Dirt Particles Research Articles

SiO2/TiO2 Antireflective Coatings With Photocatalytic Properties Prepared by Sol–Gel for Solar Glass Covers

The glass covers of solar systems are usually coated with antireflective (AR) coatings on both sides that allow to increase the efficiency of the whole system. At the same time, the accumulation of dust and dirt particles on the surface of the AR coated glass decreases the transmittance of the covers, even to values lower than the uncoated glass. This decrease in the cover transmittance reduces the solar radiation that reaches the absorber and, in this way, a decrease in the solar plant efficiency would be obtained. So, the use of films that combine high transmittance and self-cleaning capacity seems to be a promising development. This paper reports the preparation of sol–gel porous TiO2 and SiO2 bilayers on borosilicate glass. The porosity and thickness of both layers have been optimized in order to obtain the optimal photocatalytic and optical properties. Solar transmittance values of 0.964 were obtained for the TiO2/SiO2 coated glass. The highest value of transmittance reached is 0.993 and it is placed at 600 nm. The self-cleaning properties were evaluated using methylene blue and trichloroethylene (TCE) as model organic molecules using UV-A light. The results showed that the SiO2/TiO2 samples degraded the colorant faster than the SiO2 sample. Moreover, the degradation of TCE in air in a continuous fix bed photoreactor for samples with different TiO2 film thicknesses was also performed. The TCE conversion was found dependent on the TiO2 thickness. Nevertheless, the increase in the thickness of this layer reduced transmittance properties. The study demonstrates that it is possible to combine antireflective and self-cleaning properties in the same material.

Spectral analysis and classification of dirt particles in pulp

Spectral analysis and classification of dirt particles in pulp

연꽃식물 조직의 표피 특성과 연잎효과

연잎효과는 연꽃의 잎에서 규명된 현상으로 표피세포에서 기원하는 미세구조에 의해 물방울이 잎 표면이나 내부조직에 침투하지 않고 경사면으로 흘러내리며 표면 위 먼지나 이물질을 함께 떨어지게 한다. 잎 표면을 항상 깨끗한 상태로 유지하는 자기정화 능력인 연잎효과에 대해서는 여러 영역에서 연구되고 다방면으로 응용되고 있으나 구조적인 측면에서 연잎을 생장단계별 또는 표피조직 부위별로 비교 조사한 연구는 거의 없는 실정이다. 이에 본 연구에서는 연잎과 줄기를 대상으로 생장단계별, 부위별 표피조직의 미세 표면구조를 연구하여 연잎효과 표면 특성을 조사하였다. 본 연구에서 조사된 연잎효과는 미세돌기와 왁스결정체가 발달한 잎의 상피조직에서만 나타나고, 왁스결정체만 발달한 하피 및 줄기의 표피조직에서는 확인되지 않았다. 이는 미세돌기의 발달이 연잎효과를 나타내는데 가장 중요한 요인이고, 왁스결정체가 돌기표면 위에 축적되면 연잎효과는 더 증가하는 것으로 밝혀졌다. The cell surface sculpture of the plant epidermis has received great interest recently. It has also been an active area of research, as the biological microstructures of the surface, such as papillae and waxes, exhibit several unique properties, including self-cleaning character; namely the "Lotus effect" first described in the leaves of the lotus, Nelumbo nucifera. The Lotus effect is the phenomenon in which the super-hydrophobic and water-repellent nature of lotus leaves allow water drops to run off easily on the surface in a rolling and sliding motion thereby facilitating the removal of dirt particles. It is well-known that surface roughness on the micro- and nanoscale is a primary characteristic allowing for the Lotus effect. This effect is common among plants and is of great technological importance, since it can be applied industrially in numerous fields. In the present study, Nelumbo nucifera leaf and stem epidermal surfaces have been examined with a focus on the features of papillae and wax crystalloids. Both young and mature Nelumbo nucifera leaf epidermis demonstrated the Lotus effect on their entire epidermal surface. The central area of the upper epidermis, in particular, formed extremely papillose surfaces, with an additional wax layer, enabling greater water repellency. Despite the presence of wax crystalloids, epidermal surfaces of the lower leaf and stem lacking papillae, were much more easily wetted.

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.

