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1. Accurate Determination of the Quantity and Spatial Distribution of Counterions around a Spherical Macroion

   https://doi.org/10.1002/anie.202013806  

   Chen, Jiahui; Bera, Mrinal K.; Li, Hui; Yang, Yuqing; Sun, Xinyu; Luo, Jiancheng; Baughman, Jessi; Liu, Cheng; Yao, Xuesi; Chuang, Steven S. C.; et al (January 2021, Angewandte Chemie International Edition)

   Abstract The accurate distribution of countercations (Rb⁺and Sr²⁺) around a rigid, spherical, 2.9‐nm size polyoxometalate cluster, {Mo₁₃₂}⁴²⁻, is determined by anomalous small‐angle X‐ray scattering. Both Rb⁺and Sr²⁺ions lead to shorter diffuse lengths for {Mo₁₃₂} than prediction. Most Rb⁺ions are closely associated with {Mo₁₃₂} by staying near the skeleton of {Mo₁₃₂} or in the Stern layer, whereas more Sr²⁺ions loosely associate with {Mo₁₃₂} in the diffuse layer. The stronger affinity of Rb⁺ions towards {Mo₁₃₂} than that of Sr²⁺ions explains the anomalous lower critical coagulation concentration of {Mo₁₃₂} with Rb⁺compared to Sr²⁺. The anomalous behavior of {Mo₁₃₂} can be attributed to majority of negative charges being located at the inner surface of its cavity. The longer anion–cation distance weakens the Coulomb interaction, making the enthalpy change owing to the breakage of hydration layers of cations more important in regulating the counterion–{Mo₁₃₂} interaction. 

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2. Accurate Determination of the Quantity and Spatial Distribution of Counterions around a Spherical Macroion

   https://doi.org/10.1002/ange.202013806  

   Chen, Jiahui; Bera, Mrinal K.; Li, Hui; Yang, Yuqing; Sun, Xinyu; Luo, Jiancheng; Baughman, Jessi; Liu, Cheng; Yao, Xuesi; Chuang, Steven S. C.; et al (January 2021, Angewandte Chemie)

   Abstract The accurate distribution of countercations (Rb⁺and Sr²⁺) around a rigid, spherical, 2.9‐nm size polyoxometalate cluster, {Mo₁₃₂}⁴²⁻, is determined by anomalous small‐angle X‐ray scattering. Both Rb⁺and Sr²⁺ions lead to shorter diffuse lengths for {Mo₁₃₂} than prediction. Most Rb⁺ions are closely associated with {Mo₁₃₂} by staying near the skeleton of {Mo₁₃₂} or in the Stern layer, whereas more Sr²⁺ions loosely associate with {Mo₁₃₂} in the diffuse layer. The stronger affinity of Rb⁺ions towards {Mo₁₃₂} than that of Sr²⁺ions explains the anomalous lower critical coagulation concentration of {Mo₁₃₂} with Rb⁺compared to Sr²⁺. The anomalous behavior of {Mo₁₃₂} can be attributed to majority of negative charges being located at the inner surface of its cavity. The longer anion–cation distance weakens the Coulomb interaction, making the enthalpy change owing to the breakage of hydration layers of cations more important in regulating the counterion–{Mo₁₃₂} interaction. 

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3. Cell-specific measurements show nitrogen fixation by particle-attached putative non-cyanobacterial diazotrophs in the North Pacific Subtropical Gyre

   https://doi.org/10.1038/s41467-022-34585-y  

   Harding, Katie J.; Turk-Kubo, Kendra A.; Mak, Esther Wing Kwan; Weber, Peter K.; Mayali, Xavier; Zehr, Jonathan P. (November 2022, Nature Communications)

   Abstract Biological nitrogen fixation is a major important source of nitrogen for low-nutrient surface oceanic waters. Nitrogen-fixing (diazotrophic) cyanobacteria are believed to be the primary contributors to this process, but the contribution of non-cyanobacterial diazotrophic organisms in oxygenated surface water, while hypothesized to be important, has yet to be demonstrated. In this study, we used simultaneous¹⁵N-dinitrogen and¹³C-bicarbonate incubations combined with nanoscale secondary ion mass spectrometry analysis to screen tens of thousands of mostly particle-associated, cell-like regions of interest collected from the North Pacific Subtropical Gyre. These dual isotope incubations allow us to distinguish between non-cyanobacterial and cyanobacterial nitrogen-fixing microorganisms and to measure putative cell-specific nitrogen fixation rates. With this approach, we detect nitrogen fixation by putative non-cyanobacterial diazotrophs in the oxygenated surface ocean, which are associated with organic-rich particles (<210 µm size fraction) at two out of seven locations sampled. When present, up to 4.1% of the analyzed particles contain at least one active putative non-cyanobacterial diazotroph. The putative non-cyanobacterial diazotroph nitrogen fixation rates (0.76 ± 1.60 fmol N cell⁻¹d⁻¹) suggest that these organisms are capable of fixing dinitrogen in oxygenated surface water, at least when attached to particles, and may contribute to oceanic nitrogen fixation. 

