Particle Surface Topography Research Articles

Rough colloids at fluid interfaces: from fundamental science to applications

Colloidal particles pinned to fluid interfaces have applications ranging from Pickering emulsions and foams to the development of 2D materials via Langmuir-Blodgett deposition. While colloids come in virtually any size, shape, and chemistry, particle surface topography, or roughness, has recently found renewed interest as a design parameter for controlling interfacial pinning, capillary interactions, assembly, and mechanics of particulate monolayers. In this review, we highlight the fundamental science regarding rough colloidal particles at fluid interfaces and how manipulating roughness can be a tool for material design, rather than merely a characteristic needing to be dealt with. While existing work reveals the importance of roughness, the field is still rather nascent and therefore this review highlights both challenges and opportunities for future research.

Effects of surface topography of SiO2 particles on the heterogeneous condensation process observed by environmental scanning electron microscopy

Heterogeneous condensation of supersaturated water vapor on submicron particles is an important phase transition process. Particle surface topography has a great influence on the whole condensation...

Nanoscale morphogenesis of nylon-sputtered plasma polymer particles

Sub-micron polymer particles are highly important in various fields including astrophysics, thermonuclear fusion and nanomedicine. Plasma polymerization offers the possibility to produce particles with tailor-made size, crosslink density and chemical composition to meet the requirements of a particular application. However, the mechanism of nucleation and growth of plasma polymer particles as well as diversity of their morphology remain far from being clear. Here, we prepared nitrogen-containing plasma polymer particles by rf magnetron sputtering of nylon in a gas aggregation cluster source with variable length. The method allowed the production of particles with roughly constant chemical composition and number density but with the mean size changing from 80 to 320 nm. Atomic Force Microscopy with super-sharp probes was applied to study the evolution of the particle surface topography as they grow in size. Height–height correlation and power spectral density functions were obtained to quantify the roughness exponent α = 0.78, the growth exponent β = 0.35, and the dynamic exponent 1/z = 0.50. The set of critical exponents indicates that the particle surface evolves in a self-affine mode and the overall particle growth is caused by the accretion of polymer-forming species from the gas phase and not by coagulation. Redistribution of the incoming material over the surface coupled with the inhomogeneous distribution of inner stress is suggested as the main factor that determines the morphogenesis of the plasma polymer particles.

Quantitative analysis of wear particles generated by cavitation erosion in glycerol-water mixtures

PurposeThis paper aimed to analyze removed particles from stationary specimen-aluminum (Al-99.92) produced by vibratory cavitation erosion tests in distilled water and glycerol-water mixtures.Design/methodology/approachThe particle morphology which include particle surface topography, size distribution, particle size parameters and particle shape parameters were examined for distilled water and glycerol-water mixtures having different viscosities.FindingsThe results showed that the variation of size parameters with viscosity was very similar to the variation of weight loss with viscosity. Both the size parameters and weight losses show a monotonic decrease in going from distilled water to glycerol-water mixtures having viscosity about 10.1 cSt, beyond which the change is very small. On the other hand, the shape parameters were much less sensitive to distinguish between the particles produced in water and glycerol-water mixtures. The mechanism of cavitation erosion is investigated in detail through observations of the removed particles. The particle surfaces topography demonstrated that the mechanism in water and glycerol-water mixtures was fatigue failure.Originality/valueCavitation often occurs in almost all machines that handle liquids, especially at high speeds, leading to irreparable damage of the components of these machines. Elucidation of such complex phenomenon demands full characterization of the erosion mechanism and controlling parameters inherent to it, so that cavitation erosion can be prevented or at least be reduced through adequate information and collection of relevant data under different operating conditions. Very few studies have been made to approach the viscosity effect upon cavitation erosion from the particle analysis standpoint. The aim of the present work is to identify the effect of liquid viscosity on the size, shape characteristics of the erosion particles and their morphological features. The prevailed mechanisms of wear and particle generation have been proposed based on the acquired information from particle analysis.

Photoluminescence from Gold and Silver Nanoparticles

This review is an attempt to highlight some of the significant results of the work carried out on the photoluminescence from nanoparticles of the noble metals, particularly gold and silver, over the past two decades. Although quite an immense amount of reports can be found, those that have contributed in throwing some light on the underlying mechanism behind photoluminescence have been considered here. Interband radiative recombination of electrons in metals or photoluminescence (PL), though very weak, was first reported in Au, Cu and Au-Cu alloys. A simple model attributes the PL to the radiative recombination of conduction band electrons below the Fermi energy with d-band holes. Most of the mechanisms are based on this concept. Only small sized clusters are known to exhibit luminescence, with the appearance of additional features which changed with the surfactants suggesting ligand to metal charge transfer. Further, the observation that more polar ligands do indeed enhance the luminescence intensity supports ligand to metal charge transfer. A non-radiative decay of excited electrons from 6sp-band to interface electron energy levels or bands (IEEB), that could be created due to charge transfer from the ligand to the metal core, followed by radiative recombination of electrons from these levels with the hole in the d-band could be another possible mechanism, which is supported by the size independence of the PL emission peak position. However, it is possible that these mechanisms operate independently or even simultaneously depending on various factors like size, ligands, dispersion medium, particle surface topography and so on.

