More Like this

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. 

   more » « less
2. Influence of substrate roughness on particle adhesion and concentration

   https://doi.org/10.1007/s42461-021-00521-9  

   Sansao, B.M.B. ( November 2021 , Mining metallurgy exploration)

   In this research study, the interaction of particles with substrates of different roughness magnitude was investigated. Particle surface treatment, relative humidity (RH), and surface roughness levels were controlled in order to achieve separation of different particles by applying removal forces. Three different approaches to reproducibly roughen surfaces were used. Initially, glass disks were laser engraved to create a reproducible, controlled roughness substrate. However, the laser engraving method produced surface features that were much greater in scale than the particles. These scale differences were such that the substrates produced were not of value to this research. The second option investigated to induce reproducible substrate roughness was to scratch the glass disk using sandpapers of known grain size. A third approach to establish reproducible roughness was to use fine stainless-steel wire mesh substrates. In tests with sanded glass disks, the interfacial energy of plasma-cleaned (hydrophilic) glass beads had a high variation at 40% RH, showing non-uniformity of area of contact between particles and substrates. As the RH increased, it was expected that the interfacial energy of hydrophilic particles would increase, but this behavior was not observed. In addition, comparing the interfacial energy results of hydrophilic particles with hydrophobic particles, a region with significant interfacial energy difference was not identified. In the case of the stainless-steel mesh substrate, the mesh asperities and particle dimensions were comparable. Thus, the smaller particles had more area of contact with the substrate than the larger particles. For the plasma-cleaned (hydrophilic) beads, the recovery values had an average of 92.5% recovery when the RH was between 46 and 85%. For the hydrophobic beads, the average recovery was 19.0% when the RH was between 46 and 75%. Thus, the hydrophobic characteristic of the particle influenced its lower interaction with the mesh substrate. The difference in recovery can be exploited to achieve separation of particles based upon adhesive forces. 

   more » « less
3. Diffusion of Anisotropic Colloidal Microparticles Fabricated Using Two‐Photon Lithography

   https://doi.org/10.1002/ppsc.202100033  

   Doan, David ; Kulikowski, John ; Gu, X. Wendy ( July 2021 , Particle & Particle Systems Characterization)

   Polymeric particles with complex shapes are required for biomedical therapies, colloidal self‐assembly, and micro‐robotics. It has been challenging to synthesize particles beyond simple shapes (e.g., spheres, cubes) with high structural accuracy using existing methods. Here, a method for fabricating polymeric microparticles of complex 3D shapes is reported using two‐photon lithography, and dispersing the particles in an aqueous solution on a glass substrate. The fabrication of polyhedrons (e.g., tetrahedron, pyramid), polypods (e.g., tetrapod, hexapod), and other shapes of 5–10 µm in size is demonstrated. Confocal microscopy is used to track the motion of the sphere, tetrahedron, tetrapod, and screw‐shaped particles near the substrate, and determine their translational diffusion coefficients. HYDRO++ is used to simulate the motion of the particles far from the substrate. The influence of particle size and substrate effects on diffusion in the spherical particles is determined and finds that the non‐spherical particles have increased hindrance at the substrate compared to the spherical particles.

    

   more » « less
4. Capillary-driven indentation of a microparticle into a soft, oil-coated substrate

   https://doi.org/10.1039/D0SM00296H  

   Glover, Justin D. ; Pham, Jonathan T. ( January 2020 , Soft Matter)

   Small scale contact between a soft, liquid-coated layer and a stiff surface is common in many situations, from synovial fluid on articular cartilage to adhesives in humid environments. Moreover, many model studies on soft adhesive contacts are conducted with soft silicone elastomers, which possess uncrosslinked liquid molecules ( i.e. silicone oil) when the modulus is low. We investigate how the thickness of a silicone oil layer on a soft substrate relates to the indentation depth of glass microspheres in contact with crosslinked PDMS, which have a modulus of <10 kPa. The particles indent into the underlying substrate more as a function of decreasing oil layer thickness. This is due to the presence of the liquid layer at the surface that causes capillary forces to pull down on the particle. A simple model that balances the capillary force of the oil layer and the minimal particle–substrate adhesion with the elastic and surface tension forces from the substrate is proposed to predict the particle indentation depth. 

   more » « less
5. Separation of particles of different surface energies through control of humidity

   Sansao, B. ; Kellar, J. ; Cross, W. ; Romkes, A. ( October 2020 , Minerals engineering)

   null (Ed.)

   Many of the methods to classify and concentrate minerals and the subsequent extraction of metals takes place in water-based environments (aqueous solutions). Sustainable processing through the reduction of water consumption will become a key factor to make mining operations viable in the long term. In humid environments, capillary condensation of water can occur between the particle and substrate. The objective herein is to identify separation windows in which control of relative air humidity (RH) yields different substrate adhesion for hydrophilic and hydrophobic particles of different values of interfacial energy. Plasma cleaned glass beads, and trichloro(octadecyl)silane (TCOD) treated beads were poured on a plasma cleaned glass disk and an impact caused the detachment of particles. Impact tests performed under a range of RH showed that separation of plasma cleaned and TCOD treated particles can be achieved in 80% of the tests at humidity levels between 45% and 55%. The recovery of plasma cleaned particles was five times greater than TCOD treated particles at humidity levels between 50% and 55%. 

   more » « less