Contact Angle Distribution Research Articles

Quantifying the Effect of Pore‐Size Dependent Wettability on Relative Permeability Using Capillary Bundle Model

AbstractRelative permeability is a key parameter for characterizing the multiphase flow dynamics in porous media at macroscopic scale while it can be significantly impacted by wettability. Recently, it has been reported in microfluidic experiments that wettability is dependent on the pore size (Van Rooijen et al., 2022). To investigate the effect of pore‐size‐dependent wettability on relative permeability, we propose a theoretical framework informed by digital core samples to quantify the deviation of relative permeability curves due to wettability change. We find that the significance of impact is highly dependent on two factors: (i) the function between contact angle and pore size (ii) overall pore size distribution. Under linear function, this impact can be significant for tight porous media with a maximum deviation of 1,000%.

Influences of external moment on the contact characteristics of angular contact ball bearings under combined loads

Angular contact ball bearings are widely used in rotating machinery. The external moment about the bearing lateral direction (i.e. the lateral moment) applied to a bearing affects the service life and performance of the bearings by influencing its internal contact characteristics. This work established a quasi-dynamic model of the ball bearing by comprehensively considering the inclination angle of the inner ring due to external lateral moment, the viscous drag, the inertial force and moment of the ball, the spin and sliding of the ball in the contact ellipse. On this basis, the operation process of angular contact ball bearings was simulated under combined radial and moment loads. The effectiveness of the model was verified experimentally, and the influences of external moments about different directions on the contact angle, slip-roll ratio, and load distribution under combined loads were analyzed. The results show that the increase in moment intensifies the spin-sliding of the rolling element. When the lateral moment and the radial load are applied together, the lateral moment can reduce the maximum load of the rolling element and causes the maximum load of the rolling element to deviate from its original position. When the lateral moment is combined with the axial and radial loads, the bearing load zone is concentrated by the rolling elements near the lateral direction. The curve of the load distribution changes from an ideal oval to a distorted oval. The research results can be used to guide the design, service life calculation, and performance evaluation of rolling bearings.

Bubble generation mechanisms in microchannel under microgravity and heterogeneous wettability

Advances in hybrid surfaces have revealed interesting opportunities for multiphase flow control under microgravity, as the surface tension force is dominant in this condition. However, a comprehensive investigation of bubble generation rates and slug flow parameters remains challenging. This research integrates hybrid wettability and modified dynamic contact angle models to address this important knowledge gap. Using the computational capabilities of the IsoAdvector multiphase method, we performed detailed simulations of complex multiphase flow scenarios with the OpenFOAM package. We then validated these simulation results through rigorous comparison with available experimental data, thereby strengthening the accuracy and reliability of our numerical simulations. Our comprehensive research demonstrates the profound effect of altering contact angle distribution patterns on several critical parameters. These results highlight the precise control that can be achieved through the strategic manipulation of these patterns, offering the possibility of adjusting factors such as bubble production rate, slug length, bubble diameter, the relationship of flow residence to bubble movement, bubble movement speed in the channel, and pressure drop. Interestingly, altering these patterns can also induce asymmetric behavior in bubbles under microgravity conditions, a phenomenon that has significant implications for various applications. Such insights are crucial for fields such as heat transfer in energy systems, reaction mechanisms in chemical processes, multiphase flow control in petrochemical industries, fluid dynamics in aerospace engineering, and cooling mechanisms in electronic devices. With the ability to modulate these fundamental parameters, we gain valuable insights into the design and optimization of microchannel systems. Consequently, this research presents a more efficient and innovative approach to multiphase flow control, promising improved operational performance, and efficiency in various engineering applications.

