Condition For Detachment Research Articles

Wetting State Transition of Laser Direct Writing Aluminum Surface Based on Coupling Effect of Micro/Nanoscale Characteristics.

Micro/nanostructured metal surfaces fabricated by laser direct writing (LDW) have been widely used in wettability-related fields. Previous studies focused on the effects of surface structural patterns or chemical composition on wettability, while the coupling mechanism and respective contributions of the two are not distinct. This paper reveals the coupling effect of micro/nanoscale characteristics on the wettability of LDW aluminum surfaces and elucidates the transition mechanism between wetting states on the surfaces with linear laser energy density. Through the contact angle experiments, a wetting state transition of the LDW surface is found from a more hydrophilic than pristine rose petal effect to lotus effect. Based on the bionic analysis method of the superhydrophobicity factors of lotus leaves, the contributions to the wettability of LDW surfaces are divided into the micro/nanoscale characteristics. The theoretical model for identifying the wetting state of a rough surface is proposed. Based on this model, the average Young's contact angle, θ̅Y, is calculated, which indicates the contribution of the nanoscale characteristics. During the transition process from rose petal effect to lotus effect, θ̅Y > 90° is a necessary condition for detachment from the rose petal effect, which is contributed by the high specific surface organic adsorption at the nanoscale. What is more, the wetting state determined by the microscale characteristics further enhances its hydrophobicity, leading to the lotus effect. Based on the wetting state identification model and the Cassie-Baxter equation, the change of micro/nanoscale characteristics on aluminum surfaces after LDW treatment is presented, and the influence of micro/nanoscale characteristics on the wetting state is decoupled and quantified. This research helps to coordinate the effects of surface structure and chemical composition on wettability in the design of specific wettability functional surfaces and can also be applied to other high heat density surface processing fields.

Sliding characteristics of bioinspired polydimethylsiloxane micropillars under bending states

Surface micropillars of soft material, inspired by biological structures, are widely designed and applicated to flexible electronics and micro/nano-robots. The surface micropillars trends to be bent during the sliding process. Herein, sliding characteristics of hexagonal polydimethylsiloxane (PDMS) micropillars under different bending states and micropillar numbers were investigated. Finite element and dynamic friction models were introduced to analyse the sliding mechanism. The friction coefficient can be adjusted by the bending states of the PDMS micropillar. The sliding characteristic is an elongating-rebounding process. The elongating process is divided into two stages (creep and peel), and the rebounding process is divided into two stages (slip and stick). The condition for mass-belt detachment is established based on the dynamic friction model.

Investigation of the detachment of oil droplets driven by water shear field on solid surfaces with different wettabilities

The movement and detachment of tiny oil droplets in water on a substrate is the key technology to strengthen oil–water separation by using corrugated plate oil–water separation technology. Here, the detachment behaviors of oil droplets adhered to substrates with different wettabilities in a laminar flow field are studied experimentally and theoretically. The morphologic changes of mother and daughter oil droplets are obtained when the adhered oil droplets are continuously separated. The shedding mechanism of oil droplets is analyzed in detail, and the critical condition for the effective detachment of oil droplets is obtained, which can be used to guide the design of the surface wettability and water flow velocity in the actual production of oil–water separation.

Vibration-induced detachment of droplets on superhydrophobic surfaces

Vibration is a robust and efficient method for droplet removal from superhydrophobic surfaces. In the present work, we experimentally investigated the dynamics of droplets on vibrating superhydrophobic surfaces, and established a mass-spring-damper theoretical model, to clarify the underlying physics of vibration-induced droplet detachment. Different droplet oscillation patterns were experimentally observed, namely, the droplet motion is in the same/opposite direction with the substrate when the vibration frequency is less/higher than the resonance frequency, respectively, and the transition occurs at the resonant frequency. The motion of the droplet is found to be composed of a transient response by the droplet free oscillation and a steady-state response by vibrating substrates. The critical condition for droplet detachment was identified to be the droplet energy (sum of the surface energy and kinetic energy) exceeds the surface adhesion energy. At the resonance frequency, the vibrational energy of the substrate is progressively accumulated in the droplet with the highest energy maintenance efficiency, and a small amplitude of vibration could therefore yield droplet detachment. The separation time shortens with the vibration amplitude and minimizes at the resonance frequency at a given amplitude. Our findings are helpful for the utilization of vibrating superhydrophobic surfaces for droplet removal.

