Self-cleaning Mechanisms Research Articles

Experimental study on effect of surface vibration on micro textured surfaces with hydrophobic and hydrophilic materials

Artificial hydrophobic surfaces have been studied in the last ten years in an effort to understand the effects of structured micro- and nano-scale features on droplet motion and self-cleaning mechanisms. Among these structured surfaces, micro-textured surfaces consisting of a combination of hydrophilic and hydrophobic materials have been designed, fabricated and characterized to understand how surface properties and morphology affect enhanced self-cleaning mechanisms. However, use of micro textured surfaces leads to a strong pinning effect that takes place between the droplets and the hydrophobic-hydrophilic edge, leading to a significant contact angle hysteresis effect. This research study focuses on the effects of surface vibrations on droplet shedding at different inclined angles on micro-textured surfaces. Surface vibration and shedding processes were experimentally characterized using a high speed imaging system. Experimental results show that droplets under the influence of surface vibration depict different contour morphologies when vibrating at different resonance frequencies. Moreover, droplet sliding angles can be reduced through surface vibration when the proper combination of droplet size and surface morphology is prescribed.

Biomimetic self-cleaning surfaces: synthesis, mechanism and applications.

With millions of years of natural evolution, organisms have achieved sophisticated structures, patterns or textures with complex, spontaneous multifunctionality. Among all the fascinating characteristics observed in biosystems, self-cleaning ability is regarded as one of the most interesting topics in biomimicry because of its potential applications in various fields such as aerospace, energy conversion and biomedical and environmental protection. Recently, in-depth studies have been carried out on various compelling biostructures including lotus leaves, shark skins, butterfly wings and gecko feet. To understand and mimic their self-cleaning mechanisms in artificial structures, in this article, recent progress in self-cleaning techniques is discussed and summarized. Based on the underlying self-cleaning mechanisms, the methods are classified into two categories: self-cleaning with water and without water. The review gives a succinct account of the detailed mechanisms and biomimetic processes applied to create artificial self-cleaning materials and surfaces, and provides some examples of cutting-edge applications such as anti-reflection, water repellence, self-healing, anti-fogging and micro-manipulators. The prospectives and directions of future development are also briefly proposed.

Robust self-cleaning and micromanipulation capabilities of gecko spatulae and their bio-mimics.

Geckos have the extraordinary ability to prevent their sticky feet from fouling while running on dusty walls and ceilings. Understanding gecko adhesion and self-cleaning mechanisms is essential for elucidating animal behaviours and rationally designing gecko-inspired devices. Here we report a unique self-cleaning mechanism possessed by the nano-pads of gecko spatulae. The difference between the velocity-dependent particle-wall adhesion and the velocity-independent spatula-particle dynamic response leads to a robust self-cleaning capability, allowing geckos to efficiently dislodge dirt during their locomotion. Emulating this natural design, we fabricate artificial spatulae and micromanipulators that show similar effects, and that provide a new way to manipulate micro-objects. By simply tuning the pull-off velocity, our gecko-inspired micromanipulators, made of synthetic microfibers with graphene-decorated micro-pads, can easily pick up, transport, and drop-off microparticles for precise assembling. This work should open the door to the development of novel self-cleaning adhesives, smart surfaces, microelectromechanical systems, biomedical devices, and more.

P.1.g.085 Gap junction-mediated modulation of modafinil pharmacological profile

Electrodialysis self-reversal (EDR) technology has attracted in the treatment of water for domestic and industrial uses. The self-reversal consists of a frequent reversal of the direction of current between the EDR-cell electrodes to combat fouling of ion exchange membranes (IEMs). Irrespective of the EDR self-cleaning processes, the role of natural organic matter and their complexing ability with metal ions on IEMs fouling is partially understood. The objective of this review is to identify the research gaps present in the elucidation of IEM fouling routes. The common IEMs’ foulants are identified, and several fouling mechanisms are briefly discussed. The effectiveness of self-cleaning mechanisms to reduce IEMs fouling is also be discussed. Dissolved organic carbon (DOC) possesses high chelation which forms metal complexes with di and trivalent cations found in water. The role of ternary complexes, e.g. M2+/3+–DOC and membrane surface, on membrane fouling via surface bridging, are also addressed. Finally, mitigation methods of IEMs membrane fouling are also discussed.