Effects of cathode gas diffusion layer porosity and contact angle distributions along through-plane direction on the performance of polymer electrolyte membrane fuel cell

In the present work, a numerical model for polymer electrolyte membrane fuel cell (PEMFC) has been employed to investigate the effects of porosity and contact angle distributions of the porous layer on the performance of PEMFC. The three-dimensional, two-phase, and non-isothermal flow solver considers heat transfer, electrochemical reaction, and liquid water saturation. Various cases with different cathode gas diffusion layer (GDL) porosities are performed. The results showed that a better performance is achieved when the GDL porosity is increased because of the reduced mass transport resistance of oxygen. The effects of the porosity distributions on the PEMFC performance were examined by comparing the predictions from the cases with non-uniform porosity and uniform porosity in the cathode GDL. It was shown that the current density of the cases with non-uniform porosity is higher than that of the uniform porosity case when the operation voltage is low. This is due to the fact that non-uniform porosity distributions in the cathode GDL enhance the reactant transport. When the operation voltage is high, the current densities of the cases with non-uniform porosity and uniform porosity are almost the same. Moreover, the influence of contact angle distributions in cathode GDL was explored. Various cases with gradient-decreasing, gradient-increasing, and uniform constant contact angles from GDL/channel interface to GDL/catalyst layer interface were studied. It was found that the case with gradient-increasing contact angle has a better performance due to the larger capillary pressure difference to remove more water. The poor performance of the case with gradient-decreasing contact angle is related to the phenomenon of flooding in the catalyst layer.

Spatial Characterization of Wetting in Porous Media Using Local Lattice-Boltzmann Simulations

Wettability is one of the critical parameters affecting multiphase flow in porous media. The wettability is determined by the affinity of fluids to the rock surface, which varies due to factors such as mineral heterogeneity, roughness, ageing, and pore-space geometry. It is well known that wettability varies spatially in natural rocks, and it is still generally considered a constant parameter in pore-scale simulation studies. The accuracy of pore-scale simulation of multiphase flow in porous media is undermined by such inadequate wettability models. The advent of in situ visualization techniques, e.g. X-ray imaging and microtomography, enables us to characterize the spatial distribution of wetting more accurately. There are several approaches for such characterization. Most include the construction of a meshed surface of the interface surfaces in a segmented X-ray image and are known to have significant errors arising from insufficient resolution and surface-smoothing algorithms. This work presents a novel approach for spatial determination of wetting properties using local lattice-Boltzmann simulations. The scheme is computationally efficient as the segmented X-ray image is divided into subdomains before conducting the lattice-Boltzmann simulations, enabling fast simulations. To test the proposed method, it was applied to two synthetic cases with known wettability and three datasets of imaged fluid distributions. The wettability map was obtained for all samples using local lattice-Boltzmann calculations on trapped ganglia and optimization on surface affinity parameters. The results were quantitatively compared with a previously developed geometrical contact angle determination method. The two synthetic cases were used to validate the results of the developed workflow, as well as to compare the wettability results with the geometrical analysis method. It is shown that the developed workflow accurately characterizes the wetting state in the synthetic porous media with an acceptable uncertainty and is better to capture extreme wetting conditions. For the three datasets of imaged fluid distributions, our results show that the obtained contact angle distributions are consistent with the geometrical method. However, the obtained contact angle distributions tend to have a narrower span and are considered more realistic compared to the geometrical method. Finally, our results show the potential of the proposed scheme to efficiently obtain wettability maps of porous media using X-ray images of multiphase fluid distributions. The developed workflow can help for more accurate characterization of the wettability map in the porous media using limited experimental data, and hence more accurate digital rock analysis of multiphase flow in porous media.

Load Distribution Analysis and Contact Stiffness Prediction of the Dual-Drive Ball Screw Pair Considering Guide Rail Geometric Error and Slide Position

The dual-drive ball screw pair serves as a crucial element within the fixed gantry machine tool with cross-rail movement. When in service, the dual-drive ball screw pair experiences variations in axial load, impacting the contact load distribution of the ball screw pair. A calculation model for determining the axial load offset of the dual-drive ball screw pair is proposed to investigate the variation in axial load. The impact of the geometric error associated with the guide rail and the position of the slide are considered. This paper presents the contact load distribution model for the dual-drive ball screw pair. This study investigates the contact load and contact angle distribution of the dual-drive ball screw pair during the machine tool in service. Additionally, based on fractal theory, the stiffness models of individual micro-convex body and contact surfaces have been established. This study provides a comprehensive analysis of the contact stiffness of the ball screw pair, considering the influence of guide rail geometric error and slide position. In addition, the three-dimensional surface morphology of ball screw pair is obtained by experiments. This paper investigates the contact stiffness distribution of dual-drive ball screw pair during service.

