Sliding and Rolling Motion of a Ferro-Liquid Droplet on the Hydrophobic Surface under Magnetic Influence.

The ferro-liquid droplet manipulation on hydrophobic surfaces remains vital for various applications in biomedicine, sensors and actuators, and oil-water separation. The magnetic influence of ferro-liquid droplets on the hydrophobic surface is elucidated. The mechanisms of a newborn droplet formation under the magnetic force are explored. The sliding and rolling dynamics of the ferro-liquid droplets are assessed for the various concentrations wt % of ferro-particles. High-speed recording and a tracker program are used to evaluate the droplet sliding and translational velocities. It is demonstrated that the mode of droplet motion changes from sliding to rolling as the magnetic Bond number increases, in which case, the droplet position becomes close to the magnet surface. The translational velocity of the droplet under rolling mode increases as the ferro-particle concentration in the droplet fluid increases. A further increase of the magnetic Bond number results in the creation of a newborn droplet attached to the magnet surface.

Liquid droplet impact on a sonically excited thin membrane.

The characteristics of droplet impact on hydrophobic surfaces can be altered by introducing surface oscillations. The contact duration, spreading, retraction, and rebounding behaviors of the impacting water droplet are examined at various sonic excitation frequencies of the hydrophobic membrane. Membrane oscillation and droplet behavior are analyzed by utilizing a high-speed camera. The restitution coefficient and membrane dynamics are formulated and the findings are compared with those of the experiments. It is found that the mode of membrane oscillation changes as the sonic excitation frequency is changed. The droplet spreading and retraction rates reduce while the rebound height and restitution coefficient increase at a sonic excitation frequency of 75 Hz. However, further increase of the excitation frequency results in reduced rebound height because of the increased energy dissipation on the impacted surface. The droplet contact (transition time) duration reduces as the excitation frequency increases. Increasing droplet Weber number enhances the droplet contact period on the membrane, which becomes more apparent at low frequencies of sonic excitation.

Droplet Rolling Dynamics over a Hydrophobic Surface with a Minute Width Channel.

Unidirectional and stabilize droplet rolling over hydrophobic surfaces is critical for self-cleaning applications of large areas. Introducing minute size channels on hydrophobic surfaces in the droplet rolling direction can minimize droplet wobbling and enables unidirectional rolling. The droplet rolling behavior over an inclined hydrophobic surface having a minute size channel is investigated. The flow field developed inside the droplet fluid is numerically simulated in a three-dimensional domain pertinent to experimental conditions. Experiments are carried out using a high-speed facility to monitor and evaluate droplet motion over channeled and flat hydrophobic surfaces. The findings revealed that predictions of the droplet translational velocity and those obtained from the experiments are in good agreement. The presence of a minute channel on the hydrophobic surface gives rise to droplet fluid inflection into the minute channel, which in turn modifies the center of mass of the droplet during rolling. This lowers the droplet wobbling height and enables the droplet to roll unidirectionally along the channel length. Enlarging the channel width on the hydrophobic surface increases droplet kinetic energy dissipation while reducing the droplet rolling speed. The complex flow structures formed in the droplet fluid modifies the pressure along the droplet centerline; however, the droplet fluid pressure remains almost the same order as the Laplace pressure in the upper region of a rolling droplet over the channeled hydrophobic surface.

On the Mechanism of Human Saliva Interaction with Environmental Dust in Relation to Spreading of Viruses.

Environmental effects such as dust mitigation can amplify the spread of viruses via inhaling infected dust particles. Infusion and the spreading rate of human saliva over the dust particles can play a critical role in contiguous virus spread. In the present study, mechanical and chemical interactions of human saliva with environmental dust particles are considered. The saliva droplet impact on dust particles is examined while mimicking saliva droplet spreading during coughing in a dusty ambience. The mechanisms of saliva infusion and cloaking on the dust particles are explored. The characteristics of saliva droplet normal and oblique impacts on a dust particle are examined experimentally and numerically to evaluate the amount of saliva residues on the impacted particle surface. The findings reveal that the saliva liquid infuses and cloaks the dust particle surfaces. The saliva droplet impact on the dust particles leaves a considerable amount of saliva residues on the impacted surfaces, which remain undried for a prolonged period in indoor environments. Weak adhesion of the saliva-infected dust particles on surfaces, such as glass surfaces, enables saliva-infected dust particles to rejoin neighboring ambient air while possessing a high potential for virus spreading.

