Insights on the synthesis mechanism of green phenolic resin derived porous carbons via a salt-soft templating approach

International audienceA combined salt-soft template approach to synthesize porous carbon materials is reported along with their synthesis mechanism. This consists in the evaporation induced self-assembly (EISA) of aqueous solutions containing green phenolic resins, a triblock copolymer template and a metallic salt, followed by thermal treatment and washing. The increase of pH up to 5 using NaOH, induces significant improvement in the carbon microporosity but in the detrimental of mesoporosity. As suggest by 13 C and 1 H NMR, the mesoporosity lost is caused by the decrease of H-bonding and self-assembly between the phenolic resin and the template due to the strong "salting-out" effect of eOH ions. For higher pH (pH-9), the porosity start to decrease and graphene-sheet like morphology is formed. The microporosity varies with the salt in the following order: KCl > NaCl > LiCl, while the mesoporosity in the opposite way. The structure changes as well from smooth turbostatic (KCl) to defective graphitic one (NaCl, LiCl). These textural and structural modifications are explained in terms of cation hydration enthalpy and cation-p binding energy and by the competition between the metal salt cations and the Na ions (used to regulate the pH) for water or phenolic resin aromatic ring sites

Direct synthesis of graphitic mesoporous carbon from green phenolic resins exposed to subsequent UV and IR laser irradiations

International audienc

Platicizer effect on network structure and hydrolytic degradation

The hydrolytic degradation of fully cured polyester-urethane networks polymerized in the presence of several weight ratios of triacetin was monitored by the residual concentration in elastically active chains obtained from modulus and equilibrium solvent swelling measurements. The presence of triacetin does not change the water uptake but induces a lower rate of degradation. Comparisons were performed with networks in which triacetin was removed before ageing, and with networks in which polyester-urethane was first polymerized and then impregnated by triacetin. Data suggest that the presence of triacetin during polymerization induces the presence of elastically inactive chains such as dangling chains, loops… the hydrolysis of which does not change the elastic properties of the network. This explanation was checked from relaxation measurements by n.m.r and d.m.a, and by the analysis of the soluble fraction generated by hydrolysis

Impact of ionic liquids on the processing and photo-actuation behavior of SBR composites containing graphene nanoplatelets

The effects of butylpyridinium bromide-based ionic liquids (ILs) on the vulcanization kinetics, mechanical properties and photo-actuation ability of styrene-butadiene rubber (SBR) composites filled with graphene nanoplatelets (GnPs) were investigated. Two different ILs, 1-butylpyridinium bromide (BBP) and 4-methyl-1-butylpyridinium bromide (BMBP), were introduced into rubber compounds. The methodology of IL incorporation into the rubber compounds was studied as well. The ILs were added either directly as a single component or after immobilization onto the GnPs surface. High values of the modulus and tensile strength, which are important mechanical properties, were observed for the composites filled with immobilized BMBP. Freely dispersed BBP resulted in composites with the fastest scorch time, highest thermal and electrical conductivity, and best photo-actuation response of 0.230 mm. © 2020 The AuthorsMinistry of Education, Youth and Sports of the Czech republic - DKRVO [RP/CPS/2020/003]; National Science Centre, Poland through POLONEZ project [UMO-2016/23/P/ST5/02131]; European Unions's Horizon 2020 research and innovation program under Marie Sklodowska -Curie [665778]; Qatar University [QUCGCAM-19/20-2

Etude des mécanismes d exfoliation d argile montmorillonite de synthèse par des poly(diméthylsiloxanes) PDMS

Confronté à la compréhension des mécanismes de formation de matériaux nanocomposites par intercalation ou exfoliation d argile dans des matrices polymères, ce travail s est inscrit dans une approche multidisciplinaire. Pour en contrôler les propriétés, la montmorillonite a été synthétisée selon un procédé hydrothermal et modifiée organiquement par un tensioactif cationique alkylammonium (C18TMABr) pour accroître la distance interfoliaire. L étude des propriétés physico-chimiques (CGI, extraction) et structurales (SAXS, WAXS, DSC) nous a mené à la différenciation de deux états d'adsorption référencés thermodynamiquement et structuralement et semblable quantitativement, l un correspondant à l échange cationique pur, l autre à la physisorption du tensioactif. Ce dernier s est révélé propice à un agrandissement plus conséquent de l espace interfoliaire et à une organisation cristalline des molécules organiques dont la fusion est mise en évidence par DRX et DSC. Les études des comportements dynamiques, mécaniques et thermiques (DMTA, DSC) des mélanges polymère/argile (modifiée ou non) ont montré que l agrandissement de l ouverture interfoliaire ne garantit pas l exfoliation de l argile. De plus, la diminution de l énergie de surface de l argile ( SD), mesurée par chromatographie gazeuse inverse suite à sa modification, n assure pas d avantage ce processus. Seul des interactions spécifiques fortes, mises en évidence par l étude d adsorption en fonction de la masse moléculaire et de la polarité du PDMS (terminaisons triméthylsiloxy et hydroxylées) par microcalorimétrie à écoulement, sont capables de surpasser les forces de cohésion des feuillets et mener à l exfoliation.Confronted with the understanding of the formation mechanism of the nanocomposites by the intercalation or the delamination of a clay in a polymer matrix, this study was in line with a multidisciplinary work. In order to control its properties, the montmorillonite was synthesized in the lab by an hydrothermal reaction and then, organically modified by a alkylammonium cationic surfactant (C18TMABr). The study of the physico-chemical (IGC, extraction) and structural (SAXS, WAXS, DSC) properties has led to the differentiation of two thermodynamical and structural reference states with quantitative properties : the first state corresponds to a pure cationic exchange whereas the second corresponds to the physical adsorption of the surfactant. This late shows a very enlarged interlayer space and a crystalline organization of the organic molecules with a melting point which is highlighted by XRD and DSC. The study of dynamical, mechanical and thermal behaviour (DMTA, DSC) of the mixture polymer-pristine or modified clay have demonstrated that an enlarged interlayer distance doesn t insure the delamination. On the other hand, the decrease of the surface energy of the clay ( SD) after modification (proved by inverse gas chromatography) doesn t seem to be a better insurance of the same reaction. Conversely, the study by flow microcalorimetry of the adsorption of the PDMS chains in function of the molecular weight and the polarity of the terminations (triméthylsiloxy- and silanol-terminated PDMS) have highlighted the requirement of the development of strong specific interactions polymer-filler to surpass the cohesive forces between the layer and lead to the exfoliation.MULHOUSE-SCD Sciences (682242102) / SudocSudocFranceF