Multi-component multiphase lattice Boltzmann modeling of water purging during supercritical carbon dioxide extraction from geothermal reservoir pores

Carbon dioxide becomes supercritical and purges subcritical liquid water in the rock channels as extracted from geothermal reservoir pores. A pseudopotential multi-component multiphase lattice Boltzmann method is presented to simulate the dynamic behavior of the water droplets under the purge of the supercritical carbon dioxide. The model is verified by thermodynamic consistency, surface tension independence regulation, the coexistence of the two components at different viscosities, and surface contact angle distribution laws. The results show that the stronger the hydrophobicity of the wall with uniform adhesion, the faster the motion of the droplet, and when the wall adhesion is not uniform, the stronger the hydrophobicity of the upstream, the faster the purge. When there are two droplets, the volume of the first one rapidly becomes larger because of the absorption of moisture and encounters enhanced shear force to obtain greater velocity. The second droplet receives the shear force weakened by the first, so its growth rate and movement do not change significantly and will gradually be caught up, leading to the coalescence of the two droplets. As the droplets move and grow, the obstruction to flow increases and the pressure drop will increase.

Stiffness Constitutive Characteristics of Elastic Disordered Microporous Metal Rubber Considering Temperature Effects

Elastic disordered microcellular metal rubber (EDMMR) is a lightweight metal material widely employed for damping or support in high‐temperature environments, addressing the limitations of traditional polymer rubbers. Herein, three sets of solid finite element models of EDMMR with different relative densities are developed using virtual manufacturing technology (VMT). Thermal–mechanical coupled finite element simulations explore the dynamic evolution of two typical spatial topological structures in the material's microstructure: unit contact characteristics and angle distribution under temperature variations. Results indicate that the mechanical performance of the material under high‐temperature loads exhibits distinct spatial topological structures compared to those at room temperature. At 100, 200, and 300 °C, the material experiences internal stress distributions of up to 0.5, 1.2, and 1.8 MPa, respectively, due to expansion. Additionally, during the initial loading stage, stress differentials of approximately 0.4 MPa are observed between different temperatures due to boundary effects. Furthermore, the study investigates the probability density distribution of typical microstructural combinations of EDMMR along the forming direction based on VMT, enhancing the generality of the constitutive model. Finally, three groups of EDMMR samples with different relative densities are prepared using standardized processes, and the model is validated through high‐temperature quasistatic compression experiments.

Various waste polystyrene for useful membrane fabrication: Comparative experimental study

Plastic waste recycling is drawing great attention to prevent the harmful effects resulting from the accumulation of plastic waste, especially as an integrated waste-to-product process. This study introduced a comparative study of two polystyrene (PS) wastes for polymeric membrane fabrication. Two types of polystyrene wastes, transparent and white-coloured, used for yoghurt packaging, were utilized. The commercial PS membrane was also fabricated for comparison. Polystyrene membranes were prepared by a non-solvent induced phase separation (NIPS) method. The prepared membranes were characterized by Fourier-transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), measurements of contact angle (CA), porosity, and pore size distribution. According to the results, the prepared membranes showed an asymmetric structure with a blocked skin layer. Also, the prepared membrane surfaces were partially hydrophilic. Increasing polymer concentration (from 10 to 18 wt.%) enhanced the structural homogeneity of the membrane by obtaining smaller pores. On the other hand, the membranes' porosity decreased with the rise in the polymer concentration. Measurements highlighted the successful fabrication of similar membrane characteristics using two types of PS wastes, making them vivid candidates for water desalination and gas separation applications.

