Vellalapalayam Nallagounder Vijayakumar

The purpose of this study is to investigate the structure–property correlations of Li2SO4 · H2O to better understand the function of the disordered phase with respect to its dielectric and thermal properties. The lattice Raman spectral results show that the order of the molecular units during the ordered-to-disordered phase transition is primarily contributed by H2O > SO4 > Li2+. This indicates that the rearrangement of the H2O and SO4 molecular units is primarily responsible for the change in functional properties. In contrast to the ordered phase, the disordered phase exhibits abnormal dielectric behavior, as evidenced by the impedance spectral data, which indicate increased electrical conductivity and a larger dielectric constant at higher frequencies, primarily due to the rearrangement of H2O units and the rotational disorder of SO4 units. The title compound's dehydration and decomposition processes provide compelling evidence that it is possible to understand the ordered–disordered phase transition, which causes dehydration to take longer in the disordered state. On account of the uneven thermal decomposition process, the endothermic peak, which represents the β–α Li2SO4 conversion, exhibits peak splitting at ∼575 °C. The observed anomalous dielectric behavior (e.g., higher dielectric constant at higher frequency, @ 1 MHz) is likely for the first time to date, based on the current findings and the 80 years of literature already available on the title crystal. The disordered phase of Li2SO4 · H2O may be an excellent fit for electrolyte applications in solid-state batteries because of its remarkable dielectric characteristics.

The fascinating supramolecular structures formed through intermolecular hydrogen bonding (HB) interactions gain importance in the research of materials and biological sciences. Pyridine-infused molecular units are more prone to form HB interactions with other moieties like carboxylic acids, alcohols, thiols etc. The high thermal span of mesomorphism, low melting and clearing temperatures, appropriate dielectric and bi-refringence anisotropy, high spontaneous polarization, low threshold voltage, low switching times etc. are some of the important properties required for technical appli-cations of liquid crystalline materials. Chemists mainly focus on design and synthesis of new materials with device desired properties. In this study, an attempt has been made to develop new mesomorphic materials with large thermal span and towards ambient temperatures through Hydrogen bonding interactions. New pyridine deriva-tives of Schiff’s base with dihalo substituents are prepared and are used to form the in-termolecular HB interactions with 4-n-alkyloxybenzoic acids (nOBAs). The 4-n-alkyloxybenzoic acids (nOBAs) are inherently mesomorphic whereas the new pyridine derivatives are non-mesogenic. The 1:1 binary mixtures of pyridine derivatives and nOBAs are found to involve HB interactions and the inherent mesomorphism of nOBAs is varied. The nematic and smectic-C mesophases of nOBAs are quenched and smectic-A mesophase is induced towards the ambient temperatures. The infrared spectroscopy is used to ascertain the intermolecular HB interactions, polarizing optical microscope (POM) in conjunction with a temperature controller and differential scan-ning calorimeter (DSC) are used to ascertain the mesomorphism and phase transition temperatures respectively. The mesomorphic thermal spans are found to be enhanced in present studies as the chain length of carboxylic acids increases.