Surface micro- and nanostructural modifications of dental and orthopedic implants have shown promising in vitro, in vivo and clinical results. Surface wettability has also been suggested to play an ...important role in osteoblast differentiation and osseointegration. However, the available techniques to measure surface wettability are not reliable on clinically relevant, rough surfaces. Furthermore, how the differentiation state of osteoblast lineage cells impacts their response to micro/nanostructured surfaces, and the role of wettability on this response, remain unclear. In the current study, surface wettability analyses (optical sessile drop analysis, environmental scanning electron microscopic analysis and the Wilhelmy technique) indicated hydrophobic static responses for deposited water droplets on microrough and micro/nanostructured specimens, while hydrophilic responses were observed with dynamic analyses of micro/nanostructured specimens. The maturation and local factor production of human immature osteoblast-like MG63 cells was synergistically influenced by nanostructures superimposed onto microrough titanium (Ti) surfaces. In contrast, human mesenchymal stem cells cultured on micro/nanostructured surfaces in the absence of exogenous soluble factors exhibited less robust osteoblastic differentiation and local factor production compared to cultures on unmodified microroughened Ti. Our results support previous observations using Ti6Al4V surfaces showing that recognition of surface nanostructures and subsequent cell response is dependent on the differentiation state of osteoblast lineage cells. The results also indicate that this effect may be partly modulated by surface wettability. These findings support the conclusion that the successful osseointegration of an implant depends on contributions from osteoblast lineage cells at different stages of osteoblast commitment.
•Dynamic wetting is studied on surfaces with 3D roughness by GPU-LBM.•The 3D roughness morphology effects are investigated.•The overall surfaces remain hydrophilic and Wenzel state at low Ca, ...different from 2D simulations.
Dynamic wetting on rough surface is important in imbibition processes in micro- and nano- channels. Due to high computational costs, the previous studies by direct numerical simulations mostly adopted two-dimensional (2D) simplifications of surface with roughness. The cutting-edge advances in high performance computing make it possible to conduct three-dimensional (3D) direct simulations. This work presents 3D simulations on channel flows with roughness on walls via the GPU-based multiphase lattice Boltzmann method (LBM). The effects from 3D roughness morphology are investigated. In contrast to the wettability alternation in 2D rough ones, the 3D rough hydrophilic surfaces remain hydrophilic and Wenzel state at even low capillary numbers (Ca). The apparent contact angle follows the hydrodynamic model on rough surfaces except for a more sensitivity to Ca. The results also indicate that the 2D simplifications overestimate the pressure drop for rough channels, while underestimate over 20% for smooth channels. Therefore, it is crucial to consider 3D structures of surface roughness for dynamic wetting in real channels.
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A comprehensive study of molten alloy capillary flow in the wetting/non-wetting wedge-tee configuration is presented. The horizontal Al2O3 substrate is non-wetting, while the vertical, AlMn alloy ...AA3003, is wetting. The braze alloy is a composite of an aluminum‑silicon alloy (Al10Si) with potassium fluoro-aluminate flux embedded. The purpose for selecting such a wetting/non-wetting configuration is for repair and construction in space by means of brazing. When capillary forces are not opposed by gravity, the spreading of a liquid braze may be controlled by a non-wetting surface.
Specifically, we study: (i) the evolution of the free surface shape of a large melt mass in the gravity field, (ii) kinetics of advancing/receding triple lines and dynamic contact angles, and (iii) microstructure of the resolidified molten alloy on the substrates.
The receding contact line exhibits a sudden withdrawal towards the corner, then a long-time stagnation before final equilibrium in the corner. In contrast to the typical monotonic evolution of the advancing contact angle, the receding contact angle features an anomalous non-monotonic behavior. The microstructure of the re-solidified sample features a phase macrosegregation.
Characterizing the contact line dynamics on solid walls is often a crucial problem encountered in the simulation of complex interfacial unsteady flows, such as drop impacts on solid surfaces. In this ...work, a new model is proposed to reproduce the contact line dynamics in a simple but effective way, based on introducing in the momentum equation a force term proportional to the deviation of the calculated contact angle from the value predicted by a dynamic model that takes into account wettability hysteresis. The model has been implemented in a volume of fluid (VOF) method and is applied to the simulation of drop impacts leading to deposition outcomes, although it could be extended to other interface tracking methods and is also applicable to more complex drop impacts involving fingering and splashing. Numerous tests have been performed to evaluate the accuracy and robustness of the proposed model over a wide range of Reynolds and Weber numbers. The results substantially improve those obtained by imposing only the contact angle as a boundary condition at the contact line, and satisfactorily predict a variety of experimental results from the literature for very different impact and wettability conditions.
•A new force model for accurate reproduction of contact line dynamics is proposed.•Force based on deviation of the computed contact angle from a dynamic model.•Isosurface extraction to measure the contact angle and locate the contact line.•Experimental and numerical validation of the model in drop deposition VOF simulations.
