CALCULATION OF VAN DER WAALS FORCES WITH DIFFUSE COATINGS: APPLICATIONS TO ROUGHNESS AND ADSORBED POLYMERS

A novel method using Lifshitz continuum theory to account for the effects of surface roughness was developed. The method treats roughness as a diffuse film whose dielectric properties vary continuously between those of the substrate and those of the solvent: AFM measurements of surface topography are used to deduce the volume-fraction profile of substrate in solvent which in turn is converted into a dielectric-permittivity profile using the Clausius-Mossoti equation as a mixing rule. Calculations show orders of magnitude of reduction in the van der Waals force between rough surfaces at contact compared with smooth surfaces, with the amount of reduction dependent on the shape of the volume-fraction profile as well as the total depth of the roughness. These predictions help account for discrepancies observed previously between the Total Internal Reflection Microscopy (TIRM) data and calculations for smooth polystyrene surfaces in water, with or without physisorbed polymer, without introducing any adjustable parameters.     

CALCULATION OF VAN DER WAALS FORCES WITH DIFFUSE COATINGS: APPLICATIONS TO ROUGHNESS AND ADSORBED POLYMERS

A novel method using Lifshitz continuum theory to account for the effects of surface roughness was developed. The method treats roughness as a diffuse film whose dielectric properties vary continuously between those of the substrate and those of the solvent: AFM measurements of surface topography are used to deduce the volume-fraction profile of substrate in solvent which in turn is converted into a dielectric-permittivity profile using the Clausius-Mossoti equation as a mixing rule. Calculations show orders of magnitude of reduction in the van der Waals force between rough surfaces at contact compared with smooth surfaces, with the amount of reduction dependent on the shape of the volume-fraction profile as well as the total depth of the roughness. These predictions help account for discrepancies observed previously between the Total Internal Reflection Microscopy (TIRM) data and calculations for smooth polystyrene surfaces in water, with or without physisorbed polymer, without introducing any adjustable parameters.     

蛇纹石对不同粗糙度45~#钢表面的减摩行为

利用MMW-1A型万能摩擦磨损试验机研究蛇纹石对3种不同粗糙度45#钢表面的减摩行为。采用三维视频显微镜、扫描电子显微镜和能谱仪对实验前后磨损表面形貌和化学组成进行分析。结果表明：蛇纹石的减摩效果对于光滑磨损表面更为显著。当表面粗糙度Ra=0.742μm时,磨损表面被有效修复,摩擦系数大幅下降,表面粗糙度下降了72.1%,并且磨损量仅有1.3mg;当Ra=1.424μm和3.706μm时,摩擦副磨损遵循一般金属材料的磨损特征。修复层平整光滑,其形成与磨损存在一个动态平衡。     

Cellular Behavior of Human Adipose-Derived Stem Cells on Wettable Gradient Polyethylene Surfaces

Appropriate surface wettability and roughness of biomaterials is an important factor in cell attachment and proliferation. In this study, we investigated the correlation between surface wettability and roughness, and biological response in human adipose-derived stem cells (hADSCs). We prepared wettable and rough gradient polyethylene (PE) surfaces by increasing the power of a radio frequency corona discharge apparatus with knife-type electrodes over a moving sample bed. The PE changed gradually from hydrophobic and smooth surfaces to hydrophilic (water contact angle, 90º to ~50º) and rough (80 to ~120 nm) surfaces as the power increased. We found that hADSCs adhered better to highly hydrophilic and rough surfaces and showed broadly stretched morphology compared with that on hydrophobic and smooth surfaces. The proliferation of hADSCs on hydrophilic and rough surfaces was also higher than that on hydrophobic and smooth surfaces. Furthermore, integrin beta 1 gene expression, an indicator of attachment, and heat shock protein 70 gene expression were high on hydrophobic and smooth surfaces. These results indicate that the cellular behavior of hADSCs on gradient surface depends on surface properties, wettability and roughness.     

Heat transfer in condensation and boiling in a tubular film evaporator

The results of a study of heat transfer in condensation and boiling in a tubular evaporator with smooth and rough surfaces under the gravity flow of a water film are presented. Relationships are derived for calculating a heat-transfer coefficient, and the effect of helical roughness on heat transfer is revealed.     

