Effect of particle morphology and surface roughness on the flow behaviour of cementitious blends

The influence of particle shape and surface roughness on the hydraulic mean radius are investigated, and quantitative measures for each are proposed. A particle shape factor is estimated with the aid of a new mathematical approximation for the surface area of an ellipsoid. The particle surface roughness is calculated based on inferences made from surface area data previously obtained for a sample of rocks described in Garga et al. (1991). The effect of surface roughness on the hydraulic mean radius was found to be greater than that of shape for this sample of crusher-run quarried limestone. A diagram is presented to show the relative importance particle shape and surface roughness.

Inconsistent experimental findings in the literature regarding the influence of particle size on small-strain shear modulus (Gmax) highlight the need for deeper mechanical insights. A series of resonant column tests was conducted on glass beads and silica sands to investigate the effects of particle size on Gmax considering various particle surface roughness. Results indicate that Gmax decreases with increasing particle surface roughness (Sq) and decreasing mean particle size (d50) under otherwise similar conditions. There is a unified correlation between Gmax and Sq/d50 when the effects of gradation and particle shape are properly considered, showing that Gmax initially decreases with increasing Sq/d50, but then stabilises for a given confining pressure and void ratio. This study further confirmed the combined effects of particle size and surface roughness on Gmax through a semi-analytical analysis. These results suggest that the inconsistent findings regarding the effects of particle size on Gmax may be related to the neglect of particle surface roughness.

Particle shape irregularity is a notable feature of granular materials that exerts a profound influence on their mechanical behavior. This study examines the effects of particle overall regularity and surface roughness on the fabric evolution of granular materials using the Discrete Element Method (DEM). By connecting multiple spheres with varying sizes and positions, a diversity of clump particles characterized by distinct overall regularity () and surface roughness () are generated. A series of DEM simulations on drained triaxial compression tests have then been performed on granular assemblies with varying shapes, whereby their characteristics of contact intensity and the anisotropy of various fabric entities defined by contact normal, branch vector, and particle orientation, have been thoroughly investigated. The results show that increasing particle shape irregularity, indicated by smaller values of and , is generally associated with an enhanced internal structure within the granular assembly, exhibiting a higher mechanical coordination number and a greater fabric anisotropy. Conversely, in granular assemblies with relatively high overall regularity, the fabric anisotropy is notably reduced, and this reduction cannot be compensated by enhancements in particle surface roughness. The evolution of two contact‐related fabric anisotropies is analyzed in relation to particle orientation‐based fabric anisotropy, which is more profoundly influenced by particle overall regularity, underscoring its significant role in fabric evolution of granular materials.

Particle morphology of pharmaceutical solids has practical importance for several reasons. In particular, surface roughness can influence formulation development and pharmaceutical performance for a wide range of delivery types including oral tablets and dry powder formulations for inhalation. For instance, the surface roughness can influence dissolution, friability, and adhesion of coatings and films for bare tablets (1–5). To illustrate, surface roughness correlated strongly with tablet friability for erythromycin acistrate tablets (3). The surface roughness has also been related to gloss and permeability, such that the reflectivity and surface texture of coated tablets were directly correlated (6,7). The surface roughness of particles also has been correlated to powder flow and powder packing (8), where the smoother particles led to an improvement of powder packing and flow properties. The adhesion of particles to surfaces or other particles can also be greatly affected by surface roughness. This is of particular concern for dry powder inhalation (DPI) formulation development. Dry powder formulations are often composed of small drug particles and inert larger carrier particles. Interactions between these particles can be dominated by physico-chemical properties of the particle, such as size, shape, morphology, contact area, and hygroscopicity (9,10). In particular, it has been shown that the surface roughness of the carrier particles has a significant impact on the adhesion and friction forces between the carrier and drug particles (11,12). Adhesion, blend homogeneity, and stability have been directly related to the surface roughness of the carrier particle (13). The ultimate performance properties of DPI blends as determined by in vitro testing has also been correlated to the primary particle surface roughness (13–15). There is an important balance between the relative scaling in the roughness of the particles and the relative size of the carrier and drug particles when considering the effects of surface roughness on particle–particle adhesion. This was previously described (16) and is illustrated by the schematic in Fig. 1. Assuming no other changes in particle properties (i.e., surface energy, particle size, amorphous content, hygroscopicity, etc.), the rank order of drug-carrier adhesion would obey the following trend in roughness of the larger carrier particle: macro-rough surface (Fig. 1a) > smooth surface (Fig. 1b) > micro-rough surface (Fig. 1c). This trend is strictly dependent on the contact area between drug and carrier. If adhesion is too weak, the active drug may be released during inhalation before the particles reach the deep lung. On the contrary, if adhesion is too strong, the active may not be released at all. This phenomenon has been observed and described in detail for several DPI studies (15–19). Fig. 1 Illustration of macro-roughness (a), smooth surface (b), and micro-roughness (c) affects on particle–particle contact and adhesion In this study, we focus on the measurement of micro-scale roughness using fractal dimensions determined from sorption isotherms with different adsorbates.

