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1. Catalytic Halogen Exchange in Miniemulsion ARGET ATRP: A Pathway to Well‐Controlled Block Copolymers

   https://doi.org/10.1002/marc.202000264  

   Wang, Yi ; Matyjaszewski, Krzysztof ( June 2020 , Macromolecular Rapid Communications)

   Halogen exchange in atom transfer radical polymerization (ATRP) is an efficient way to chain‐extend from a less active macroinitiator (MI) to a more active monomer. This has been previously achieved by using CuCl/L in the equimolar amount to P_n−Br MI in the chain extension step. However, this approach cannot be effectively applied in systems based on regeneration of activators (ARGET ATRP), since they operate with ppm amounts of catalysts. Herein, a catalytic halogen exchange procedure is reported using a catalytic amount of Cu in miniemulsion ARGET ATRP to chain‐extend from a less active poly(n‐butyl acrylate) (PBA) MI to a more active methyl methacrylate (MMA) monomer. Influence of different reagents on the initiation efficiency and dispersity is studied. Addition of 0.1mNaCl or tetraethylammonium chloride to ATRP of MMA initiated by methyl 2‐bromopropionate leads to high initiation efficiency and polymers with low dispersity. The optimized conditions are then employed in chain extension of PBA MI with MMA to prepare diblock and triblock copolymers.

    

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2. Toward MBenes Battery Electrode Materials: Layered Molybdenum Borides for Li‐Ion Batteries

   https://doi.org/10.1002/smtd.202300193  

   Majed, Ahmad ; Torkamanzadeh, Mohammad ; Nwaokorie, Chukwudi F. ; Eisawi, Karamullah ; Dun, Chaochao ; Buck, Audrey ; Urban, Jeffrey J. ; Montemore, Matthew M. ; Presser, Volker ; Naguib, Michael ( May 2023 , Small Methods)

   Lithium‐ion and sodium‐ion batteries (LIBs and SIBs) are crucial in our shift toward sustainable technologies. In this work, the potential of layered boride materials (MoAlB and Mo₂AlB₂) as novel, high‐performance electrode materials for LIBs and SIBs, is explored. It is discovered that Mo₂AlB₂shows a higher specific capacity than MoAlB when used as an electrode material for LIBs, with a specific capacity of 593 mAh g⁻¹achieved after 500 cycles at 200 mA g⁻¹. It is also found that surface redox reactions are responsible for Li storage in Mo₂AlB₂, instead of intercalation or conversion. Moreover, the sodium hydroxide treatment of MoAlB leads to a porous morphology and higher specific capacities exceeding that of pristine MoAlB. When tested in SIBs, Mo₂AlB₂exhibits a specific capacity of 150 mAh g⁻¹at 20 mA g⁻¹. These findings suggest that layered borides have potential as electrode materials for both LIBs and SIBs, and highlight the importance of surface redox reactions in Li storage mechanisms.

    

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3. Manipulating Conjugated Polymer Backbone Dynamics through Controlled Thermal Cleavage of Alkyl Side Chains

   https://doi.org/10.1002/marc.202200533  

   Zhao, Haoyu ; Shanahan, Jordan J. ; Samson, Stephanie ; Li, Zhaofan ; Ma, Guorong ; Prine, Nathaniel ; Galuska, Luke ; Wang, Yunfei ; Xia, Wenjie ; You, Wei ; et al ( August 2022 , Macromolecular Rapid Communications)

   The morphological stability of an organic photovoltaic (OPV) device is greatly affected by the dynamics of donors and acceptors occurring near the device's operational temperature. These dynamics can be quantified by the glass transition temperature (T_g) of conjugated polymers (CPs). Because flexible side chains possess much faster dynamics, the cleavage of the alkyl side chains will reduce chain dynamics, leading to a higherT_g. In this work, theT_gs for CPs are systematically studied with controlled side chain cleavage. Isothermal annealing of polythiophenes featuring thermally cleavable side chains at 140 °C, is found to remove more than 95% of alkyl side chains in 24 h, and raise the backboneT_gfrom 23 to 75 °C. Coarse grain molecular dynamics simulations are used to understand theT_gdependence on side chain cleavage. X‐ray scattering indicates that the relative degree of crystallization remains constantduring isothermal annealing process. The effective conjugation length is not influenced by thermal cleavage; however, the density of chromophore is doubled after the complete removal of alkyl side chains. The combined effect of enhancingT_gand conserving crystalline structures during the thermal cleavage process can provide a pathway to improving the stability of optoelectronic properties in future OPV devices.