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4. In‐Plane Direct‐Write Assembly of Iridescent Colloidal Crystals

   https://doi.org/10.1002/smll.201905519  

   Tan, Alvin T. L.; Nagelberg, Sara; Chang‐Davidson, Elizabeth; Tan, Joel; Yang, Joel K. W.; Kolle, Mathias; Hart, A. John (December 2019, Small)

   Abstract Materials made by directed self‐assembly of colloids can exhibit a rich spectrum of optical phenomena, including photonic bandgaps, coherent scattering, collective plasmonic resonance, and wave guiding. The assembly of colloidal particles with spatial selectivity is critical for studying these phenomena and for practical device fabrication. While there are well‐established techniques for patterning colloidal crystals, these often require multiple steps including the fabrication of a physical template for masking, etching, stamping, or directing dewetting. Here, the direct‐writing of colloidal suspensions is presented as a technique for fabrication of iridescent colloidal crystals in arbitrary 2D patterns. Leveraging the principles of convective assembly, the process can be optimized for high writing speeds (≈600 µm s⁻¹) at mild process temperature (30 °C) while maintaining long‐range (cm‐scale) order in the colloidal crystals. The crystals exhibit structural color by grating diffraction, and analysis of diffraction allows particle size, relative grain size, and grain orientation to be deduced. The effect of write trajectory on particle ordering is discussed and insights for developing 3D printing techniques for colloidal crystals via layer‐wise printing and sintering are provided. 

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5. Comparison of surface energy and adhesion energy of surface-treated particles

   Sansao, B.; Kellar, J.; Cross, W.; Romkes, A. (February 2021, Powder technology)

   null (Ed.)

   The mineral industry uses tremendous amounts of water every year in the processing of ores. Sustainable practices associated with the processing of ores are, therefore, of critical importance. The project described herein is the first step toward producing a dry, particle-separation process based upon control and exploitation of adhesive forces. In this research, the goal is to determine the surface energy of particles, and further, whether the solid sur- face energy can be used to understand the adhesion between these particles and surface-modified substrates. Glass spheres were chosen to represent silicate minerals, the most abundant type of minerals found in mineral deposits. The solid surface energy was found by using contact angle measurements and by applying the van Oss-Good-Chaudhury (VOGC) method. The VOGC method utilizes three-liquid triads to determine the Lifshitz- van der Waals, Lewis acid and Lewis base surface energy components. Surface energies from plasma-cleaned glass were between 40.2 and 60.2 mJ/m2; for the same glass with a hydrophobic chemical surface treatment, trichloro(octadecyl)silane (TCOD), the surface energy was between 20.8 and 20.9 mJ/m2; and for the glass with a hydrophilic chemical surface treatment (n1-(3-trimethoxysilylpropyl) diethylenetriamine (TMPA)) the surface energy was between 46.3 and 61.6 mJ/m2. The particle-substrate adhesion was also measured using a mechanical impact tester. Glass disks and beads were used, cleaned and surface treated with TCOD and TMPA. A custom horizontal impact tester was designed and used to measure the adhesion force between the glass spheres and a glass disk substrate. Impact of the disk/particle puck causes particle removal as tensile forces act on the particles. The tensile detachment force and adhesive force are equal at a critical particle size. Johnson- Kendall-Roberts (JKR) theory was used to determine the interfacial energy between the particles and the surface. The average interfacial energy of plasma cleaned glass, glass treated with TCOD and with TMPA were 44.8 mJ/m2, 21.6 mJ/m2, and 40.1 mJ/m2, respectively. These values are in good agreement with the literature values and with the interfacial energy determined using the VOGC method described above, demonstrating that two approaches compare favorably, despite the dramatically different methods (molecular vs mechanical) utilized. 

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