The simplified ray-tracing technique reported in Part I of this paper is employed to compute the single-scattering properties of hexagonal columns with maximum dimensions ranging from 2 to 3500 mum with a size-bin resolution of 2 mum at wavelengths of 0.86 and 2.13 mum. For small ice crystals, the current treatment of surface roughness may not be adequate because the applicability of the principles of geometric optics breaks down for small roughness scale. However, for ice crystals smaller than 40 mum, the aspect ratios of these particles are close to one, and the effect of surface roughness is quite small. In this paper, the diffraction is accounted for in the same way as in the case of smooth particles. It is essentially unfeasible to incorporate the effect of surface roughness into the numerical computation of the diffraction contribution. The scattering properties of individual ice crystals are then averaged over 18 particle size distributions whose effective particle radii (re) range from 5 to 90 mum. The single-scattering properties of ice clouds are strongly sensitive to surface roughness condition. Lookup tables that are built for the correlation between the bidirectional reflectances at wavelengths of 0.86 and 2.13 mum with different roughness conditions are used to retrieve ice cloud optical thickness and effective particle size over oceans. Pronounced differences are noticed for the retrieved cirrus cloud optical thickness and effective particle sizes in conjunction with different surface roughness conditions. The values of the retrieved cirrus cloud optical thickness in the case of the rough surface are generally smaller than their counterparts associated with smooth surface conditions. The effect of surface roughness on the retrieved effective particle radii is not pronounced for slight and moderate roughness conditions. However, when the surfaces of ice crystals are substantially rough, the retrieved effective radii associated with roughened particles are larger and smaller than their smooth surface counterparts forlarge (re>50 mum) and small (re<35 mum) ice crystals, respectively, whereas the effect of surface roughness on the retrieved effective radii shows a nonmonotonic feature for moderate particle sizes (35 mum<re<50 mum). In general, the dominant effect of surface roughness on cloud property retrievals is to decrease the retrieved optical thickness and to increase the retrieved effective particle size in comparison with their counterparts in the case of smooth ice particles.

The influence of particle size, shape, and particle surface roughness of lactose monohydrate carrier particles on the adhesion properties of drug particles in interactive powder mixtures similar in quality of a commercial product (Serevent Diskhaler®) has been investigated. None of the ten lactose monohydrate batches tested was found to be similar in terms of particle size. To obtain more information about particle shape and surface roughness, mathematical analysis was undertaken to structure the data. The lactose monohydrate batches could be split into four different types of particle shape. In terms of particle surface roughness, as measured by a laser profilometer, three different roughness categories were identified. Two sets of mixtures were prepared to relate the physical properties of the lactose monohydrate particles to the adhesion properties of the drug formulations: (a) constant mixing time and speed (25 min, 42 rpm), and (b) optimal mixing time (speed 42 rpm) to match the adhesion properties of the Serevent Diskhaler®. All ten lactose monohydrate batches provided different adhesion properties under test condition (a) and the optimum mixing time [test condition (b)] was also different for each batch. Multivariate data analysis showed that the adhesion force between drug and lactose monohydrate increases with a decrease in particle size and for more irregularly shaped, elongated carrier particles. The effect of surface roughness could only be qualitatively assessed and thus no definitive conclusions can be drawn to judge whether adhesion will increase or decrease as surface roughness changes.

