Self-cleaning Mechanism Research Articles

Self-cleaning filtration: A novel concept for rainwater harvesting systems

The treatment of rainwater is typically performed by the diversion of the first flush and the use of strainers to retain gross particles (e.g. leaves). To date, there is a lack of rainwater treatment systems with both high efficiency to remove small suspended particles, and simple operation without energy consumption and associated greenhouse gas emissions. The objective of this work was to develop and test a novel concept for the filtration of particles in raw rainwater with no energy usage, self-cleaning mechanism, and simple installation and operation in buildings. For this purpose, an innovative concept was developed based on an up-flow filtration with down-flow backwashing operation. The concept was tested by building a prototype, in which the treatment efficiency for particle removal as well as the backwash efficiency were assessed for three different filter media. Results showed that the system designed under the proposed concept operated effectively with the correct selection of the filter medium. Therefore, the proposed rainwater treatment concept offers an opportunity to enhance water security by treating and using rainwater in buildings in an efficient, simple, and energy-free way.

Self-cleaning of superhydrophobic surfaces by self-propelled jumping condensate

The self-cleaning function of superhydrophobic surfaces is conventionally attributed to the removal of contaminating particles by impacting or rolling water droplets, which implies the action of external forces such as gravity. Here, we demonstrate a unique self-cleaning mechanism whereby the contaminated superhydrophobic surface is exposed to condensing water vapor, and the contaminants are autonomously removed by the self-propelled jumping motion of the resulting liquid condensate, which partially covers or fully encloses the contaminating particles. The jumping motion off the superhydrophobic surface is powered by the surface energy released upon coalescence of the condensed water phase around the contaminants. The jumping-condensate mechanism is shown to spontaneously clean superhydrophobic cicada wings, where the contaminating particles cannot be removed by gravity, wing vibration, or wind flow. Our findings offer insights for the development of self-cleaning materials.

Self-cleaning in tree frog toe pads; a mechanism for recovering from contamination without the need for grooming

Tree frogs use adhesive toe pads for climbing on a variety of surfaces. They rely on wet adhesion, which is aided by the secretion of mucus. In nature, the pads will undoubtedly get contaminated regularly through usage, but appear to maintain their stickiness over time. Here, we show in two experiments that the toe pads of White's tree frogs (Litoria caerulea) quickly recover from contamination through a self-cleaning mechanism. We compared adhesive forces prior to and after contamination of (1) the whole animal on a rotatable platform and (2) individual toe pads in restrained frogs mimicking individual steps using a motorised stage. In both cases, the adhesive forces recovered after a few steps but this took significantly longer in single toe pad experiments from restrained frogs, showing that use of the pads increases recovery. We propose that both shear movements and a 'flushing' effect of the secreted mucus play an important role in shedding particles/contaminants.

Dynamic self-cleaning in gecko setae via digital hyperextension

Gecko toe pads show strong adhesion on various surfaces yet remain remarkably clean around everyday contaminants. An understanding of how geckos clean their toe pads while being in motion is essential for the elucidation of animal behaviours as well as the design of biomimetic devices with optimal performance. Here, we test the self-cleaning of geckos during locomotion. We provide, to our knowledge, the first evidence that geckos clean their feet through a unique dynamic self-cleaning mechanism via digital hyperextension. When walking naturally with hyperextension, geckos shed dirt from their toes twice as fast as they would if walking without hyperextension, returning their feet to nearly 80 per cent of their original stickiness in only four steps. Our dynamic model predicts that when setae suddenly release from the attached substrate, they generate enough inertial force to dislodge dirt particles from the attached spatulae. The predicted cleaning force on dirt particles significantly increases when the dynamic effect is included. The extraordinary design of gecko toe pads perfectly combines dynamic self-cleaning with repeated attachment/detachment, making gecko feet sticky yet clean. This work thus provides a new mechanism to be considered for biomimetic design of highly reuseable and reliable dry adhesives and devices.