A parametric study of the hydrophobicity of rough surfaces based on finite element computations

Several biological and artificial hydrophobic surfaces exhibit self-cleaning mechanisms, which ensure smooth sliding/rolling of liquid droplets, allowing them to sweep pollutant particles away from the surface. While enhancing of the self-cleaning property is a major topic in numerous industrial applications, the underlying physics is not yet fully understood. The first step towards analyzing this mechanism is studying the surface hydrophobicity, which is characterized by the contact angle and surface topography. In this article, we investigate the wetting of hydrophobic surfaces at three different length-scales, over a range of surface and droplet parameters. A mathematical model describing multi-scale surface topographies is presented, using exponential functions. The contact between liquid droplets and these surfaces is numerically studied using a finite element (FE) droplet model. The introduced models are verified numerically and experimentally. Numerical examples are shown for axisymmetric droplets of different size on surfaces with various contact angles and various levels of surface roughness, representing different length-scales. The corresponding wetted area is computed in order to evaluate the hydrophobicity of the surface. Significant differences are observed in contact angles and wetted areas captured at different length-scales. This highlights the importance of the multi-scale structure of hydrophobic surfaces on wetting. Furthermore, the presented work provides guidelines for the design of artificial hydrophobic surfaces.

Scarcity and environmental quality in river hydrological basins

Fauna and flora depend on water of hydrological river basins to remain alive, where a conjunctive use of surface and ground water should take place. Also, water is a human right and must be treated as such to meeting other human rights such as civil and political. Except for drinking purposes, activities such as agriculture, industry, transportation, electricity and amenities make use of water. The last decade there is a growing concern that water is at scarcity and far exceeds the potential for its natural recharge. Degraded water quality deteriorates further the situation. Such worrisome concerns about water quality can be attributed to both natural processes and human activities. Significant environmental health issues and desalination processes at Greek hydrological river basins cannot be ignored. Over 20 countries worldwide are depending on water that is flowing from other nations, and more than 300 of the world hydrological river basins are considered transboundary. The tropics and mid-level northern hemisphere have the potential for freshwater than other parts of the world. According to the UK’s Center for Ecology and Hydrology, rich developed nations are guilty of mismanaging and overusing water resources. In developing countries, water is extraordinarily inefficient because 68% of it is lost in evaporation or returned to rivers and aquifers. The long-term effects arising from irrigation comprise loss of biodiversity and the hydrological river basin waters the ability to natural self-cleaning mechanisms. Shortage of water deprives the fauna and flora of their ecosystems. Besides their contributions to water scarcity, irrigation, industry and domestic effluent are major sources of water pollution and contamination. According to the World Bank in Middle East and North Africa region, many countries fulfil their water demand partially or totally by desalinating seawater. River basins in the region have around 60% of the world’s desalination capacity (7.2 × 109 m3/year). According to the countries plans and their historic desalination capability, the total capacity is expected to increase and reach 19.1 × 109 m3/year by the year 2016 and possibly 31.4 × 109 m3/year by 2025. This will count for around 39% of the anticipated region’s deficit. Preferably, the remaining deficit will be bridged through efficient demand and supply management. Comparing with Middle East and North Africa, Greece is still in an infantile stage.

Математическая модель прогноза экологической безопасности источников воды*

Mathematical modeling techniques of self-cleaning separate mechanisms, and also the models, which consider the impact of toxicants on the course of biological processes are offered. The functions reflecting a system reaction nature on internal and
 external factors are received.
 The obtained results qualitatively correctly describe the "biomass – resource" system evolution, which allows during comparison of model equations’ solutions and experimental data to calculate the kinetic constants of model.

Surfactant-induced growth of a calcium hydroxide coating at the concrete surface

In addition to its remarkable mechanical properties, high-performance concrete (HPC) also exhibits a very smooth surface with low porosity, which makes it particularly suitable for esthetic applications. Unfortunately, the constant environmental aggressions to which the urban buildings are exposed (organic or inorganic particles, algae, micro-organisms, staining from various sources) are a threat to their structural and esthetic durability. This article proposes an innovative method to protect HPC surfaces based on Ca(OH)2 growth at the fresh concrete/formwork interface. With the adequate surfactants used as demolding agents, it is possible to grow a continuous layer of Ca(OH)2 at the concrete surface which closes the porosity, reduces the water uptake, and gives the surface super-hydrophilic properties, facilitating self-cleaning mechanisms.

