Reactions of a Prototypical Phenolic Antioxidant with Radicals in Polyethylene: Insights from Density Functional Theory.

Phenolic antioxidants are widely used to prevent oxidation, which is the main degradation process for many polymers, in particular polyolefins among which polyethylene is the most employed one. Although it is generally understood that one of the main mechanisms by which phenolic antioxidants prevent or slow down oxidation is by deactivating radicals and preventing the formation of alkyl radicals, detailed understanding at the atomic scale of the hierarchy of radical reactions is still lacking. Here, we investigate the interaction of a prototypical phenolic antioxidant, butylated hydroxytoluene (BHT), with radicals in a polyethylene model by means of static and dynamic simulations based on density functional theory.

Controlled Growth of ZIF-8 Membranes on GO-Coated α-Alumina Supports via ZnO Atomic Layer Deposition for Improved Gas Separation.

This study presents a novel approach for fabricating ZIF-8 membranes supported on α-alumina hollow fibers through the introduction of a graphene oxide (GO) gutter layer and the application of zinc oxide (ZnO) Atomic Layer Deposition (ALD). The method successfully addressed key challenges, including excessive precursor penetration and membrane thickness. The introduction of the GO layer and subsequent ZnO ALD treatment significantly reduced membrane thickness to approximately 300 nm and eliminated delamination issues between the GO layer and the alumina support.

Remotely Modulating the Optical Properties of Organic Charge-Transfer Crystallites via Molecular Packing.

Organic charge-transfer complex (CTC) formation has emerged as an effective molecular engineering strategy for achieving the desired optical properties via intermolecular interactions. By synthesizing organic CTCs with carbazole-based electron donors and a 7,7,8,8-tetracyanoquinodimethane acceptor and adopting a molecular linker located remotely from the charge-transfer interface within the donors, we were able to modulate near-infrared absorptive and short-wavelength infrared emissive properties. Structural characterizations performed by using single-crystal X-ray diffraction confirmed that the unique molecular arrangements induced by the steric hindrance from the remotely located linker significantly influence the electronic interactions between the donor and acceptor molecules, resulting in different photophysical properties.

Selective CO Capture from CO/N Gas Mixtures Utilizing Tetrabutylammonium Fluoride Hydrates.

Gas hydrates, a type of inclusion compound capable of trapping gas molecules within a lattice structure composed of water molecules, are gaining attention as an environmentally benign gas storage or separation platform. In general, the formation of gas hydrates from water requires high-pressure and low-temperature conditions, resulting in significant energy consumption. In this study, tetrabutylammonium fluoride (TBAF) was utilized as a thermodynamic promoter forming a semi-clathrate-type hydrate, enabling gas capture or separation at room temperature.

Solution-processable polytriazoles from spirocyclic monomers for membrane-based hydrocarbon separations.

The thermal distillation of crude oil mixtures is an energy-intensive process, accounting for nearly 1% of global energy consumption. Membrane-based separations are an appealing alternative or tandem process to distillation due to intrinsic energy efficiency advantages. We developed a family of spirocyclic polytriazoles from structurally diverse monomers for membrane applications.

Combining Experimental and Theoretical Tools to Probe Radio-Oxidation Products in Polyethylene.

Polyethylene is one of the most used polymers in a variety of sectors. A typical technique used to assess aging is infrared spectroscopy. Under oxidation, the region of the spectrum that is most studied is the one containing the carbonyl signature.

Atomic Scale Mechanisms Controlling the Oxidation of Polyethylene: A First Principles Study.

Understanding the degradation mechanisms of aliphatic polymers by thermal oxidation and radio-oxidation is very important in order to assess their lifetime in a variety of industrial applications. We focus here on polyethylene as a prototypical aliphatic polymer. Kinetic models describing the time evolution of the concentration of chain defects and radicals species in the material identify a relevant step in the formation and subsequent decomposition of transient hydroperoxides species, finally leading to carbonyl defects, in particular ketones.

Enantioselective Mixed Matrix Membranes for Chiral Resolution.

Most pharmaceuticals are stereoisomers that each enantiomer shows dramatically different biological activity. Therefore, the production of optically pure chemicals through sustainable and energy-efficient technology is one of the main objectives in the pharmaceutical industry. Membrane-based separation is a continuous process performed on a large scale that uses far less energy than the conventional thermal separation process.

Temperature- and Pressure-induced Structural Transition of Binary Clathrate Hydrates.

We discover new structure II (sII) hydrate forming agents of two C H O molecules (2-methyl-2-propen-1-ol and 2-butanone) and report the abnormal structural transition of binary C H O+CH hydrates between structure I (sI) and sII with varying temperature and pressure conditions. In both (2-methyl-2-propen-1-ol+CH ) and (2-butanone+CH ) systems, the phase boundary of the two different hydrate phases (sI and sII) exists at the slope change of the phase-equilibrium curve in the semi-logarithmic plots. We confirm the crystal structures of two hydrates synthesized at low (278 K and 6 MPa) and high (286 K and 15 MPa) temperature and pressure conditions by using high-resolution powder diffraction and Raman spectroscopy.

Thermodynamic Stability of Structure II Methyl Vinyl Ketone Binary Clathrate Hydrates and Effects of Secondary Guest Molecules on Large Guest Conformation.

Clathrate hydrates have received massive attention because of their potential application as energy storage materials. Host water frameworks of clathrate hydrates provide empty cavities that can capture not only small molecular guests but also radical species induced by γ-irradiation. In this work, we investigated structure II methyl vinyl ketone (MVK) binary clathrate hydrates with CH, O, and N and the effects of secondary guest species on MVK conformation in the cavity of hydrate and on the thermodynamic stability of unirradiated and γ-irradiated hydrate phases.