Showing papers on "Surface roughness published in 2011"

Surface Characteristics of a Self-Polymerized Dopamine Coating Deposited on Hydrophobic Polymer Films

Abstract: This study aims to explore the fundamental surface characteristics of polydopamine (pDA)-coated hydrophobic polymer films. A poly(vinylidene fluoride) (PVDF) film was surface modified by dip coating in an aqueous solution of dopamine on the basis of its self-polymerization and strong adhesion feature. The self-polymerization and deposition rates of dopamine on film surfaces increased with increasing temperature as evaluated by both spectroscopic ellipsometry and scanning electronic microscopy (SEM). Changes in the surface morphologies of pDA-coated films as well as the size and shape of pDA particles in the solution were also investigated by SEM, atomic force microscopy (AFM), and transmission electron microscopy (TEM). The surface roughness and surface free energy of pDA-modified films were mainly affected by the reaction temperature and showed only a slight dependence on the reaction time and concentration of the dopamine solution. Additionally, three other typical hydrophobic polymer films of polytetrafluoroethylene (PTFE), poly(ethylene terephthalate) (PET), and polyimide (PI) were also modified by the same procedure. The lyophilicity (liquid affinity) and surface free energy of these polymer films were enhanced significantly after being coated with pDA, as were those of PVDF films. It is indicated that the deposition behavior of pDA is not strongly dependent on the nature of the substrates. This information provides us with not only a better understanding of biologically inspired surface chemistry for pDA coatings but also effective strategies for exploiting the properties of dopamine to create novel functional polymer materials.

Modeling and prediction of surface roughness in turning operations using artificial neural network and multiple regression method

Abstract: Research highlights? The surface roughness is measured during turning at different cutting parameters such as speed, feed, and depth of cut by full factorial experimental design. ? Artificial neural networks (ANN) and multiple regression approaches are used to model the surface roughness of AISI 1040 steel. ? The ANN model estimates the surface roughness with high accuracy compared to the multiple regression model. Machine parts during their useful life are significantly influenced by surface roughness quality. The machining process is more complex, and therefore, it is very hard to develop a comprehensive model involving all cutting parameters. In this study, the surface roughness is measured during turning at different cutting parameters such as speed, feed, and depth of cut. Full factorial experimental design is implemented to increase the confidence limit and reliability of the experimental data. Artificial neural networks (ANN) and multiple regression approaches are used to model the surface roughness of AISI 1040 steel. Multiple regression and neural network-based models are compared using statistical methods. It is clearly seen that the proposed models are capable of prediction of the surface roughness. The ANN model estimates the surface roughness with high accuracy compared to the multiple regression model.

Effect of Surface Wettability and Topography on the Adhesion of Osteosarcoma Cells on Plasma-modified Polystyrene

Abstract: Biomaterials interact with the biological environment at their surface, making accurate biophysical characterization of the surface crucially important for understanding subsequent biological effects. In this study, the surface of polystyrene (PS) was systematically altered in order to determine the effect of plasma treatment and surface roughness on cell adhesion and spreading. Surfaces with water contact angle from hydrophilic (12°) to superhydrophobic (155°) were obtained through a combination of modifying surface roughness (R (a)), the deposition of siloxane coatings and the fluorination of the PS surface. R (a) values in the range of 19-2365 nm were obtained by grinding the PS surface. The nanometer-thick siloxane coatings were deposited using an atmospheric pressure plasma system, while the fluorination of the PS was carried out using a low-pressure radio frequency (RF) plasma. The siloxane coatings were obtained using a liquid poly(dimethylsiloxane) precursor that was nebulized into helium or helium/oxygen plasmas. Water contact angles in the range of 12-122° were obtained with these coatings. Cell adhesion studies were carried out using human MG63 osteosarcoma cells. It was observed that higher polymer surface roughness enhanced cell adhesion, but had a negative effect on cell spreading. Optimum cell adhesion was observed at ∼64° for the siloxane coatings, with a decrease in adhesion observed for the more hydrophilic and hydrophobic coatings. This decrease in cell adhesion with an increase in hydrophobicity was also observed for the fluorinated PS surfaces with water contact angles in the range of 110-155°.

The investigation of the influence of laser re‐melting on density, surface quality and microstructure of selective laser melting parts

Abstract: Purpose – Selective laser melting (SLM) is a powder metallurgical (PM) additive manufacturing process whereby a three‐dimensional part is built in a layer‐wise manner. During the process, a high intensity laser beam selectively scans a powder bed according to the computer‐aided design data of the part to be produced and the powder metal particles are completely molten. The process is capable of producing near full density (∼98‐99 per cent relative density) and functional metallic parts with a high geometrical freedom. However, insufficient surface quality of produced parts is one of the important limitations of the process. The purpose of this study is to apply laser re‐melting using a continuous wave laser during SLM production of 316L stainless steel and Ti6Al4V parts to overcome this limitation.Design/methodology/approach – After each layer is fully molten, the same slice data are used to re‐expose the layer for laser re‐melting. In this manner, laser re‐melting does not only improve the surface qualit...

