Capillary bonding of wet surfaces - the effects of contact angle and surface roughness

Capillary bonding of wet solids through a water film is common and important for a variety of problems. An existing experimental technique for the measurement of capillary bonding forces was improved and used to show how fractional wetted area and capillary bonding force vary with water 'tension' for glass, polyethylene, and aluminum on porous ceramic. The effects of contact angle and roughness were explored. The results show that increasing the contact angle clearly reduces the capillary bonding, but the effects of surface roughness were much more complicated. Roughness can increase or decrease capillary bonding, depending on the exact conditions.     

On surface roughness effects in wetting phenomena

A survey of the literature which builds on concepts put forth by Good in 1952 relating to surface roughness effects in wetting phenomena is performed. Good proposed a thermodynamic equation which could be used to derive the relationship between the various interfacial energies in a solid/fluid/fluid system and the angle of interception at the three-phase line of contact. This formulation allowed the derivation of Young's equation and its variations, such as Wenzel's equation, which accounts for surface roughness effects on the equilibrium contact angle. In the same work, Good also proposed the free energy barrier concept as a possible cause for contact angle hysteresis as the three-phase line of contact undergoes contortion between mechanically stable configurations. Mechanistic arguments were needed to account for hysteresis effects not predicted in the strictly thermodynamic approach. Subsequent works which extended the global thermodynamic or mechanistic perspectives were examined. Common critical underlying assumptions were inspected in both the thermodynamic and the mechanistic views, such as local enforcement of Young's equation.     

Thermal effects on stereolithography injection mold inserts

Stereolithography is a process in which a photopolymerizable resin is used to make parts. This method is used here to produce mold inserts for small injection molding runs. This paper focuses on the effects of the heat due to the injection of the polymer on these mold inserts. As the number of shots increases, the degree of cure of the insert changes. Differential Scanning Calorimetry (DSC) was used to determine the thermal property changes of the material. The evolution of the ejection forces for different post‐cure treatments was investigated. The ejection force decreased with increasing cure of the mold inserts.     

The effects of surface roughness on varnish adhesion strength of wood materials

In this study, the effects of surface roughness of wood material on the adhesion strength of varnish layers have been tested. For this purpose, test samples of beech (Fagus orientalis L.), Scots pine (Pinus sylvestris L.), and cherry (Prunus cerasus) wood species were prepared and sanded with 80, 120, and 180 grit abrasives. The surface roughness values of specimens were determined using a stylus-type profilometer TIME TR 200 according to the ISO 4287 standards. Then, water-based, polyurethane, and acrylic varnish were applied to the surfaces of the samples in accordance with ASTM-D 3023. Layer adhesion strength was determined to the TS EN ISO 4624 standards. As a result, the highest adhesion strength value (2.52 N/mm²) was found in cherry, while the Scots pine had the lowest value (2.32 N/mm²). For the varnish types, polyurethane varnish types gave the highest value (3.15 N/mm²), while the lowest value was obtained from the water-based varnish. Looking at interactions between adhesion strength and surface roughness, the water-based varnish had the strongest correlation with adhesion strength (69%) and acrylic varnish also had a similar result (67%), while polyurethane varnish had the weakest result (33%) in this interaction.     

Effect of femtosecond laser beam angle and formed shape on surface roughness and shear bond strength between zirconia and resin cement

Achieving adhesion between resin cement and zirconia requires pretreatment of the surface. This in vitro study aimed to evaluate the effect of femtosecond laser beam angle and the shape of the formed surfaces, on the roughness and shear bond strength (SBS) of resin cement to zirconia ceramic. Seventy Y-TZP ceramic specimens were divided into seven groups (n = 10). A femtosecond laser irradiation was performed on the ceramic surface of three shapes (spiral (SP), square (SQ) and circular (CI) and at two angles (30 and 90°) to give SP-30, SQ-30 and CI-30 and SP-90, SQ-90 and CI-90, respectively. After treatment, the surface roughness of all specimens was evaluated using a profilometer. One specimen from each group was analysed using a scanning electron microscope. The bonded specimens were thermocycled 5000 times and then an SBS test was performed. Kruskal-Wallis and Mann-Whitney U tests were used to analyse surface roughness and SBS values. The control group had statistically lower surface roughness (R_a) values than the treated groups (p < 0.05). SP-30 and SQ-30 laser treated specimens showed higher R_a values than the other specimens. Statistically significant SBS values (p = 0.000) were observed between the groups. All laser treated samples showed greater SBS compared to the control group. SP-30, SQ-30 and SQ-90 groups showed the highest SBS values. Within the limitations of this experimental study, the highest mean values for R_a and SBS were achieved with SP and SQ surfaces using a 30° angle laser beam.     

