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  1. Functionalized cellulosics have shown promise as naturally derived thermoresponsive gelling agents. However, the dynamics of thermally induced phase transitions of these polymers at the lower critical solution temperature (LCST) are not fully understood. Here, with experiments and theoretical considerations, we address how molecular architecture dictates the mechanisms and dynamics of phase transitions for cellulose ethers. Above the LCST, we show that hydroxypropyl substituents favor the spontaneous formation of liquid droplets, whereas methyl substituents induce fibril formation through diffusive growth. In celluloses which contain both methyl and hydroxypropyl substituents, fibrillation initiates after liquid droplet formation, suppressing the fibril growth to a sub-diffusive rate. Unlike for liquid droplets, the dissolution of fibrils back into the solvated state occurs with significant thermal hysteresis. We tune this hysteresis by altering the content of substituted hydroxypropyl moieties. This work provides a systematic study to decouple competing mechanisms during the phase transition of multi-functionalized macromolecules. 
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  2. Abstract Bond breaking and forming are essential components of chemical reactions. Recently, the structure and formation of covalent bonds in single molecules have been studied by non-contact atomic force microscopy (AFM). Here, we report the details of a single dative bond breaking process using non-contact AFM. The dative bond between carbon monoxide and ferrous phthalocyanine was ruptured via mechanical forces applied by atomic force microscope tips; the process was quantitatively measured and characterized both experimentally and via quantum-based simulations. Our results show that the bond can be ruptured either by applying an attractive force of ~150 pN or by a repulsive force of ~220 pN with a significant contribution of shear forces, accompanied by changes of the spin state of the system. Our combined experimental and computational studies provide a deeper understanding of the chemical bond breaking process. 
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  3. Abstract

    This study presents a new material, “HxCrS2” (denotes approximate composition) formed by proton‐exchange of NaCrS2which has a measured capacity of 728 mAh g−1with significant improvements to capacity retention, sustaining over 700 mAh g−1during cycling experiments. This is the highest reported capacity for a transition metal sulfide electrode and outperforms the most promising proposed sodium anodes to date. HxCrS2exhibits a biphasic structure featuring alternating crystalline and amorphous lamella on the scale of a few nanometers. This unique structural motif enables reversible access to Cr redox in the material resulting in higher capacities than seen in the parent structure which features only S redox. Pretreatment by proton‐exchange offers a route to materials such as HxCrS2which provide fast diffusion and high capacities for sodium‐ion batteries.

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  4. Structural disorder inherent to amorphous materials affords them unique, tailorable properties desirable for diverse applications, but our ability to exploit these phenomena is limited by a lack of understanding of complex structure-property relationships. Here we focus on nonlinear optical absorption and derive a relationship between disorder and the two-photon absorption (2PA) coefficient. We employ an open-aperture Z-scan to measure the 2PA spectra of arsenic (III) sulfide (As2S3) chalcogenide glass films processed with two solvents that impart different levels of structural disorder. We find that the effect of solvent choice on 2PA depends on the energy of the exciting photons and explain this as a consequence of bonding disorder and electron state localization. Our results demonstrate how optical nonlinearities inAs2S3can be enhanced through informed processing and present a fundamental relationship between disorder and 2PA for a generalized amorphous solid.

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  5. Cryo-electron microscopy (cryo-EM) single particle analysis (SPA) has revolutionized biology, revealing the hydrated structure of numerous macromolecules. Yet, the potential of SPA to study inorganic materials remains largely unexplored. An area that could see great impact is solution-processed device materials, where solution changes affect everything from crystal morphology for perovskite photovoltaics to stability of photoluminescent quantum dots. While with traditional microscopy, structures underlying these effects can only be analyzed after drying, cryo-EM allows characterization of in-solution structures, revealing how features arise during processing. A top candidate for such characterization is found in chalcogenide glasses (ChGs), which researchers in the 1980s proposed take on solvent-dependent solution nanostructures whose morphologies have yet to be confirmed. Here we show that cryo-EM can directly image ChGs in solution and combine with other techniques to connect solution structure to film characteristics. Our results bring closure to a long open question in optoelectronics and establish SPA as a tool for solution-processed materials.

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