Surfaces Of Different Roughness Research Articles

A systematic evaluation of DEM input parameters measurement and calibration

Rotary drums are widely used in industry, however, determining granular dynamics within them is still a complex task, thus remaining a focal point of research over the years. In this context, experimental techniques require numerical support to obtain data that is not easily acquired experimentally. One well-established numerical technique for studying particulate systems is the Lagrangian approach embed with Discrete Element Method (DEM). Although, DEM has limitations related to the definition of input parameters. It is crucial that DEM input parameters be measured and/or calibrated to reliably represent the granular behavior. These parameters are related to particle properties such as density, Young’s modulus, Poisson’s ratio, among others, and particle interactions, such as coefficients of restitution, static friction, and rolling friction. This study explores the experimental determination of interaction parameters preceding the acquisition of DEM input parameters in a rotary drum. Statistical analysis highlights the importance of each parameter and their combined interactions with the static angle of repose. The granular materials used were: soybeans, glass beads, polyacetal, 6 mm steel, and 4 mm steel. The coefficient of restitution was determined via free-fall methodology using equipment that verifies particle trajectory, static friction coefficient through equilibrium between weight and resistance forces, rolling friction coefficient using a launching device on surfaces of different roughness, and static angle of repose in a rectangular box with sections where particles rested. After removing the partition, angles were measured at both top and bottom sections. Regression techniques using a neural network created in Python were employed for both measurements. Experimental investigations and numerical simulations using DEM indicated that the coefficient of restitution depends on the thickness and type of material of the flat surfaces, showing an asymptotic behavior with increasing surface thickness. The static friction coefficient increased on rougher surfaces and in particles with greater imperfections. Rolling friction coefficient also increased on rough surfaces. Analysis of the angle of repose revealed that granular properties influence the response, such as static and rolling friction coefficients, whereas the coefficient of restitution had no significant influence. Neural network correlation coefficients exceeded 0.95, indicating a strong association between the variables. Our findings revealed that mathematical models can be used in conjunction with static repose angle experiments to calibrate DEM parameters for more robust and complex simulations. This research also quantifies and provides insights into the interactions between DEM parameters in direct measurement experiments, promoting more efficient calibration for future research.

Estimation of Multiple Contact Conductances in a Silicon-Indium-Silicon Stack

Abstract This report documents evaluation of simultaneous estimation of multiple interfacial heat transfer coefficients (HTCs) using transient measurements from an experiment designed for steady-state operation. The design of a mirror system for directing X-rays under cryogenic conditions requires knowledge of the interfacial HTC (contact conductance) between silicon and indium. An experimental apparatus was constructed to measure temperatures in a stack of five 7.62-mm thick pucks of silicon separated by 0.1-mm thick sheets of indium, which is operated under cryogenic temperatures in vacuum. Multiple pucks and interfaces are incorporated into the apparatus to allow evaluation of HTCs for surfaces of different roughness from a single experiment. Analysis of the sensitivity of each of the measured temperatures to each of the unknown HTCs reveals lack of linear independence of these sensitivities and suggests the recovery of the HTCs will be challenging. Artificially noised “data” were created from two different computational models by solving for temperatures and adding random Gaussian noise with a specified standard deviation. These data are subsequently analyzed using two different iterative parameter estimation methods: a Levenberg scheme and a Tikhonov iterative scheme. The required sensitivity matrix is computed using forward finite difference approximations. The results for the heat transfer coefficients for this model problem suggest that coefficients cannot be estimated independently, but the ratios relative to one of the unknowns can be recovered.

Mechanochemical Formation of Poly(melamine-formaldehyde) Microplastic Fibers During Abrasion of Cleaning Sponges.