Impacting Water Droplets Can Alleviate Dust from Slanted Hydrophobic Surfaces.

Water droplet impacting on a slanted dusty hydrophobic surface is examined in relation to dust mitigation from surfaces. Impacting droplet characteristics including droplet spreading/retraction rates, slipping length, and rebound heights are analyzed via high-speed recording and a tracker program. The environmental dust characteristics in terms of size, shape, elemental composition, and surface free energy are evaluated by adopting the analytical methods. The findings reveal that the dynamic characteristics of the impacting droplet on the slanted hydrophobic surface are significantly influenced by the dust particles. The maximum droplet spreading over the dusty surface becomes smaller than that of the nondusty surface. The presence of the dust particles on the slanted hydrophobic surface increases energy dissipation, and the water droplet slipping length over the surface becomes less than that corresponding to the nondusty surface. Impacting droplet fluid infuses over the dust particle surface, which enables mitigation of dust from the surface to the droplet fluid. A dust-mitigated area on the slanted surface is larger than that corresponding to the horizontal surface; in which case, the area ratio becomes almost six-fold, which slightly reduces with increasing Weber number. The optical transmittance of the dust-mitigated surface by the impacting droplet remains high.

Hydrophobized metallic meshes can ease water droplet rolling.

Rolling liquid droplets are of great interest for various applications including self-cleaning of surfaces. Interfacial resistance, in terms of pinning and shear rate, has a critical role in droplet rolling dynamics on hydrophobic surfaces. Lowering the interfacial resistance requires reducing the droplet wetting length and droplet fluid contact area on hydrophobic surfaces. The present study examines droplet rolling behavior on inclined hydrophobized metallic meshes, which facilitate reduced wetting length and contact area of droplets. Experiments are carried out using a high-speed recording facility to evaluate droplet translational and rolling velocities over various sizes of hydrophobized meshes. The flow field inside the droplet fluid is simulated in 3-dimensional space mimicking the conditions of experiments. The findings reveal that droplet translational velocity attains significantly higher values for hydrophobized meshes than plain hydrophobized metallic surfaces. Increasing the mesh size enhances the droplet velocity and reduces the droplet kinetic energy dissipation created by interfacial surface tension and shear forces. Increasing the droplet volume enhances the droplet velocity despite the fact that pinning and frictional forces increase at the liquid-mesh interface. Hence, for rolling droplets on the mesh surface, the increase in the gravitational force component becomes larger than the increase in interfacial pinning and frictional forces.

Sliding Water Droplet on Oil Impregnated Surface and Dust Particle Mitigation.

Self-cleaning of surfaces becomes challenging for energy harvesting devices because of the requirements of high optical transmittance of device surfaces. Surface texturing towards hydrophobizing can improve the self-cleaning ability of surfaces, yet lowers the optical transmittance. Introducing optical matching fluid, such as silicon oil, over the hydrophobized surface improves the optical transmittance. However, self-cleaning ability, such as dust mitigation, of the oil-impregnated hydrophobic surfaces needs to be investigated. Hence, solution crystallization of the polycarbonate surface towards creating hydrophobic texture is considered and silicon oil impregnation of the crystallized surface is explored for improved optical transmittance and self-cleaning ability. The condition for silicon oil spreading over the solution treated surface is assessed and silicon oil and water infusions on the dust particles are evaluated. The movement of the water droplet over the silicon oil-impregnated sample is examined utilizing the high-speed facility and the tracker program. The effect of oil film thickness and the tilting angle of the surface on the sliding droplet velocity is estimated for two droplet volumes. The mechanism for the dust particle mitigation from the oil film surface by the sliding water droplet is analyzed. The findings reveal that silicon oil impregnation of the crystallized sample surface improves the optical transmittance significantly. The sliding velocity of the water droplet over the thick film (~700 µm) remains higher than that of the small thickness oil film (~50 µm), which is attributed to the large interfacial resistance created between the moving droplet and the oil on the crystallized surface. The environmental dust particles can be mitigated from the oil film surface by the sliding water droplet. The droplet fluid infusion over the dust particle enables to reorient the particle inside the droplet fluid. As the dust particle settles at the trailing edge of the droplet, the sliding velocity decays on the oil-impregnated sample.