Wettability and osteoblastic cell adhesion on ultrapolished commercially pure titanium surfaces: the role of the oxidation and pollution states

The oxidation state of the surfaces of titanium-based biomaterials strongly depends on their previous history. This factor affects the titanium wettability and it probably conditions the success of the implanted biomaterials. However, the separate role of the pollution and oxidation states of metallic titanium surfaces remains still controversial. To elucidate this, it is required to standardize the initial surface state of titanium in terms of roughness and surface chemistry, and then, to monitor its wettability after the corresponding treatment. In this work, we studied finely polished surfaces of commercially pure titanium (cpTi) which were subjected to cleaning surface treatments. X-Photoelectron spectroscopy was used to characterize the surface chemistry and the oxide film thickness. The contact angle hysteresis in underwater conditions was measured with the growing/shrinking captive bubble method, which allowed for mimicking the real conditions of implantable devices. The water wettability of smooth cpTi surfaces was stabilized with weak thermal oxidation (230?°C, 30?min). The osteoblastic cell response of the stabilized and non-stabilized cpTi surfaces was analyzed. Although the oxidation and pollution states were also stabilized and normalized, no correlation was observed between the stable response in wettability of titanium and its cell adhesion.     

Effect of surface morphology of calcium phosphate on osteoblast-like HOS cell responses

Calcium phosphate (CaP) films with different surface roughness are synthesized on a polystyrene surface as a possible candidate for improving the biocompatibility of solid surfaces. These CaP films are used to investigate the influences of the surface roughness and chemical composition on the HOS osteoblast-like cells adhesion, spreading, proliferation, and differentiation. A polystyrene culture plate is used as the control surface. The CaP substrates are designated as a smooth, moderate, and rough surface according to the surface roughness. For smooth and moderate surfaces, a relatively small difference in the surface roughness is observed but the difference in their chemical composition is more significant than the others. Cell adhesion, spreading, proliferation, and differentiation appear to be dependent on surface roughness. These cellular responses are more active on the smoother surfaces than on the rough surface but are more pronounced on the moderate surface. The cell responses are reduced when HOS cells are cultured on the rough surface. The number of cells released from the control surface by trypsinization is greater than the CaP surfaces after a short period of incubation (5 h). However the cells released from smooth and moderate CaP surfaces are equivalent to or greater than the control at the longer period of incubation (17 h). Spreading and proliferation are greater on the CaP surfaces than on the control. The alkaline phosphatase-specific activity is very low during 1 and 2 weeks of culturing but dramatically increases after 3 weeks on all surfaces. The enzyme activity on the control is greater than on the CaP surfaces. The moderate surface shows the greatest enzyme activity in all cases among the CaP surfaces. Although a direct relation between surface chemistry and cell responses has not been established, the surface composition may play a cooperative role in characterizing the cellular responses. According to these results, the moderate surface is the most favorable substrate in terms of surface roughness and chemical composition for cell adhesion, spreading, proliferation and differentiation among all the CaP surfaces.     

Surface structure,topology, and liquid wetting behavior in oriented polymers

The structure and the properties of oriented polymer surfaces were studied for three series of uniaxially oriented films of polypropylene (PP), polystyrene (PS), and poly(ethylene terephthalate) (PET). The surface structure was characterized in terms of relative crystallinity and molecular orientation along with topology and roughness by using FT-IR-ATR dichroism technique, optical microscopy and surface profilometer. In all three polymers, the surface orientation function increases with draw ratio. The relative surface crystallinity and the trans con-former also increases for PP and PET, respectively. In uniaxially drawn PP, the surface becomes rough with increasing draw ratio and the roughness is anisotropic with peaks and valleys elongated along the draw direction. For drawn PP, the equilibrium contact angles for four different liquids all exhibit anisotropy with higher values in perpendicular direction than that in parallel to the draw direction. In contrast, both drawn PET and PS films show smooth surfaces, and the equilibrium contact angles were all isotropic. When roughness is removed from the drawn PP by polishing without altering the molecular orientation, the anisotropy becomes negligible and the contact angles approach the value for undrawn PP. When surface roughness was created deliberately on undrawn PET and PS films, the contact angle anisotropy was clearly observed. Therefore, the anisotropy in surface topology rather than the molecular orientation seems to play a dominant role in developing anisotropic wetting behavior. The equilibrium contact angles for smooth surfaces have been calculated using the experimentally obtained roughness and anisotropic contact angle data from the rough surface. These values are in reasonable agreement with the measured contact angles for smooth surfaces, suggesting that the observed contact angle anisotropy can be attributed entirely to the roughness anisotropy rather than to the molecular orientation.     