The abrasion of synthetic textile fibers is a significant factor in the generation of environmental microplastic fibers (MPFs). The extent to which polymer sponges designed specifically for surface cleaning have a tendency to release MPFs during normal use remains unknown. Here, the tribological behaviors of melamine cleaning sponges (also known as "magic erasers") with different strut densities against metal surfaces of different roughness were investigated using a reciprocating abrader. The MPFs formed by sponge wear under various conditions were characterized in terms of their morphology, composition, and quantity. They were mainly composed of poly(melamine-formaldehyde) polymer with linear or branched fiber morphologies (10-405 μm in length), which were formed through deformation and fracture of the struts within open cells of the sponges, facilitated by friction-induced polymer decomposition. The rate and capability of MPF production generally increased with increasing roughness of the metal surface and density of the struts, respectively. The sponge wear could release 6.5 million MPFs/g, which could suggest a global overall emission of 4.9 trillion MPFs due to sponge consumption. Our study reveals a hitherto unrecognized source of the environmental MPF contamination and highlights the need to evaluate exposure risks associated with these new forms of MPFs.

Study on Strength of Slip Soil–Tuff Contact Surfaces in Tuff Landslide Based on Model Test

In the exploration tunnels of the Xiageliao landslide, slide failures were found not only inside the slip soil but also on the contact surface between the slip soil and the tuff. The undisturbed slip soil was collected from the exploration tunnel for testing to explore the pattern of slide failure occurrence. The surfaces of concrete blocks of different shapes were used to simulate slip soil–tuff contact surfaces of different roughness. The shear strength of these contact surfaces with different roughness was tested using a large-scale shear test system and analyzed through comparison with the shear strength of the slip soil. The test results showed that the interface roughness significantly affected the shear strength of the slip soil contact interface and determined the shear failure mode of the slip soil. When the roughness is below a certain level, the shear strength of the contact surface is less than the soil shear strength, and when the roughness reaches a certain level, the shear strength of the contact surface exceeds the strength of the slip soil itself. Thus, the strength of the slip soil itself sometimes differs from the strength of the slip surface. Based on the Moore–Cullen law, the test results found a formula for calculating the contact surface shear strength. These results provide some references for the risk evaluation of landslides.

Surface roughness discrimination with the long cane: Effects of cane tips, handle, shaft rigidity, and swinging speed

This study examined the effects of cane tip type, cane tip size, cane shaft rigidity, cane handle material, and cane swing speed on the cane user’s ability to discriminate surfaces of different roughness. A repeated-measures design with block randomization was used for each of the three studies. Blindfolded sighted and visually impaired participants attempted to identify which of the two grooved aluminum plates was rougher by swiping the plates using different cane tips, shafts, handles, and swing speeds. Participants correctly identified the rougher plate at a higher percentage with smaller cane tips (77.6% ± 8.7%) than with larger cane tips (72.1% ± 7.2%), p = .029, r = .54. Pencil tips (76.9% ± 8.4%) were more advantageous than ball tips (72.8% ± 6.5%), p = .028, r = .55. Slower cane swing speed (84.4% ± 2.6%) also allowed the participants to better discriminate the surfaces than faster swing speed (76.6% ± 6.0%), p = .002, r = .80. However, the cane shaft rigidity ( p = .499, r = .22) and cane handle material ( p = .694. w2 = 0.02) did not have a significant effect on the cane user’s ability to discriminate the surfaces of different roughness. Given these findings, a cane user may want to use a smaller and/or cylindrical cane tip as opposed to larger and/or spherical cane tip for better surface texture change detection. In addition, a cane user may not want to swing the cane too wide or walk too fast since wider cane swing and faster walking speed tend to result in faster cane swing speed, which can compromise one’s ability to detect sudden changes in walking surface texture. That being said, an Orientation and Mobility (O&M) specialist should assess each person’s traveling environment when determining which cane tip and swing speed to use in a given situation.

Influence of TiN Coating on the Drawing Force and Friction Coefficient in the Deep Drawing Process of AlMg4.5Mn0.7 Thin Sheets.

