Intermediate Rotator Phase in Lead(II) Alkanoates

Abstract

Lead(II) alkanoates, from hexanoate to dodecanoate, have been analyzed by means of XRD, optical microscopy, DSC, FTIR, and electric spectroscopy. Four different phases have been identified, corresponding to the three thermal transitions measured by DSC: two of them solid (crystal and “intermediate” phases), and another two fluid (neat phase and isotropic liquid). Powder crystal XRD data indicate that the samples present a bilayered structure. The analysis of the (00l) spacing dependence with temperature in the three ordered phases strongly points to the intermediate phase to be a rotator phase. Optical microscopy and FTIR versus temperature also confirm a structural change from the crystal to the intermediate phase and its solid-state nature. Electrical conductivity maps the thermal transitions of the samples and shows a high ionic conductivity in the intermediate phase, which does not depend much on the carbon chain length. The high conductivity values (3 orders of magnitude higher in comparison with that of the ordered crystal at room temperature) obtained for the intermediate phase gave a further support to the existence of a rotator mesophase in the lead(II) alkanoate series.

Hydrogenated Dimer Acid as a Corrosion Inhibitor for Lead Metal Substrates in Acetic Acid

“…In addition, weak bands ascribed to localized gtg (kink) sequences around 1306 cm −1 can be observed. [71][72][73] The same can be concluded for the rocking modes.…”

The interaction of long chain sodium carboxylates and sodium dodecylsulfate with lead(II) ions in aqueous solutions

“…This is relevant to corrosion inhibition [32][33][34], but also plays an important role in areas as diverse as studies on the lipid organization in human hair [35], and art conservation, where lead carboxylates have been shown to slowly form through the reaction between lead pigments and drying oils in historic paintings and other art works [36,37]. In addition, long chain lead carboxylates show a rich, and chain length dependent thermotropic phase behavior [38][39][40][41][42], and an understanding of the driving forces for the precipitation of these systems from solution is likely to be important for interpreting phase stability.…”

The kinetics of metal soap crystallization in oil polymers

“…We could not detect any signs of intermediate PbPa species between the starting amorphous complex and the crystalline product by applying singular value decomposition to spectral series acquired during crystallization. While Martínez-Casado and co-workers report the existence of a rotator phase between the melt and crystalline PbPa, 31 this phase is likely to be either too short-lived and/or not spectroscopically distinct enough to be detected in our experiments.…”

“…In the high-temperature FTIR spectrum of liquid lead soaps, a single asymmetric carboxylate stretch vibration band can be observed, though it is shifted to higher wavenumbers. 31 The hemi structure is also favoured for shorter fatty acids, which, like in the melt, is a situation where the van der Waals interactions between fatty acid alkyl chains are reduced. 23 Finally, Martínez-Casado and co-workers demonstrated with Pair Distribution Function (PDF) analysis that there are similarities in coordination in the liquid phase of long-chain lead soaps and the hemi structure of short-chain soaps.…”