Effects of surface roughness on microinjection molding

Injection molding is one of the most common processes for cost‐effective mass production of microplastic parts. When the dimensions of the part, and thus the cavity of the mold, are small, microscale factors which are normally neglected in the analysis of conventional injection molding may play an important role. This investigation addresses the effects of mold surface roughness on the injection of polymer melt, which is a non‐Newtonian fluid, during the filling stage of microinjection molding. The surface roughness effect on the volume of the mold cavity is discussed. A simple, but effective model, to describe the conductivity and the specific heat of the surface roughness is proposed. Subsequently, by employing the finite volume method and the level set method, a numerical procedure incorporating the proposed surface roughness model to describe the flow behavior of the polymer melt in the cavity is implemented. Finally, simulation on the melt flow injected into a microdisk cavity is performed using the proposed model and the results are found to be in good agreement with experiment. POLYM. ENG. SCI., 47:2012–2019, 2007. © 2007 Society of Plastics Engineers     

The effects of tannins on adhesion strength and surface roughness of varnished wood after accelerated weathering

This study evaluated the effect of accelerated weathering on the adhesion strength and surface roughness of beech wood (Fagus orientalis) treated with mimosa and quebracho extracts and coated with polyurethane, water-based, and cellulosic varnishes. Untreated beech wood blocks and beech wood blocks treated with Tanalith-E were used as control samples. Test samples were exposed to accelerated weathering processes of 100 and 300 h. According to the test results, the mean adhesion strength of the wood samples impregnated with mimosa and quebracho tannins decreased by a maximum of 20%, while increases in the mean surface roughness (R _a) were detected. The highest adhesion strength and lowest mean surface roughness were obtained with polyurethane varnish. Moreover, the mean adhesion strength increased with the accelerated weathering up to 100 h and then decreased thereafter. As a result of the weathering process, the mean surface roughness increased and was thus negatively affected.     

Experimental investigation of key parameters on the effects of cavity surface roughness in microinjection molding

For microinjection molding, it is envisaged that cavity surface roughness plays an important role in the cavity filling of polymer melt. This article presents an experimental investigation into the surface roughness effects on the flow area of a microthickness disk through injection molding. Three core inserts, each of which has different surface roughness on its two semicircular halves but with the same roughness mean lines, were machined and formed the mold cavity. The difference in flow area (or volume) between these two semicircular halves of the molded part was investigated by varying the mold and melt temperatures. Regressive analysis of the significance of mold and melt temperatures and cavity thickness on the surface roughness effects was carried out. Experimental results obtained indicated that the flow area on the smoother half is larger than that on the rougher half during cavity filling. For the same surface roughness, its effect on cavity filling is a function of mold temperature, melt temperature, and cavity thickness. An increase in mold temperature or melt temperature will result in smaller surface roughness effect on the flow area. When cavity thickness is reduced, the surface roughness effect will become more significant. Moreover, a larger difference in the surface roughness between the two semicircular halves of the insert will result in a larger difference in the flow area between the two halves of the molded part. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers.     

The effect of surface roughness on condensing steam

Heal transfer coefficients for steam condensing on the outside of a smooth, and three artificially roughened pipes have been obtained for a condensate film Reynolds Number range of 1,500 to 9,000. Dimensionless local and mean heat transfer coefficient are presented, and in all cases significant increases in tht coefficients for the rough pipes are observed.     

Thermometry of the working surface of glass molds

Translated from Steklo i Keramika, No. 1, p. 9, January, 1988.     

花岗石磨抛光表面粗糙与光泽度比较

对三种不同晶粒度的花岗石抛光表面的和光泽度特性进行了研究,对同一块花岗石不同测量点的光泽度的离散性进行了分析,比较了粗糙度和光泽度作为花岗石抛光表面质量评价指标适用性,指出光泽度更适合作为评价花岗石抛光表面质量的指标,该研究为花岗石抛光表面质量的评价提供了依据.     

Tailoring of Seebeck coefficient with surface roughness effects in silicon sub-50 nm films

ABSTRACT: The effect of surface roughness on the seebeck coefficient in the sub 50 nm scale silicon ultra thin films is investigated theoretically using nonequilibrium Green's function formalism. For systematic studies, the surface roughness is modelled by varying thickness periodically with square wave profile characterized by two parameters: amplitude (A0) and wavelength (lambda). Since high Seebeck coefficient is obtained if the temperature difference between the ends of device produces higher currents and higher induced voltages, we investigate how the generated current and induced voltage is affected with increasing A0 and lambda. The theoretical investigations show that pseudoperiodicity of the device structure gives rise to two effects: firstly the threshold energy at which the transmission of current starts is shifted towards higher energy sides and secondly transmission spectra of current possess pseudobands and pseudogaps. The width of the pseudobands and their occupancies determine the total generated current. It is found that current decreases with increasing A0 but shows a complicated trend with lambda. The trends of threshold energy determine the trends of Seebeck voltage with roughness parameters. The increase in threshold energy makes the current flow in higher energy levels. Thus the Seebeck voltage i.e. voltage required to nullify this current increases. Increase in Seebeck voltage results in increase in Seebeck coefficient. We find that threshold energy increases with increasing A0 and frequency (1/lambda). Hence Seebeck voltage and Seebeck coefficient increases vice versa. It is observed that Seebeck coefficient is tunable with surface roughness parameters.     