Preparation and characterization of acrylic polymer nanocomposite films obtained from aqueous dispersions

AbstractA functionalized fumed silica was dispersed in water using a nonionic surfactant, yielding a stable nanodispersion. This was blended with an aqueous acrylic polymer dispersion to produce hybrid nanocomposite films. The silica particles were shown to be well dispersed in the polymer matrix, with little agglomeration. Further evidence of good compatibility between the silica and acrylic polymer was given by the improved thermal stability of the nanocomposite compared with the pristine polymer. The nanocomposite films exhibited significantly lower dirt pick‐up behavior, which seems to be associated to the nanoroughness of the composite film surface observed in AFM analysis. This decreases the contact area between film and micrometric dirt particles. Surface tension and hardness do not seem to be significantly different in the composite and noncomposite materials. This approach may provide a strategy to obtain hybrid coatings with self‐cleaning properties, taking advantage of the relatively low cost, and large availability of fumed silica. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Literature review on superhydrophobic self‐cleaning surfaces produced by electrospinning

AbstractSelf‐cleaning surface is potentially a very useful addition for many commercial products due to economic, aesthetic, and environmental reasons. Super‐hydrophobic self‐cleaning, also called Lotus effect, utilizes right combination of surface chemistry and roughness to force water droplets to form high contact angle on a surface, easily roll off a surface and pick up dirt particles on its way. Electrospinning is a promising technique for creation of superhydrophobic self‐cleaning surfaces owing to a wide set of parameters that allow effectively controlling roughness of resulted webs. This article gives a brief introduction to the theory of super‐hydrophobic self‐cleaning and basic principles of the electrospinning process and reviews the scientific literature where electrospinning was used to create superhydrophobic surfaces. The article reviewed are categorized into several groups and their results are compared in terms of superhydrophobic properties. Several issues with current state of the art and highlights of important areas for future research are discussed in the conclusion. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012

The Natural Patterns of Self-Cleaning Surfaces: RIMAPS Analysis of Superhydrophobic Leaves

In the last decades, a new interdisciplinary science called biomimetics has emerged that has significantly influenced the design of certain new materials. Nature, as a source of inspiration, can give us ideas and concepts to implement new functional properties. One example is the self-cleaning property (superhydrophobicity) of certain plant leaves, better known as the Lotus Effect. This term comes from the lotus leaf (Nelumbo nucifera), the best-known self-cleaning surface in nature. On this kind of leaf, water droplets roll over the leaf surface and collect dirt and other particles from the surfaces. The superhydrophobicity of these leaves is caused, in general, by a hierarchical surface structure, built by a randomly oriented small hydrophobic wax structure on the top of convex cell papillae. The wetting condition of the solid surface is a particular property of materials and depends on both surface energy and surface topography. Many papers have been written to show how superhydrophic surfaces with periodic and random patterns can be made, but few describe and characterize biological self-cleaning surfaces. These papers usually analyze them by using optical profilers and scanning electron microscopy with specific sample preparation (for example, fixation) and in some cases atomic force microscopy. The main conclusion of those works is that binary structures (hierarchical microstructures and nanostructures) and unitary structures (basically nanostructures) are found in superhydrophobic plant leaves. However, no information regarding the general micro-nano structural pattern of biological surfaces on the x-y plane has been reported. These surfaces seem to have a random pattern in most of the cases or at least a vague arrangement of its constitutive elements whose morphologies can be represented by geometrical figures (for example, hexagonal/pentagonal polygons, circles, and straight lines).

Superhydrophobic RTV silicone rubber insulator coatings

On wet days, environmental contamination of outdoor insulation surfaces can reduce the reliability of electrical transmission systems and lead to flashover and arcing over the entire insulator. The use of superhydrophobic coatings would resolve this problem due to their self-cleaning effect. Water droplets can pick up dirt particles and remove contamination from the surfaces of insulators. This paper reports on a study to make a superhydrophobic RTV silicone rubber coating that has contact angles of higher than 145° and good UV durability. The Inclined Plane Test, water durability test and adhesion test are presented to show the effectiveness of this coating and the best formulations. The results of tracking and erosion resistance test (Inclined Plane Test) showed that formulations with at least 35wt% ATH can be used for superhydrophobic RTV insulator coatings.

Post‐traumatic Pseudallescheria apiosperma osteomyelitis: positive outcome of a young immunocompetent male patient due to surgical intervention and voriconazole therapy

The present case describes thesuccessful treatment of an immunocompetent youngmale patient suffering from a severe, post-traumaticPseudallescheria apiosperma osteomyelitis of the tibia.Cure of the patient was achieved by long-termvoriconazole administration and surgical debridementof infected soft tissue and bone.

