Conductometric Studies of Thermodynamics of 1,10-Didecyl-1,10-diaza-18-crown-6 Complexes with , , , , , , and Ions in Acetonitrile, Methanol, and Ethanol Solutions

The complexation reactions between 1,10-didecyl-1,10-diaza-18-crown-6 (DD18C6) and , , , , , and ions were studied conductometrically in acetonitrile, methanol, and ethanol at various temperatures. The formation constants of the resulting 1 : 1 complexes were calculated from the computer fitting of the molar conductance-mole ratio data at different temperatures. In the solvents studied, the stability of the resulting complexes varied in the order acetonitrile ≫ methanol > ethanol. The enthalpy and entropy changes of the complexation reactions were evaluated from the temperature dependence of formation constants. The versus plot of thermodynamic data obtained shows a linear correlation indicating the existence of enthalpy-entropy compensation in the complexation reactions. The ab initio studies calculated at B3LYP/6-31G level of theory indicate that the binding energy of complexes decreases with increasing cation size in the gas phase. The experimental data obtained in the solvents show different trends so that the stability constant of Li+and Mg2+complexes is lower than other alkali and alkaline earth ions, respectively due to the solvation of these small ions in solution.

Luminescence and Morphological Kinetics of Functionalized ZnS Colloidal Nanocrystals

This paper reports functionalized zinc sulphide (ZnS) semiconductor nanocrystals (quantum dots, approx., 2.5 nm) which are an important building block in self-assembled nanostructures. ZnS is functionalized by organic stabilizer Thio glycolic acid (TGA). The samples have been synthesized by colloidal technique at relatively low temperature (below 100°C) at an atmospheric pressure of 10−3 torr. Manganese (Mn) doping ions have been incorporated (doped) in ZnS host lattice and observed its effect on growth morphology and optical properties of ZnS colloidal nanocrystals. By XRD, SEM, TEM, and PL, the obtained cubic phase nanosized TGA-capped ZnS materials were characterized. The morphology of ZnS obtained at different temperatures are analyzed by SEM. The crystallite size of the ZnS nanoparticles was estimated from the X-ray diffraction pattern by using Scherrer’s formula (approximately 2.5 nm) which is confirmed by TEM. The estimated bandgap value of ZnS NC’s by ()2 versus plot was 4.89 eV. Gaussian fitting curve in photoluminescence (PL) spectra indicated room temperature emission wavelength range from 300 to 500 nm in undoped and Mn-doped ZnS, with different emission peak intensities, and suggested the wide band emission colours in visible and near UV region which has wider applications in optical devices.

Survey of BGFA Criteria for the Cu-Based Bulk Amorphous Alloys

To verify the effect of composition on the bulk glass forming ability (BGFA) of Cu-based alloys, properties have been collected from the literature (~100 papers, more than 200 alloys). Surveying the BGFA criteria published so far, it has been found that the atomic mismatch condition of Egami-Waseda is fulfilled for all the Cu-based BGFAs, the value being above 0,3. The Zhang Bangwei criterion could be applied for the binary Cu-based alloys. The Miracle and Senkov criteria do not necessarily apply for Cu based bulk amorphous alloys. The critical thickness versus plot of Lu and Liu extrapolates to , somewhat higher than the 0.33 value found in other BGFA alloys. The Park and Kim parameter correlates rather poorly with the critical thickness for Cu based alloys. The Cheney and Vecchino parameter is a good indicator to find the best glass former if it is possible to calculate the exact liquids projection. In 2009 Xiu-lin and Pan defined a new parameter which correlates a bit better with the critical thickness. Based on this survey it is still very difficult to find one parameter in order to characterize the real GFA without an unrealized mechanism of crystallization.