A core is formed at the center of a quasi-two-dimensional rotating drum filled more than half with granular material. The core rotates slightly faster than the drum (precession) and decreases in radius over time (erosion) due to the granular creeping motion that occurs below the freely flowing layer. This paper focuses on the effect of the surface roughness of particles on core dynamics, core precession, and core erosion. Two different surface roughness of glass particles having the same diameter were used in the experiments. The surface structures of the particles were quantitatively compared by measuring the coefficients of friction and using a simple image contrast method. The experiments were performed with five different filling levels in a 50-cm-diameter rotating drum. According to the results, core precession and core erosion are both dependent on the particle surface roughness. Core precession becomes weaker and erosion becomes stronger when using particles having a rough surface in the experiments. To explain the physics of core dynamics, the particles' surface roughness effect on the freely flowing layer and the creeping motion region were also investigated. The granular bed velocity field, maximum flowing layer depth δ, shear rate in the flowing layer γ[over ̇], and the creeping region decay constant y_{0} were also calculated in this paper. The effect of the particles' surface roughness on these physical variables well illustrates the physics of core dynamics and creeping granular motion.

Effect of surface roughness on particle-bubble interaction: A critical review

To investigate the effects of solid particles on the point contact mixed lubrication, this paper aims to introduce solid particles into rough interfaces under mixed hydrodynamic lubrication. Statistical three-body micro-contact is utilized in modeling mixed EHL. The model is verified by comparing results without considering particles and roughness with those from classical EHL formula. Factors, such as particle physical parameters, surface roughness and operating condition acting on the system are discussed. The results show that the distribution of hydrodynamic pressure and oil film thickness on the point contact with particles still show typical characteristics of elastohydrodynamic lubrication. The physical parameters of particles and operating condition change the proportion of each part to the load carrying capacity, where an increase in particle size, concentration and surface orientation parameters increases the load ratio of particle and conversely an increase in surface roughness and sliding velocity decreases it. Both an increase in particle size and surface roughness result in an increase in the minimum oil film thickness, with the effect of surface roughness being more significant. In addition, the shear strength, size and concentration of the particles play an important role in the friction characteristics.

Forces between colloidal particles determine the performances of many industrial processes and products. Colloidal force measurements conducted between a colloidal particle AFM probe and particles immobilized on a flat substrate are valuable in selecting appropriate surfactants for colloidal stabilization. One of the features of inorganic fillers and extenders is the prevalence of rough surfaces-even the polymer latex particles, often used as model colloidal systems including the current study, have rough surfaces albeit at a much smaller scale. Surface roughness is frequently cited as the reason for disparity between experimental observations and theoretical treatment but seldom verified by direct evidence. This work reports the effect of nanoscale surface roughness on colloidal force measurements carried out in the presence of surfactants. We applied a heating method to reduce the mean surface roughness of commercial latex particles from 30 to 1 nm. We conducted force measurements using the two types of particles at various salt and surfactant concentrations. The surfactants used were pentaethylene glycol monododecyl ether, Pluronic F108, and a styrene/acrylic copolymer, Joncryl 60. In the absence of the surfactant, nanometer surface roughness affects colloidal forces only in high salt conditions when the Debye length becomes smaller than the surface roughness. The adhesion is stronger between colloids with higher surface roughness and requires a higher surfactant concentration to be eliminated. The effect of surface roughness on colloidal forces was also investigated as a function of the adsorbed surfactant layer structure characterized by AFM indentation and dynamic light scattering. We found that when the layer thickness exceeds the surface roughness, the colloidal adhesion is less influenced by surfactant concentration variation. This study demonstrates that surface roughness at the nanoscale can influence colloidal forces significantly and should be taken into account in colloidal dispersion formulations.

The influence of particle shape, size, and surface roughness on the strength of granular materials has been the subject of much discussion in the fields of soil mechanics and asphalt paving technology. A number of investigations have been conducted to determine the effect of variations in particle size and shape, but the results of these investigations have been somewhat varied and have led to conflicting conclusions; and although the effect of surface roughness has been the subject of much discussion, very few data are available to demonstrate its influence. This paper presents the results of a laboratory investigation to provide further evidence of the influence of these factors in the hope that the results might serve to clarify some of the controversial aspects of their effects.