THE USE OF FRACTAL DIMENSION TO QUANTIFY THE EFFECT OF SURFACE ROUGHNESS ON FILM MASS TRANSFER ENHANCEMENT

Experimental results from previous work, contained in a companion paper by Van Vliet and Weber (1988), have shown qualitatively that the external film transfer coefficient for adsorption on particulate adsorbents is very dependent on the roughness of the mass transfer surface. Until recently a suitable method to quantify surface roughness was not available. Experimental data of film mass transfer coefficients of various activated carbons, carbonaceous adsorbents, and polymeric adsorbents are investigated. It is shown that film mass transfer is enhanced by the effect of surface roughness. The fractal dimensions of the adsorbent particle surfaces are determined and are shown to be linked to the degree of mass transfer enhancement. This suggests that the external mass and heat transfer enhancement properties of a rough surface are related to its fractal dimension.     

The effect of bond formation on the tack of polymers

The tack of polymers to be used as adhesives is measured by a two-stage process of bond formation and bond separation. Bond formation is governed by the contact time, the contact force, the roughness of the surfaces, surface and interfacial tensions, and the mechanical or viscoelastic properties of the adhesive and substrate. This paper presents experimental studies of the contact formation of various model polymers on steel surfaces with well-defined and different degrees of roughness. The tack was measured with an instrument of the probe tack type, which determines the adhesive (interfacial) fracture energy per unit of interface as a measure of the tack and by means of which the most important parameters during bond formation and separation, such as the contact time, contact force, rate of separation, and temperature, can be adjusted and measured over sufficiently wide ranges. In the typical time interval for the contact time, the polymers are found in the plateau range of their viscoelastic spectrum. This means that entanglements strongly affect their bonding behaviour. Good agreement was found between the experimental results presented in this study and a model of contact formation on rough surfaces, published recently by Creton and Leibler [1], especially concerning the dependence of the adhesive fracture energy on the contact force and the contact time for smooth and rough substrate surfaces. The influence of the surface roughness becomes significant at low contact forces, where full contact is not yet developed on a rough substrate surface, and for polymers with comparatively high moduli. The fracture energy increases with the contact time and shows the same time dependence as the reciprocal modulus.     

An experimental study of the flow of dry powders over inclined surfaces

The behavior of dry particulate solids during unconfirmed flow over inclined surfaces has been investigated. The motion of individual particles is found to depend strongly on the nature of the surface over which they flow. For smooth surfaces, flow occurs primarily by sliding at the surface, and little or no shear is introduced into the stream. In the case of highly roughened surfaces consisting of, for example, a stationary layer of the same particles, there appears to be no slip at the surface, and flow occurs entirely by shear within the flowing stream. Surfaces of intermediate roughness lead to flow in which both slip at the surface and shear within the bed contribute significantly.Velocity profiles have been measured experimentally under a variety of conditions, and the effects of such variables as roughness and inclination of the surface, depth of the flowing stream and particle size have been evaluated quantitatively. Empirical relationships have been obtained which describe the flow behavior in all cases studied.     

PARTLCLE SURFACE ROUGHNESS EFFECTS ON THE INTERFACIAL MASS TRANSFER DYNAMICS OF MICROPOROUS ADSORBENTS

The surface roughness characteristics of several microporous adsorbents are qualitatively explored by scanning electron microscopy. Interfacial (film) mass transfer coefficients for adsorption of a number of different solutes by these adsorbents are investigated. Significant differences between coefficients for different adsorbents are reported. Rough spheres are shown to exhibit a seven-fold mass transfer enhancement over smooth spheres. The results indicate that mass transfer enhancement is more dependent on surface roughness than on overall particle shape. The surface roughness is investigated quantitatively by fractal analysis in a companion paper (Van Vliet and Young, 1988).     

