Experimental and theoretical studies of tetramethoxy-p-benzoquinone: infrared spectra, structural and lithium insertion properties

International audienceIn the search for low-polluting electrode materials for batteries, the use of redox-active organic compounds represents a promising alternative to conventional metal-based systems. In this article we report a combined experimental and theoretical study of tetramethoxy-p-benzoquinone (TMQ). In carbonate-based electrolytes, electrochemical behaviour of this compound is characterized by a reversible insertion process located at approximately 2.85 V vs. Li+/Li0. This relatively high potential reactivity, coupled with our effort to develop computational methodologies in the field of organic electrode materials, prompted us to complement these experimental data with theoretical studies performed using density functional theory (DFT). Single crystals of TMQ were synthesized and thoroughly characterized showing that this quinonic species crystallised in the P21/n space group. The experimental crystal structure of TMQ was then used to assess various DFT methods. The structural features and vibrational spectra were thus predicted by using as a whole five common density functionals (PBE, LDA, revPBE, PBEsol, B3PW91) with and without a semi-empirical correction to account for the van der Waals interactions using either Grimme's (DFT-D2) or Tkatchenko-Scheffler (TS) scheme. The most reliable combination of the DFT functional and the explicit dispersion correction was chosen to study the Li-intercalated molecular crystal (LiTMQ) with the view of indentifying Li insertion sites. A very close agreement with the experiment was found for the average voltage by using the most stable relaxed hypothetical LiTMQ structure. Additionally, a comparison of vibrational spectra gained either for TMQ molecule and its dimer in gas phase or through periodic calculation was undertaken with respect to the experimentally measured infrared spectra. The topological features of the bonds were also investigated in conjunction with estimates of net atomic charges to gain insight into the effect of chemical bonding and intermolecular interaction on Li intercalation. Finally, π-electron delocalization of both quinone and alkali salts of p-semiquinone were determined using the Harmonic Oscillator model of Aromaticity (HOMA) or aromatic fluctuation index (FLU) calculations

Morphology Development in Thermoplastic Vulcanizates (TPV)

International audienc

Morphology Development in Thermoplastic Vulcanizates (TPV)

International audienc

Voltage Gain in Lithiated Enolate-Based Organic Cathode Materials by Isomeric Effect

International audienceLi-ion batteries (LIBs) appear nowadays as flagship technology able to power an increasing range of applications starting from small portable electronic devices to advanced electric vehicles. Over the past two decades, the discoveries of new metal-based host structures, together with substantial technical developments, have considerably improved their electrochemical performance, particularly in terms of energy density. To further promote electrochemical storage systems while limiting the demand on metal-based raw materials, a possible parallel research to inorganic-based batteries consists in developing efficient and low-polluting organic electrode materials. For a long time, this class of redoxactive materials has been disregarded mainly due to stability issues but, in recent years, progress has been made demonstrating that organics undeniably exhibit considerable assets. On the basis of our ongoing research aiming at elaborating lithiated organic cathode materials, we report herein on a chemical approach that takes advantage of the positive potential shift when switching from para to ortho-position in the dihydroxyterephthaloyl system. In practice, dilithium (2,3-dilithium-oxy)-terephthalate compound (Li4C8H2O6) was first produced through an eco-friendly synthesis scheme based on CO2 sequestration, then characterized, and finally tested electrochemically as lithiated cathode material vs. Li. This new organic salt shows promising electrochemical performance, notably fast kinetics, good cycling stability and above all an average operating potential of 2.85 V vs. Li+/Li (i.e., +300 mV in comparison with its para-regioisomer), verifying the relevance of the followed strategy

Viscoelasticity of randomly crosslinked EPDM networks

International audienceThe network structure of plasticized EPDM compounds, crosslinked with resol at different concentrations, was studied by means of rheological methods consisting in oscillatory shear tests, to determine the equilibrium modulus Ge, and long-time relaxation tests in compression followed by strain recovery (a protocol that also yielded values of the compression set of the samples). Ge results were analyzed with respect to the phenomenological model of Langley and Graessley which takes into account the contribution of crosslinks and trapped entanglements to the shear equilibrium modulus. A correction was introduced in order to take into account the presence of plasticizer. The measurement of the soluble polymer fraction in the different samples allowed a more detailed characterization of the networks to be carried out, following a molecular approach by Pearson and Graessley. This method enabled to calculate the crosslink density and trapping factor, but also to compute the probability ψ1 for an un-crosslinked polymer unit to belong to a dangling chain. This probability was shown to increase as resol concentration, and then crosslink density, decreased. The empirical Chasset–Thirion equation was used to model the long-time relaxation data for each sample. Chasset–Thirion parameters were interpreted by Curro and Pincus within a theoretical framework based on the idea that the longest relaxation times are associated with the pendent chains of the network. The relaxation times, obtained from the fitting of experimental relaxation moduli, dramatically increased as the crosslink density decreased. This result corroborates the evolution of ψ1: both tend to demonstrate that in the present compounds, the decrease of crosslink density is accompanied by an increase of the number and length of the dangling chains, leading to increasing relaxation times. The large soluble fraction and long pendent chains of samples showing the lowest crosslink densities were responsible for their poor elastic recovery. The relaxation data were used to model the elastic recovery of the compounds and predict their compression set profiles. Very satisfactory agreement was obtained between experimental data and computations

Co-continuous morphology and stress relaxation behaviour of unfilled and silica-filled PP/EPDM blends

International audienceThese researches aimed at bringing significant and useful information regarding the morphologies and relaxation behaviour of PP/EPDM blends as detailed morphological studies of such uncrosslinked blends are still lacking in the literature. This work allowed a fruitful study of the correlation between their morphology and final mechanical properties, especially concerning their relaxation behaviour. In particular, among all the expected morphologies, the co-continuity is virtually undescribed in the literature whereas it is surely one of the most interesting one regarding the confinement effect of two continuous phases having such a lowinterfacial tension. The experimental conditions leading to such an atypical morphology have been thoroughly described, and its final properties have shown amazing results especially regarding the relaxation and strain recovery behaviours encountered during compression set experiments. As a matter of fact, these experiments highlighted interesting industrial properties related to such a particular morphology: uncrosslinked co-continuous blends reveal a final strain recovery of nearly 40% after a 25% strain applied for 10 h at 100 ◦C which could be discussed on the basis of several physical and rheological considerations. Additionally, the study of the stabilization of such a morphology has also brought interesting results. Finally,we have also studied the influence of hydrophilic and hydrophobic silica nanoparticles on such a specific morphology and its correlated compression set properties