Carbonated Water Droplet Can Ease Dust Mitigation from Hydrophobic Surfaces.

Carbonated water droplets can ease the difficulties faced by distilled water droplets mitigating dust particles from hydrophobic surfaces. Rising of CO2 bubbles in carbonated water droplets and their interaction with the flow structure, created by Marangoni and buoyancy possessions, in droplets are investigated. Spreading and infusion (cloaking) of carbonated water on dust surfaces are analyzed, and the rate at which bubbles formed inside the carbonated water droplet, as placed on a dusty hydrophobic surface, is examined. Flow structures formed inside the carbonated water droplet are simulated, and findings are compared to those corresponding to the distilled water droplet. Dust mitigation from the hydrophobic surface toward droplet liquid inside is evaluated using the high-speed recording system, and the results are compared with those of predictions. It is found that carbonated water spreads and infuses onto dust particles at a higher rate than that at which distilled water does. The rising bubble generates wake-like flow in the fluid while modifying the flow structure inside the droplet; hence, the number of circulating structures increases from two to four in droplet fluid. The dust particles picked up by flow currents are redistributed over the entire carbonated water droplet, while mitigated dust particles remain in the lower region of the distilled water droplet. Bubbles formed inside the carbonated water droplet improve dust lifting and rate of dust mitigation from the surface.

Carbonated water droplets on a dusty hydrophobic surface.

Dust mitigation from surfaces remains essential, particularly for the efficient operation of energy harnessing devices. Although various dust removal methods have been introduced, the self-cleaning method is favorable because of the cost-effective cleaning process. Dust mitigation from surfaces by water droplets, mimicking nature, is fruitful because it involves low-cost operations. The dust removal rate from surfaces by rolling water droplets can be increased by creating bubbles inside the rolling droplets through which dust pinning on surfaces can be lowered and the droplet liquid infusion on dust surfaces can be enhanced. This study provides insight into bubble formation and dust mitigation in carbonated and distilled water droplets located on hydrophobic surfaces by examining bubble formation and dust distribution inside the water droplets. The behavior of bubbles inside the carbonated water droplet and emanating from the hydrophobic surface was recorded and analyzed by incorporating high-speed camera data. The influence of environmental dust particles on bubble formation was also assessed. Bubble velocity was formulated analytically and the findings are compared with those of the experimental values. Findings revealed that the bubble formation inside the carbonated droplet fluid had a significant effect on the transition of dust particles from the hydrophobic surface towards the droplet fluid. The volume concentration of dust particles in the carbonated water droplet was almost 1.5 to 2.5 times larger than that of the distilled water droplet. The dissolution of alkaline and alkaline earth metal compounds in the carbonated droplet fluid acted like nucleation centers for bubble formation; hence, the number of bubbles formed on the dusty hydrophobic surface was greater than that of the clean hydrophobic surface. Some bubbles attached at the dust particle surface contributed to dust mobility in the droplet fluid, which occurred particularly in the droplet bottom region. This enhanced the velocity of the dust particles transiting from the dusty hydrophobic surface to the droplet fluid interior by almost 1.5 times in the early period.

Droplet Rolling and Spinning in V-Shaped Hydrophobic Surfaces for Environmental Dust Mitigation.

The motion of a water droplet in a hydrophobic wedge fixture was examined to assess droplet rolling and spinning for improved dust mitigation from surfaces. A wedge fixture composed of two inclined hydrophobic plates had different wetting states on surfaces. Droplet rolling and spinning velocities were analyzed and findings were compared with the experiments. A wedge fixture was designed and realized using a 3D printing facility and a high speed recording system was adopted to evaluate droplet motion in the wedge fixture. Polycarbonate sheets were used as plates in the fixture, and solution crystallization and functionalized silica particles coating were adopted separately on plate surfaces, which provided different wetting states on each plate surface while generating different droplet pinning forces on each hydrophobic plate surface. This arrangement also gave rise to the spinning of rolling droplets in the wedge fixture. Experiments were extended to include dust mitigation from inclined hydrophobic surfaces while incorporating spinning- and rolling droplet and rolling droplet-only cases. The findings revealed the wedge fixture arrangement resulted in spinning and rolling droplets and spinning velocity became almost 25% of the droplet rolling velocity, which agrees well with both predictions and experiments. Rolling and spinning droplet gave rise to parallel edges droplet paths on dusty hydrophobic surfaces while striations in droplet paths were observed for rolling droplet-only cases. Spinning and rolling droplets mitigated a relatively larger area of dust on inclined hydrophobic surfaces as compared to their counterparts corresponding to rolling droplet-only cases.

