against aggregation, and to modulate their adhesion onto inorganic surfaces or living organisms

Anisotropy development during HDPE necking studied at the microscale with in situ continuous 1D SAXS scans

International audienceQuantitative information about microstructural reorganizations which occur during mechanical solicitation is important to increase our knowledge on the rheology of semi-crystalline polymers. This point is investigated here on High Density Polyethylene through the measurement of an anisotropy index calculated from small-angle X-ray scattering (SAXS) patterns. These were obtained in situ on a coherent synchrotron beamline with a very fast scanning of the specimen under tensile test. This allows the anisotropy development of many material points which undergo different deformation paths to be followed, thanks to necking development and propagation. With this field information, the microstructural anisotropy observable is shown to have a given value at a given true strain, meaning that strain pilots the bulk topology. Results apparently departing from that premise are shown indeed to be an experimental artifact: true strains are measured on the specimen surface, necking introduces strain heterogeneities in thickness, and the SAXS technique probes the full volume producing averaging

Assessing the interactions between a single dendrimer and (bio)surfaces using AFM

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NMR use to quantify phlorotannins: The case of Cystoseira tamariscifolia, a phloroglucinol-producing brown macroalga in Brittany (France)

International audienceAmong the most renowned natural products from brown algae, phlorotannins are phloroglucinol polymers that have been extensively studied, both for their biotechnological potential and their interest in chemical ecology. The accurate quantification of these compounds is a key point to understand their role as mediators of chemical defense. In recent years, the Folin-Ciocalteu assay has remained a classic protocol for phlorotannin quantification, even though it frequently leads to over-estimations. Furthermore, the quantification of the whole pool of phlorotannins may not be relevant in ecological surveys. In this study, we propose a rapid 1H qNMR method for the quantification of phlorotannins. We identified phloroglucinol as the main phenolic compound produced by the brown macroalga Cystoseira tamariscifolia. This monomer was detected in vivo using 1H HR-MAS spectroscopy. We quantified this molecule through 1H qNMR experiments using TSP as internal standard. The results are discussed by comparison with a standard Folin-Ciocalteu assay performed on purified extracts. The accuracy and simplicity of qNMR makes this method a good candidate as a standard phlorotannin assay

Transport of EOR polymer solutions in low permeability porous media: impact of clay type and injection water composition

International audienceThe application of polymer flooding for enhanced oil recovery (EOR) to low-permeability porous media (below 100mD) can be very challenging as high polymer retention and poor injectivity are frequently observed. The challenges are mostly related to polymer solutions properties (ionic strength and hardness) and porous media mineralogy (clay content). This paper reports on an experimental study that aims at drawing a better picture of the mechanisms governing the transport of polymer solutions in low permeability clayey porous media. Results confirm the major role played by the injection water composition (salinity and hardness) on polymer conformation and on polymer-minerals interactions. Strong interactions between polymer and clay are also evidenced with significant differences according to the clay type: good propagation and high polymer retention in an uncharged and non-swelling clay (kaolinite) and poor propagation with lower than expected retention in charged or swelling clays (illite, smectite). For kaolinite, the results are interpreted in terms of fast formation of a polymer adsorbed layer on the solids surface whereas, for illite and smectite, they can be explained by the slow diffusion of polymer into clay aggregates, whose presence was evidenced by microscopic analysis. These outcomes stand as new elements for understanding and modeling the transport of polymer solutions in low permeability sandstone reservoirs. They also allow classifying the clays in view of their practical impact on the feasibility of polymer flooding operations

ISC 235 : Characterization of the Opalinus clay after experimentation IC. Technical note TN 2016-63

Note technique rédigée dans le cadre d'une collaboration avec l'ANDRA sur des échantillons issus d'une expérience effectuée dans le cadre du Mont Terri Projec

Transport of HPAM Solutions in low Permeability Porous Media: Impacts of Salinity and Clay Content

International audienceChemical EOR is now considered as an attractive option for low permeability reservoirs, in particular wherelack of gas supply does not allow gas injection processes. However, its application can be challenging forpermeabilities below 100 mD, as poor injectivity and high chemical retention are frequently observed inthese cases. This work aimed at investigating the impact of both chemical and mineralogical parameters onthe transport of polymer solutions in well-controlled low permeability porous media.The intrinsic viscosity and hydrodynamic size of partially hydrolyzed polyacrylamide (HPAM)solubilized in brines of variable ionic strengths and hardnesses were firstly investigated. Polymer injectioncorefloods were then conducted using granular packs (sand and clays mixtures) with similar petrophysicalcharacteristics (permeability 60-80 mD) but having several controlled mineralogical compositions. Thegranular packs were especially characterized in terms of structure (SEM) and specific surface area (BET)before and after polymer injections. The main observables from the coreflood tests were the resistanceand residual resistance factors generated by the polymer, the polymer inaccessible pore volume and itsirreversible retention.Homogenous and reproducible granular packs were successfully prepared thanks to a dedicatedmethodology and using different ratios of quartz and clays (kaolinite and illite separately).Results from the viscometric analysis showed that the intrinsic viscosity of the HPAM solutions decreasedwith increasing total salinity, as expected from charge screening, and that it decreased sharply in presenceof divalent cations, even at low ionic strength, which was less expected.Coreflood experiments showed that polymer retentions, resistance factors and irreversible resistancefactors increased significantly:– with increasing ionic strength and hardness for porous media of a given mineralogicalcomposition. This appeared consistent with the outcomes of the viscometric study andconfirmed the major impact of hardness;– in presence of kaolinite and illite, even at low ionic strength and hardness.The polymer inaccessible pore volume was significantly impacted by the presence of clays, but not bythe ionic strength and hardness. Analysis of the results indicated that these effects could not be attributedonly to polymer adsorption linked to the increase of specific surface area, but that more complex polymeradsorption/retention mechanisms occur depending on the clay type (layer charge and expandability).This systematic study allows dissociating the impacts of salinity, hardness and clay contents/types on thetransport of polymer solutions in low permeability porous media. The results obtained should be of interestto the chemical EOR industry as they provide guides to help tuning the injection brine composition andpolymer concentration to the reservoir properties

Nanoparticle (NP) interactions with (bio)surfaces probed by single-NP force spectroscopy

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