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Co-crystals of Co(II) salt and 1H,1'H-[3,3']bipyridinyl-6,6'-dione 1 with the composition 1*Co[(CHOO).sub.2][([H.sub.2]O).sub.4] were obtained by mixing both reactants. The single-crystal structure reveals that the metal salt and organic ratio is 1:1. The supramolecular organization of the two components in the co-crystal was mainly dictated by hydrogen bonds between 1 and Co(II) complex. Infrared and powder X-ray diffraction were used to confirm the homogeneity and the phase purity of the bulk crystalline sample of 1*Co[(CHOO).sub.2][([H.sub.2]O).sub.4]. TGA/DTA was recorded to evaluate the thermal stability of the co-crystals. Key words: tecton, hydrogen bonds, co-crystals, self-assembly. Nous avons obtenu des cocristaux formes d'un sel de Co(II) et de 1H,1'H-[3,3']bipyridinyl-6,6'-dione (1), de formule 1*Co[(CHOO).sub.2][([H.sub.2]O).sub.4], en combinant ces deux reactifs. L'analyse cristallographique a revele que le rapport entre le sel metallique et la fraction organique est de 1:1. L'organisation supramoleculaire des deux composants dans le cocristal est obtenue essentiellement par les liaisons hydrogene entre le compose 1 et le complexe de Co(II). Nous avons utilise la spectroscopie infrarouge et la diffraction des rayons X sur poudre pour confirmer l'homogeneite et la purete de phase dans l'echantillon du materiau cristallin 1*Co[(CHOO).sub.2][([H.sub.2]O).sub.4]. Nous avons egalement evalue la stabilite thermique des cocristaux a l'aide d'analyses thermogravimetriques et thermodifferentielles (ATG-ATD). [Traduit par la Redaction] Mots-cles: tecton, liaisons hydrogene, cocristaux, autoassemblage., Introduction Co-crystals are single-phase crystalline solid materials with distinctive properties involving a stoichiometric ratio of at least two or more different molecular compounds that are neither solvates nor salts. (1) [...]

The purpose of this study is to investigate the synthesis of graft copolymer nanocomposite based on hydroxypropyl guar (HPG) graft acrylamide (AM) and 2-acryloamido-2-methyl propane sulfonic acid (AMPS), reinforced with graphene oxide (GO), and study its suitability for the development of the copolymer-based hydrogel systems by chromium triacetate crosslinker to use in oil recovery applications. The characterization outcomes acknowledged the grafting of AM and AMPS onto HPG in the attendance of the GO. The uniform dispersion of GO at 0.1 wt.% was observed in the morphology analysis. Moreover, not only the viscosity but also, the storage and loss modulus of graft copolymer nanocomposites hydrogel improved by adding GO. The effect of graft copolymer nanocomposite and crosslinker concentrations on the performance of hydrogel was also evaluated and optimized by a rheological test. These results showed the outstanding performance of crosslinked hydrogel structure of HPG-g-poly (AM-co-AMPS)/GO, owing to the linking of AM with AMPS and grafting on the HPG chains and the surface of GO in attendance of chromium triacetate. This makes the copolymer hydrogel system more stable against salinity, shearing, and high temperatures. Therefore, this nanocomposite hydrogel system is potentially useful for oil recovery applications. [ABSTRACT FROM AUTHOR]

The aim of the present work is to evaluate the influence of graphene oxide (GO) on copolymer nanocomposites hydrogel structure based on acrylamide (AM) and 2-acryloamido-2-methylpropane sulfonic acid (AMPS) in the presence of the N, N-methylene-bis-acryl-amide (NMBA) by the free radical copolymerization technique. The influence of poly (AM-co-AMPS)/GO as a rheology modifier along with fluid loss controller on the rheological and mechanical properties of brine cement slurry was also investigated. The characterization results confirmed the synthesis of AM monomer and AMPS and showed their grafting with GO surface. The poly (AM-co-AMPS)/GO hydrogel improved the rheological properties of the cement slurry as compared to conventional cement slurry. Furthermore, free water and fluid loss of cement slurry declined by adding the copolymer nanocomposites hydrogel at elevated temperatures. Moreover, not only the thickening time of cement slurry dropped but also, the compressive strength increased with a rise of nanocomposites hydrogel concentrations. However, the nanocomposite hydrogels showed a great effect on early compressive strength than the final compressive strength. The results of this investigation revealed the excellent performance of crosslinked structure of copolymer nanocomposites hydrogel due to the linking of sulfonated AMPS and AM on the surface of GO nanosheet in the attendance of NMBA. This renders greater stability to the cement slurry against salinity and temperature changing of well formations during cementing operation. Thus, poly (AM-co-AMPS)/GO as a suitable rheology modifier and property enhancer can be applied in oil well cementing. [ABSTRACT FROM AUTHOR]

SrFe12O19 (SHF) has been synthesized by tartrate-precursor sol–gel method and then has been coated with polyvinyl alcohol (PVA). The structural, magnetic and electrical properties of the prepared PVA-coated SHF films have been compared with SHF powder using powder X-ray diffractometer (PXRD), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM) and impedance analyzer. A retainment of hexaferrite structure is observed after PVA coating as evident from PXRD. A decrease in particle size, lattice constants a and c and cell volume is observed upon PVA coating indicating a compression of the SHF crystal lattice. SEM images show hexagonal SHF particles embedded in PVA sheets. An enhancement of dielectric constant is observed in PVA-coated SHF films compared to SHF powder in 20 –120 MHz frequency range. The saturation and remanent magnetisation (MS and Mr, respectively) decrease in PVA-coated SHF; however coercivity (HC) remains constant. In addition, SHF powder synthesized herein, by slightly modifying the previously used reaction conditions in tartrate-precursor sol–gel method, shows a quite high value of MS (93.16 emu/g) which is among the highest values reported so far for undoped SHF powder prepared by sol–gel method. Besides, the value of HC is also relatively high. This study also highlights the fact that a slightest change in the reaction conditions determines the final properties of SHF powder. [ABSTRACT FROM AUTHOR]