J. Bennett Addison

Molecular mobility below the glass transition temperature ( T _g ) governs physical aging, mechanical relaxation, and long‐term stability in polymer glasses, yet remains difficult to quantify with chemical and timescale specificity. We use solid‐state NMR relaxometry to probe sub‐ T _g dynamics in a sequence‐ and composition‐tuned series of diphenyl‐substituted siloxane polymers spanning 14%–100% phenyl sidechain content. Variable‐temperature ¹ H lineshapes establish the onset of motional averaging near T _g , while ¹ H T ₁ , ¹ H T _{1 ρ} , and site‐resolved Lee–Goldburg cross‐polarization T _{1 ρ} (LGCPH T _{1 ρ} ) measurements disentangle nanosecond to microsecond motions across methyl siloxane and aromatic environments. Above T _g , all phenylated copolymers exhibit similar reduced‐temperature behavior in ¹ H T ₁ , with a common T ₁ minimum at ~70°C ± 10°C above T _g , indicating that fast local dynamics track T _g without strong composition‐dependent changes. In contrast, rotating‐frame relaxometry reveals a composition‐dependent divergence below T _g : methyl siloxane‐rich materials retain temperature‐responsive microsecond‐scale dynamics, whereas increasing phenyl incorporation progressively suppresses sub‐ T _g segmental mobility and produces flattened T _{1 ρ} profiles. Site‐specific LGCPH T _{1 ρ} confirms that these trends reflect intrinsic differences in segmental dynamics rather than proton spin‐diffusion averaging. Together, these results map how phenyl substitution and sequence regulate residual glassy‐state mobility in polysiloxanes and provide a chemically resolved, multi‐timescale view of sub‐ T _g polymer dynamics.

Tin halide perovskites (THPs) offer narrower bandgaps and improved environmental safety compared with the widely studied lead-based perovskites, but their air sensitivity has hindered their progress and demands new material design to enable their practical applications. Here we report stable and efficient 2D/3D tin perovskite solar cells enabled by new ultrastable 2D and quasi-2D THPs based on the 4-chloro-phenethylammonium (4ClPEA) cation. The stronger π-stacking interactions and tighter interlayer packing in (4ClPEA)₂SnI₄ among (4XPEA)₂SnI₄ structures (X = H, F, Cl, Br) substantially impede oxygen and water diffusion, enabling superior air and moisture stability and bright photoluminescence lasting several months in ambient air. The addition of 4ClPEA markedly improves 2D/3D THP film crystallinity and orientation, leading to 16.2% efficient 2D/3D THP solar cells that show prolonged storage stability and operational stability at 55 °C surpassing 1,000 h. This study establishes a new strategy for designing stable and efficient THPs towards their practical applications.

This study outlines a method for producing chemically recyclable crosslinked polyesters using renewable polyols—glycerol and sorbitol—combined with adipic acid (AA), which is transformed/activated into a polyanhydride mixture prior to use. A three‐step procedure has been designed: 1) an acid‐catalyzed reaction of AA with nontoxic isopropenyl acetate or acetic anhydride to form a crosslinking mixture (CLM) made of adipic‐acetic mixed polyanhydrides; 2) a solvent‐ and additive‐free process where glycerol or sorbitol, or a combination thereof, is reacted with the CLM to achieve a prepolymer, and 3) a casting/molding of the liquid viscous prepolymer to yield a thermoset as the end product. Different thermosets (eight examples) are prepared by changing the reagents ratio. These solids are thoroughly characterized by tensile tests, DMA, high‐resolution magic angle spinning and solid‐state NMR, thermal gravimetric analysis, DSC, and fourier transformed infra red (FT‐IR) spectroscopy. The formation of cross‐linked polyesters is confirmed in all cases, but mechanical properties varied significantly from one specimen to another. Interestingly, a tensile strength up to 18 MPa—approximately an order of magnitude higher than similar polymers—is achieved when sorbitol and the CLM are used in a 1:1 wt% ratio. The chemical recycle of the resulting polymers is achieved via methanolysis with quantitative recovery of the monomeric units.