The influence of various process parameters on the deep drawing process is a current research topic in sheet metal forming technology. Starting from the application of the previously constructed original testing device, an original tribological model was developed based on the process of sheet metal strip sliding between flat contact surfaces under variable pressures. A complex experiment was executed using an Al alloy sheet, tool contact surfaces of different roughness, two types of lubricants and variable contact pressures. The procedure included analytically pre-defined contact pressure functions based on which, for each of the mentioned conditions, the dependencies of the drawing forces and friction coefficients were obtained. The pressure in function P1 constantly decreased from a high initial value until the minimum, while in function P3 the pressure increased until the minimum value at the halfway point of the stroke, after which it increased up to the initial value. On the other hand, the pressure in function P2 constantly increased from the initial minimum value until the maximum value, while in function P4 the pressure increased until reaching the maximum value at the halfway point of the stroke, after which it decreased to the minimum value. This enabled the determination of the influence of tribological factors on the process parameters of intensity of traction (deformation force) and coefficient of friction. The pressure functions starting with decreasing trends produced higher values for the traction forces and the friction coefficient. In addition, it was established that the roughness of the contact surfaces of the tool, especially those with titanium nitride coating, has a significant influence on the process parameters. For surfaces of lower roughness (polished), a tendency of the Al thin sheet to form a glued-on layer was noticed. This was especially prominent for lubrication with MoS2-based grease under conditions of high contact pressure (functions P1 and P4 at the beginning of the contact).

Biological response of epithelial and connective tissue cells to titanium surfaces with different ranges of roughness: An in-vitro study.

This study aimed to investigate how titanium (Ti) surface with different range roughness created by industrial machining influence the biological response of primary human gingival fibroblasts (HGFB) and keratinocytes (HGKC) in terms of cell proliferation and cytotoxicity. Four Ti surfaces of different roughness ranges were investigated: smooth (S: 0.08-0.1µm), minimally rough (MM: 0.3-0.5µm), moderately rough (MR: 1.2-1.4µm) and rough (R: 3.3-3.7µm). Discs topography and surface roughness were evaluated by scanning electron microscopy (SEM) and non-contact profilometer. Both cell lines were cultured, expanded, and maintained according to their supplier's protocols. Cell proliferation and cytotoxicity were evaluated at days 1, 3, 5, and 10 using cell viability and cytotoxicity colorimetric assays. Data were analysed via two-way ANOVA, one-way ANOVA and Tukey's post hoc test (p=0.05 for all tests). Both cell lines showed comparable initial proliferation activity of 70-86% for all the investigated roughnesses. HGKC showed better and higher proliferation % with S surface at all time points than all the other investigated surfaces which was significantly higher than MM at day 3 and higher than all the other investigated surfaces at day 5 and 10. On the other hand, HGFB exhibited the best proliferation with both MM and R surfaces with no significant differences from the other two surfaces (S and MR). Different surface roughnesses and exposure times showed significant effect on cell proliferation in both cell lines. Cytotoxicity for both cell lines was generally the highest on day 3, with the following order from highest to lowest: S (19.86%)>R>MR>MM for HGKC and MM (39.48%)>MR>S>R for HGFB. Different exposure times showed a significant effect on cell cytotoxicity in both cell lines and a significant effect of surface roughness in HGFB. All investigated roughness levels were sufficiently biologically compatible with cells representative of the major population of the soft tissue surrounding dental implants. However, the S surface was most cytotoxic to HGKC, while the MM surface was most cytotoxic to HGFB cells.

Runup of breaking solitary waves on rough uniform slopes

An experiment consisting of 122 tests was conducted for breaking solitary waves on rough and smooth slopes. The constant water depth and the incident wave height were varied to cover a wide range of solitary wave nonlinearity, i.e., from 0.039 to 0.458. Free surface elevations, velocities and maximum runup heights were measured for four slope surfaces of different roughness. A surf similarity parameter proposed previously for smooth slopes was used to analyze the runup data on rough slopes. A reduction factor was introduced to compare the runup heights of breaking solitary waves on rough and smooth slopes and to unify the runup formula for smooth and rough slopes. The fitted reduction factor for each of the rough surfaces was less than unity (smooth slope) and in the range of 0.48–0.88. Existing runup formulas are used to confirm the accuracy and applicability of runup height predictions. The measured free surface elevations and velocities were analyzed to quantify the roughness effect on solitary wave runup. Laboratory observations reveal that the slope roughness noticeably influences the hydrodynamics in the surf and swash zones.