Mechanisms of swelling inhibition and seepage promotion of weathered crust elution-deposited rare earth ore by hydroxypropyl methyl cellulose

In-situ leaching process of weathered crust elution-deposited rare earth ore (WCE-DREO) often faces problems such as poor permeability and occurrence of landslides. The main reasons are the swelling of clay minerals by water absorption and blockage of seepage channels by fine particles. This study proposed using hydroxypropyl methyl cellulose (HPMC) as a novel green swelling inhibitor with the combination of ammonium sulfate ((NH4)2SO4) as an efficient composite leaching agent. The swelling inhibition performance of HPMC on swelling inhibition was evaluated through linear swelling tests and mud ball immersion tests. The mechanisms of HPMC on swelling inhibition and seepage promotion were analyzed by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Scanning electron microscopy (SEM), Surface area analysis (BET), X-ray photoelectron spectroscopy (XPS), Thermogravimetric analysis (TGA), and the contact angle, zeta potential and particle size distribution were characterized. The results indicated that HPMC showed a good performance on swelling inhibition, which improved with the increase of HPMC concentration. HPMC expels the water from the interlayer. Moreover, HPMC adsorbs onto the surface of clay minerals by hydrogen bonding to form a hydrophobic film, which can prevent the clay minerals from hydration swelling. Due to the electric neutrality property of HPMC, the electrostatic repulsion of clay minerals can be reduced. Therefore, the fine particles of the clay minerals can be bridged to form larger particles by the long carbon chain of HPMC which leads to expansion of the seepage channels as well as the improvement of the permeability of the ores. According to the column leaching tests, the novel leaching agent composed of 0.05 wt% HPMC and 2 wt% (NH4)2SO4 not only showed a good leaching capacity of rare earth, but also inhibited the swelling of clay and enhanced the seepage when comparing with traditional leaching agent ((NH4)2SO4). Developing a novel leaching agent benefits the green, safe and high-efficiency exploitation of WCE-DREO.

Variations in pore size and contact angle distributions control rhizosphere rewetting

Rhizosphere wettability decreases upon severe drying leading to periods of prolonged low water content around roots after precipitation or irrigation. These observations were explained by the temporal hydrophobic character of mucilage, while structural alterations of the pore space caused by mucilage, such as pore clogging, remained mostly unexplored. In this study, time-series neutron radiography and a pore network model were used to assess the impact of pore geometry and wettability on water flow following the addition of mucilage in a sand substrate. To do so, we monitored the capillary rise of ethanol and water separately for mucilage contents, ranging from 0.0 to 2.0 mg g−1. A pore network model was developed to analyze the impact of alterations in pore geometry and wettability. Results are compared with analytical solutions of the Lucas-Washburn equation. Rewetting dynamics were explained by a combination of a decrease in effective pore throat size and a global decrease in wettability. The local distribution of wettability, however, appeared of minor importance as dynamics of water imbibition could be matched by a uniform effective contact angle. For 0.1 mg g−1 mucilage content increased wettability was predicted for both approaches: the analytical solution and the pore network model fit. At larger contents, a decrease in wettability occurred which was accompanied by a decrease in derived effective pore and pore throat size. On a minute scale, rewetting appeared to steadily progress at all mucilage contents with accelerated rewetting observed at 0.6 mg g−1 likely related to an increased wetting front length. This study highlights the importance of mucilage on pore geometry in combination with wettability modifications in the rhizosphere. Aside from rhizosphere rewetting, the presented approach provides an opportunity to investigate further wettability-related processes in other soil environments on various spatial scales.