Surface roughness of AlN films deposited on negatively biased silicon and diamond substrates

Our previous studies on AlN microstructures have shown that smooth amorphous films (a-AlN) can be grown on negatively biased Si substrates by the versatile physical vapour deposition technique under reactive magnetron sputtering. These a-AlN films are produced by energetic Ar ion bombardment under negative bias whereas those grown without bias were columnar crystallized ones (c-AlN). Here, we show first that depositing an a-AlN layer on c-AlN/Si structures by switching a suitable bias to the Si substrate can efficiently reduce their surface roughness. We then extend this smoothening method to a c-AlN/Poly-crystallized diamond (PCD) structure to reduce its high surface roughness that hampers using such structures in SAW device design. In fact, the piezoelectric c-AlN surfaces grown on rough diamond surfaces are equally rough. Effectively, the a-AlN layer deposited on the c-AlN/PCD structure brings down the latter's RMS surface roughness to one tenth of its initial RMS roughness, as confirmed here by TEM and AFM observations. The insulating property of the diamond as biased substrate doesn't impede the growth of this a-AlN layer. This smoothening method is without process interruption, where simply a negative bias is switched on to the diamond substrate once the desired piezoelectric c-AlN film thickness as monitored here by in-situ reflectometry, is attained. This as-grown smoothening method can be therefore easily and rapidly implemented and can thus replace time-consuming and costly PCD ionic and/or mechanical polishing. Hopefully, the method can be advantageously applied to c-AlN/nano-crystallized diamond structures (NCD) where the NCD films are not prepared under rigorous conditions meant to minimize their surface roughness.     

Improved Electrodes/Electrolyte Interfaces for Solid Oxide Fuel Cell by Using Dual‐Sized Powders in Electrolyte Slurry

The dense electrolyte film with the rough surfaces for solid oxide fuel cell (SOFC) was fabricated on NiO/yttria‐stabilized zirconia (YSZ) anode substrate by using dual‐sized YSZ powders without additional effort to roughen electrolyte film. The dual‐sized YSZ powders consisted of the fine YSZ powder and the coarse YSZ powder at different weight ratios. Incorporation of the coarse YSZ powder into the fine YSZ powder is in order to increase the surface roughness of electrolyte film, and the surface roughness obviously increased with the increase of coarse YSZ powder. The rough surfaces resulted in an enlargement of the electrochemical active area. It was found that electrode polarization was reduced evidently and cell electrochemical performance was enhanced, as the surface roughness increased. However, the excessive coarse YSZ powder was not beneficial for densification of electrolyte film and thus the open‐circuit voltage (OCV) was declined. The cell with 17 wt.% coarse YSZ powder in the electrolyte exhibited the best performance and the maximum power density was 1,930 mW cm^–2 at 800 °C.     

PEMFC中粗糙GDL表面对液态水在GC中传输过程的影响

采用商业软件FLUENT中VOF模型模拟了质子交换膜燃料电池（PEMFC）中液态水在具有粗糙气体扩散层（GDL）表面的气体通道（GC）中的传递过程。考察了GDL表面润湿特性和粗糙度对液态水传输过程的影响。研究结果表明：和亲水GDL表面相比,疏水GDL表面有利于液态水的排出;和光滑疏水GDL表面相比,粗糙疏水GDL表面加快了液滴的排出,减小了液滴覆盖GDL表面的面积;同时,粗糙GDL表面增加了GC相似文献   

Gloss and surface topography of ABS: A study on the influence of the injection molding parameters

Acrylonitrile butadiene styrene is used in applications where the surface appearance is important. Plates with surface texture, varying from highly smooth to very rough, were injection molded with various processing conditions. Morphology, roughness, and gloss of the surface were assessed in relation to the processing parameters. The surface characterization of the moldings was done using reflected differential interference contrast microscopy and laser microtopography. It was observed that the surface properties are affected by the molding parameters. The mold temperature, followed by the injection temperature and the holding pressure are the more influent parameters. The contribution of each parameter to the gloss varies with the type of surface, but for most of the surfaces the contribution of the mold temperature was above 90%. In general, higher values of these parameters improve the replication accuracy that reduce the roughness (and increase the gloss) of very smooth surfaces and cause the opposite effect in other surfaces. In surfaces with an anisotropic texture the gloss depends on the measuring direction. POLYM. ENG. SCI. 46:1394–1401, 2006. © 2006 Society of Plastics Engineers.     