Multiscale Analysis of Topographic Surface Roughness in the Midland Valley, Scotland

Abstract: Surface roughness is an important geomorphological variable which has been used in the Earth and planetary sciences to infer material properties, current/past processes, and the time elapsed since formation. No single definition exists; however, within the context of geomorphometry, we use surface roughness as an expression of the variability of a topographic surface at a given scale, where the scale of analysis is determined by the size of the landforms or geomorphic features of interest. Six techniques for the calculation of surface roughness were selected for an assessment of the parameter's behavior at different spatial scales and data-set resolutions. Area ratio operated independently of scale, providing consistent results across spatial resolutions. Vector dispersion produced results with increasing roughness and homogenization of terrain at coarser resolutions and larger window sizes. Standard deviation of residual topography highlighted local features and did not detect regional relief. Standard deviation of elevation correctly identified breaks of slope and was good at detecting regional relief. Standard deviation of slope (SDslope) also correctly identified smooth sloping areas and breaks of slope, providing the best results for geomorphological analysis. Standard deviation of profile curvature identified the breaks of slope, although not as strongly as SDslope, and it is sensitive to noise and spurious data. In general, SDslope offered good performance at a variety of scales, while the simplicity of calculation is perhaps its single greatest benefit.

High-Performance Organic Solar Cells with Spray-Coated Hole-Transport and Active Layers

Abstract: In this study, we report high performance organic solar cells with spray coated hole-transport and active layers. With optimized ink formulations we are able to deposit films with controlled thickness and very low surface roughness (<10 nm). Specifically we deposit smooth and uniform 40 nm thick films of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as well as films composed of a mixture of poly(3-hexyl thiophene) (P3HT) and the C60-derivative (6,6)-phenyl C61-butyric acid methyl ester (PCBM) with thicknesses in the range 200–250 nm. To control film morphology, formation and thickness, the optimized inks incorporate two solvent systems in order to take advantage of surface tension gradients to create Marangoni flows that enhance the coverage of the substrate and reduce the roughness of the film. Notably, we achieve fill factors above 70% and attribute the improvement to an enhanced P3HT crystallization, which upon optimized post-drying thermal annealing results in a favorable morphology. As a result, we could extend the thickness of the layer to several hundreds of nanometers without noticing a substantial decrease of the transport properties of the layer. By proper understanding of the spreading and drying dynamics of the inks we achieve spray coated devices with power conversion efficiency of 3.75%, with fill factor, short circuit current and open circuit voltage of 70%, 9.8 mA cm−2 and 550 mV, respectively.

Manufacturing by combining Selective Laser Melting and Selective Laser Erosion/laser re-melting

Abstract: This study presents an experimental investigation to improve Selective Laser Melting (SLM) regarding aspects such as surface roughness, density, precision and micro machining capability by employing secondary processes such as Selective Laser Erosion (SLE) and laser re-melting. SLM is a layered additive manufacturing technique for the direct fabrication of functional parts by fusing together metal powder particles. Laser re-melting, applied after each layer or only on the top surfaces, is used to improve the roughness and density while SLE, a subtractive process, is combined with SLM to improve the precision and micro machining capability.

Biomimetic micro∕nanostructured functional surfaces for microfluidic and tissue engineering applications

Abstract: This paper reviews our work on the application of ultrafast pulsed laser micro/nanoprocessing for the three-dimensional (3D) biomimetic modification of materials surfaces. It is shown that the artificial surfaces obtained by femtosecond-laser processing of Si in reactive gas atmosphere exhibit roughness at both micro- and nanoscales that mimics the hierarchical morphology of natural surfaces. Along with the spatial control of the topology, defining surface chemistry provides materials exhibiting notable wetting characteristics which are potentially useful for open microfluidic applications. Depending on the functional coating deposited on the laser patterned 3D structures, we can achieve artificial surfaces that are (a) of extremely low surface energy, thus water-repellent and self-cleaned, and (b) responsive, i.e., showing the ability to change their surface energy in response to different external stimuli such as light, electric field, and pH. Moreover, the behavior of different kinds of cells cultured on laser engineered substrates of various wettabilities was investigated. Experiments showed that it is possible to preferentially tune cell adhesion and growth through choosing proper combinations of surface topography and chemistry. It is concluded that the laser textured 3D micro/nano-Si surfaces with controllability of roughness ratio and surface chemistry can advantageously serve as a novel means to elucidate the 3D cell-scaffold interactions for tissue engineering applications.