Currents and intensity of turbulent processes in the Gavan’ Gaidamak Inlet (Vostok Bay, Peter the Great Bay, Sea of Japan)

Presented are the data of observations carried out in the fall of 2000 in the Gavan’ Gaidamak Inlet (Vostok Bay, Peter the Great Bay, Sea of Japan). It is revealed that the main transport of water takes place in the surface horizons from 0 to 1–2 m predominantly in the meridional direction (north-south). It is demonstrated that in spite of not being under wind influence, the inlet area has a high degree of water flow turbulization. It was also registered that the wind-induced phenomena promote the development of turbulent processes and serve as the main self-cleaning mechanism of the inlet.

Effect of pulsed deposition of Al2O3 for native oxides reduction of GaAs by atomic layer deposition technique

The reduction of native oxides on GaAs substrates is studied by predeposition cleaning as well as by short time pulsing of the metal precursor for the self-cleaning mechanism using atomic layer deposition (ALD) of trimethyl aluminum (TMA). The role of the predeposition cleaning followed by ALD application has significant effects in restraining the regrowth of native oxides. The short time pulsing of the TMA is effective for the self-cleaning mechanism to reduce the intensity of GaAs native oxides. The reduction in native oxides on GaAs surface during ALD of TMA was investigated using x-ray photoelectron spectroscopy. X-ray photoelectron studies demonstrated that the pulsed deposition of TMA in the range of 2 to 4 s is the most effective way of cleaning the GaAs native oxides. Our studies demonstrate a full proof self-cleaning process for GaAs wafers for any potential applications.

Morphologies of small droplets on patterned hydrophobic substrates

For situations, in which the size of a droplet is comparable to the roughness scale of the solid substrate, we explore possible wetting morphologies on patterned hydrophobic substrates and investigate their dependence on the initial droplet position, droplet volume and the surface geometry. For a regular array of cubical pillars, small perturbations of a symmetric droplet state are restored by capillary forces. Larger deviations, on the other hand, may lead to completely new morphologies. Our studies also suggest that the previously reported ‘reentrant transition’ upon quasi-static evaporation (a transition from the suspended state to partial penetration and then back to the suspended state) (Gross et al 2009 Europhys. Lett. 88 26002) is not restricted to a symmetric initial state but may occur for quite non-symmetric morphologies as well. In contrast, a change in the substrate geometry may lead to a completely different behavior, fully precluding the reentrant transition. This underlines the importance of substrate design for the use of reentrant transition as a self-cleaning mechanism.

Epithelial migration on the canine tympanic membrane

Epithelial migration (EM) is a process that serves as a self-cleaning and repair mechanism for the ear canal and tympanic membrane (TM). Epithelial migration has been evaluated in humans and several other species, but not in dogs. The objective of this study was to determine the rate and pattern of EM on the TM in clinically normal laboratory dogs. Eighteen dogs were anaesthetized, and three drops of waterproof drawing ink were placed on two sites of the pars tensa (PT) and one on the pars flaccida (PF). Images were recorded with a video otoscope and digital capture system. Each dog was evaluated and images were recorded every 6-8 days for four evaluations. Migration pattern analysis and EM rate calculation were performed with image-processing software. Descriptive statistics for EM rate (mean, SD, 95% confidence interval) were calculated for all ink-drop locations on the TM (PT1, PT2 and PF) at each time point. No significant differences in the mean EM rates were identified between right and left ears of the fox hounds breeds (beagle or fox hound), or locations PT1 and PT2. The mean overall EM rates (± SD) were 96.4 (± 43.1) and 225.4 (± 128.1) μm/day for the PT and PF, respectively. All ink drops moved outwards, the majority in a radial direction, from the original location to the periphery of the TM. The ink-drop placement method used in this study can be used in future studies to determine the EM rate of the canine TM.