Lignocellulosic biomass offers a vast and renewable resource for biofuel production and carbon management solutions. The effective conversion of lignocellulosic biomass into economically competitive biofuels and bioproducts demands a comprehensive understanding of its complex structure and composition, often requiring a range of analytical tools to achieve meaningful insights. However, for the analysis of rigid solids, many traditional methods necessitate dissolution or chemical/physical modification of the sample, which limit our ability to capture an intact view of its structural components. This highlights the need for non-destructive approaches, such as solid-state nuclear magnetic resonance (ssNMR), which preserves the sample’s natural state while providing deep, molecular-level insights. While advanced multi-dimensional ssNMR on 13C-enriched materials has recently proven exceptionally valuable for elucidating the complex macrostructure of biomass, isotopic enrichment is expensive, laborious and is clearly infeasible at large scales. In this review, we explore the role of solid-state NMR methods at natural isotopic abundance as essential tools for the non-destructive, in-depth characterization of lignocellulosic biomass and bioenergy materials in their native and unaltered state. After a brief introduction to the basic principles of solid-state NMR, we first describe the acquisition and interpretation of routine 1D 13C ssNMR spectra of lignocellulose and other related biopolymers and products. We then delve into more advanced ssNMR approaches, including key spectral editing techniques, probing polymer dynamics, and various 2D methods applicable at natural abundance. Understanding of domain miscibility as observed from proton-based spin diffusion effects is a theme throughout. Our aim is to highlight key examples where ssNMR provides valuable insights into the composition, structure, dynamics, and morphology of rigid biomaterials relevant to the bioenergy economy, revealing both the native structures and fundamental transformations that occur across conversion and decomposition pathways. We hope that this review encourages a broader adoption of ssNMR methods in bioenergy research, where it can serve as a pivotal analytical tool for achieving sustainable biomass utilization and advancing a carbon-efficient bioeconomy.

In hybrid metal halide perovskites, chiroptical properties typically arise from structural symmetry breaking by incorporating a chiral A-site organic cation within the structure, which may limit the compositional space. Here we demonstrate highly efficient remote chirality transfer where chirality is imposed on an otherwise achiral hybrid metal halide semiconductor by a proximal chiral molecule that is not interspersed as part of the structure yet leads to large circular dichroism dissymmetry factors (g_CD) of up to 10⁻². Density functional theory calculations reveal that the transfer of stereochemical information from the chiral proximal molecule to the inorganic framework is mediated by selective interaction with divalent metal cations. Anchoring of the chiral molecule induces a centro-asymmetric distortion, which is discernible up to four inorganic layers into the metal halide lattice. This concept is broadly applicable to low-dimensional hybrid metal halides with various dimensionalities (1D and 2D) allowing independent control of the composition and degree of chirality.

Halide argyrodite solid-state electrolytes of the general formula Li6PS5CNX exhibit complex static and dynamic disorder that plays a crucial role in ion transport processes. Here, we unravel the rich interplay between site disorder and dynamics in the plastic crystal argyrodite Li6PS5CN and the impact on ion diffusion processes through a suite of experimental and computational methodologies, including temperature-dependent synchrotron powder X-ray diffraction, AC electrochemical impedance spectroscopy, Li-7 solid-state NMR, and machine learning-assisted molecular dynamics simulations. Sulfide and (pseudo)halide site disorder between the two anion sublattices unilaterally improves long-range lithium diffusion irrespective of the (pseudo)halide identity, which demonstrates the importance of site disorder in dictating bulk ionic conductivity in the argyrodite family. Furthermore, we find that anion site disorder modulates the presence and time scales of cyanide rotational dynamics. Ordered configurations of anions enable fast, quasi-free rotations of cyanides that occur on time scales of 10(11) Hz at T = 300 K. In contrast, we find that cyanide dynamics are slow or frozen in Li6PS5CN when site disorder between the cyanide and sulfide sublattices is present at T = 300 K. We rationalize the observed differences in cyanide dynamics in the context of elastic dipole interactions between neighboring cyanide anions and local strain induced by the configurations of site disorder that may impact the energetic landscape for cyanide rotational dynamics. Through this study, we find that anion disorder plays a decisive role in dictating the extent and time scales of both lithium ion and cyanide dynamics in Li6PS5CN.