Estimation of soil detachment capacity on steep slopes in permanent gullies under wetting-drying cycles

Permanent gullies, mainly distributed on granite weathering mantles in tropical and subtropical areas, are the major threat to the sustainable development for economy and ecosystem of southern China. Collapsing wall, with its stability influenced by the frequent wetting-drying cycles under the hot and rainy climatic conditions, is the most active part of permanent gully. The free surface along the collapsing wall provides a favorable condition for soil detachment by runoff scouring, however, little attention has been given to the detachment capacity of granite soils under the influence of wetting-drying cycles in permanent gullies. To quantify the impacts of wetting-drying cycles on soil erosion resistance in permanent gullies, the detachment capacity of granite soils (surface soil layer A; lateritic layer B; sandy layer C1; and detritus layer C2) that were collected from the collapsing wall was investigated under 0, 2, 5, and 10 cycles of wetting-drying. The impacts of wetting-drying cycles could be well quantified by soil pore size distribution that was calculated by soil-water characteristic curve (p < 0.01). The content of macro-porosity (>30 μm) increased constantly with increasing W-D cycles, while micro-porosity (<0.2 μm) decreased, especially for soils in the surface and lateritic layers (A and B). Soil erosion resistance of granite soils under the W-D cycles was determined by the integrated effects of soil porosity, and the tested soil detachment capacity soil detachment capacity in a range of 0.008–12.488 kg.m-2 s−1, increased with the increase of W-D cycles. In addition, the rill erodibility (Kr) was significantly influenced by soil bulk density, macro-porosity, and micro-porosity (R2 = 0.930, Nash-Sutcliffe efficiency = 0.910), demonstrating a power function relationship. Moreover, the critical shear stress (τc) had a significant and positive correlation with soil cohesion (R2 = 0.576, p < 0.010). Furthermore, soil detachment capacity could be well predicted by these measurable parameters including bulk density, macro-porosity, micro-porosity, soil cohesion, and shear stress of flowing water (R2 = 0.950, NSE = 0.980), under the theoretical foundation of WEPP model. The obtained results would facilitate the understanding of the formation mechanisms of the permanent gullies, as well as the development of soil conservation measures in southern China.

The dynamics of droplet detachment in reversed electrowetting (REW)

Droplet actuation by electrowetting (EW) has drawn significant interest due to the potential applications in micro- and nano-fluidics, and the droplet departure is crucial for separation of the drop phase from the solid surface. However, the operating condition for droplet detachment, induced by the traditional electrowetting is quite strict, making it inconvenient for practical application. Recently, we considered the reversed electrowetting (REW) phenomenon, where a non-conductive droplet, settled on an adhesive surface, is dewetted continuously by applying the potential different between the substrate and surrounding fluid (Wang et al. 2020). Detachment of the oil drop is induced naturally and the detaching process is controllable. We have investigated the physical process of REW in the previous experiments. However, the dynamics of droplet detachment and the underlying mechanism are not well explained by the macroscopic experimental approach. For complementation, we build a numerical scheme in this study and examine the transient dynamics of droplet motion in the REW. The interface of the liquid-liquid system is captured by a phase-field method, and a correlation for the dynamic contact angle is incorporated in the numerical model. The simulated results are validated with the experimental cases. The process of droplet detachment and the critical condition are investigated by analyzing the energy transition during the droplet motion.

Actuation of a Nonconductive Droplet in an Aqueous Fluid by Reversed Electrowetting Effect.

Manipulation of a conductive droplet by electrowetting has been a popular topic in microfluidics whereby wettability of the droplet on a solid surface is increased by applying a voltage between the conductive droplet and the insulated surface. However, the opposite phenomenon, e.g., decreasing the wettability of a nonconductive droplet and increasing its contact angle (CA) by the reversed electrowetting (REW) effect, has been scarcely reported. Such a process involves not only the transient dynamics of droplet dewetting but also a critical condition for droplet detachment from the adhesive surface. In this work, actuation of a nonconductive droplet in an aqueous surrounding fluid by REW is studied experimentally. Silicone oil is used for the actuated droplet, and filtered water is used as the surrounding fluid. The solid substrate is made of a glass substrate coated with an indium tin oxide (ITO) film and then deposited by a dielectric layer of Parylene C. Potential difference is applied between the substrate and the surrounding fluid, eliminating the disturbance from the top needle on the motion of the droplet. Three different regimes are identified in the full range of operation. An underactuated regime occurs at low applied voltages, in which the CA of the droplet shows a monotonic increase with the increase of voltage (V). The friction coefficient of the contact line decreases with V before the CA saturation (Vs) but shows little change when V > Vs. At high voltages, the contact line of the sessile droplet is contracted excessively by REW. The droplet shows oscillation, and it refers to the overactuated regime. A combined time scale is proposed, and it verifies that the viscous dissipation of the contact line and liquid inertia show comparable contributions in the droplet dynamics. At sufficiently high voltages, the droplet is rejected completely from the surface. A critical equation for the threshold voltage of droplet detachment is built, and its validity is confirmed by experimental results.

Critical Conditions for Jumping Droplets.

