More Like this

1. Streaming Instability and Turbulence: Conditions for Planetesimal Formation

   https://doi.org/10.3847/1538-4357/ad47a2  

   Lim_임, Jeonghoon 정훈; Simon, Jacob B; Li_李, Rixin 日新; Armitage, Philip J; Carrera, Daniel; Lyra, Wladimir; Rea, David G; Yang_楊, Chao-Chin 朝欽; Youdin, Andrew N (July 2024, The Astrophysical Journal)

   Abstract The streaming instability (SI) is a leading candidate for planetesimal formation, which can concentrate solids through two-way aerodynamic interactions with the gas. The resulting concentrations can become sufficiently dense to collapse under particle self-gravity, forming planetesimals. Previous studies have carried out large parameter surveys to establish the critical particle to gas surface density ratio (Z), above which SI-induced concentration triggers planetesimal formation. The thresholdZdepends on the dimensionless stopping time (τ_s, a proxy for dust size). However, these studies neglected both particle self-gravity and external turbulence. Here, we perform 3D stratified shearing box simulations with both particle self-gravity and turbulent forcing, which we characterize via a turbulent diffusion parameter,α_D. We find that forced turbulence, at amplitudes plausibly present in some protoplanetary disks, can increase the thresholdZby up to an order of magnitude. For example, forτ_s= 0.01, planetesimal formation occurs whenZ≳ 0.06, ≳0.1, and ≳0.2 atα_D= 10⁻⁴, 10^−3.5, and 10⁻³, respectively. We provide a single fit to the criticalZrequired for the SI to work as a function ofα_Dandτ_s(although limited to the rangeτ_s= 0.01–0.1). Our simulations also show that planetesimal formation requires a mid-plane particle-to-gas density ratio that exceeds unity, with the critical value being largely insensitive toα_D. Finally, we provide an estimation of particle scale height that accounts for both particle feedback and external turbulence. 

   more » « less
2. 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. 

   more » « less
3. 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. 

   more » « less
4. Mesoscopic flow simulation to understand the percolation through fine-ground electronic waste particle bed

   https://doi.org/10.1016/j.powtec.2025.120703  

   Diermyer, Zachary; Xia, Yidong; Hamed, Ahmed; Klinger, Jordan; Thompson, Vicki; Li, Zhen; Li, Jiaoyan (March 2025, Powder Technology)

   Mechanical size reduction is a critical pretreatment for hydrometallurgical recovery of valuable metals in electronic waste. The particle size resulting from milling ranges from a few micrometers to a few millimeters, presenting challenges of achieving sufficient leaching percolation in portions occupied by fine particles. This work investigates the hydrodynamics of percolation through micrometer-sized fine particle beds by using many-body dissipative particle dynamics flow simulations. The results show that higher effective pore size resulting from high aspect-ratio particle packing contributes to higher permeability than spherical particle packing. Increasing surface wettability enhances maximum saturation rates but reduces permeability. Moreover, increasing tortuosity negatively impacts permeability and the degree of reduction in permeability caused by increased surface wettability decreases with increasing tortuosity. These findings imply possible complex relationships between tortuosity, pore size, and surface wettability that collectively impact percolation in loosely packed fine particle beds and can be used to guide improvement in pretreatment. 

   more » « less
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. 

   more » « less