Formulation of Nanoencapsulated Catechin with Chitosan as Encapsulation Material

Gambier is one of Indonesian superior estate crop. Among several chemical compounds in gambier, catechin from polyphenols group has the greatest benefit for health. However, catechin has a limitedness of stability that causes a low bioavailability property. One way to maintain and improve the stability of catechin is the application of nanotechnology. The objective of this study is to obtain the best formulation in producing a solution of catechin nanoparticles with particle droplet size <300nm as an antioxidant material. Observations were conducted to the formulations of the concentration of the solution of chitosan (0.2 and 0.4%), sodium tripolyphosphate (Na-TPP) (0.1 and 0.2%), catechin extract (0.3, 0.4, 0.5 and 0.6%) and the ratio of chitosan solution with catechin solution in Na-TPP (5: 1 and 7: 1) in order to determine one that yields the best solution. Observations were carried on the stability and characteristics of catechin nanoparticle solution including particle size, particle surface topography and internal structure. Catechin nanoparticles with best particle size was found in formula with 0.2% chitosan solution, 0.4% catechin solution, 0.1% Na-TPP solution and ratio of chitosan solution with withcatechin in Na-TPP solution 7: 1, that is 137.6nm. Physically, the best formulation of catechin nanoparticleshas good particle surface topography, internal particle structure and emulsion stability.

Tuning innate immune activation by surface texturing of polymer microparticles: the role of shape in inflammasome activation.

Polymeric microparticles have been widely investigated as platforms for delivery of drugs, vaccines, and imaging contrast agents and are increasingly used in a variety of clinical applications. Microparticles activate the inflammasome complex and induce the processing and secretion of IL-1β, a key innate immune cytokine. Recent work suggests that although receptors are clearly important for particle phagocytosis, other physical characteristics, especially shape, play an important role in the way microparticles activate cells. We examined the role of particle surface texturing not only on uptake efficiency but also on the subsequent immune cell activation of the inflammasome. Using a method based on emulsion processing of amphiphilic block copolymers, we prepared microparticles with similar overall sizes and surface chemistries but having either smooth or highly microtextured surfaces. In vivo, textured (budding) particles induced more rapid neutrophil recruitment to the injection site. In vitro, budding particles were more readily phagocytosed than smooth particles and induced more lipid raft recruitment to the phagosome. Remarkably, budding particles also induced stronger IL-1β secretion than smooth particles through activation of the NLRP3 inflammasome. These findings demonstrate a pronounced role of particle surface topography in immune cell activation, suggesting that shape is a major determinant of inflammasome activation.

DEM investigation of particle anti-rotation effects on the micromechanical response of granular materials

The importance of particle rotation to the mechanical behavior of granular materials subject to quasi-static shearing has been well recognized in the literature. Although the physical source of the resistance to particle rotation is known to lie in the particle surface topography, it has been conveniently studied using the rolling resistance model installed typically on spherical particles within the DEM community. However, there has been little effort on assessing the capability of the rolling resistance model to produce more realistic particle rotation behavior as exhibited by irregular-shaped particles. This paper aims to eliminate this deficiency by making a comprehensive comparison study on the micromechanical behavior of assemblies of irregular-shaped particles and spherical particles installed with the rolling resistance model. A variety of DEM analysis techniques have been applied to elucidate the full picture of micromechanical processes occurring in the two types of granular materials with different particle-level anti-rotation mechanisms. Simulation results show that the conventional rheology-type rolling resistance models cannot reproduce the particle rotation and strain localization behavior as displayed by irregular-shaped materials, although they demonstrate clear effects on the macroscopic strength and dilatancy behavior, as have been adequately documented in the literature. More insights into the effects of particle-level anti-rotation mechanism are gained from an in-depth inter-particle energy dissipation analysis.

Rapid Degradation of Azo Dye by Fe‐Based Metallic Glass Powder

AbstractThe outstanding efficiency of Fe‐based metallic glass powders in degrading organic water contaminants is reported. While the glassy alloy contains 24% chemically inactive metalloid elements, the powders are capable to completely decompose the C32H20N6Na4O14S4 azo dye in aqueous solution in short time, about 200 times faster than the conventional Fe powders. The metastable thermodynamic nature and the particle surface topography are the major factors controlling the chemical performance of the metallic glass. Our findings may open a new opportunity for functional applications of metallic glasses.