Ti6Al4V is widely used in industrial fields due to its many excellent properties, but it still has the disadvantages of poor wear resistance. In order to broaden its application range, it needs to be ...connected with other materials with complementary properties. The method of sealing glass to connect dissimilar materials is widely used because of its low cost and low difficulty. In this study, Ti6Al4V was pre-oxidized by thermal oxidation method, and it was found that the oxidation temperature and holding time had a significant effect on the surface morphology and properties of the alloy. The wetting behavior between bismuthate sealing glass and Ti6Al4V under atmospheric conditions was investigated by sessile drop method. The effect of pre-oxidation temperature on the wettability of the alloy surface was studied by high temperature contact angle measuring instrument during the dynamic heating process. Combined with interface analysis, it was found that the sealing glass reacted with the Ti6Al4V alloy to form Bi4Ti3O12, and the reaction degree of Ti4+ and Bi3+ was the main reason for the wetting of the glass on the alloy surface. It was concluded that the higher the proportion of TiO2 on the surface, the better the wettability.
Typical VOF algorithms rely on an implicit slip that scales with mesh refinement, to allow contact lines to move along no-slip boundaries. As a result, solutions of contact line phenomena vary ...continuously with mesh spacing; this paper presents examples of that variation. A mesh-dependent dynamic contact angle model is then presented, that is based on fundamental hydrodynamics and serves as a more appropriate boundary condition at a moving contact line. This new boundary condition eliminates the stress singularity at the contact line; the resulting problem is thus well-posed and yields solutions that converge with mesh refinement. Numerical results are presented of a solid plate withdrawing from a fluid pool, and of spontaneous droplet spread at small capillary and Reynolds numbers.
Liquid water flow behavior in the microchannel is of crucial importance to the water management in proton exchange membrane fuel cells (PEMFCs). In this study, the liquid water flow regimes in a ...single straight microchannel are numerically investigated using the volume of fluid (VOF) method with the dynamic contact angle (DCA). Various air and liquid water inlet flow velocities are considered in the simulation to study their effects on the gas-liquid behaviors and flow structure. It was found that the liquid water injection rate is the dominant factor for the formation of different flow regimes: the increase of water inlet velocity will lead to the transition from squeezing flow to partial-jetting flow and jetting flow. Meanwhile, the air inlet velocity can also significantly affect the flow patterns: the higher inertial air flow will facilitate the detachment of liquid water under the squeezing flow, and greatly accelerate the transition process from liquid water blob to the film under the jetting flow.
•Liquid water flow regimes in a microchannel are simulated using VOF method.•Dynamic contact angle model is employed to conduct numerical simulation.•Various air and water inlet flow velocities are considered in the simulation.•Squeezing flow, partial-jetting flow and jetting flow are observed and discussed.
In the numerical simulation of water management for proton exchange membrane fuel cells (PEMFCs), the static contact angle (SCA) model is generally used. However, an empirical correlation for dynamic ...contact angle (DCA), known as Hoffman function or Kistler's law, was recently employed to numerically simulate the droplet behaviors either in a microchannel or on a surface. In this paper, for the first time, a DCA evolution map is created based on Hoffman function and related experiments to better understand the DCA evolving mechanism; based on this evolution map, the Advancing-Receding DCA (AR-DCA) model is proposed and explained, in addition to the Advancing DCA (A-DCA) model that is based on the original Hoffman's experiments; using user defined function (UDF), the A-DCA and AR-DCA models are implemented with Volume of Fluid (VOF) method in ANSYS Fluent; a series of numerical simulations are conducted with the SCA, A-DCA and AR-DCA models for droplet impact on horizontal and inclined surfaces; the validations of these contact angle models are performed, qualitatively and quantitatively, by comparing the numerical simulation results with the corresponding experimental results from the literature. It is indicated that the AR-DCA model can better simulate the droplet deformation and evolvement, showing its potential for the DCA simulations in a more complex gas-liquid flow domain such as the cathode of PEMFCs.
•DCA evolution map is created to better understand the DCA evolving mechanism.•The concept of A-DCA and AR-DCA models are proposed for the first time.•Comparisons of A-DCA, AR-DCA and SCA models are conducted for the first time.•Validations of contact angle models are performed qualitatively and quantitatively.•AR-DCA model has potential to better capture DCA features in PEMFC-simulations.
•The effect of eccentricity on the threshold capture velocity of droplets with fiber is studied.•Increasing eccentricity decreases the threshold capture velocity.•The analytical solution considering ...the surface wettability is presented.•The analytical model can estimate the threshold velocity with fair accuracy.•The hydrophobic fibers may only capture the small droplets in a central impact.
The experimental study and volume of fluid numerical simulation are performed to study the capturing mechanism of liquid droplets in fibrous filters. The study is done by focusing on the single droplet impact on a horizontal fiber. In the meantime, analytical expression based on the energy balance method incorporating the effect of variation of wall adhesion and droplet eccentricity is developed for the threshold capture velocity of the droplet. The comparison of experimental results with the analytical expression shows a better agreement than the previous analytical methods where the effects of variation of wall adhesion and droplet eccentricity were not taken into account. The results of our study show that increasing the eccentricity and the ratio of droplet radius to fiber radius result in decreasing the threshold velocity of droplet capture with hydrophilic fibers. In the case of hydrophobic fibers with receding angle over 90°, the droplet capture is only observed for the central impact of small droplets.
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