Carboxymethylation enhances the low oil absorption of freeze-thawed tapioca starch in fried ham sausage batter

Excessive consumption of high oil content deep-fried foods increases the risk of obesity and cardiovascular disease. In this study, carboxymethylation was utilized to improve the oleophobic ability of freeze-thawed tapioca starch for deep-fried ham sausage batter. The smallest specific surface area, largest contact angle and oil distribution of the freeze-thawed carboxymethyl tapioca starch (CM-FTS) proved that it had the weakest oil absorption capacity. Carboxymethylation damaged long-range crystalline structures in FTS, but the oil absorption did not increase. Furthermore, carboxymethylation appropriately increased the viscosity of FTS batter which evenly improved its coagulation and adhesion and reduced oil absorption during frying. The decrease of tan δ also indicated that the improvement of gel property of batter inhibited the oil absorption in CM-FTS-batter for the lowest oil penetration. These results demonstrate that carboxymethylation enhances the oleophobic structure of FTS and maintains low oil absorption properties of the batter and the internal ham sausage.

The direct observation and distribution regularity of contact angle for spherical particle attached to air bubble in static three-phase system

Contact angle is a typical parameter to indicate the hydrophobicity of solid surface, and it is usually used to evaluate the wettability and floatability of mineral particles. Directly measurement on contact angle of particles is critical for laboratory research and industrial practice in flotation. By combining the image processing analysis and force balance calculation, a composite method to directly measure contact angle of particle was proposed. The good agreement between observed contact angle and calculated contact angle during lots of experiments proved the accuracy and convenience of this measurement method. The fundamental effects of particle size, hydrophobized time, and bubble size on contact angle distribution of particle were investigated using hydrophobized glass beads with different particle size. For glass beads with same surface hydrophobicity, the contact angle showed a nearly constant trend with varying particle size and bubble size. The essence of distribution regularity of contact angle was uncovered through force calculation analysis. Besides, the central angle is always larger than half of contact angle if a smooth spherical particle successfully attached to an air bubble and achieved equilibrium state.

Investigation on the effect of functional groups on the wettability of coal dust: Experiments and theoretical validation

The interaction between the functional groups of pulverized coal and water molecules is essential to study the wettability of pulverized coal surfaces. Coal dust samples with the same degree of deterioration were modified in this study using appropriate concentrations of nitric acid and hydrogen peroxide. Based on macroscopic experiments such as Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), the functional group content and surface wettability changes of coal dust before and after modification were investigated, respectively. Experiments demonstrated that the increase in the percentage of oxygen-containing functional groups (OFGs) before and after the modification of coal samples improved the hydrophilicity of the coal surface, which was mainly dominated by the effect of O = C-O. Eight simulation systems were also constructed by grafting different functional groups with flaky graphene as the substrate in combination with molecular dynamics (MD) theory. The results of simulated contact angle, interaction energy, and radial distribution function were used to analyze the influence law of these groups on the wettability of pulverized coal in detail. Simulations indicate that the diffusion of water molecules on the coal surface is related to the number of hydrogen bonds formed between water and coal. In the simulated system of polar groups, the hydrophilicity of the interface is enhanced due to the strong hydrogen bonding between water molecules and functional groups. However, for the analysis of non-polar groups, the hydrophobic nature is improved due to the increase of carbon chains. The results of the experiments and the simulations correspond to each other, revealing the reasonableness of the simulations. It was finally confirmed that the wetting ability of water molecules for the eight functional groups was in the order of: –COOH > –OH > –CHO > –NH2 > –COC > –CH3 > -C2H5 > -C3H7.

PH Responsiveness of Microwave Polymer-Type Modified Magnetic Nanoparticles for Synergistic Emulsion-Breaking Effect on Thick Oil

