Activation energies for metastable to stable phase transition of 4,4'-di-n-heptyl- oxyazoxybenzene

Complexes of adenine, AdH, with cobalt, nickel and copper chlorides were prepared and their thermodynamic functions were determined. The complexing processes are endothermic in nature. The thermal behaviour of complexes was followed up by using TG and DTA analyses. The stoichiometry of thermal decomposition of the investigated complexes was suggested. This revised version was published online in August 2006 with corrections to the Cover Date.     

Study of the Phase Situation in 4-n-pentylphenyl-4′-n-heptyloxythiobenzoate (7S5)

Results of measurements of the specific heat of 4-n-pentylphenyl-4′-n-heptyloxythiobenzoate in the temperature range from about 90 K to about 370 K are presented. They were carried out with an adiabatic calorimeter, a differential scanning calorimeter and a polarizing microscope. Adiabatic calorimetry revealed four anomalies in the specific heat vs. temperature curve viz., two associated with transitions in the solid phase, one with melting and one with the liquid-crystalline nematic-to-isotropic phase transition. Also, two modifications of the solid, stable and metastable, were found to exist. In addition, the DSC method applied in the 285 K to 370 K range revealed a smectic C phase, but only when the sample is being cooled. The polarizing microscope showed the structural polymorphism of the solid phase in the 297 K to 327 K range to be more complex than would stem from adiabatic calorimetry and DSC measurements alone. It also confirmed the occurence of the S_c phase on cooling as ascertained by the DSC method.     

Non-equivalent water molecules in [Ni(H2O)6](ClO4)2 and in [Ni(D2O)6](ClO4)2 in the thermogravimetric investigations

The thermal decomposition of [Ni(H₂O)₆](ClO₄)₂ and [Ni(D₂O)₆](ClO₄)₂ were studied by thermogravimetric analysis (TG) and simultaneous differential thermal analysis (SDTA) at a constant heating rate. The gaseous products of the decomposition were on-line identified by a quadrupole mass spectrometer (QMS). In both cases the process of decomposition starts at ca. 410 K and is connected with removal of water molecules in a stepwise way; at the beginning the first water molecule is lost, then the second and at higher temperature the third one. The rest of the water molecules are lost in the temperature region of ClO₄⁻ decomposition. The energy of activation of the process was calculated in both cases.     

Equilibrium and non-equilibrium phase transitions studied by adiabatic calorimetry

An adiabatic calorimetry was used for some investigations of equilibrium and non-equilibrium phase transitions. For one of the substances studied (4,4′-di-n-heptyloxyazoxybenzene) it was possible to determine temperature dependence of an order parameter and number of clusters of high temperature phase in a region of a phase transition. For another substance (liquid 3,4 dimethylpiridine) an anomaly on the specific heat curves was interpreted as being responsible for a decay of molecules’ clusters. Non-equilibrium phase transitions were investigated for some liquid crystal substances. The process of transformation between metastable and stable phases was described quantitatively. The conclusions obtained concern the stability of metastable phases.     

DSC study of the phase transitions in [Ni(D2O)6](ClO4)2 and [Ni(H2O)6](ClO4)2

DSC measurements were carried out for [Ni(H₂O)₆](ClO₄)₂ (sampleH) and [Ni(D₂O)₆](ClO₄)₂ (sampleD) in the temperature range 300–380 K. For both compounds two anomalies on the DSC curves were detected. The results for sampleH are compared to those previously obtained using adiabatic calorimetry method. For both compounds studied in this work the high-temperature transition appears at the same temperature while the low-temperature one is shifted towards higher temperatures in sampleD. Disorder connected with H₂O or D₂O groups is suggested in the intermediate phase between the low- and high-temperature transitions.