Faraday Discussions最新文献

Reversible addition–fragmentation chain-transfer (RAFT) depolymerization offers a promising and (comparatively) low-temperature chemical recycling strategy, enabling high yields of recovery of monomers. Conducting this process under continuous flow conditions, in combination with an inline dialysis set-up was recently demonstrated to accelerate depolymerization. However, several kinetic aspects of the process remain poorly understood, complicating the optimization of flow processes. In this study, we determined the kinetics of RAFT depolymerization under continuous flow conditions on the example of poly(butyl methacrylate), polyBMA. Depolymerizations were followed at temperatures from 120 °C to 160 °C, and the activation energy of the process was determined to be 79.5 kJ mol⁻¹. Further, a square root dependence of the rate on the initial polymer concentration was determined. Comparison of the rates of depolymerization with clearance rates during in-flow membrane dialysis showed that the dialysis process is, by a large margin, the rate-determining step in the entire process. Removal of monomer was accelerated by increasing the cross-flow rate in the dialysis, providing a first step towards optimal conditions in the flow depolymerization.

Biomineralisation integrates complex biologically assisted physico-chemical processes leading to an extraordinary diversity of calcareous biomineral crystalline architectures, in intriguing contrast with the consistent presence of a submicrometric granular structure. While the repeated observation of amorphous calcium carbonate is interpreted as a precursor to the crystalline phase, the crystalline transition mechanisms are poorly understood. Access to the crystalline architecture at the mesoscale, i.e., over a few granules, is key to building realistic crystallisation models. Here we exploit three-dimensional X-ray Bragg ptychography microscopy to provide a series of nanoscale maps of the crystalline structure within the “single-crystalline” prism of the prismatic layer of a Pinctada margaritifera shell. The mesocrystalline organisation exhibits several micrometre-sized iso-oriented/iso-strained crystalline domains, the detailed studies of which reveal the presence of crystalline coherence domains ranging from 130 to 550 nm in size. The further increase in the lattice parameter with the size of the coherence domain likely results from the crystallisation mechanism, pointing towards a maturation process occurring after the initial amorphous-to-crystalline transition.

Recent progress in circular 3D-printable photocurable resins that enable closed-loop recycling marks a significant step forward in reducing wasteful manufacturing methods and non-recyclable printed plastics. However, with 3D printing technologies shifting from prototyping to full-scale production, the demand for high-scale processes and easily tuneable resin compositions can benefit from the design of automated systems. Herein, we report on the on-demand preparation of a circular 3D-printable resin, achieved through a continuous flow approach. A supported enzyme (Lipase B from Candida antarctica) was used to promote a green esterification of the lipoic acid with biobased alcohols to prepare circular biobased photocurable resins. The supported enzyme was employed for the preparation of a packed bed reactor and was easily recycled and reused to achieve the continuous production of lipoate-based photocurable resins with tuneable composition. Lastly, the environmental impact of the developed on-demand manufacturing process was compared to the previously reported esterification protocols through life cycle assessment, showing the effectiveness of continuous enzymatic flow synthesis in enhancing environmental performance across multiple areas, from human health to ecosystem impact and resources.

We report the first solvent- and catalyst-free synthesis of crosslinked polyhydroxyurethanes (PHUs) at room temperature from five-membered cyclic carbonates (5CC). A trifunctional carbonate (tri-5CC) combined with tetraethyleneglycol diamine (tDA) formed homogeneous, gelled networks within 24 h (carbonate conversion = 90%, gel time = 6 h). By blending tri-5CC with a tetrafunctional analogue (tetra-5CC), we achieved tunable gel times (1–6 h) and crosslink densities. All systems completed crosslinking under ambient conditions within one month and displayed robust thermal and mechanical properties. Ambient moisture enhanced network formation, confirming the practical relevance of these systems. This study repositions carbonate–amine chemistry as a promising route for the room-temperature synthesis of isocyanate-free thermosetting polyurethanes.

To address current industrial needs and modern legislation, a series of rapidly degradable and strongly adhering crosslinked polyurethanes featuring the commercially available and degradable chain-extender 2,2′-sulfonyldiethanol have been made for use as depolymerisable coatings and ‘debond-on-demand’ hot-melt adhesives. Variation of the chain-extended polyurethane (CEPU) composition, through increased hard segment content, provided a route to tailor the mechanical, adhesive, and degradable characteristics, whereby CEPUs with ultimate tensile strengths and elongation at break of up to 42.68 MPa and 17.59 ε, respectively, could be achieved. The adhesive shear strength of the CEPUs was investigated on a selection of substrates with the highest shear strength observed of 7.80 MPa on aluminium. Depolymerization was triggered via exposure of the CEPUs to tetrabutylammonium fluoride (TBAF), causing the solubilisation of the CEPUs and the generation of low molecular weight species. Rapid ‘debond-on-demand’ adhesion was also achieved upon exposure to 1 M TBAF_(aq), with losses in shear strength of up to 34% on aluminium when exposed for 30 minutes.