Summary In this study, a polymeric magnetic emulsion-breaking compound of ferric tetroxide and cationic polyacrylamide (Fe3O4@CPAM) was designed and synthesized, and its functional groups, chemical bonding, magnetic properties, and thermal stability were characterized. Finally, the pH-responsive behavior of the microwave-modified magnetic nanoparticles (MNPs) in terms of their demulsification effect on thick oil-in-water emulsions was investigated using the morphology and distribution of oil droplets, zeta potential, and contact angle of the MNPs. The results showed that with increasing pH, the water separation of the emulsion initially decreased and then increased, and the best emulsion-breaking effect was achieved at pH 3. The highest water partition of the emulsion was 64.39% at a concentration of 175 mg/L for Fe3O4 MNPs alone before modification. Under the same conditions, the water separation rate of the emulsion for Fe3O4@CPAM was 78.95%, indicating that, compared with the conventional demulsification method, microwaves can promote oil-water separation. The highest water separation rate of MNPs before microwave modification was 85% at pH 3, whereas the water separation rate of MNPs after microwave modification reached 94.70% under the same conditions. This proves that microwaves and modified MNPs have a synergistic emulsion-breaking effect, mainly because the combination of microwaves and polymer modification enhances the hydrophobicity and neutralizes the charge of the MNPs, thus improving the emulsion-breaking efficiency.

Dynamics of microswimmers near a liquid–liquid interface with viscosity difference

Transport of material across liquid interfaces is ubiquitous for living cells and is also a crucial step in drug delivery and in many industrial processes. The fluids that are present on either side of the interfaces will usually have different viscosities. We present a physical model for the dynamics of microswimmers near a soft and penetrable interface that we solve using computer simulations of Navier–Stokes flows. The literature contains studies of similar isoviscous fluid systems, where the two fluids have the same viscosity. Here, we extend this to the more general case where they have different viscosities. In particular, we investigate the dynamics of swimmers approaching a fluid–fluid interface between phase-separated fluids with distinct viscosities. We find that the incoming angle, viscosity ratio, and swimming type (i.e., pusher, puller, or neutral) strongly influence the collision, resulting in four distinct dynamical modes: bouncing, sliding, penetrating, and hovering. The former three modes are also observed for isoviscous systems, while the hovering, in which strong pullers swim parallel to the interface at a non-zero distance, requires mismatched viscosities. Furthermore, swimmers exhibit a preference for lower viscosity fluids, known as viscotaxis. This implies that, for a wide distribution of contact angles, more swimmers will transition into the low-viscosity environment than vice versa. Consequently, a swimmer starting in a low-viscosity fluid is more likely to bounce back at the interface, while a swimmer in a high-viscosity fluid is more likely to penetrate the interface and enter the lower viscosity fluid.

Preparation and Physico-Chemical Characterization of OSA-Modified Starches from Different Botanical Origins and Study on the Properties of Pickering Emulsions Stabilized by These Starches.

Native starch (NS) from different botanical origins (native rice/tapioca/oat starch, NRS/NTS/NOS) were hydrophobically modified by octenyl succinic anhydride (OSA), and the octenyl succinic (OS) groups were successfully introduced in the starch molecules which obtained OS-starch (OSRS, OSTS and OSOS) with different levels of modification (0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%) and degree of substitution (DS). The structural properties of the OS-starch, such as granule size, crystal, wettability and morphology were studied, and the OS-starch was used as particulate stabilizers to produce oil-in-water (O/W) Pickering emulsions. The emulsion index, droplet size distribution and microstructures of Pickering emulsions produced by different OS-starches were compared. OSA modification had almost no effect on the morphology or crystal structure types of three kinds of NS and OS-starch but markedly increased the contact angle and particle size distribution of OSRS, OSTS and OSOS. Esterification reaction of OSA and starch mainly occurred in amorphous regions of starch, and the OSA significantly improved the emulsifying capacity of OSRS, OSTS and OSOS granules and thus stabilized emulsions formed at higher levels (2.5% and 3.0%) of modification of OS-Starch exhibited better stability; the ability of OS-starch to stabilize Pickering emulsion was 3.0% OSRS > 3.0% OSOS > 3.0% OSTS, respectively. Observation and structural properties analysis of OS-starch granules and Pickering emulsion droplets showed that the number and thickness of the starch granules on the oil-water interface of the emulsion droplets increased with improvement of the OSA modification level, and an aggregation state was formed between the OS-starch granules, which was also enhanced with the OSA modification levels. These were all necessary for the Pickering emulsion stabilized by starch granules to remain in a steady state.