Adhesion-cohesion balance of prepreg tack in thermoset automated fiber placement. Part 1: Adhesion and surface wetting

The constitution of prepreg tack in automated fiber placement (AFP) is affected by a sensitive balance between adhesive interfacial bond strength and cohesive strength of the prepreg resin. In an effort to explore the role of interfacial liquid-solid interaction on the tack of commercial aerospace-grade epoxy prepreg, a surface wetting analysis was performed on AFP-related substrates. The standard test liquid combination water/diiodmethane and extracted neat epoxy resin were used for contact angle measurement employing the sessile drop method and the Owens-Wendt-Rabel-Kaelble (OWRK) model. Additional rheological and topographical analyses were carried out to account for viscous resin flow on surfaces of different roughness. The results from the material characterization are discussed against the background of tack measurement by probe tack testing utilizing a rheometer. Significant differences between the investigated surfaces in terms of both the maximum tack level and the onset temperatures of adhesion were found as a function of test parameters relevant for contact formation. General agreement with the experimental tack results was observed employing a topographically extended version of the Dahlquist criterion. For each substrate, a temperature-dependent critical storage modulus could be determined that conforms to the onset temperature of tackiness. Contact angle measurements revealed a correlation between the thermodynamic work of adhesion and maximum tack and, moreover, the tack onset in the adhesive regime when additionally incorporating surface topography. Matching ratios of polar and dispersive surface free energy and surface tension components were found to favor the molecular interaction at the interface between prepreg resin and substrate.

Study of Low Terahertz Radar Signal Backscattering for Surface Identification

This study explores the scattering of signals within the mm and low Terahertz frequency range, represented by frequencies 79 GHz, 150 GHz, 300 GHz, and 670 GHz, from surfaces with different roughness, to demonstrate advantages of low THz radar for surface discrimination for automotive sensing. The responses of four test surfaces of different roughness were measured and their normalized radar cross sections were estimated as a function of grazing angle and polarization. The Fraunhofer criterion was used as a guideline for determining the type of backscattering (specular and diffuse). The proposed experimental technique provides high accuracy of backscattering coefficient measurement depending on the frequency of the signal, polarization, and grazing angle. An empirical scattering model was used to provide a reference. To compare theoretical and experimental results of the signal scattering on test surfaces, the permittivity of sandpaper has been measured using time-domain spectroscopy. It was shown that the empirical methods for diffuse radar signal scattering developed for lower radar frequencies can be extended for the low THz range with sufficient accuracy. The results obtained will provide reference information for creating remote surface identification systems for automotive use, which will be of particular advantage in surface classification, object classification, and path determination in autonomous automotive vehicle operation.

Assessment of implant surface and instrument insert changes due to instrumentation with different tips for ultrasonic-driven debridement

BackgroundTo assess the changes of implant surfaces of different roughness after instrumentation with ultrasonic-driven scaler tips of different materials.MethodsExperiments were performed on two moderately rough surfaces (I—Inicell® and II—SLA®), one surface without pre-treatment (III) and one smooth machined surface (IV). Scaler tips made of steel (A), PEEK (B), titanium (C), carbon (D) and resin (E) were used for instrumentation with a standardized pressure of 100 g for ten seconds and under continuous automatic motion. Each combination of scaler tip and implant surface was performed three times on 8 titanium discs. After instrumentation roughness was assessed by profilometry, morphological changes were assessed by scanning electron microscopy, and element distribution on the utmost surface by energy dispersive X-ray spectroscopy.ResultsThe surface roughness of discs I and II were significantly reduced by instrumentation with all tips except E. For disc III and IV roughness was enhanced by tip A and C and, only for IV, by tip D. Instrumentation with tips B, D and E left extensive residuals on surface I, II and III. The element analysis of these deposits proved consistent with the elemental composition of the respective tip materials.ConclusionAll ultrasonic instruments led to microscopic alterations of all types of implants surfaces assessed in the present study. The least change of implant surfaces might result from resin or carbon tips on machined surfaces.