A Study in Balance: How Microbiomes Are Changing the Shape of Environmental Health

The agents we now know as bacteria have been known for centuries to play a key role in certain kinds of illnesses and ailments. But aside from infectious diseases, the communities of microbes we carry in specific parts of our bodies—our microbiomes—are a relatively new topic in human health. Now this field of study has taken an evolutionary leap forward with new research showing human microbiomes may play a far greater role in environ-mental health than ever imagined. The excitement around this field was obvious at a National Academy of Sciences (NAS) workshop on the interplay of the microbiomes, environ-mental agents, and human health held 27–28 April 2011,1 where talks by researchers working in this area inspired numerous “eureka!” moments. New findings about the ways in which human microbiomes transform arsenic and mercury—two of our most prevalent and well-defined external human health hazards—suggest the role of commensal bacteria may equal or exceed that of genetic polymorphisms that regulate metal transformations within the body, says Ellen Silbergeld, a professor of environmental health sciences at the Johns Hopkins University Bloomberg School of Public Health. The implications of these new insights are staggering. Environmental health scientists may need to expand the toxicokinetics of metals and other environmental agents, as well as associated biomarkers, to include the microbial component. “This is a huge thing that has never been thought of before in environmental health sciences,” Silbergeld told workshop attendees. Emerging findings also demand a re-examination of what it means to be exposed to environmental agents, Silbergeld says. To a toxicologist, she explains, a contaminant is only “in the body” once it has crossed from the external environment into circulating blood, or a cell, or an organ. But new findings suggest biologically relevant transformations may take place prior to absorption, when contaminants interact with the microbiome in the mouth, intestines, or other tissues. Because of the metabolic processes mediated by microbiomes, a great deal of what toxicologists attribute to human metabolism—such as methylation of arsenic—may actually take place at least in part before contaminants cross into the internal environment of our bodies.

Body feathers as a potential new biomonitoring tool in raptors: A study on organohalogenated contaminants in different feather types and preen oil of West Greenland white-tailed eagles ( Haliaeetus albicilla)

We investigated the variation in concentrations and profiles of various classes of organohalogenated compounds (OHCs) in different feather types, muscle tissue and preen oil from 15 white-tailed eagle ( Haliaeetus albicilla) carcasses from Greenland. The influence of moult patterns and potential external contamination onto the feather surface was examined, while the present study is also the first to investigate the use of body feathers for OHC monitoring. Concentrations of sum polychlorinated biphenyls (PCBs) in feathers from white tailed eagles ranged from 2.3 ng/g in a primary wing feather to 4200 ng/g in body feathers. Using 300 mg of body feathers, almost 50 different OHCs could be quantified and median concentrations in body feathers were 10 fold higher than concentrations in tail feathers (rectrices) or primary wing feathers. Body feathers could be very useful for biomonitoring taking into account their easy sampling, short preparation time and high levels of OHCs. In addition, the effects of confounding variables such as feather size, moult and age are also minimised using body feathers. Correlations with concentrations in muscle tissue and preen oil were high and significant for all feather types ( r ranging from 0.81 to 0.87 for sum PCBs). Significant differences in concentrations and profiles of OHCs were found between different primary feathers, indicating that the accumulation of OHCs in feathers varies over the moulting period (maximum three years). Washing of feathers with an organic solvent (acetone) resulted in a significant decrease in the measured concentrations of OHCs in feathers. However, our results indicated that preen oil is probably not the only contributor to the external contamination that can be removed by washing with acetone. Possibly dust and other particles may be of importance and may be sticking to the preened feathers. Rectrices washed only with water showed high and significant correlations with concentrations in muscle and preen oil as well. Washing with acetone therefore does not seem to be of great influence when relating to internal tissue concentrations. We recommend washing feathers only with distilled water in order to remove dirt and dust particles before analysis.

Spectral and Physical Properties of Electrochemically Formed Colored Layers on Titanium Covered with Clearcoats

We present the application and characterization of two commercial polymer clearcoats to electrochemically formed colored passive layers on titanium with the aim of providing physical protection required in many of titanium's applications, while allowing the unique appearance of the colored layers to show through. Thin layers of an acrylic automotive clearcoat (∼3.5 μm thick) and an epoxy marine clearcoat (∼6.5 μm thick) are applied to the colored titanium surfaces using spin coating, and are found to slightly modify their visual properties, while maintaining their bright, well-defined sparkling colors. Both clearcoats are found to significantly reduce the surface roughness, thereby reducing potential wear from friction and the adhesion of fine dirt particles. They are also found to notably decrease the wetting properties of colored titanium, furthering its protection against damage from ambient and aqueous media. The clearcoats show the ability to protect colored titanium from physical and chemical damage, with the automotive clearcoat exhibiting superior adhesion. Our electrochemical coloring technique combined with the application of clearcoats creates a new and unique system that does not rely solely on a polymer coating for its colorful appearance and protection against corrosion.