Forced imbibition and uncertainty modeling using the morphological method

The morphological approach is a computationally attractive method for calculating relative permeability and capillary pressure saturation functions. In the corresponding workflow, morphological operations are used to calculate the fluid phase distribution in the pore space of a digital twin. Once the pore space is occupied, the conductivity of the individual fluid phases and thus the relative permeability can be calculated by direct flow simulations. It therefore combines computationally favorable geometric operations with direct flow simulations. In contrast to pore network modeling, all calculations are directly performed on the digital twin without abstraction of the pore space. While the morphological operations conceptually correctly describe primary drainage processes and delivers good results, the method so far failed to describe imbibition processes and the influence of wettability. In this work, we implement contact angle distributions in a deterministic and stochastic way. In this manner, we extend the simulated saturation range from purely spontaneous to forced imbibition, resulting in a full-range imbibition relative permeability. Furthermore, by introducing stochastic contact angle distributions, different fluid phase distributions are obtained, which now allow for an uncertainty analysis. To verify the simulation results, we check (a) whether the simulation results agree with SCAL measurements and (b) compare morphologically and experimentally derived results on the pore scale. With the newly introduced concepts, the imbibition process behaves as physically expected, and shows a good agreement with experimentally derived relative permeability curves and microscopic fluid-phase distributions.

Retention Forces for Drops on Microstructured Superhydrophobic Surfaces.

Accurate models of retention forces between drops and superhydrophobic (SH) surfaces are required to predict drop dynamics on the surface. This retention force is, in turn, useful in modeling heat transfer rates for dropwise condensation on a SH surface. Drop contact angle distribution and base area on SH surfaces are essential factors for predicting retention forces. The present work measures the contact angle distribution and base area shapes of various drop sizes over a wide range of solid fraction for inclined microstructured SH surfaces at the point of drop departure. Base area shape was found to be well approximated using two ellipses with different aspect ratios, and the contact angle distribution was found to be best fit by a sigmoid function. At an incline near the roll-off angle, drop base area for surfaces with solid fraction close to 1 and close to 0 were found to be nearly circular, whereas the base area of drops on surfaces with an intermediate solid fraction deviated from circular behavior. In this work, maximum advancing and minimum receding contact angles were found as a function of solid fraction and used to calculate retention forces. Contact angle distribution and base area shapes are then used to calculate retention forces between drops and SH surfaces. These calculations are compared with the component of measured drop weight acting parallel to the plane on a tilted surface for validation. Previous retention force studies that investigate base area shape and contact angle distribution for smooth surfaces are not applicable for microstructured SH surfaces. The work shows that using a sigmoid contact angle distribution and modified base area shape yields retention forces that are on average 50% better than previously reported methods. Retention forces for smooth and SH surfaces calculated in this study were used to suggest retention force factor values for varying solid fraction surfaces.

Deposition of superhydrophobic film on cylindrical ceramic with atmospheric pressure plasma jet

The aim of this study is to deposit a superhydrophobic film on the cylindrical ceramic surface with APPJ. The influences of treatment parameters such as treatment duration, distance, and rotation speed, on the film hydrophobicity, are investigated. The results for static treatment show that a superhydrophobic organosilicon film is deposited on the central region of the ceramic surface at optimal treatment distance and treatment duration of over 2 min. The film hydrophobicity is constricted by short or long treatment distances due to insufficient film deposition to form micro-nano mountainous structures covering the original crystal structures of the ceramic surface. Moreover, the water contact angle distribution is discovered to present as layering ellipses, and its mechanism is explored based on the interactions between the cylindrical material and APPJ. Dynamic treatment is performed, and a uniform superhydrophobic film six times longer than the plasma plume diameter is obtained within the rotation speed of 120 r/min. Results in this paper serve as guidance for the application of plasma jets in film deposition on non-planar material surfaces.