Effects Of Particle Surface Roughness Research Articles

Creep and recovery in dense suspensions of smooth and rough colloids

We report the effect of particle surface roughness on creep deformation and subsequent strain recovery in dense colloidal suspensions. The suspensions are composed of hard-spherelike poly(methyl methacrylate) smooth (S) and rough (R) colloids with particle volume fractions ϕS = 0.64 ± 0.01 and ϕR = 0.56 ± 0.01, corresponding to a distance of 3.0% and 3.4% based on their jamming volume fractions (ϕJS=0.66±0.01, ϕJR=0.58±0.01). The suspensions are subject to a range of shear stresses (0.01–0.07 Pa) above and below the yield stress values of the two suspensions (σyS=0.035Pa, σyR=0.02Pa). During creep, suspensions of rough colloids exhibit four to five times higher strain deformation compared to smooth colloids, irrespective of the applied stress. The interlocking of surface asperities in rough colloids is likely to generate a heterogeneous microstructure, favoring dynamic particle activity and percolation of strain heterogeneities, therefore resulting in higher magnitude of strain deformation and an earlier onset of steady flow. Strain recovery after the cessation of stress reveals a nonmonotonic recoverable strain for rough colloids, where the peak recoverable strain is observed near the yield stress, followed by a steep decline with increasing stress. This type of response suggests that frictional constraints between geometrically frustrated interlocking contacts can serve as particle bonds capable of higher elastic recovery but only near the yield stress. Understanding how particle roughness affects macroscopic creep and recovery is useful in designing yield stress fluids for additive manufacturing and product formulations.

Effect of particle surface roughness on the flowability and spreadability of Haynes 230 powder during laser powder bed fusion process

The flowability and spreadability of powders are the important factors for additive manufacturing as these two factors directly impact the powder bed packing density, which further affect the quality and mechanical properties of the built components. The flowability and spreadability of powders are dramatically influenced by particle surface roughness as well as the surface energy. The present research attempt to demonstrate the effect of the particle surface roughness on the flowability and spreadability of Haynes 230 powder. The virgin atomized Haynes 230 powder and the atomized powder after ball milling treatment were employed in the present research. The results show that after ball milling, the surface roughness root mean square (rms) of the initial powder increased from 14.87 nm to 42.54 nm and the surface energy of powder increased from 41.19 mJ/m2 to 77.21 mJ/m2, the rest angle of powder increased 30% and the static cohesion index increased from 0.63 to 2.00. According to the calculated Bog coefficient of the two powders (from 2.85 to 15.56), the increase of particle surface roughness leading to the increase of contact force and non-contact force among particles, which were caused by the increased cohesion, leading to the decrease of powder flowability and spreadability as well as the powder bed packing density.

A concise treatise on model-based enhancements of cohesive powder properties via dry particle coating

• Advances in model-guided dry coating of cohesive powder flow enhancement presented. • Chen-NJCEP model explains the mechanism of dry coating induced flow enhancements. • Models offered for the guest amount and type, and granular Bond number estimation. • Dry coating led to drastically enhance flow, packing, agglomeration, dissolution. • Agglomeration, indicator of flowability, dramatically reduced with dry coating. This paper presents a review of our key advances in model-guided dry coating-based enhancements of poor flow and packing of fine cohesive powders. The existing van der Waals force-based particle-contact models are reviewed to elucidate the main mechanism of flow enhancement through silica dry coating. Our multi-asperity model explains the effect of the amount of silica, insufficient flowability enhancements through conventional blending, and the predominant effect of particle surface roughness on cohesion reduction. Models are presented for the determination of the amount and type of guest particles, and estimation of the granular Bond number, used for cohesion nondimensionalization, based on particle size, particle density, asperity size, surface area coverage, and dispersive surface energy. Selection of the processing conditions for LabRAM, a benchmarking device, is presented followed by key examples of enhancements of flow, packing, agglomeration, and dissolution through the dry coating. Powder agglomeration is shown as a screening indicator of powder flowability. The mixing synergy is identified as a cause for enhanced blend flowability with a minor dry coated constituent at silica < 0.01%. The analysis and outcomes presented in this paper are intended to demonstrate the importance of dry coating as an essential tool for industry practitioners.