Analytical modeleing of contact mechanics of helical gear tooth by considering surface roughness effects

Abstract

Release of metal debris from a pair of gear teeth is a consequence of their contact. Any excessive metal debris can lead to the onset of fatigue and failure. This paper aims to derive a contact mechanics-based model to obtain the energy absorption of helical gear teeth. The proposed model includes the roughness effect of teeth contact surfaces. The mean value of the asperity summit curvature, the standard deviation of the asperity height distribution and the area density of the asperity height distribution are the three statistical parameters that describe the micron-scale surface roughness. An explicit approximation is obtained to relate the contact load and the minimum surface separation and to estimate the energy loss. Then an analytical expression is derived for the plastic energy dissipation per cycle as a function of plasticity index for gear teeth. The proposed function can be applied in the design of gears by engineers and manufacturers. Additionally, a pertinent lumped mass at the area of interaction is assumed to describe the contact frequency and damping ratio using a nonlinear dynamic model.     

微流道粗糙壁面对流动阻力和控制的影响

研究了3种粗糙单元(三角形、矩形、三角形与矩形交错混合)壁面对微流道内流动和摩擦阻力的影响。利用二维模型模拟了量纲一泊肃叶数与粗糙单元的几何特性和分布的关系。结果发现:在模拟条件下,粗糙壁面摩擦阻力(泊肃叶数)总是大于光滑壁面的摩擦阻力;壁面粗糙单元的高度对摩擦阻力的影响较大,可有近乎指数型的增长,粗糙单元的长度和间隔的影响居中,而雷诺数的影响较小。说明壁面粗糙度可有效改变槽道内的流动状态,增大混合效率。     

Surface roughness effects onmicroparticle adhesion

A new self-consistent model is developed to treat the static contact of a microparticle with a flat barrier in the presence of molecular adhesion and surface roughness. Separation between their mean datum planes is modeled considering the elastic deformation of the microparticle and surface. The contact pressure is computed from the Lennard-Jones law following the Derjaguin approximation. The elastic deflection of the mean datum plane is calculated from the effective pressure by the half-space elastic theory. Roughness is modeled by introducing a Gaussian distribution to the gap between the surfaces. An effective pressure is defined as the statistical average of the contact pressure over the roughness heights. A solution satisfying all of the above conditions gives a self-consistent method of modeling adhesion between the microparticle and the flat barrier. Using collocation methods the equations are discretized as a large system of nonlinear algebraic equations. A continuation method is used to find the multiple numerical solutions for the mean separation and the effective contact pressure. Finally, adhesive contacts of both smooth and rough surfaces are simulated in a comparative manner to elucidate the features of surface roughness in the presence of molecular adhesion. The standard deviation of the Gaussian distribution is used as a parameter to assess the effects of roughness on the pull-off force. It is shown that increasing surface roughness significantly reduces the pull-off force and decreases the tendency for the microsphere to snap-on and snap-off.     

The effects of surface roughness and bond thickness on the fatigue life of adhesively bonded tubular single lap joints

Since the surface roughness of adherends greatly affects the strength of adhesively bonded joints, the effect of surface roughness on the fatigue life of adhesively bonded tubular single lap joints was investigated analytically and experimentally by a fatigue torsion test. The stiffness of the interfacial layer between the adherends and the adhesive was modelled as a normal statistical distribution function of the surface roughness of the adherends. From the investigation, it was found that the optimum surface roughness of the adherends for the fatigue strength of tubular single lap joints was dependent on the bond thickness and applied load.     

表面粗糙度对镍镀层结合性能的影响

对玻璃基双层镍表面进行阳极活化以提高镍层之间的结合强度。阳极活化液组成和工艺条件为:NiCl2·6H2O 100 g/L,H3BO3 25 g/L,pH 4.0,温度45°C,阳极电流密度10~30 mA/cm2,时间5~15 min。研究了电流密度和处理时间对镍镀层表面形貌、孤岛结合力、表面粗糙度和界面结合强度的影响,探讨了双层镍表面粗糙度和界面结合强度的关系。结果表明,在30 mA/cm2下阳极活化10 min后,双层镍的界面结合强度为629.8 MPa,比盐酸活化试样高了近2倍。镍层表面粗糙度与界面结合强度之间有明显的对应关系,表面粗糙度越大,界面结合强度越高。采用阳极活化法可有效提高微机电系统微器件的可靠性。