Effect of polishing method on surface roughness and bacterial adhesion of zirconia-porcelain veneer

The purpose of this study was to evaluate the effect of various polishing methods on surface roughness of zirconia-porcelain veneer and to correlate the findings with early bacterial adhesion. The study specimens were glazed (control group), glazed after fine polishing (glazed group) and polished with Exa Cerapol (Cerapol group) or with Shofu porcelain adjustment kit (Shofu group) (n =20). Surface roughness was then measured using profilometer and scanning electron microscope (SEM). After artificial saliva coating, the specimens were incubated in Streptococcus mitis suspension for 4 h at 37 °C. Adherent bacteria were quantified from SEM images. Streptococcal viability was assessed by LIVE/DEAD staining kit and fluorescent microscope. There were significant differences in surface roughness according to polishing method and surface material. Relatively smoother surfaces were found in zirconia surfaces and glazed porcelain surfaces. There were also significant differences in bacterial adhesion according to polishing method and surface material. Cerapol group showed minimal bacterial adhesion with more dead cells when compared to other groups. A positive correlation between surface roughness and bacterial adhesion was found in glazed porcelain surface and a negative correlation in zirconia surface of Cerapol group, both with no statistical significance. Within the limitations of in vitro study, surface roughness and bacteria adhesion were significantly influenced by polishing method and surface material. Also, there was a positive correlation and negative correlation between surface roughness and bacterial adhesion in glazed porcelain surface and in zirconia surface of Cerapol group, respectively.     

Quantitative Analysis of Brittle Fracture Surfaces Using Fractal Geometry

Fractal geometry is a non-Euclidean geometry which has been developed to analyze irregular or fractional shapes. In this paper, fracture in ceramic materials is analyzed as a fractal process. This means that fracture is viewed as a self-similar process. We have examined the fracture surfaces of six different alumina materials and five glass-ceramics, with different microstructures, to test for fractal behavior. Slit island analysis and Fourier transform methods were used to determine the fractal dimension, D , of successively sectioned fracture surfaces. We found a correlation between increasing the fractional part of the fractal dimension and increasing toughness. In other words, as the toughness increasing the fracture surface increases in roughness. However, more than just a measure of roughness, the applicability of fractal geometry to fracture implies a mechanism for generation of the fracture surface. The results presented here imply that brittle fracture is a fractal process; this means that we should be able to determine processes on the atomic scale by observing the macroscopic scale by finding the generator shape and the scheme for generation inherent in the fractal process.     

Surface roughness induced by plasma etching of Si-containing polymers

Interfacial properties of polymers and their control become important at submicrometer scales, as polymers find widespread applications in industries ranging from micro- and nanoelectronics to optoelectronics and others fields. In this work, we address the issue of controlled modification of surface topography of Si-containing polymers when subjected to oxygen-based plasma treatments. Treated surfaces were examined by atomic force microscopy to obtain surface topography and roughness of plasma-treated surfaces. Our experimental results indicate that an appropriate optimization of plasma chemistry and processing conditions allows, on one hand, small values of surface roughness, a result crucial for the potential use of these polymers for sub-100 nm lithography, and, on the other hand, desirable topography, applicable for example in sensor devices. Plasma processing conditions can be modified to result either in smooth surfaces (rms roughness < 1 nm) or in periodic structures of controlled roughness size and periodicity.     

Osteoblasts attachment on amorphous carbon films

In this work we studied the osteoblasts response to amorphous carbon (a-C) films deposited on stainless steel substrates with different surface textures. For osteoblasts cells, attachment to the substrate is the first step in the process of cell/surface interactions which affects subsequent cellular and tissue response. Amorphous carbon films are characterized by very smooth surfaces that imaged the surface roughness of the substrate and many of their applications rely on this property. However, in the biomedical field the cell response is strongly influenced by the topography and particularly, for osteoblasts cells it has been shown that rough surfaces enhances cellular attachment and differentiation. Therefore, in this work we modified the surface roughness of the substrate in order to obtain carbon films with different values of average surface roughness. The substrates were abraded or fine-polished to obtain four different average roughness: 0.01, 1.5, 2.1 and 3.5 μm. Surface topography before and after deposition of the a-C films was evaluated by profilometry and scanning electron microscopy (SEM), while chemical composition was determined by X-ray photoelectron spectroscopy. Human osteoblasts cells were used to evaluate the effect of the different surface finishes on the adhesion. The number of attached cells was determined by a colorimetric technique after 24 h of incubation, while morphological and cytoskeletal changes were monitored using SEM. The cellular attachment on a-C surfaces increases monotonically with the roughness attaining up to 160% more cells than the positive control.