On the occurrence of two-stage combustion in alkali metals

Pool combustion experiments have been conducted for three alkali metals, namely, lithium (Li), sodium (Na) and potassium (K). Lithium and sodium are found to show a two-stage combustion behaviour which has been reported for a number of other metals. Here, the combustion is characterized by a sporadic rise in the flame temperature accompanied by a bright glow. Potassium is found to burn in vapour phase combustion in all cases without sporadic temperature excursions. In the present study, this different burning behaviour is attributed to the formation of thick oxide agglomerates in the case of Li and Na through the pores of which oxygen/metal vapour has to diffuse for combustion to occur. In such cases, a second stage of vapour phase combustion occurs when the oxide agglomerate is heated sufficiently so that the vapour of the liquid metal trapped in the pores breaks through to the surface. In the case of potassium, a self-cleaning mechanism, attributable to the high solubility of the metal oxides in liquid potassium and the relatively low melting point of the potassium oxides, enables a clear liquid surface to be exposed throughout for vapour phase combustion to prevail always. Recorded temperature profiles, SEM analysis of the oxide agglomerates as well as calculations of the metal–oxygen equilibrium thermo-chemistry for the three metals confirm this scenario.

Laser desorption/ionization mass spectrometry on nanostructured semiconductor substrates: DIOS™ and QuickMass™

In the era of systems biology, new analytical platforms are under demand. Desorption/ionization on silicon mass spectrometry (DIOS-MS) is a promising high throughput laser mass spectrometry approach that has attracted a lot of attention, and has been commercialized. Another substrate material manufactured by physical method has also been made commercially available under the trade name of QuickMass™. These two commercial substrates, DIOS™ and QuickMass™, were investigated independently from the manufacturers and were characterized by a number of advanced surface techniques. This work determined (1) the correlation between the substrate physicochemical properties and their LDI activity, (2) the feasibility of metabolic profiling from complex biological matrices and (3) the laser desorption/ionization mechanism. The DIOS™ substrate was characterized with a thick nano-sized porous layer, a high surface concentration of fluorocarbon and silicon oxides and super-hydrophobicity. In contrast, the QuickMass™ substrate consisted of a non-porous germanium thin-film. The relatively high ionization efficiency obtained from the DIOS™ substrate was contributed to the fluorosilane manufacturing processes and its porous morphology. Despite the QuickMass™ substrate being less effective, it was noted that the use of germanium affords a self-cleaning mechanism and suppresses background interference of mass spectra. The suitability of DIOS™ substrates for metabolic profiling of complex biological matrices was demonstrated. DIOS mass spectra of human blood plasma, human urine and animal liver tissue extracts were produced. Suitable extraction methods were found to be important, but relatively simplified approaches were sufficient. Further investigations of the DIOS desorption/ionization mechanism were carried out. The previously proposed sub-surface state reaction could be a molten-solid interfacial state reaction of the substrate and this had a significant effect toward the protonation reaction of amines.

Growth performance of blue shrimp, Litopenaeus stylirostris in self-cleaning microcosm tanks

Outdoor microcosm tanks were used to grow the penaeid blue shrimp, Litopenaeus stylirostris, in Brunei Darussalam. The tanks were cylindrical, free standing fiber glass tanks of 1827 L water holding capacity and had a self-cleaning mechanism. In three eight-week feeding trials, juvenile shrimp of 0.9–4.3 g were stocked at a density of 28 shrimp/m 2. At the end of each trial, survival rates exceeded 80%. Growth rates ranged from 1.19 to 2.46 g/week. Water quality remained stable and within suitable ranges for L. stylirostris growth in all trials. The tanks had algae and bacterial floc developing within a few days of starting the trials. Fourteen commercial shrimp feeds, each containing more than 40% crude protein, were tested in the trials. In spite of the presence of natural food organisms, significant feed-related differences among treatments were found in each trial. In conclusion, microcosm tanks support excellent growth and survival of L. stylirostris and are appropriate for conducting trials to evaluate feeds for pond growout.