Ceratomyxa azevedoi n. sp. (Myxozoa: Myxosporea) parasitizing the gallbladder of Lutjanus ehrenbergii in the Arabian Gulf.

A novel myxosporean species, Ceratomyxa azevedoi sp. n. is described from the gallbladder of the blackspot snapper, Lutjanus ehrenbergii (Peters), captured from the Arabian Gulf off Saudi Arabia. A total of 45 (26.8%) out of 168 fish specimens were found to be infected with Ceratomyxa azevedoi sp. n., the highest prevalence being observed in winter (42.9%, 18/42) and the lowest in autumn (11.9%, 5/42). Mature spores appeared as crescent to slightly elliptical-shaped, measuring 5-7 (6) µm in length and 12 (10-14) µm in thickness, with spherical polar capsules containing three polar filament coils. The morphometric and morphological comparison with similar species revealed the taxonomic novelty of this form, suggesting that it should be considered as new species. The phylogenetic analysis of C. azevedoi sp. n., based on partial SSU rDNA sequences, revealed close genetic relatedness to C. buri with 91.3% homogeneity and to C. hamour, with 90.1% homogeneity.

Molecular and morphometric characteristics of Ceratomyxa hamour n. sp. (Myxosporea: Bivalvulida) infecting the gallbladder of the orange-spotted grouper Epinephelus coioides from the Arabian Gulf, Saudi Arabia.

Ceratomyxa hamour n. sp. was found to infect the gallbladder of the orange-spotted grouper, Epinephelus coioides located off the Saudi Arabian coast of the Arabian Gulf. The infection was reported as a free-floating spore in the bile, and pseudoplasmodia were not observed. Mature spores were crescent-shaped and measured on average 7 µm in length and 16 µm in thickness. The polar capsule, meanwhile, had length to width measurements of 4 µm and 3 µm on average. A periodical survey was conducted throughout a sampling period between December 2012 and December 2013, with the results showing that the parasite was present throughout the year with a mean prevalence of 32.6%. The objective of this study was to characterize this new species based on its morphological and molecular differences from previously described species. Molecular analysis based on the partial sequence of the SSU rDNA gene, showed the highest similarity (97.8%) to Ceratomyxa buri, reported in the cultured yellow tail Seriola quinqueradiata in Japan. Indeed, C. buri and the new species described here formed an individual cluster with a high degree of bootstrap support. This is the first reported species of genus Ceratomyxa from the Arabian Gulf fishes off Saudi Arabia.

Glugea jazanensis sp. nov. infecting Lutjanus bohar in the Red Sea: ultrastructure and phylogeny.

During a survey of the microsporean fauna of the two-spot red snapper Lutjanus bohar Forsskål, 1775, from the Red Sea off Jizan (Saudi Arabia), a species of Glugea Thélohan, 1891 was found that did not conform to any known species. The species is characterized by the presence of spherical xenomas (ca. 2-5 mm in diameter) in the host body cavity. Examination of the lifecycle stages and mature spores using light and transmission electron microscopy also revealed morphological characteristics typical of species of the genus Glugea. Spores were elongated-ovoid with a posterior vacuole surrounded by the polar filament coils. Mature spores were 4.5 (4.0-4.8) µm long and 2.5 (2.0-2.5) µm wide. The polar filament was isofilar with 28 to 30 coils, although in most cases 29 coils, organized in 3 rows. Phylogenetic study based on the partial sequence of the small subunit (SSU) rRNA gene clustered the new microsporidia within the clade grouping species of the genus Glugea. The comprehensive analysis of the parasite's ultrastructural characteristics, together with molecular data for the SSU rDNA gene, suggests that this parasite is a new species of the genus Glugea, for which the name Glugea jazanensis sp. nov. is proposed.