Aktuelle Konzepte zur Pathogenese des erworbenen Cholesteatoms

The pathogenesis of acquired middle ear cholesteatoma is still unknown and subject of controversial discussions. Based on clinical and histological findings, several theories for cholesteatoma pathogenesis have been developed: 1) retraction pocket theory; 2) proliferation theory; 3) immigration theory, and 4) metaplasia theory. Additionally cholesteatoma development was grouped in particular stages. Immunohistochemical examinations of the matrix and perimatrix have considerably improved the knowledge of cholesteatoma pathogenesis. In this review the current concepts of cholesteatoma pathogenesis are discussed: a retraction pocket occurs due to a tubal dysfunction. Local infection leads to a disturbance of self-cleaning mechanisms, with cell debris and keratinocytes accumulate inside the retraction pocket, and this is followed by an immigration of immune cells, i. e. Langerhans' cells, T-cells, macrophages. There is an imbalance and a vicious circle of epithelial proliferation, keratinocyte differentiation and maturation, prolonged apoptosis, and disturbance of self-cleaning mechanisms. The inflammatory stimulus will induce an epithelial proliferation along with expression of lytic enzymes and cytokines. As a consequence, some "microcholesteatoma" occur which will confluent. Bacteria inside the retraction pocket produce some antigens which will activate different cytokines and lytic enzymes, i. e. ICAM, RANKL, IL-1, IL-2, IL-6, MMP-2, and MMP-9. These cytokines lead to activation and maturing of osteoclasts with the consequence of degradation of extracellular bone matrix and hyperproliferation, bone arrosion and finally progression of the disease. The question why not all cholesteatomas show the same progression process is still unclear. A probable explanation could be that in most retraction pockets migration and self-cleansing mechanisms for keratinocytes are well functioning, with normal migration of the squamous epithelium from the basal layers to the surface. Nevertheless, future research will have to evaluate this topic which might be crucial for the understanding of cholesteatoma pathogenesis and for therapy.

Ecoremediations – a new concept in multifunctional ecosystem technologies for environmental protection

Ecoremediation (ERM) comprises methods of protection or restoration of the environment by means of natural processes existing in ecosystems. The establishment of ERM systems provides sustainable environmental management solutions that contribute to the preservation of biodiversity and pollution reduction, increase the quality of water and soil, and can be applied in protected and sensitive areas. The functions of ERM are based on aquatic, waterside, and wetland ecosystems, and are characterized by high retention capacity, flooding prevention, and reduction of specific physical, chemical, and toxic pollution. This chapter reviews the operational performance of ERM in Slovenia, including constructed wetlands for sewage, landfill leachate, industrial wastewater, drinking water, highway runoff, ponds/wetlands, vegetated drainage ditches for agricultural runoff, landfill restoration, and river revitalization. A further aim of the ERM concept is to promote the idea of unifying different kinds of ‘‘green technologies’’ that are based on nature’s self-cleaning mechanisms, enhanced by the latest scientific developments, in the search for sustainable solutions that do not rely on the passive role of nature, but look to nature in building sustainable models through an understanding of human–environmental relations.

Distribution of mercury in the water and bottom sediment of the J.A. Alzate Dam, Mexico

In this paper, mercury concentration in the soluble, particulate and total fractions of water and in the sediment from the Jose Antonio Alzate Dam in the State of Mexico was evaluated using neutron activation analysis in order to determine the bioavailability and distribution of this metal. Sampling was carried out on three separate seasons – cold dry season, hot dry season and rainy season – such that, at least one complete hydrological cycle in the dam was covered. Results show that mercury constitutes a significant problem in the dam. Concentration in the water column is higher than the maximum acceptable level (10 ng/L) as established by national environment criteria and is present at considerable levels in the bottom sediments (up to 500 µg/kg). In the water, mercury presents a seasonal variation, where the highest concentrations are found during the dry period and the lowest concentrations at the end of the rainy season due to dilution of the metal in water. Sediment concentration of mercury shows evidence of self-cleaning mechanisms in the dam in which, principally through processes of sedimentation, part of the metal is removed from the water column, improving the outflow water quality.

Contamination of multi-use closed tracheal suction catheters: an in-vitro study

The use of closed multi-use tracheal suction systems in ventilated patients is increasingly popular as it offers a number of potential physiological and microbiological advantages. As the use of these systems has been associated with an increased prevalence of tracheal colonization, effective self-cleaning mechanisms employed in these catheters are necessary. Using an in-vitro model we assessed the degree of catheter colonization in two multi-use catheter systems; Stericath and Trach-Care. Fifty of each catheter type were tested for colonization with five challenge organisms: Staphylococcus aureus (NCTC 6571); Pseudomonas aeruginosa (NCTC 10662); Haemophilus influenzae type b; S. epidermidis (slime producer); and S. epidermidis (slime non-producer). All five challenge strains had colonized both catheter types after 24 h and all 100 catheter tips were colonized. The extent and density of colonization was variable and interspecies variation in the pattern of catheter colonization was observed. The mean colonized lengths of Stericath catheters was 10·9 ± 1·4 cm and of Trach-Care 2.7 ± 1·3 cm ( P < 0·0001).