How can the effect of particle surface roughness on the contact area be predicted?

This paper describes a systematic study of the effect of fractal rough surfaces on the contact area with the aim of advancing contact constitutive laws used in the Discrete Element Method. An in-house Boundary Element code is adopted to investigate the mechanical behaviour of computer-generated surface roughness. Surfaces are generated to have methodically controlled root mean square height (Sq), root mean square gradient (Sdq), short wavevector (q0), large wavevector (q1), Hurst exponent (H) and fractal dimension (Df). The effect of each parameter on the contact area is investigated. Two recently proposed analytical solutions in tribology (i.e. Persson-Tosatti and Pastewka-Robbins) are applied to predict the real contact area. A parameter based on Sq, q0, and H is proposed and its sensitivity for real contact area prediction is demonstrated. Surfaces of natural sand are simulated and their mechanical response shows similar trend as the computer-generated surfaces, albeit more complex.

Effects of Particle Surface Roughness on In-Die Flow and Tableting Behavior of Lactose

Particle rearrangement takes place during the initial phase of tablet compaction. In this study, rough lactose particles were prepared by roller compaction, and their surface roughness modified by partial surface dissolution using a fluidized bed processor. Flow characteristics of the particles were determined using various flow methods, and their compaction characteristics studied using a compaction simulator with punches of different geometry and compaction pressure. Rougher particles demonstrated poorer compressibility and powder flow due to the higher interparticulate frictional forces required for particle movement. Rearrangement energy during tablet compaction was found to be correlated with compressibility (R2 = 0.92) and increased with surface roughness of the particles. Particle rearrangement was found to be dependent on interparticulate frictional forces, which could be measured using FT4 powder rheometer variable flow rate test and compressibility test. Plastic energy decreased as a result of the increased rearrangement energy requirements. Decrease in tensile strength as a result of decrease in plastic energy was not significantly different. Roller-compacted lactose particles produced tablets of higher tensile strength than crystalline lactose because of prefragmentation of the crystalline structure during roller compaction.

Experimental and DEM assessment of the stress-dependency of surface roughness effects on shear modulus

This contribution assesses the effect of particle surface roughness on the shear wave velocity (VS) and the small-strain stiffness (G0) of soils using both laboratory shear plate dynamic tests and discrete element method (DEM) analyses. Roughness is both controlled and quantified to develop a more comprehensive understanding than was achieved in prior contributions that involved binary comparisons of rough and smooth particles. Glass beads were tested to isolate surface roughness effects from other shape effects. VS and G0 were accurately determined using a new design configuration of piezo-ceramic shear plates. Both the experimental and the DEM results show that increasing surface roughness reduces G0 particularly at low stress levels; however, the effect is less marked at high pressures. For the roughest particles, the Hertzian theory does not describe the contact behaviour even at high pressures; this contributes to the fact that the exponent in the G0 – mean effective stress relationship exceeds 0.33 for sand particles. Particle-scale analyses show that the pressure-dependency of the surface roughness effects on G0 can be interpreted using roughness index α which enables the extent of the reduction in G0 due to surface roughness to be estimated.

The influence of particle surface roughness on elastic stiffness and dynamic response

Discrete-element method (DEM) simulations of planar wave propagation are used to examine the effect of particle surface roughness on the stiffness and dynamic response of granular materials. A new contact model that considers particle surface roughness is implemented in the DEM simulations. Face-centred cubic lattice packings and random configurations are used; uniform spheres are considered in both cases to isolate fabric and contact model effects from inertia effects. For the range of values considered here surface roughness caused a significant reduction in stiffness, particularly at lower confining stresses. The simulations confirm that surface roughness effects can at least partially explain the value of the exponent in the relationship between stiffness and mean confining stress for an assembly of spherical particles. Frequency domain analyses showed that the maximum frequency transmitted through the sample is reduced when surface roughness is considered. The assumption of homogeneity of stress and contacts in analytical micromechanical models is shown to lead to an overestimation of stiffness.