Impact of Surface Roughness on Crystal Nucleation

We examine the effect of rough surfaces on crystal nucleation by means of kinetic Monte Carlo simulations. Our work makes use of three-dimensional kMC models, explicit representation of transport in solution and rough surfaces modeled as randomly varying height fluctuations (roughness) with exponentially decaying correlation length (topology). We use Forward-Flux Sampling to determine the nucleation rate for crystallization for surfaces of different roughness and topology and show that the effect on crystallization is a complex interplay between the two. For surfaces with low roughness, small clusters form on the surface but as clusters become larger they are increasingly likely to be found in the bulk solution while rougher surfaces eventually favor heterogeneous nucleation on the surface. In both cases, the rough surface raises the local supersaturation in the solution thus leading to another mechanism of enhanced nucleation rate.

Introduction of a New In-Situ Measurement System for the Study of Touch-Feel Relevant Surface Properties.

The touch-feel sensation of product surfaces arouses growing interest in various industry branches. To entangle the underlying physical and material parameters responsible for a specific touch-feel sensation, a new measurement system has been developed. This system aims to record the prime physical interaction parameters at a time, which is considered a necessary prerequisite for a successful physical description of the haptic sensation. The measurement setup enables one to measure the dynamic coefficient of friction, the macroscopic contact area of smooth and rough surfaces, the angle enclosed between the human finger and the soft-touch surfaces and the vibrations induced in the human finger during relative motion at a time. To validate the measurement stand, a test series has been conducted on two soft-touch surfaces of different roughness. While the individual results agree well with the literature, their combination revealed new insights. Finally, the investigation of the haptics of polymer coatings with the presented measuring system should facilitate the design of surfaces with tailor-made touch-feel properties.

Study on laser-stricken damage to alumina ceramic layer of different surface roughness

This study examines the laser-stricken damage to different alumina ceramic surfaces of different roughness through multi-physical field coupling simulations and laser-striking experiments. The surfaces of different morphologies can be described by waves of different frequencies and amplitudes, and the waves which are discretized can be described by rectangular microstructures of different heights. In this paper, we found that the reaction of roughness surfaces to gauss lasers stricken on them could be simulated by the reaction of rectangular microstructures of different heights to laser strike. The simulation was carried out through the multi-physical field coupling method. The distribution of temperature and stress on rectangular microstructure were examined after being treated by high energy laser. It was found that overhigh temperature and stress were the main causes of laser-stricken damage, but there existed a critical rectangular column height value. The microstructure became increasingly prone to damage and fall-off with the increase of the rectangular column’s height, but it became decreasingly prone to damage after the rectangular column reached the critical value. In the experiments, seven roughness zones of alumina ceramic layer were chosen as sample surfaces for laser-striking experiment. The results showed that there was a critical roughness value at a fixed laser energy density. As a result, the amount of particles falling off the surfaces caused by laser strike was rising when the roughness was increasing. However, the amount of particles falling off the surfaces was decreasing after roughness reached the critical value. The critical rectangular column height value in the simulation corresponded to the critical roughness value in the experiment. Therefore, an appropriate selection of roughness is an important factor for obtaining high laser-stricken damage threshold.

Surface and thickness effect on the ferroelectric, dielectric and pyroelectric properties of Mn-doped Pb(Mg1/3Nb2/3)O3–0.28PbTiO3 single crystals

Ferroelectric, dielectric and pyroelectric properties of Mn-doped Pb(Mg1/3Nb2/3)O3–0.28PbTiO3 (PMN-0.28 PT) single crystals has been investigated with surfaces of different roughness, and thickness in the range of 487–16 μm. The crystals were grown by modified Bridgman method and treated by mechanical lapping and chemical mechanical polishing (CMP) for different thickness and surface. The experimental results indicate that the lapping process deteriorates the ferroelectric, dielectric, and pyroelectric performances by introducing domain reorientation and damage into the surface, which can be substantially reduced by polishing process. The surface state exhibits greater impact on the ferroelectric, dielectric and pyroelectric performances when the sample thickness becomes smaller. By lapping, the 109° and 71° domain reorientation occurs along with the generation of non-ferroelectric damage layer, the surface stress and defects.