Global surface slopes and roughness of the Moon from the Lunar Orbiter Laser Altimeter

Abstract: [1] The acquisition of new global elevation data from the Lunar Orbiter Laser Altimeter, carried on the Lunar Reconnaissance Orbiter, permits quantification of the surface roughness properties of the Moon at unprecedented scales and resolution. We map lunar surface roughness using a range of parameters: median absolute slope, both directional (along‐track) and bidirectional (in two dimensions); median differential slope; and Hurst exponent, over baselines ranging from ∼17 m to ∼2.7 km. We find that the lunar highlands and the mare plains show vastly different roughness properties, with subtler variations within mare and highlands. Most of the surface exhibits fractal‐like behavior, with a single or two different Hurst exponents over the given baseline range; when a transition exists, it typically occurs near the 1 km baseline, indicating a significant characteristic spatial scale for competing surface processes. The Hurst exponent is high within the lunar highlands, with a median value of 0.95, and lower in the maria (with a median value of 0.76). The median differential slope is a powerful tool for discriminating between roughness units and is useful in characterizing, among other things, the ejecta surrounding large basins, particularly Orientale, as well as the ray systems surrounding young, Copernican‐age craters. In addition, it allows a quantitative exploration on mare surfaces of the evolution of surface roughness with age.

On the effect of surface roughness height, wettability, and nanoporosity on Leidenfrost phenomena

Abstract: In recent quenching heat transfer studies of nanofluids, it was found that deposition of nanoparticles on a surface raises its Leidenfrost point (LFP) considerably [Kim et al., Int. J. Multiphase Flow 35, 427 (2009) and Kim et al., Int. J. Heat Mass Transfer 53, 1542 (2010)]. To probe the physical mechanism underlying this observation, the effects of surface properties on LFP of water droplets were studied, using custom-fabricated surfaces for which roughness height, wettability, and porosity were controlled at the nanoscale. This approach reveals that nanoporosity is the crucial feature in efficiently increasing the LFP by initiating heterogeneous nucleation of bubbles during short-lived solid-liquid contacts, which results in disruption of the vapor film.

Replication of micro and nano surface geometries

Abstract: The paper describes the state-of-the-art in replication of surface texture and topography at micro and nano scale. The description includes replication of surfaces in polymers, metals and glass. Three different main technological areas enabled by surface replication processes are presented: manufacture of net-shape micro/nano surfaces, tooling (i.e. master making), and surface quality control (metrology, inspection). Replication processes and methods as well as the metrology of surfaces to determine the degree of replication are presented and classified. Examples from various application areas are given including replication for surface texture measurements, surface roughness standards, manufacture of micro and nano structured functional surfaces, replicated surfaces for optical applications (e.g. optical gratings), and process chains based on combinations of repeated surface replication steps.

Multi-objective optimization of surface roughness and cutting forces in high-speed turning of Inconel 718 using Taguchi grey relational analysis (TGRA).

Abstract: In this paper, a new effective approach, Taguchi grey relational analysis has been applied to experimental results in order to optimize the high-speed turning of Inconel 718 with consideration to multiple performance measures. The approach combines the orthogonal array design of experiments with grey relational analysis. Grey relational theory is adopted to determine the best process parameters that give lower magnitude of cutting forces as well as surface roughness. The response table and the grey relational grade graph for each level of the machining parameters have been established. The parameters: cutting speed, 475 m/min; feed rate, 0.10 mm/rev; depth of cut, 0.50 mm; and CW2 edge geometry have highest grey relational grade and therefore are the optimum parameter values producing better turning performance in terms of cutting forces and surface roughness. Depth of cut shows statistical significance on overall turning performance at 95% confidence interval.

The role of nanopore shape in surface-induced crystallization

Abstract: Crystallization of a liquid usually starts at a solid surface — for instance, that of impurities or of a container's walls — and surface roughness is known to enhance crystal nucleation rates. It is now shown with polymer films patterned with spherical nanopores 15–120 nm in size that the shape of the pores can either enhance or hinder crystal nucleation.

Adhesion, growth and differentiation of osteoblasts on surface-modified materials developed for bone implants.

Abstract: This review briefly outlines the history and possibilities of bone reconstruction using various types of artificial materials, which allow interaction with cells only on the surface of the implant or enable ingrowth of cells inside the material. Information is also provided on the most important properties of bone cells taking part in bone tissue development, and on diseases and regeneration. The most common cell types used for testing cell-material interaction in vitro are listed, and the most commonly used approaches to this testing are also mentioned. A considerable part of this review is dedicated to the physical and chemical properties of the material surface, which are decisive for the cell-material interaction, and also to modifications to the surface of the material aimed at integrating it better with the surrounding bone tissue. Special attention is paid to the effects of nanoscale and microscale surface roughness on cell behaviour, to material surface patterning, which allows regionally-selective adhesion and growth of cells, and also to the surface chemistry. In addition, coating the materials with bioactive layers is examined, particularly those created by deposition of fullerenes, hybrid metal-fullerene composites, carbon nanotubes, nanocrystalline diamond films, diamond-like carbon, and nanocomposite hydrocarbon plasma polymer films enriched with metals.