Revealing pseudorotation and ring-opening reactions in colloidal organic molecules

Colloids have a rich history of being used as ‘big atoms’ mimicking real atoms to study crystallization, gelation and the glass transition of condensed matter. Emulating the dynamics of molecules, however, has remained elusive. Recent advances in colloid chemistry allow patchy particles to be synthesized with accurate control over shape, functionality and coordination number. Here, we show that colloidal alkanes, specifically colloidal cyclopentane, assembled from tetrameric patchy particles by critical Casimir forces undergo the same chemical transformations as their atomic counterparts, allowing their dynamics to be studied in real time. We directly observe transitions between chair and twist conformations in colloidal cyclopentane, and we elucidate the interplay of bond bending strain and entropy in the molecular transition states and ring-opening reactions. These results open the door to investigate complex molecular kinetics and molecular reactions in the high-temperature classical limit, in which the colloidal analogue becomes a good model.

Crossover from hydrogen to chemical bonding

Hydrogen bonds (H-bonds) can be interpreted as a classical electrostatic interaction or as a covalent chemical bond if the interaction is strong enough. As a result, short strong H-bonds exist at an intersection between qualitatively different bonding descriptions, with few experimental methods to understand this dichotomy. The [F-H-F]− ion represents a bare short H-bond, whose distinctive vibrational potential in water is revealed with femtosecond two-dimensional infrared spectroscopy. It shows the superharmonic behavior of the proton motion, which is strongly coupled to the donor-acceptor stretching and disappears on H-bond bending. In combination with high-level quantum-chemical calculations, we demonstrate a distinct crossover in spectroscopic properties from conventional to short strong H-bonds, which identify where hydrogen bonding ends and chemical bonding begins.

Mechanisms and measures for the ductility of materials failure

An operational definition for the ductility of failure is given. Many examples illustrate the procedure for specific applications. The ductile/brittle transition is an integral part of the formalism. Further applications are made to the solids forming elements in the Periodic Table. The cases of graphene and diamond are used to verify the procedure. Bond bending and bond stretching are shown to provide an atomic scale criterion for ductile versus brittle failure behaviours.

Preliminary Assessment of Sweet Chestnut and Mixed Sweet Chestnut-Poplar OSB

Poplar Oriented Strand Board (OSB) has been produced since 2012 in Italy, and is well-established on the market. Nonetheless, some doubts have recently emerged about the raw material supply due to the trend towards reduction in plantations. Sweet chestnut is widespread in Italy, where its woodlands cover around 800,000 ha, mainly based on coppice. Partly or entirely replacing poplar with sweet chestnut would result in a new OSB with relevant perspectives for the national forest-wood sector, also interesting other European countries where sweet chestnut is widespread. The present study investigates the properties of OSB manufactured at an industrial scale with different shares of poplar and sweet chestnut wood (respectively, 50–50%, 40–60%, and 100% in weight). Density, internal bond, bending strength, modulus of elasticity and swelling were tested according to EN 300. Overall, the results indicate that sweet chestnut OSB/2 (for load-bearing use in dry conditions) can be manufactured through the process currently used for manufacturing poplar OSB, a key aspect in terms of industrial feasibility. Overall, specific adjustments in the process (concerning pressures applied, gluing system and strand cutting optimization) could make the above boards compliant with the requirements of OSB/3 (for load-bearing use in humid conditions).

Vibrational, mechanical and thermodynamical properties of RE2Ti2O7 (RE = Sm, Gd, Dy, Ho, Er and Yb) pyrochlores

Vibrational, mechanical, thermodynamical properties and thermal conductivities of RE2Ti2O7 (RE = Sm, Gd, Dy, Ho, Er and Yb) pyrochlores have been calculated using a proposed eight-parameter bond-bending force constant model. The main outcome of present calculation is that the first neighbor interaction (Ti–O) is stronger than the second neighbor interactions (RE–O). This means that the bonding between Ti and O is more ionic than the one between RE and O. It is also found that the bond strength of RE–O and the bulk modulus decrease in the sequence Sm [Formula: see text] Gd [Formula: see text] Dy [Formula: see text] Ho [Formula: see text] Er [Formula: see text] Yb. The bulk moduli and Young’s moduli of RE2Ti2O7 also decrease when RE changes from Sm to Yb.

Bond-bending isomerism of Au2I3−: competition between covalent bonding and aurophilicity

Two isomers, different only by bond angles, are discovered for Au2I3−, due to competition between aurophilic interactions and covalent bonding.