Reliable Analysis of Residual Dirt Particles

Reliable Analysis of Residual Dirt Particles

Electroacoustic miniature transducer for a hearing aid

The penetration of moisture and dirt often leads to a premature failure of electroacoustic miniature transducers that are used in hearing aids. A transducer membrane of a miniature transducer is provided at least in part with a hydrophobic and/or oliophobic and/or biofilm-inhibiting coating that, because its layer thickness is less than 10 μm, does not significantly influence the acoustic characteristic of the miniature transducer, and that prevents degradation of the transmission characteristic due to moisture, or moisture-caused damage to the miniature transducer. In addition, the adherence of dirt particles is prevented.

Simulation of filtration processes in deformable media

A Lagrangian solver to realistically model large, non-spherical dirt particles and their behavior in the vicinity of deformable filtration fibres has been programmed. While this paper focuses on the realization of interaction effects and result verification, a related article, concerning basic solver concepts as well as drag force implementations, has been published, [3]. A digitally reconstructed, deformable filter fibre structure gives the framework for all particle interactions with their surroundings. Particle–fibre deposition effects, are being modelled in detail. Fibre forces, that act on a particle and confine it, can be applied on a user-defined basis. The collision module handles particle–particle interactions, detects exact particlesurface impact locations and calculates translational- as well as rotational collision effects. In order to validate Computational Fluid Dynamics results, like filter fibre efficiency and particle penetration depth, a semi-analytical verification approach for simplified fibre geometries has been devised. In addition to that, extensive, experimental test runs are currently conducted.

Simulation of filtration processes in deformable media

A Lagrangian solver to realistically model large, non-spherical dirt particles and their behaviour in the vicinity of deformable filtration fibres has been programmed. While this paper focuses on basic solver concepts as well as drag force implementations, a related article, concerning the realisation of interaction effects and result verification, is forthcoming, [3]. Within the framework of a digitally reconstructed, deformable filter fibre geometry, the solver traces the governing multi physics effects down to the occurrence of single force- and torque vectors. In order to go from an initial, spherical particle model [2], to a more sophisticated, non-spherical model, the capabilities of a Six Degrees of Freedom Solver have been included in the programming. A panel model and the concept of satellite help points are used to handle particles that encompass several fluid calculation cells. An innovative drag force implementation allows the consideration of rotational- and shear flow effects on particle motion. Results are evaluated and compared to an analytical formulation.

Biomimetic Artificial PVDF Film Reproduce the Superhydrophobic Property of a Lotus Leaf

Lotus flower is a symbol of purity in Asian cultures, when growing from muddy waters it stays clean and uncontaminated. The "self-cleaning" surface of lotus leaf is hydrophobic and rough, showing hierarchical micro- and nano-scale structures. Stimulated by “lotus effect”, the microreliefs of lotus leaf was mimicked using PVDF film and the nano-scale protrusions on the top of the microreliefs were implemented by the mixed solution of dimethyldichlorosilane (DDS) and methyltrichlorosilane (MTS). A lotus-leaf-like surface of the PVDF film was clearly observed by SEM. Elemental composition analysis by XPS revealed that the nanostructure materials of PVDF film were polymethylsiloxane and polydimethylsiloxane. The superhydrophobic property of the mimicked self-cleaning surface was validated by the water contact angle and sliding angle on the lotus-leaf-like PVDF film, which are 155°and 4°, respectively. In this case, water drops can easily move across the PVDF film surface, carrying dirt particles away, leaving no contamination.

A Mechanical Model for the Adhesion of Spiders to Nominally Flat Surfaces

In dry attachment systems of spiders and geckos, van der Waals forces mediate attraction between substrate and animal tarsus. In particular, the scopula of Evarcha arcuata spiders allows for reversible attachment and easy detachment to a broad range of surfaces. Hence, reproducing the scopula's roughness compatibility while maintaining anti-bunching features and dirt particle repellence behavior is a central task for a biomimetic transfer to an engineered model. In the present work we model the scopula of E. arcuata from a mechano-elastic point of view analyzing the influence of its hierarchical structure on the attachment behavior. By considering biological data of the gecko and spider, and the simulation results, the adhesive capabilities of the two animals are compared and important confirmations and new directives in order to reproduce the overall structure are found. Moreover, a possible suggestion of how the spider detaches in an easy and fast manner is proposed and supported by the results.