Behaviour of self-cleaning glass in urban atmosphere

In order to analyse the self-cleaning mechanism of TiO 2-coated window float glass, a field experiment was conducted in Paris, at a site representative of background urban pollution. Two hydrophilic photocatalytic TiO 2-coated industrial glasses and a traditional float glass (reference) were exposed in unsheltered and sheltered condition for various time duration. The sheltered exposure allowed to study the soiling and self-cleaning mechanism without the disturbing effect of rain washing. In parallel, air filtrations were carried out in order to assess the chemical composition of airborne particulate. Analytical measurements were performed on the deposit and on the weathered glass layer. The analyses of the deposit on glass and of atmospheric particles on filters consisted in the determination of the organic fraction (organic carbon, particulate organic matter, water-soluble organic carbon), elemental carbon and the inorganic soluble fractions. The impairment of glass optical properties was followed by haze measurements. Investigation of the weathered surfaces was performed using EPMA and scanning electron microscopy (SEM)/EDX. Only a moderate weathering of the glass surfaces after 24 months of exposure was detected. The self-cleaning mechanism was evidenced by a significant decrease of the organic fraction in the deposit on the TiO 2-coated glasses.

One automaton model in biology

We construct an automaton model of lung self-cleaning mechanism both in the pure environment and in the conditions of possible dust loading into the lungs from the environment in breathing. We analyse this model and find the complexity (time) of self-cleaning of the lungs for an arbitrary initial dust load.

Photocatalytic discoloration of organic compounds on outdoor building cement panels modified by photoactive coatings

Cement based Eternit plates modified by TiO 2/SiO 2 surface layers acquired self-cleaning properties. The TiO 2/SiO 2 coating was transparent indicating that the small TiO 2 (rutile) crystals cause no significant scattering. The parameters related to the composition of the TiO 2/SiO 2 coating were investigated in relation to concentration and ratio of the components and the time and temperature necessary for the colloid networking to produce the self-cleaning effect. The repetitive discoloration of natural pigments on the TiO 2/SiO 2/Eternit plates was observed showing the stable performance of the TiO 2/SiO 2coating. FTIR spectroscopy shows the stability of the acrylic and cellulose components on the TiO 2/SiO 2/Eternit plates after repetitive self-cleaning cycles. A self-cleaning mechanism is suggested in agreement with the experimental findings. The SiO 2 layers seem to avoid the radical attack on the acrylic topmost layers of the Eternit plates due to the TiO 2 (h + vb) generated under solar simulated radiation. The profile and thickness of the coating was estimated by confocal microscopy. X-ray diffraction showed that the Eternit plates had a structure forming function on the TiO 2/SiO 2 layers leading to the formation of rutile from the Ti-colloids at temperatures as low as ∼80 °C.

“Zero Fouling” Self-Cleaning Heat Exchanger

Conventional shell and tube heat exchangers sometimes have to use two severely fouling process streams, one in the tubes and one in the shell. This paper presents the design of a self-cleaning heat exchanger that applies the self-cleaning mechanism in the tubes of two parallel bundles handling the fouling process streams. For the transfer of heat between both bundles, a small circulating flow of conditioned water is used as an intermediate fluid, a fraction of which evaporates on the outside of the tubes of the high-temperature bundle and condenses on the outside of the tubes of the low-temperature bundle. This novel design, which consists of two parallel bundles in one shell, experiences very high film coefficients at the outside surface of both tube bundles and does not suffer from any fouling. Therefore, it is referred to as a “zero fouling” self-cleaning heat exchanger. In this paper, a conventional severely fouling crude oil preheater will be compared with a zero fouling self-cleaning heat exchanger for the same service.

Speciation Gamma-Spectrometry: the Fate of Environmental Radio-Nuclides in Hard-Water Lakes

A sequential fractionation method for simultaneous and absolute measurement of environmental radio-nuclides, 241Am, 210Pb, 226Ra, 137Cs, 40K and 234Th/238U, by gamma-spectrometry was tested and applied to hard-water lake-sediments. The carbonate, fulvic, humic and mineral insoluble fractions were extracted from the sediments. Correction of self-absorption and geometrical effects, arising from the conditioning of bulk and fractionated sediments, were done using Monte Carlo simulations. This “non-destructive” fractionation procedure allows further analysis of other chemical species in the same fractions thus creating possibilities to study the dynamics of self-cleaning mechanism in lakes. The results demonstrate that the procedure is quantitative and suitable for the determination of environmental key radio-tracers in different fractions. Unlike other fresh-water sediments the major part of the environmental radio-nuclides is associated with “mineral” fractions. This speciation gamma-spectrometry procedure was supplemented by isotope-dilution alpha-spectrometry 210Po (210Pb), for determining the acid-soluble organic fractions in fresh-water lakes. The overall speciation procedure demonstrated that carbonate fractions, extracted from hard-water lake sediments, could be separated either free from, or associated with, fulvic-compounds. This speciation procedure can be applied to other aquatic deposits, however supplementary steps can be added if other data are required.