    

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4. Influences of Environmental Relative Humidity and Horizontal Scale of Subcloud Ascent on Deep Convective Initiation

   https://doi.org/10.1175/JAS-D-21-0056.1  

   Morrison, Hugh ; Peters, John M. ; Chandrakar, Kamal Kant ; Sherwood, Steven C. ( February 2022 , Journal of the Atmospheric Sciences)

   This study examines two factors impacting initiation of moist deep convection: free-tropospheric environmental relative humidity (ϕ_E) and horizontal scale of subcloud ascent (R_sub), the latter exerting a dominant control on cumulus cloud width. A simple theoretical model is used to formulate a “scale selection” hypothesis: that a minimumR_subis required for moist convection to go deep, and that this minimum scale decreases with increasingϕ_E. Specifically, the ratio ofto saturation deficit (1 −ϕ_E) must exceed a certain threshold value that depends on cloud-layer environmental lapse rate. Idealized, large-eddy simulations of moist convection forced by horizontally varying surface fluxes show strong sensitivity of maximum cumulus height to bothϕ_EandR_subconsistent with the hypothesis. IncreasingR_subby only 300–400 m can lead to a large increase (>5 km) in cloud height. A passive tracer analysis shows that the bulk fractional entrainment rate decreases rapidly withR_subbut depends little onϕ_E. However, buoyancy dilution increases as eitherR_suborϕ_Edecreases; buoyancy above the level of free convection is rapidly depleted in dry environments whenR_subis small. While deep convective initiation occurs with an increase in relative humidity of the near environment from moistening by earlier convection, the importance of this moisture preconditioning is inconclusive as it is accompanied by an increase inR_sub. Overall, it is concluded that small changes toR_subdriven by external forcing or by convection itself could be a dominant regulator of deep convective initiation.

    

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5. Etching Asymmetric Germanium Membranes with Hydrogen Peroxide for High‐Capacity Lithium‐Ion Battery Anodes

   https://doi.org/10.1002/pssa.201900963  

   Wu, Ji ; Jin, Congrui ; Larson, Emilee ; Williams, Logan ( January 2020 , physica status solidi (a))

   Germanium (Ge) is deemed as one of the most promising alloying anodes for rechargeable lithium‐ion batteries (LIBs) due to its large theoretical capacity, high electrical conductivity, fast lithium‐ion diffusivity, and mechanical robustness. However, Ge‐based anodes suffer from large volume changes during lithiation and delithiation, which can deteriorate their electrochemical performance rapidly. Herein, the large volume change issue is effectively addressed using an asymmetric membrane structure that is prepared using a phase‐inversion method in combination with hydrogen peroxide etching and surface coating. The asymmetric Ge membrane etched by ≈30 wt% H₂O₂at 90 °C for 30 s demonstrates a capacity retention higher than 80% in 50 cycles at 160 mA g⁻¹. Coating the H₂O₂‐etched Ge membrane with carbonaceous membranes can further improve the retention up to 95% in 50 cycles at 160 mA g⁻¹, whereas ≈100% capacity of 700 mAh g⁻¹can be maintained in 170 cycles at 400 mA g⁻¹. A combination of electron microscopy, spectrophotometry, and X‐ray analyses confirms the electrochemical performance of asymmetric Ge membranes as the LIB anode can be significantly affected by membrane geometry, the duration of hydrogen peroxide etching, carbonaceous membrane coating, and Ge concentration.

    

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