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1. 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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2. The Surface Energy of Hydrogenated and Fluorinated Graphene

   https://doi.org/10.1021/acsami.2c18329  

   Carpenter, James; Kim, Hyunchul; Suarez, Jules; van der Zande, Arend; Miljkovic, Nenad (January 2023, ACS Applied Materials & Interfaces)
3. Surface Energy Budgets of Arctic Tundra During Growing Season

   https://doi.org/10.1029/2019JD030650  

   El Sharif, Husayn; Zhou, Wenbo; Ivanov, Valeriy; Sheshukov, Aleksey; Mazepa, Valeriy; Wang, Jingfeng (July 2019, Journal of Geophysical Research: Atmospheres)
4. Consensus-based construction of high-dimensional free energy surface

   Lyu, Liyao Lyu; Lei, Huan (November 2023, arXivorg)

   One essential problem in quantifying the collective behaviors of molecular systems lies in the accurate construction of free energy surfaces (FESs). The main challenges arise from the prevalence of energy barriers and the high dimensionality. Existing approaches are often based on sophisticated enhanced sampling methods to establish efficient exploration of the full-phase space. On the other hand, the collection of optimal sample points for the numerical approximation of FESs remains largely under-explored, where the discretization error could become dominant for systems with a large number of collective variables (CVs). We propose a consensus sampling-based approach by reformulating the construction as a minimax problem which simultaneously optimizes the function representation and the training set. In particular, the maximization step establishes a stochastic interacting particle system to achieve the adaptive sampling of the max-residue regime by modulating the exploitation of the Laplace approximation of the current loss function and the exploration of the uncharted phase space; the minimization step updates the FES approximation with the new training set. By iteratively solving the minimax problem, the present method essentially achieves an adversarial learning of the FESs with unified tasks for both phase space exploration and posterior error-enhanced sampling. We demonstrate the method by constructing the FESs of molecular systems with a number of CVs up to 30. 

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5. Onset of energy equipartition among surface and body waves

   https://doi.org/doi.org/10.1098/rspa.2020.0775  

   Borcea, L; Garnier, J; Solna, K. (April 2021, Proceedings of the Royal Society of London)

   null (Ed.)

   We derive a radiative transfer equation that accounts for coupling from surface waves to body waves and the other way around. The model is the acoustic wave equation in a two-dimensional waveguide with reflecting boundary. The waveguide has a thin, weakly randomly heterogeneous layer near the top surface, and a thick homogeneous layer beneath it. There are two types of modes that propagate along the axis of the waveguide: those that are almost trapped in the thin layer, and thus model surface waves, and those that penetrate deep in the waveguide, and thus model body waves. The remaining modes are evanescent waves. We introduce a mathematical theory of mode coupling induced by scattering in the thin layer, and derive a radiative transfer equation which quantifies the mean mode power exchange.We study the solution of this equation in the asymptotic limit of infinite width of the waveguide. The main result is a quantification of the rate of convergence of the mean mode powers toward equipartition. 

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