Flotation of methylated roughened glass particles and analysis of particle–bubble energy barrier

The impact of the shape and/or anisotropy of particles (in terms of surface energy, surface charge, or wetting) on their flotation separation has been receiving more attention in recent years. The effect of particle surface roughness on interactions with other surfaces or gas bubbles has rarely been studied. The objective of this study was, therefore, to prepare spherical particles of different surface roughness characteristics and test them for their response to flotation separation. Towards this aim, glass particles with a size of 106–150μm were either acid etched or abraded to manipulate their surface roughness. The particles were also methylated using trimethylchlorosilane to enhance their hydrophobicity and interactions with air bubbles. Micro-flotation separations were then carried out with methylated smooth and roughened particles to examine the effect of particle surface nano-roughness on flotation kinetics and their corresponding recoveries. The results confirmed that the flotation rate constants of roughened particles increased consistently with increasing dimensions of surface asperities. To explain the effect of particle surface roughness on flotation, a theoretical model based on the extended-DLVO interactions was formulated and used to quantify the effect of hydrophobic asperities on particle–bubble surface interactions. The theoretical modeling results suggest, for the first time, that the size of nano-sized hydrophobic asperities distributed over spherical microscopic particles dictate the magnitude of the energetic barrier that particles need to overcome in order to attach to bubbles.

Accurate simulation of the optical properties of atmospheric ice crystals with the invariant imbedding T-matrix method

The invariant imbedding T-matrix method (II-TM) is employed to compute the optical properties of randomly oriented ice crystals of various shapes including hexagonal columns, hollow columns, droxtals, bullet rosettes and aggregates. The II-TM is shown to be numerically stable and capable of obtaining the single-scattering properties of hexagonal ice crystals with size parameters up to 150. The 22° and 46° halo peaks in the phase function of compact hexagonal ice crystals begin to emerge at a size parameter of approximately 80 and tend to become insensitive to particle size as the corresponding size parameter approaches 150. Furthermore, the II-TM solutions are shown to be in agreement with their counterparts based on the discrete dipole approximation (DDA) method and the pseudo-spectral time-domain (PSTD) method. In addition, the accuracy of the improved geometric-optics method (IGOM) is examined for randomly oriented hexagonal ice crystal cases over a wide size-parameter range from the resonant to geometric-optics regimes. The II-TM is also used to study the effects of particle surface roughness and internal inclusions on the single-scattering properties of ice particles.

Assessment of K0 correlation to strength for granular materials

The coefficient of lateral stress at rest K0 is a state soil variable, yet is well correlated to strength. As different types of friction angles can be defined, it is important to examine the applicability of K0-strength correlation and further clarify the mechanism of K0-stress state. In this study, the values of K0 were experimentally investigated for different types of granular materials, focusing on its correlation to material strength and the effect of particle shape and surface roughness. For this purpose, laboratory tests were conducted to directly measure K0 of natural sand, spherically shaped glass bead, and surface-etched glass bead packings under various stress and soil conditions. Triaxial and other basic property tests were also conducted to characterize the test granular materials. It was revealed that the effect of material density on K0 differed depending on the stress history whereas the effect of particle surface roughness, within the range considered in this study, was relatively small. Test results highlight that the values of the friction angle employed into Jaky's K0 equation to match measured K0 values are not unique, showing a state-dependent aspect. Inter-particle stress analysis was introduced to assess the correlation of K0 to the friction angle as postulated by Jaky's K0 equation.

Particle migration in a Couette apparatus: Experiment and modeling

Suspensions comprised of neutrally buoyant spheres in Newtonian fluids undergoing creeping flow in the annular region between two rotating, coaxial cylinders (a wide-gap Couette) display a bulk migration of particles towards regions of lower shear rate. A series of experiments are performed to characterize this particle migration, including the influence of particle size, surface roughness, and volume fraction. Little, if any, effect of particle surface roughness is observed. An existing continuum diffusive-flux model [Phillips et al. (1992)] for predicting particle concentration profiles in monomodal suspensions is evaluated using the current series of experimental data. This model predicts a dependence of the migration rate on the square of the suspended particles’ radius, a2; whereas the present experiments indicate that systems with average particle volume fractions of 50% display a rate that scales with a3. Previous use of the diffusive-flux model has assumed constant values for diffusion coefficients which serve as tuning parameters in the phenomenological equation. Here the experimental data are used to investigate variations of the model in which the diffusion coefficients depend upon either the local or global particle volume fraction. For initially uniform suspensions, the coefficients are found to be best modeled as functions of the local particle volume fraction.