Attachment Beyond the Adhesive System: The Contribution of Claws to Gecko Clinging and Locomotion.

Attachment is imperative for many biological functions, such as holding position and climbing, but can be challenged by natural conditions. Adhesive toe pads and claws have evolved in multiple terrestrial lineages as important dynamic attachment mechanisms, and some clades (e.g., geckos) exhibit both features. The functional relationship of these features that comprise a complex attachment system is not well-understood, particularly within lizards (i.e., if pads and claws are redundant or multifunctional). Geckos exhibit highly adept frictional adhesive toe pads that continue to fuel biological inquiry and inspiration. However, gecko claws (the ancestral lizard clinging condition) have received little attention in terms of their functional or evolutionary significance. We assessed claw function in Thecadactylus rapicauda using assays of clinging performance and locomotor trials on different surfaces (artificial and natural) and inclines with claws intact, then partially removed. Area root mean square height (Sq), a metric of 3D surface roughness, was later quantified for all test surfaces, including acrylic, sandpaper, and two types of leaves (smooth and hairy). Maximum clinging force significantly declined on all non-acrylic surfaces after claw removal, indicating a substantial contribution to static clinging on rough and soft surfaces. With and without claws, clinging force exhibited a negative relationship with Sq. However, claw removal had relatively little impact on locomotor function on surfaces of different roughness at low inclines (≤30°). High static and dynamic safety factor estimates support these observations and demonstrate the species' robust frictional adhesive system. However, maximum station-holding capacity significantly declined on the rough test surface after partial claw removal, showing that geckos rely on their claws to maintain purchase on rough, steeply inclined surfaces. Our results point to a context-dependent complex attachment system within geckos, in which pads dominate on relatively smooth surfaces and claws on relatively rough surfaces, but also that these features function redundantly, possibly synergistically, on surfaces that allow attachment of both the setae and the claw (as in some insects). Our study provides important novel perspectives on gecko attachment, which we hope will spur future functional studies, new evolutionary hypotheses, and biomimetic innovation, along with collaboration and integration of perspectives across disciplines.

Modeling the process of microbial biofilm formation on stainless steel with a different surface roughness

This paper reports a study into the process of bacteria adhesion to surfaces of different roughness depending on sizes and shapes. It was determined that at the surface of stainless steel with a roughness of 2.687±0.014 µm, the film formation process in E. coli and S. aureus occurred equally over 3 to 24 hours and did not depend on the size of bacteria. This makes it possible to argue that rod-shaped and coccal bacteria freely attach themselves in the grooves of roughness, followed by the initial process related to the first stage of a biofilm formation. During sanitization, the hollows of roughness could host both the coccal and rod-shaped bacteria. At the surface of steel with a roughness of 0.95±0.092 μm the process of film formation in S. aureus occurred more intensely than in E. coli. Within 3 h of incubation, density of the formed biofilms S. aureus was 1.2 times larger compared to the biofilms E. coli. Over the following 15 hours of incubation, the biofilms S. aureus were on average 1.3 times denser. This suggests that S. aureus, due to a spherical form, can stay put in the hollows of roughness of 0.95±0.092 µm and quicker attach to the surface. At the same time, E. coli, owing to a rod-shaped shape, would attach at such a surface roughness to the hollows lengthwise only. It has been proven that at a surface roughness of 0.63±0.087 µm the intensity of the S. aureus film formation was on average 1.4 times faster than in E. coli. However, at a roughness of 0.16±0.018 μm the process of film formation occurred equally in E. coli and S. aureus, but the biofilms demonstrated lower density compared to those that formed at a roughness of 0.63±0.087 µm. Thus, the use of equipment with a roughness of less than 0.5 µm in the dairy industry will make it possible to reduce the attachment of microorganisms to surface and to decrease contamination of dairy products