A droplet initially overstretched on a solid substrate pulls back to lower the contact area and may jump away from the substrate. The condition to realize such macroscopic behaviors is often dictated by microscopic characteristics, such as contact-line pinning, in nontrivial ways. Here we theoretically and experimentally reveal the hidden contribution of contact-line pinning in forming the critical condition for detachment of a droplet from a solid substrate, among other dominating hydrodynamical effects. Our results demonstrate the relation between classical theories on contact-line pinning and various droplet manipulating applications in microfluidics and bioprinting.

Detach Yourself: The Positive Effect of Psychological Detachment on Patient Safety in Long-Term Care.

Delivering health care is emotionally demanding. Emotional competencies that enable caregivers to identify and handle emotions may be important to deliver safe care, as it improves resilience and enables caregivers to make better decisions. A relevant emotional competence could be psychological detachment, which refers to the ability to psychologically detach from work and patients in off-duty hours. The objective of this study was to examine the relationship between psychological detachment and patient safety. In addition, the ability of teams to create a safe environment to discuss errors and take personal risks, i.e., psychological safety, was explored as an underlying condition for psychological detachment. A total of 1219 caregivers (response rate = 44%) from 229 teams in two long-term care organizations completed a survey on psychological safety and psychological detachment at T0. Team managers rated patient safety of those teams at two points in time (T0 and T1). Two-level regression analysis showed that both psychological safety (β = 0.72, P < 0.01) and psychological detachment (β = 0.54, P < 0.05) relate directly to patient safety. Psychological safety relates positively to psychological detachment (β = 0.48, P < 0.01) but was, however, not an underlying condition. Perceived patient safety is enhanced by emotional competencies, at individual level by psychological detachment and at team level by psychological safety. Caregivers should be aware of the important influence emotional competencies have on patient safety and be trained to develop these competencies. Future research should focus on exploring underlying conditions for emotional competencies.

A Heideggerian Perspective on the Relationship Between Mintzberg’s Distinction Between Engaged and Disconnected Management: The Role of Uncertainty in Management

In the context of uncertainty and anxiety regarding the role of leadership and management, this article explores the relationship between Mintzberg’s concept of the distinction between the engaged and disconnected manager, Heidegger’s notion authentic and inauthentic being and Benner and Wrubel’s distinction between two forms of professional practice attunement: an attunement to technique and an attunement to lived experience. It argues that while Mintzberg outlines the distinction between engaged and disengaged management, he does not develop an understanding of the conditions which lead a manager to be either engaged or disconnected. The role of anxiety in Heidegger’s distinction between authentic and inauthentic being and the role of stress and worry in Benner and Wrubel’s distinction between an attunement to technique and an attune- ment to the lived experience of professional practice provides the basis for understanding the relationship between engaged and disconnected management. After developing the theoretical perspectives of Mintzberg, Heidegger, Benner and Wrubel, two examples are presented: one of the way in which an engaged manager experiences anxiety as an opportunity for greater attune- ment to lived experience and one who experiences anxiety as a condition for disconnection and detachment from the lived experience of his leadership practice.

1435 マイクロ流路における気泡離脱条件の検討(S38-2 気泡・粒子,S38 マイクロ・ナノフルイズ)

1435 マイクロ流路における気泡離脱条件の検討(S38-2 気泡・粒子,S38 マイクロ・ナノフルイズ)

Recombination and ion loss in C-Mod detached divertor discharges

We present detailed profiles of the magnitude and location of volumetric recombination occurring in the Alcator C-Mod divertor region during detached divertor discharges. The recombination sink (for ions) is compared to the ion current collected at the divertor plates both as a function of location on the plate and across the entire divertor. We find that, depending on plasma conditions, volume recombination can account for the removal of 10–75% of the ions flowing on detached flux surfaces. A similarly important cause of the observed ion current loss appears to be the reduction in divertor ion sources upstream from the plate. Changes in the ion source rate are consistent with changes in power flowing from the SOL into the divertor region. The lowest levels of recombination are found in H-mode discharges where detachment is induced through puffing of N 2 gas. In these cases the observed ion current loss is due almost entirely to decrease in the ion source. This shows that recombination is not a necessary condition for detachment.