Measurement of the translational and rotational velocities of a noncolloidal sphere rolling down a smooth inclined plane at low Reynolds number

The translational and rotational velocities of a sphere rolling down an inclined plane at low Reynolds number were measured as a function of the angle of inclination of the plane. Both 140 μm glass and 6350 μm diam acrylic particles were used. A theoretical model including the effects of particle surface roughness was developed, and is in quantitative agreement with the measurements. In addition, statistically significant velocity fluctuations were measured and are explained by variation in the coefficient of friction of the sphere. The disagreement between the measurements of Carty (B.S. thesis, Massachusetts Institute of Technology, 1957) and the theory of Goldman et al. [Chem. Eng. Sci. 22, 637 (1967)] is explained.

Effects of particle surface roughness on particle interactions in concentrated suspensions

On determine l'importance relative des effets hydrodynamiques et de surface dans les mouvements et les interactions des particules dans des suspensions fortement concentrees

Scattering and depolarization of linearly polarized waves by finitely conducting particles of irregular shape

In this work a layer consisting of a large variety of randomly distributed finitely conducting particles with irregular shapes is assumed to be excited at infrared and optical frequencies by a linearly polarized wave. The resulting incoherent specific intensities, as well as the copolarized and cross polarized intensities, are evaluated. Both single scatter and multiple scatter results are presented for particles with smooth and rough surfaces, and the effects of particle surface roughness on the degree of polarization are considered in detail.

Effect of Particle Surface Roughness on Mechanical Impedance of Coarse‐Textured Soil Materials

AbstractPacking energy required to increase bulk density in coarse‐textured soils is influenced by particle surface roughness, i.e., by interparticle friction. It was, therefore, hypothesized that particle surface roughness would influence soil resistance to movement of a cone penetrometer, because soil bulk density is increased in the zone surrounding the penetrometer tip during its advance. The cone index (C.I.) was calculated for all penetrometer measurements, and C.I. was compared in both disturbed and undisturbed coarse‐textured soil material, with each soil having a unique particle surface roughness as determined by the dense soil angle of repose measurement. For soil materials with similar particle size distributions and bulk densities, C.I. increased as particle surface roughness increased.The role of particle surface roughness in tillage pan formation and in root growth restriction is discussed. It is suggested that, due to poorer aeration during rainy periods and higher mechanical resistance during drier conditions, tillage pans formed in soil materials having smoother‐surfaced particles will be more restrictive to root growth compared to those pans formed in soil materials having rougher‐surfaced particles. Consequently, among soils having root‐restricting tillage pans, the greater enhancement of rooting depth due to subsoiling would likely occur on soils with smooth particles compared to soils with rough soil particles.

Effect of Particle Surface Roughness on Densification of Coarse‐Textured Soil

AbstractIt has been observed that soils on the Atlantic Coastal Plain compact to different bulk densities under the same compactive effort. It is hypothesized that densification differences observed among Ap horizon materials of these soils are partially due to variations in soil particle surface roughness. Surface roughness of Coastal Plain soil materials and sand size fractions derived from these materials were photographed and/or characterized by measuring the dense soil angle of response (DSAR) over a range of bulk densities. Altering the particle size distribution of a given material did not significantly influence the DSAR vs. Db (soil bulk density) relationship; the slopes and intercepts of these linear plots were not statistically different. However, plots of DSAR vs. Db for materials with different particle surface roughness had similar slopes, but different intercepts. It is proposed that the intercept of the DSAR vs. Db curve, or the value of DSAR at a given Db, be used to characterize soil particle roughness for coarse‐textured materials.It was further hypothesized that the DSAR at a given Db was directly related to particle packing arrangement stability, or resistance to further densification, of the soil material. To test this hypothesis, different levels of vibrational energy were applied to materials with different particle roughness but similar particle size distributions. Soil materials with the smoothest particles, i.e., those with the lowest DSAR at each Db, consistently produced the highest Db at each vibrational energy level.