Comparison of structural, thermal and proton conductivity properties of micro- and nanocelluloses.

Our search for a cellulose-based proton conducting material is continued. This paper presents selected physicochemical properties of cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) together with cellulose microcrystals (CMCs) and cellulose microfibrils (CMFs), determined by X-ray diffraction (XRD), thermogravimetric analysis (TGA + DTA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR), and electrical impedance spectroscopy (EIS). The CNCs and CNFs were studied in the forms of powder and film. They were produced in the process of transition metal catalyzed oxidative process or by TEMPO-mediated oxidation. It has been shown that regardless of the production method and the form of the sample the celluloses retained the cellulose Iß crystalline structure, the cellulose films showed similar thermal properties in the relevant temperature range from room temperature to about 200 °C, and the TEMPO-oxidized CNF film showed the highest proton conductivity when compared with those of the other samples studied.

Order-disorder phase transition in an anhydrous pyrazole-based proton conductor: the enhancement of electrical transport properties.

The crystal structure of 1H-pyrazol-2-ium hydrogen oxalate has been studied at 100 K. It consists of two-dimensional layers built with one-dimensional chains that contain pyrazolium and oxalate acids bonded by N-HO and O-HO hydrogen bonds. According to the X-ray data and the Quantum Theory of Atoms in Molecules, it was shown that weak and moderate hydrogen bonds are present in the crystal at room temperature. The thermal stability was studied with the DSC, TGA, and DTG methods: three endothermic peaks are observed at 384, 420, and 469 K. Conductivity measurements have been performed in the temperature range from 300 to 433 K. At 383 K the pyrazole-oxalic acid framework loses its rigidity and the crystal undergoes an ordered-disordered phase transition. At this temperature, the value of the activation energy of proton conductivity changes from 1.14 to 2.31 eV. The proton conduction pathways and the transport mechanism have been studied with theoretical methods.

New 2-methylimidazole-dicarboxylic acid molecular crystals: crystal structure and proton conductivity.

Three new proton conducting molecular crystals, 2-methylimidazole glutarate, 2-methylimidazole suberate and 2-methylimidazole azelate, were obtained and their structure was determined by the x-ray diffraction method. The structure of the crystals was found to be of layer-type. A hydrogen bond network between the heterocycle, glutaric acid and water molecules was apparent in a single layer of 2-methylimidazole glutarate, whereas chains consisting of two heterocyclic molecules linked with hydrogen bonds with dicarboxylic acid were distinguished in a single layer of 2-methylimidazole suberate and azelate crystals. Thermal stability of the crystals was characterized by differential scanning calorimetry and the electrical conductivity was studied by the impedance spectroscopy method. The maximum conductivity of 2-methylimidazole glutarate pellets amounts to 3.3 × 10(-2) S m(-1) at 325 K, in the case of 2-methylimidazole suberate pellets the maximum conductivity is 2.4 × 10(-4) S m(-1) at 348 K and for 2-methylimidazole azelate pellets the maximum conductivity reaches 6.9 × 10(-4) S m(-1) at 353 K.