Nanofabrication with step and flash imprint lithography

Step and flash imprint lithography (SFIL) has made tremendous progress since its initial development at The University of Texas at Austin in the late 1990s. The SFIL process went from laboratory to commercialization in under five years, and the number of technical hurdles that must be cleared before it is recognized as fully competitive with optical or EUV lithography for sub-50-nm patterning is dwindling. Patterning resolution has been demonstrated down to 20 nm, with the limit so far being only the template fabrication process. The SFIL method was developed from the beginning with the precision overlay/alignment requirements of multilevel device fabrication in mind. It was recognized that it would be inherently easier to achieve overlay and alignment accuracy with a constant temperature and low pressure imprinting process, and already tool designers have built on SFIL's advantages to produce tools that are viable for multilayer device fabrication. Early tools have demonstrated better than 10-nm alignment resolution, and no insurmountable fundamental issues have been identified that would prevent alignment resolution from reaching the tight tolerances required for integrated circuit manufacturing. With any contact printing method, process-generated defects are a concern, but the SFIL process has proven to be surprisingly robust with an inherent self-cleaning mechanism for removing particle contamination. Furthermore, new template surface treatments have been developed that improve mold lifetime and minimize defect generation. SFIL shows promise as a low cost manufacturing tool for a wide variety of semiconductor, microelectromechanical, optoelectronic, microfluidic, and other devices. This work summarizes the state of development of step and flash imprint lithography and discusses its potential as a general nanofabrication tool.

Improvement of the automatic endoscopic reprocessor: self-cleaning disinfecting connectors between endoscope and reprocessor.

We have previously pointed out a defect of automatic endoscopic reprocessors, i. e. the contamination of the connecting part between the endoscope and the reprocessor. We evaluated a newly designed connector (MH-861; Olympus, Tokyo, Japan) with a self-cleaning and disinfection mechanism, which enabled cleaning and disinfection of both the connector itself and its interface with the suction and air/water valves during a reprocessing cycle, which was not previously possible. Ten upper gastrointestinal endscopes were examined in the study. Swabs were taken from the suction and air/water valves for microbiological culture before and after reprocessing by the washer-disinfector. The numbers of contaminated endoscopes before and after reprocessing with the new connector were compared. Before the procedure there were five contaminated endoscopes and none after the procedure. When the new connector was used, the difference in cleaning and disinfection of the connecting parts was significant (P = 0.0325). We conclude that the newly developed connector permits effective cleaning and disinfection by automatic reprocessors.

Nuclear medicine diagnosis of the lung

Scintigraphic recording of regional ventilation and perfusion with 99mTc-Aerosol and 99mTc-MAA remain in the foreground of nuclear medicine pulmonary diagnostics. The most important indication for ventilation scintigraphy is the prediction of postoperative pulmonary function, which is still performed in many hospitals with perfusion scintigraphy, and with which, in turn, intrapulmonary right-left shunts can be simply and also semiquantitatively recorded. Combined ventilation/perfusion scintigraphy offers a very high degree of sensitivity in the proof of acute pulmonary embolism, is therefore exceptionally well suited for exclusion diagnostics, while specificity compared to pulmonary angiography and spiral CT still needs some clarification. The self-cleaning mechanism of the lung can be quantitatively examined using mucociliary and resorptive clearance. The clinical areas of application are limited for methodical reasons. Primary diagnostics of bronchial carcinoma and dignity differentiation of solitary pulmonary nodules, preferably with 18F-FDG PET are gaining steadily in importance.

Epithallus sloughing: a self-cleaning mechanism for coralline algae

Epithallus sloughing: a self-cleaning mechanism for coralline algae