Mensuration of microstructure multi-fractal spectra of calcined limestone particle surfaces

The microstructure of the surface of a calcined limestone particle is multi-fractal. We develop an analytic method that surveys the boundary curve multi-fractal dimensions with SEM, gets a three-dimensional surface structure α − f( α) curve via zero-sets, and finally calculates the multi-fractal spectrum values of the particle surface's microstructural topography. After analyzing two spectra from limestone particles calcined at 850 °C and 900 °C, it was shown that the microstructural topographies of the surfaces of calcined limestone multi-particle system have some degree of self-similarity. This mensuration method is proposed to describe the multi-fractal characteristics of a micro-scale particle's surface topography.

Surface characterization of wear particles

Wear particles are three-dimensional objects. Recent advances, accelerated by the application of computer technology, allow numerical characterization of particle shape in two dimensions. However, three-dimensional (3D) characterization of wear particle surface topography is still largely an unresolved problem. There are two issues associated with this problem, i.e., the acquisition of accurate wear particle surface topography data and the numerical description of 3D surface features. The usually small size of wear particles restricts the techniques that could be used to acquire accurate data from the particle surface. Surface profilometers, e.g., Talysurf, the instruments traditionally used in surface topography imaging, cannot be used because of the small size of particles. The limitation of an atomic force microscope is its relatively small vertical range, while the horizontal resolution of laser confocal or interferometric microscopes is too low to obtain accurate particle surface topography data. The application of a combination of SEM and stereoscopy techniques seems to alleviate this problem. 3D surface topography data obtained using this technique can be processed and presented in many different ways. The usefulness of various methods of surface data representation in visualization and numerical characterization of wear particle surfaces is discussed. One of the major difficulties associated with the characterization of surface topographies is the accurate description of surface spatial properties, i.e., their anisotropy and directionality. Recently, a specially modified Hurst Orientation Transform (HOT), to suit wear particle surface data, has been developed and applied to characterize the surface topography of particles. The Hurst coefficients are related to fractal dimensions and are a measure of surface roughness, i.e., a rougher surface is represented by lower Hurst coefficients. It was found that the modified HOT can be applied to reveal the surface anisotropy of wear particles. Although none of the other methods developed so far allow such a thorough characterization of wear particle surfaces as does the modified HOT, this method still does not provide a full description of the surface topography. Therefore, it appears that a totally different approach is needed in order to make a fundamental breakthrough in the characterization of wear particle surfaces. Since many of the complex structures observed in nature can be described and modelled by a combination of simple mathematical rules, it may be possible to describe the surface of a particle by a set of such rules. In our first attempt, a Partitioned Iterated Function System (PIFS) was applied to encode the wear particle surface topography information. This information can then be used to calculate the relevant surface descriptors. In this paper, an overview of recent advances and developments in the numerical characterization of wear particle surfaces is presented.

The development of the modified Hurst orientation transform for the characterization of surface topography of wear particles

A modified Hurst orientation transform (HOT) method for characterization of wear particle surfaces is proposed and described in this paper. The method involves the calculation of self-affine Hurst coefficients in all directions and displays the calculated coefficient values in a form of rose plot. The calculation of individual Hurst coefficients, H, is based on the rescale range (r/s) analysis (r(d)/s∼ d H ). The rose plot is then used to obtain three texture surface parameters, i.e.: texture aspect ratio, texture minor axis and texture direction. The effectiveness of this modified HOT and resulting surface texture parameters was evaluated. The method was first applied to computer-generated images of isotropic and anisotropic particle fractal surfaces and then to field emission scanning electron microscope images of wear particles found in synovial joints. The ability of the surface parameters to reveal surface isotropy or anisotropy, measure roughness and determine the dominant direction of surface texture was assessed. The effects of measurement conditions such as noise, gain variations and focusing on the surface parameters were also investigated. The results demonstrate that the HOT and surface texture parameters developed can successfully be used in the characterization of wear particle surface topography.

Characterization of surface topography of wear particles by SEM stereoscopy

A method of characterizing the surface topography of wear particles by the application of computer image analysis to scanning electron microscope (SEM) stereoscopic pairs of images is proposed and described in this paper. The image analysis consists of noise reduction, edge detection, thresholding, stereoscopic matching, calculation of elevation points and interpolation. An improved automatic stereoscopic matching algorithm has been developed. The algorithm was initially applied to computer-generated images of a polished marble sphere and a polished marble cube and later to SEM images of wear particles found in artificial and synovial joints. The results demonstrate that SEM stereoscopy can successfully be used in the characterization and measurements of wear particle surface topography.