Micro-particle adhesion, detachment and resuspension from surfaces have attracted considerable attention due to their numerous applications in semiconductor, xerographic, and pharmaceutical industries, and, more recently, in understanding indoor air quality. However, most earlier studies have focused on idealized spherical particles and smooth surfaces, and the effects of particle irregularities and surface roughness on the rate of particle removal and resuspension are not well understood. In this work, a Monte Carlo simulation of particle resuspension from a surface under turbulent flow conditions was developed and resuspension of nearly spherical and irregular shaped particles with rough surfaces from substrates under turbulent flow condition was studied. Following our earlier approach, compact irregular shaped particles were modeled as spherical particles with a number of hemispherical bumps. It was assumed that the bump surfaces also have fine roughness. The extended Johnson-Kendall-Roberts (JKR) adhesion theory for rough surfaces was used to model the particle adhesion and detachment. A number of assumptions were made to apply the model. It was assumed that the particles have a Gaussian size distribution. The number of bumps of the irregular particles and surface roughness values of particle are assumed to be random, respectively, with Poisson and log-normal distributions. For particle detachment from the surface, the theory of critical moment was used. The effects of particle size, turbulent flow, particle irregularity and surface roughness on particle detachment and resuspension were studied for different cases. The Monte Carlo model predictions show probabilistic distributions of the particle resuspension. The simulation results are compared with the available experimental data and good agreement was found. The study provided information on the random nature of particle resuspension due to the randomness in the airflow, particle size distribution and surface roughness.

Effects of surface roughness in multiple microchannels on mixed convective heat transfer

Considering the effects of surface roughness and slip flow, the extended Reynolds equation presented by Makino et al [1] is used to set up the finite element model for a non-contact spiral groove dry gas face seal (S-DGS). The analyses for a typical S-DGS at low speed (≤ 500 rpm) and low pressure (≤ 0.606 MPa) showed that the effect of slip flow on the sealing performance is significant for 0.05≤ Kn &lt; 1.0, where Kn refers to the Knudsen number, but the effect of surface roughness on the sealing performance varies with the different areas of both the two faces. When the standard deviation of composite roughness is less than 1.0 micron and in the range of 0.5≤ Kn≤ 1.0, the effects of surface roughness and slip flow diminished on gas film stiffness and frictional work but are still significant on the leakage rate. The effect of surface roughness of the spiral groove bottom is significant and should be considered, but the effects of the other surface roughness, i.e. the soft ring surface roughness and the un-grooved hard ring surface roughness, are negligible only when the value of the standard deviation of composite roughness meets with API standards.

In this study, we evaluate the effect of the surface roughness on estimation of the relative soil moisture change in repeat-pass L-band radar measurements. It has found the surface roughness has a significant impact and a correction technique has been developed. I. INTRODUCTION During recent years, theoretical modeling and field experiments have established the fundamentals of active microwave remote sensing as an important tool in determining physical properties of soil. In attempt to use active microwave remote sensors in estimation of soil moisture, we are mainly facing two major problems: effects of surface roughness and vegetation cover. There are several algorithms developed for measurement of bare soil moisture quantitatively using dual or three polarization L-band SAR image data. A common idea beyond these algorithms is to separate the effects of the surface dielectric and roughness properties on the backscattering signals to present the model, which the inversion was based on, as a product of a dielectric function and a roughness function. They are first-order statistical inversion models. Depending on the data source, the selection of the surface roughness parameters and the backscattering measurements of the different polarizations or their linear combinations, the models have a great difference in terms of both the dielectric and roughness functions. The temporal variability of surface roughness is generally at much longer time scale than that of soil moisture, unless there was a human activity. Commonly, we can reasonably assume that the surface roughness is same at certain time interval. The change in SAR measurements between the repeat-passes, therefore, is resulted from the change of ground dielectric properties or soil moisture. Therefore, the repeat-pass measurements provide additional relative surface soil moisture change information and make it possible to directly estimate the relative moisture change and improving the accuracy of estimating the bare surface soil moisture. However, there has no quantitative algorithm being developed to estimate the relative soil moisture change using repeat-pass measurements. In this study, we evaluate 1) the effects of surface roughness in L-band repeat-pass measurements using IEM simulated data, 2) developing a quantitative algorithm to estimate relative soil moisture change, and 3) validating this technique with JPL/AIRSAR 92's experiment data over the little Washita test site.