Magnetic resonance insights into the heterogeneous, fractal-like kinetics of chemically recyclable polymers.

Moving toward a circular plastics economy is a vital aspect of global resource management. Chemical recycling of plastics ensures that high-value monomers can be recovered from depolymerized plastic waste, thus enabling circular manufacturing. However, to increase chemical recycling throughput in materials recovery facilities, the present understanding of polymer transport, diffusion, swelling, and heterogeneous deconstruction kinetics must be systematized to allow industrial-scale process design, spanning molecular to macroscopic regimes. To develop a framework for designing depolymerization processes, we examined acidolysis of circular polydiketoenamine elastomers. We used magnetic resonance to monitor spatially resolved observables in situ and then evaluated these data with a fractal method that treats nonlinear depolymerization kinetics. This approach delineated the roles played by network architecture and reaction medium on depolymerization outcomes, yielding parameters that facilitate comparisons between bulk processes. These streamlined methods to investigate polymer hydrolysis kinetics portend a general strategy for implementing chemical recycling on an industrial scale.

Multivariate Machine Learning Models of Nanoscale Porosity from Ultrafast NMR Relaxometry.

Nanoporous materials are of great interest in many applications, such as catalysis, separation, and energy storage. The performance of these materials is closely related to their pore sizes, which are inefficient to determine through the conventional measurement of gas adsorption isotherms. Nuclear magnetic resonance (NMR) relaxometry has emerged as a technique highly sensitive to porosity in such materials. Nonetheless, streamlined methods to estimate pore size from NMR relaxometry remain elusive. Previous attempts have been hindered by inverting a time domain signal to relaxation rate distribution, and dealing with resulting parameters that vary in number, location, and magnitude. Here we invoke well-established machine learning techniques to directly correlate time domain signals to BET surface areas for a set of metal-organic frameworks (MOFs) imbibed with solvent at varied concentrations. We employ this series of MOFs to establish a correlation between NMR signal and surface area via partial least squares (PLS), following screening with principal component analysis, and apply the PLS model to predict surface area of various nanoporous materials. This approach offers a high-throughput, non-destructive way to assess porosity in c.a. one minute. We anticipate this work will contribute to the development of new materials with optimized pore sizes for various applications.

Coils for large standoff relaxometry with unilateral magnets.

Maximizing standoff distance by direct placement of probe coils on magnet bodies, while maximizing signal-to-noise is critical to the successful application of unilateral NMR. Two types of radio frequency (rf) coils for linear array, unilateral magnets are described: "simple fringe" and "split fringe coils." These coils are designed to fully exploit the standoff distance of the unilateral magnet by placement directly on the magnet surface. Such placement fails for normal surface coils used for magnetic resonance due to eddy current induced shielding by the conductive magnet surface. The coil design strategy includes a rectangular cross section solenoid coil, either continuous or split in the center, mounted with the center axis of the coil parallel to the magnet surface. These geometries, when placed on a conducting surface, enhance the rf field produced in the sample region, outside of the solenoid coil. The spatial homogeneity of both rf coils are characterized using the ANSYS™ finite element modelling software. ANSYS™ modeled coil geometries led to homogeneous, surface displaced rf fields. These coils were then constructed and characterized with magnetic resonance imaging. Finally, two experiments that use these coils to perform large standoff relaxation measurements are described.