The initiation of biomineralisation is crucial to the ecology of shelled organisms, for instance providing protection during early life stages when animals are particularly vulnerable. In oysters, the processes involved in early shell deposition remain debated—whether amorphous calcium carbonate (ACC) is deposited initially and transforms into aragonite, or aragonite is directly deposited—largely due to challenges examining the youngest age classes and the limited diversity of model species. Early larval shell deposition has primarily been studied in pearl oysters (Pinctada spp.) due to commercial interests in pearl formation. Edible oyster biomineralisation, however, remains relatively unexplored, despite the commercial importance of post-settlement survival. In this study, we provide a comparative analysis of shell crystallography of a relatively unexamined, ecologically and commercially important edible species, the Hong Kong oyster (Magallana hongkongensis). We focus on three important life stages—D-larvae (3 days post fertilisation), pediveliger (14 days post fertilisation) and spat (three months post settlement)—over which the shell increases drastically in thickness and alters its microstructure. Employing Scanning Electron Microscopy-based Electron BackScatter Diffraction (SEM-EBSD), we show: (1) larval shells are made entirely of aragonite crystals with no traces of ACC detected, whereas spat exhibit calcitic shells; (2) relative to spats, larval shells show a stronger alignment of their crystal c-axes perpendicular to the shell surface, suggesting perhaps a tighter control of mineralisation processes in early life stages; (3) shell grain area increases as the oyster matures, likely linked to the aragonite-to-calcite shift, but also maturation of the larval shell. These quantitative data on ultra- and microstructural changes in oyster shell architecture advance our understanding of early biomineralisation in edible oysters; by elucidating the mechanisms of crystal deposition and organization, we provide a foundation for designing novel materials inspired by natural biomineralisation processes.

Mollusk shells are composed of biominerals. While their mineral polymorphs are limited, their organic components number in the hundreds, if not thousands. Identifying these individual components is only the first step; understanding how they interact to form a shell remains an ongoing challenge. Infrared (IR) spectroscopy is a powerful technique for analyzing the structure and composition of these components while preserving their topographic relationships. This study employed three scales of observation and three samples: Concholepas, Pinctada, and cultivated pearls. Previously available data on their microstructure and compositions were utilized to explore potential correlations with results obtained from various techniques. IR analysis, being non-destructive, facilitates subsequent comparisons with other analytical methods such as Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and X-ray Absorption Near Edge Structure (XANES), thanks to the precise localization of IR data. The findings reveal that data from earlier non-IR analyses align with results from new IR techniques, including Diffuse Reflectance Infrared Fourier Transform (DRIFT), Optical Photothermal Infrared Spectroscopy (O-PTIR), and Scattering-Type Scanning Near-Field Optical Microscopy (sSNOM). This concordance validates the application of these new IR methods for studying biogenic calcium carbonate. Furthermore, the high spatial resolution of O-PTIR and sSNOM enables detailed visualization of structural and compositional features. For instance, the techniques reveal the intricate inner structure of three-month-old pearls, the distribution of proteins, lipids, and sulphated sugars in Concholepas, and the nanoscale differences in the arrangement of nacre and prisms in Pinctada.

The Southern Ocean, wintertime cities, the upper troposphere, the Arctic and Antarctica, and alpine mountains are places where atmospheric chemistry impacts human health, air quality, climate, or geochemical cycles and that are characterized by low temperatures where ice or snow can be present. The atmospheric impact is evident from the role of polar biogenic sulphur emissions on aerosol formation, multiphase nitrogen and sulphur chemistry on wintertime haze, and industrial emissions in snow-covered areas on the ozone budget. The Cryosphere and ATmospheric CHemistry community (CATCH) addresses the environmental processes within these coupled cryosphere–atmosphere systems, and here we present open research questions specific to the cold environments, focusing on the unique interplay of chemistry and physics. These research needs call for interdisciplinary approaches to address atmospheric science in a warming climate with changing human impact in Earth's cold regions.