A comparative evaluation of the effectiveness of wipe sampling materials to remove beryllium from differently textured surfaces using zinc oxide as a surrogate

Wipe sampling is a commonly used method for testing a surface for beryllium or other metal particle contamination. Existing wipe sampling methods have only been validated for smooth surfaces. On rough surfaces contaminant particles may be located behind surface projections where they would not be collected by the wipe. This could lead to an underestimate of surface contamination levels. Worker exposure to surfaces contaminated with beryllium could contribute to beryllium sensitization leading to chronic beryllium disease. Likewise, exposure to surfaces contaminated with other toxic metals could have their own health effects. This study investigated the efficiency of collecting 1–5 μm diameter zinc oxide particles by five commercially available wipe materials (SKC Smear Tabs, Whatman® 41 filter paper, Kimtech Prep* ScottPure* Critical Task Wipers, Ghost Wipes, and Hygenall LeadOff wipes) from surfaces of different roughness (sandpaper of 60–6,000 grit). Zinc oxide was used as a surrogate for beryllium because of its much lower toxicity. Overall, the wipes were most efficient at collecting particles from the fine grits and poor at collecting particles from the coarse grits. The Smear Tabs and Whatman filters performed poorly in both durability and particle collection efficiency. In both respects, the superior performers were the Ghost Wipes and LeadOff wipes. However, even in the best case, the wipe still left behind 20% of the particles. These results indicate that underestimating metal particle contamination levels is a serious possibility when conducting wipe sampling on textured surfaces.

Contact angle and induction time of air bubble on flat coal surface of different roughness

The wettability of coal is an important parameter for representing the surface hydrophobicity and floatability of coal particle, and hence determines coal flotation behavior. The wettability of coal is primarily governed by the surface functional groups. However, the role of surface topography in the wettability of coal has not attracted enough attentions. This paper was to investigate the effect of roughness on the wettability of coal by measuring the contact angle between air bubble and flat coal surface. Besides, a new method to measure the contact angle is introduced. The shape of the bubble is fitted by both the circle and the ellipse. The lump coal particles were used as coal sample and polished by sand papers of different meshes to gain the specific flat coal surfaces of different roughness. The attachment time measurements and Wenzel theory were used to further explain why the surface roughness has significant effects on the contact angle of air bubble on coal surface. Throughout this paper, it was found that the wettability of coal was decreased with the increase of surface roughness. The water may be entrapped in the pores/cracks of rough coal surface which prevents the attachment between coal surface and bubble as well as the spreading of three-phrase contact line. Therefore, both the attachment time and contact angle were decreased with the increase of roughness.

Adsorption of silica colloids onto like-charged silica surfaces of different roughness

Particle adsorption was explored in a model optical polishing system, consisting of silica colloids and like-charged silica surfaces. The adsorption was monitored in situ under various suspension conditions, in the absence of surfactants or organic modifiers, using a quartz crystal microbalance with dissipation monitoring (QCM-D). Changes in surface coverage with particle concentration, particle size, pH, ionic strength and ionic composition were quantified by QCM-D and further characterized ex situ by atomic force microscopy (AFM). A Monte Carlo model was used to describe the kinetics of particle deposition and provide insights on scaling with particle concentration. Transitions from near-zero adsorption to measurable adsorption were compared with equilibrium predictions made using the Deraguin-Verwey-Landau-Overbeek (DLVO) theory. In addition, the impact of silica surface roughness on the propensity for particle adsorption was studied on various spatial scale lengths by intentionally roughening the QCM sensor surface using polishing methods. It was found that a change in silica surface roughness at the AFM scale from 1.3nm root-mean-square (rms) to 2.7nmrms resulted in an increase in silica particle adsorption of 3-fold for 50-nm diameter particles and 1.3-fold for 100-nm diameter particles—far exceeding adsorption observed by altering suspension conditions alone, potentially because roughness at the proper scale reduces the total separation distance between particle and surface.