Self-Cleaning Efficiency of Artificial Superhydrophobic Surfaces

The hierarchical structured surface of the lotus (Nelumbo nucifera, Gaertn.) leaf provides a model for the development of biomimetic self-cleaning surfaces. On these water-repellent surfaces, water droplets move easily at a low inclination of the leaf and collect dirt particles adhering to the leaf surface. Flat hydrophilic and hydrophobic, nanostructured, microstructured, and hierarchical structured superhydrophobic surfaces were fabricated, and a systematic study of wettability and adhesion properties was carried out. The influence of contact angle hysteresis on self-cleaning by water droplets was studied at different tilt angles (TA) of the specimen surfaces (3 degrees for Lotus wax, 10 degrees for n-hexatriacontane, as well as 45 degrees for both types of surfaces). At 3 degrees and 10 degrees TA, no surfaces were cleaned by moving water applied onto the surfaces with nearly zero kinetic energy, but most particles were removed from hierarchical structured surfaces, and a certain amount of particles were captured between the asperities of the micro- and hierarchical structured surfaces. After an increase of the TA to 45 degrees (larger than the tilt angles of all structured surfaces), as usually used for industrial self-cleaning tests, all nanostructured surfaces were cleaned by water droplets moving over the surfaces followed by hierarchical and microstructures. Droplets applied onto the surfaces with some pressure removed particles residues and led to self-cleaning by a combination of sliding and rolling droplets. Geometrical scale effects were responsible for superior performance of nanostructured surfaces.

Auswertung der durch den HIP-Prozess diffusions- geschweissten CMU- und FW-Testproben

To manufacture a cooling plate and a first wall with internal cooling channels for a fusion reactor, several diffusion bonding attempts with the material EUROFER97-2 have been so far conducted systematically. Some bonding parameter sets are predicted according to a diffusion bonding model. These predictions have then been verified in laboratory experiments with different samples. Beginning with unstructured samples up to samples with cooling channels, the experiments have been conducted in a uniaxial diffusion bonding device. The optimal parameter set has been determined. For the technological transfer to the real components two diffusion bonding samples (a compact mock-up (CMU) and a first wall (FW)) have been manufactured. Due to the large format of the FW test sample, the diffusion bonding by the HIP process is used. The process parameter set is modified from the optimal parameter set determined before. The cleaning method of the surfaces which will be diffusion bonded has been changed to the dry ice cleaning procedure. The bonding samples are examined first by a leakage test with helium. With a pressure of 130 bar and test duration of 2 h, leakage rate smaller than 10- 9 mbar I/s is detected. The measurements at the ligament of the channels after the bonding process show excessive inelastic deformations, which are even non uniform for the FW test sample. The microscopic investigations show the variation of bonding quality on each of the examined bars from CMU and FW. This is confirmed by investigation of the remaining voids in the bonding seam. The grain coarsening due to the additional thermal treatment stage for 2 h and those approx. 1 h extended bonding duration at 1050 °C is also observed. With the AES analysis at the fracture surface no precipitations of the alloying elements are observed. Furthermore some detached dirt particles, which contain a large quantity of atoms of oxygen, aluminum and sulfur, are found. The investigation of the mechanical behaviour of the diffusion bonded Material in a temperature range of RT ≤ T ≤ 700 °C shows that the 0.2 % yield strength (R p0,2 ) and the tensile strength (R m ) of the base material drop due to the grain coarsening. However at the same time the ultimate strains increase over the entire test temperature range. The samples with bonding seam have values of R p0,2 and R m that lie in the range of the values of the base material. The varied bonding quality of each ligament from CMU and FW is shown in the curve of the ultimate strain. This will be also verified by the impact tests in a temperature range of -150 < T ≤ RT. No evidence of USE and DBTT show the sample with bonding seam. Their impact energy has a linear dependency on the test temperatures. The results show, that the ligament 1 (edge region) of CMU with the impact energy of 4.12 J (47% the USE of the base material) and the ligament 6 (in the middle of the region) of FW with the impact energy of 3.2 J (33% the USE of the base material) at RT have the best bonding behaviour.