Morphology, phylogeny and seasonal prevalence of Ceratomyxa arabica n. sp. (Myxozoa: Myxosporea) infecting the gallbladder of Acanthopagrus bifasciatus (Pisces: Sparidae) from the Arabian Gulf, Saudi Arabia.

A new myxozoan species was recovered from the gallbladder of Acanthopagrus bifasciatus from the Arabian Gulf in Saudi Arabia. The overall prevalence of infection was 28.6 % (32/112), with the highest prevalence 42.9 % (12/28) in winter and 10.7 % (3/28) as the lowest in autumn. The new species is described using its morphological characteristics and small subunit (SSU) rDNA. Spores of Ceratomyxa arabica n. sp. are stubby-shaped with unequal shell valves, 8 (7-9) µm in length × 12 (10-14) µm in thickness. Polar capsules are sub-spherical, unequal, 3 (2.5-3.5) × 2 (1.5-2.5) µm. The polar filament has three turns and is slightly slanted towards the longitudinal axis of the capsules. The small subunit rDNA (SSU rDNA) sequence confirms that the present species is a member of the genus Ceratomyxa, being most closely related to Ceratomyxa cardinalis with a sequence similarity of 97.77 %.

Morphological and molecular aspects of Ceratomyxa mehlhorni n. sp., a parasite of the golden trevally Gnathanodon speciosus in the Arabian Gulf off the Saudi Arabian coast, with data on its seasonal prevalence.

During a survey of the myxosporean fauna of the golden trevally Gnathanodon speciosus from the Arabian Gulf off Saudi Arabia, a species of Ceratomyxa that did not conform to any known species was recorded. The infection was detected as a large number of mature spores free-floating in the bile. Mature spores were hat- or helm-like in the frontal view with two short and unequal valves. The spores measured 8 (7-9) × 12 (10-14). The two polar capsules were spherical, equal in size and measured 3 (2-4) in diameter with three filament turns. Sporoplasm was binucleated and filled the whole extracapsular space. The small subunit ribosomal DNA sequence of this species did not match any available sequences in GenBank. The lowest genetic distance was 0.017, observed with Ceratomyxa moseri infecting Pomacentrus wardi from Australia's Great Barrier Reef. A maximum likelihood phylogenetic tree showed a close association between the new species and a variety of ceratomyxid species, including Ceratomyxa arabica reported from the Arabian Gulf. Given the morphological and molecular differences between this species and other Ceratomyxa spp., we proposed the present form was a new species and the name Ceratomyxa mehlhorni sp. n. for this parasite from the gallbladder of G. speciosus.

Morphology, seasonality and phylogenetic relationships of Ceratomyxa husseini n. sp. from the gall-bladder of Cephalopholis hemistiktos (Rüppell) (Perciformes: Serranidae) in the Arabian Gulf off Saudi Arabia.

During a survey of myxosporean parasites of marine fishes from the Arabian Gulf in Saudi Arabia, spores of Ceratomyxa husseini n. sp. were found in the gall-bladders of 50 out of 148 specimens (33.8%) of the yellowfin hind Cephalopholis hemistiktos (Rüppell) (Perciformes: Serranidae). The rates of infection showed a seasonal fluctuation, with the highest prevalence in winter and the lowest in autumn. The mature spores appeared arched in frontal view with rounded valve ends and a slightly discriminated curved suture line and measured 8-9 × 14-18 (9 × 16) µm. The two polar capsules were spherical and equal in size, 4-5 (4.5) µm in diameter. The polar filament showed four turns obliquely to the longitudinal axis of the capsules and the sporoplasm filled half of the entire spore cavity. Partial sequences of the small subunit rRNA gene of C. husseini n. sp. showed percentage of identity with other species of Ceratomyxa ranging between 79.8 and 92.7%. The morphometric and molecular data, in association, confirmed that the present new species differs from all other Ceratomyxa spp. reported to date.

In-plane thermal conductivity measurements of Si µ-cantilevers using the suspended thermo-reflectance (STR) technique.