Preparation and Properties of SBR Composites Containing Graphene Nanoplatelets Modified with Pyridinium Derivative

International audienceThe goal of this work was to study the effect of graphene nanoplatelets (GnPs) modified with ionic liquid (IL) on properties of styrene–butadiene rubber (SBR) composites. GnPs were decorated with IL or were modified in bulk directly during rubber mix preparation. The ionic liquid used was 1-butyl-4-methylpyridinium tetrafluoroborate (BMPFB). The textural properties were studied to confirm surface modification of GnPs with BMPFB. In these investigations, the impact of the concentration of GnPs and the effect of the method of GnPs’ modification with IL on elastomers properties are described. Some thermal measurements (e.g., differential scanning calorimetry and thermogravimetry) were conducted to characterize the thermal stability or the vulcanization process of the investigated samples. Complementary experimental techniques were used to investigate the properties of the obtained elastomers, specifically tensile testing, and electrical and barrier property measurements. The deposition of IL on the GnPs’ surface positively influenced the mechanical and barrier properties of elastomers. However, samples containing graphene nanoplatelets modified from solution were characterized by less electrical conductivity. SEM analysis was additionally performed to investigate GnPs’ dispersion within SBR composites

Carbonaceous Materials Porosity Investigation in a Wet State by Low-Field NMR Relaxometry

The porosity of differently wetted carbonaceous material with disordered mesoporosity was investigated using low-field 1H NMR relaxometry. Spin–spin relaxation (relaxation time T2) was measured using the CPMG pulse sequence. We present a non-linear optimization method for the conversion of relaxation curves to the distribution of relaxation times by using non-specialized software. Our procedure consists of searching for the number of components, relaxation times, and their amplitudes, related to different types of hydrogen nuclei in the sample wetted with different amounts of water (different water-to-carbon ratio). We found that a maximum of five components with different relaxation times was sufficient to describe the observed relaxation. The individual components were attributed to a tightly bounded surface water layer (T2 up to 2 ms), water in small pores especially supermicropores (2 < T2 < 7 ms), mesopores (7 < T2 < 20 ms), water in large cavities between particles (20–1500 ms), and bulk water surrounding the materials (T2 > 1500 ms). To recalculate the distribution of relaxation times to the pore size distribution, we calculated the surface relaxivity based on the results provided by additional characterization techniques, such as thermoporometry (TPM) and N2/−196 °C physisorption

Self-Photopolymerization of Poly(disulfide) Oligomers

International audienceBase catalyst and oxidant are usually necessary to promote the polymerization of poly(disulfide) oligomers through oxidative coupling of the terminal SH groups into S− S bonds. In this study, we prove that self-polymerization of bifunctional (disulfide) oligomer films can take place in a matter of minutes under UVC irradiation (254 nm, 10.5 mW cm −2). The resulting insoluble polymer is characterized using solid-state NMR, 1 H T 2 NMR relaxation measurements, thermal analysis, and Fourier-transform infrared spectroscopy and proves to have similar composition as a model poly(disulfide) prepared under oxidative conditions, but distinct physical properties. These differences are explained by a change in polymer architecture due to a higher ratio of cyclization relative to linear polymerization. Homolytic photocleavage of internal S−S bonds creates thiyl groups close to each other, driving an increased kinetic feasibility for the cyclization reaction by radical coupling. The subsequent formation of mechanically interlocked macrocycles (polycatenane network) is proposed to account for film properties analogous to those of a cross-linked polymer

The role of specific and active surface areas in optimizing hard carbon irreversible capacity loss in sodium ion batteries

International audienceThe hard carbon irreversible capacity loss in Na-ion cells can be reduced by decreasing the total surface area and the active surface area (defects)

The impact of cooking on meat microstructure studied by low field NMR and Neutron Tomography

International audienceWe studied the impact of temperature of cooking on meat microstructure. The cooking temperature was verified by calorimetry, showing the disappearance of endothermic peaks when cooking temperature was increased. These observations correspond to the denaturation of different protein fractions at specific temperatures. 1H-low field NMR and neutron tomography were used to further understand the relationship between the observed protein denaturation and changes in meat microstructure after heating. Hahn’s echo and solid echo NMR sequences were applied to observe fast relaxation time corresponding to rigid protons. These protons were found to be associated with pools of protons with a strong interaction with the meat matrix. Their relaxation times (T2) are of order of 500–900 μs (for Hahn’s echo sequence) and 10 μs (for solid echo’s sequence). These protons become more rigid upon increasing the temperature. 3D neutron tomography analysis demonstrated the defects created by the contraction of meat fibers and allowed measurement of their volume, which increase for the highest cooking degrees. This analysis allowed classification of the defects as a function of their position (surface or interior) and size (threshold 0.075 % v/v). Our results demonstrate that large defects increase increasing cooking temperature and are located at the surface of the meat slice