The cycle of bubble production from a gas cavity in a supersaturated solution

Bubble nucleation, classified according to the review by Jones et al. (Adv. Colloid Interface Sci. 80 (1999) 27–50) as type IV non-classical, was examined in this study. Trains of bubbles were produced in carbonated water solutions at low levels of supersaturation, typically less than about 2, at specific sites on the surface of the vessel in contact with the liquid. Closer examination at a given site revealed a cycle of bubble formation, growth and detachment, defined by the growth time, t g, required for the bubble to grow to its detachment diameter, and the nucleation time, t n, required for a new bubble to appear following detachment. A relationship, representing the cycle of bubble production, was obtained by combining the bubble growth time, calculated using Scriven's model (Scriven, Chem. Eng. Sci. 10(1/2) (1959) 1–13), with the bubble nucleation time. That is, 1 t g = N t n + 1 t g * where N is a dimensionless number characterising the bubble nucleation time, and t g* is the growth time of the last possible bubble. Experiments conducted at a number of sites, and at different temperatures, produced results consistent with the above relationship. Most of the experiments were conducted with the contact angle at 65°, and these generally resulted in a bubble detachment diameter of about 600 μm, and a value of N∼0.3. It was concluded that the nucleation time was dependent on the diameter of the detaching bubble. This dependence was explained by considering the volume of liquid, partially depleted of carbon dioxide, in the boundary layer of the bubble. Some of this partially depleted liquid should leave with the departing bubble, and the rest should remain above the gas cavity, thus slowing down the rate of bubble growth in the cavity. A consideration of the critical condition for bubble detachment indicated that the bubble remained rooted at the cavity mouth during its growth. It was shown, using the growth time of the last possible bubble, that the critical radius of curvature of the meniscus in the cavity was about 3.3 μm at 16°C. The radius was also found to increase significantly with temperature, suggesting that the position of the meniscus inside the cavity moved when the system temperature was changed, and that the cavity was essentially conical.

Adhesion moment model for estimating particle detachment from a surface

In this paper particle detachment from a surface by a hydrodynamic moment is analyzed. The detachment occurs when this moment exceeds the moment exerted on the particle by surface forces. An expression for the moment of surface forces is derived from the existing adhesion models. This moment is a product of the force acting on the particle and the variable contact radius, which decreases when the applied force increases. Accordingly, a condition for particle detachment from a smooth surface is obtained. In addition, particle detachment from a rough surface is considered. We show that a single asperity contact is similar to the contact of a particle with a smooth surface, but the detaching moment is reduced, because of the lower adhesion force and smaller contact radius. We also consider a particle in contact with two and three asperities, and obtain a condition for particle detachment from a rough surface. It is also shown that the hydrodynamic moment can cause particle detachment, while the hydrodynamic lift force is smaller than the adhesion force by several orders of magnitude. On the other hand, the lift force exceeds the weight of the particle. Hence, the detached particle is eventually removed from the surface by this force.

Droplet impaction with a substrate—The critical condition for detachment

Abstract A new experimental device was developed for the purpose of determining the critical condition associated with the release of an attached droplet from a decelerating substrate. A droplet of known size was located on the test substrate which, in turn, was located on a spring-loaded platform. Upon release of the spring, the substrate impacted into the droplet causing an advancement followed by a receding of the triphase line. Any droplet detachment, as revealed by a high-speed video, was noted. Keeping the deceleration conditions constant, the droplet volume was varied until the critical size for detachment was obtained. A system consisting of a water droplet in contact with a PTFE substrate was examined using substrate decelerations ranging from about 200 to 4000 m s −2 . The critical condition for detachment of “small” droplets followed the simple scaling law, α ∝ D −2 , where α is the critical deceleration and D is the droplet diameter. This result is consistent with that expected from an analysis of the drop-weight model, as used for measuring surface tension. The results are relevant to the more general problem of a free droplet impacting with a substrate.

Plasma equilibrium in a toroidal chamber with a travelling magnetic field

The displacement was found of the center of a plasma column in a toroidal chamber that is maintained in equilibrium by the average pressure of the high-frequency travelling magnetic field H and the dc magnetic field ℋ of the longitudinal surface currents. The travelling hf magnetic field is created by passing ac currents with specially selected phases through the annular conductors enveloping the chamber. It is assumed that these conductors do not affect the distribution of the dc magnetic field, which is assumed to be the same as in a single ideally conducting toroid. The solution is performed in assuming that toroidality is small (expansion in powers with respect to 1/R; R is the large radius of the torus).The conditions for detachment of the column from the chamber walls in a quasi-static regime, is evaluated in the following manner. Let a plasma column of radius α be in equilibrium in a cylindrical chamber of radius b (R = ∞) at a distance δ from the walls. If the column is bent into a torus, then for detachment of the plasma from the chamber walls it is necessary that δ be larger than the displacement of the center of the plasma column Δ (a,b) = b – δ. The condition for detachment, δ > Δ (b – δ, b), limits β, the ratio of plasma pressure to full magnetic-field pressure (time average of H plus ℋ).In a concrete case that is close to the experiments described in ref. 1 (R=35 cm, b=4 cm, and 12 waves of the travelling magnetic field fill the length of the torus), the formula is h = ℋa/Hb is the ratio of x at the surface of the plasma column to H near the current conductors (on the surface of the chamber). From this formula it follows that for large longitudinal currents (h2 > 0.49), detachment is impossible. From table I we can find the maxima of β for which, with preset h2, a column can exist that is detached from the chamber walls. As is seen from this table, the conditions for detachment are very stringent.