Plant secondary cell walls (SCWs) are composed of a heterogeneous interplay of three major biopolymers: cellulose, hemicelluloses, and lignin. Details regarding specific intermolecular interactions and higher-order architecture of the SCW superstructure remain ambiguous. Here, we use solid-state nuclear magnetic resonance (ssNMR) measurements to infer refined details about the structural configuration, intermolecular interactions, and relative proximity of all three major biopolymers within air-dried Populus wood. To enhance the utility of these findings and enable evaluation of hypotheses in a physics-based environment in silico, the NMR observables are articulated into an atomistic, macromolecular model for biopolymer assemblies within the plant SCW. Through molecular dynamics simulation, we quantitatively evaluate several variations of atomistic models to determine structural details that are corroborated by ssNMR measurements.

Cross-linked elastomers are stretchable materials that typically are not recyclable or biodegradable. Medium-chain-length polyhydroxyalkanoates (mcl-PHAs) are soft and ductile, making these bio-based polymers good candidates for biodegradable elastomers. Elasticity is commonly imparted by a cross-linked network structure, and covalent adaptable networks have emerged as a solution to prepare recyclable thermosets via triggered rearrangement of dynamic covalent bonds. Here, we develop biodegradable and recyclable elastomers by chemically installing the covalent adaptable network within biologically produced mcl-PHAs. Specifically, an engineered strain of Pseudomonas putida was used to produce mcl-PHAs containing pendent terminal alkenes as chemical handles for postfunctionalization. Thiol-ene chemistry was used to incorporate boronic ester (BE) cross-links, resulting in PHA-based vitrimers. mcl-PHAs cross-linked with BE at low density (<6 mole %) affords a soft, elastomeric material that demonstrates thermal reprocessability, biodegradability, and denetworking at end of life. The mechanical properties show potential for applications including adhesives and soft, biodegradable robotics and electronics.

Two-dimensional (2D) and 3D through-space ¹³C–¹³C homonuclear spin-diffusion techniques are powerful solid-state nuclear magnetic resonance (NMR) tools for extracting structural information from ¹³C-enriched biomolecules, but necessarily long acquisition times restrict their applications. In this work, we explore the broad utility and underutilized power of a chemical shift-selective one-dimensional (1D) version of a 2D ¹³C–¹³C spin-diffusion solid-state NMR technique. The method, which is called 1D dipolar-assisted rotational resonance (DARR) difference, is applied to a variety of biomaterials including lignocellulosic plant cell walls, microcrystalline peptide fMLF, and black widow dragline spider silk. 1D ¹³C–¹³C spin-diffusion methods described here apply in select cases in which the 1D ¹³C solid-state NMR spectrum displays chemical shift-resolved moieties. This is analogous to the selective 1D nuclear Overhauser effect spectroscopy (NOESY) experiment utilized in liquid-state NMR as a faster (1D instead of 2D) and often less ambiguous (direct sampling of the time domain data, coupled with increased signal averaging) alternative to 2D NOESY. Selective 1D ¹³C–¹³C spin-diffusion methods are more time-efficient than their 2D counterparts such as proton-driven spin diffusion (PDSD) and dipolar-assisted rotational resonance. The additional time gained enables measurements of ¹³C–¹³C spin-diffusion buildup curves and extraction of spin-diffusion time constants T_SD, yielding detailed structural information. Specifically, selective 1D DARR difference buildup curves applied to ¹³C-enriched hybrid poplar woody stems confirm strong spatial interaction between lignin and acetylated xylan polymers within poplar plant secondary cell walls, and an interpolymer distance of ∼0.45–0.5 nm was estimated. Additionally, Tyr/Gly long-range correlations were observed on isotopically enriched black widow spider dragline silks.