The Suspended Thermoreflectance (STR) technique is described in this paper. This optoelectronic measurement tool performs thermal characterization of freestanding micro-/nanoscale materials. STR performs thermal mapping at the submicron level and produces unconstrained thermal conductivity unlike other optical measurement techniques where independent conductivity measurement is not possible due to their reliance on heat capacity. STR works by changing the temperature of a material and collecting the associated change in light reflection from multiple points on the sample surface. Reflection is a function of the material being tested, the wavelength of the probe light, geometry, and the composition of the specimen for transparent and quasi-transparent materials. In this article, Si µ-cantilevers are studied. In addition, a thermal analytical model is developed and incorporated with optical equations to characterize the conductivity of the Si µ-cantilevers. The analytical model is compared with a finite element model to check its applicability in the STR experiment and data analysis. To validate the technique, the thermal conductivity of 2 and 3 µm thick Si µ-cantilevers was determined using STR at a temperature range of 20-350 K and compared to simulations using the equation of phonon radiative transfer and literature values.

A comparative study for ferro particles cloaking and wetting characteristics.

Ferro hydrophobic particles possess essential properties for controlling the behavior of suspended substances in water. By adjusting the concentration of these particles, the magnetic force within the fluid carrier can be modified, leading to the emergence of distinct flow structures and patterns on the water's surface. This study examines the cloaking phenomenon exhibited by different ferroparticle conditions, employing both experimental and numerical approaches. Under the magnetic influence, hydrophilic particles can attain cloaking velocities of up to 35 mm/s, while hydrophobic particles remain unaffected by the magnetic force, remaining suspended on the water's surface. Hydrophobization of ferroparticles not only decreases their water-cloaking ability but also alters their magnetic properties. The inherent hydrophobic nature of these particles enhances water surface stability, rendering them valuable in various applications, including biomedical and self-cleaning technologies. This research holds particular significance for manipulating suspended particles in water, particularly in biomedical applications like drug delivery and tissue engineering, as well as for advancing self-cleaning technologies.

Dust mitigation by a water droplet in between movable and modified wetting states surfaces.

A novel approach for mitigating environmental dust from hydrophobic surfaces using a water droplet is presented. A sessile droplet is sandwiched between two parallel plates, one of which is moveable and hydrophilic while the other is stationary and hydrophobic. Investigations are conducted into how plate spacing affects the dust mitigation rate and the droplet's level motion. The high-speed camera analyzes the droplet motion for various plate spacing, dusty regions, and droplet sizes. In a controlled laboratory setting, the movement of fluid and dust particles inside a droplet is simulated. The results showed that when a droplet is still, it effectively reduces dust. The droplet meniscus expands by decreasing the gap between the droplet and the surface, increasing the dust removal rate. While the Magdeburg force and surface tension influence the droplet's adhesion to a hydrophobic surface, surface tension remains the primary factor affecting droplet pinning on a hydrophilic plate, more so than pinning on a dusty hydrophobic surface. When compressing, a current is created in the droplet fluid, greatly accelerating the rate at which dust is removed from the hydrophobic surface. We also move a dangling droplet over a dirty surface to evaluate its cleaning effectiveness and find that a 60 µL droplet has a 97% cleaning effectiveness and can remove dust from up to 450 mm2 of surface area. Our study provides insight into the unique method of removing dust from active surfaces and sheds light on droplet pinning forces generated by the Magdeburg effect in nano-cavities during vertical and horizontal movement.

Dynamics of droplet motion over hydrophobic surfaces with functionalized and non-functionalized ferro particles.

Dynamically manipulating droplet motion on hydrophobic surfaces is crucial in various fields, including biomedical, sensing, actuation, and oil-water separation applications. Ferrofluid droplets can be manipulated and controlled using external magnetic forces. The creation of ferrofluids involves multiple procedures that can affect the functionality and stability of droplet manipulation, limiting their use in sustainable applications. This study investigates the dynamics of droplet motion over functionalized and non-functionalized ferroparticles, considering different droplet volumes, ferroparticle layer widths, and wt% concentrations. The translational and sliding velocities of the droplets are measured using high-speed camera recording with a tracker application. The finding revealed the transformation of a droplet sliding motion into a rolling motion with propulsion under the magnetic influence. The sliding velocity increases for the droplets moving over the ordinary ferroparticles on the hydrophobic surface. However, the droplet motion is dominated by rolling in the case of hydrophobic ferro particles. The droplet sliding velocity rises sharply at high concentrations (or layer width) of ferroparticle as the magnetic bond number rises sharply to 3. A newborn droplet adheres to the magnet surface during droplet rolling and sliding motion.