Repellent Surfaces Research Articles

Fluorinated segmented polyurethane anionomers for water–oil repellent surface treatments of cellulosic substrates

AbstractThree model structures of linear segmented anionomeric polyurethanes based on perfluoropolyether dimethylol‐terminated oligomers, isophorone diisocyanate, and dimethylol propionic acid were synthesized and obtained in the form of aqueous dispersions. The structures differed from each other in the chemical nature of the chain extender (diol or diamine) and in the content of carboxylic acid. Dispersions and polymer films were characterized by dynamic light scattering, dynamic mechanical analysis, differential scanning calorimetry, and contact angle measurements. Diluted aqueous dispersions were also evaluated as protective sizing agents in paper treatment, both as bulk modifiers and as surface treatments. Paper sheets characterized by high water and oil repellence were obtained. The results showed that performance is mainly related to the ionic group content of the polymer and to its molecular architecture. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1364–1372, 2005

A new modelling approach to simulate preferential flow and transport in water repellent porous media: Model structure and validation

Water repellent soil and surface layers exhibit a complex flow and transport mechanism. Knowledge of the underlying principles is essential, for instance, to simulate water availability for crops and to estimate leaching potentials of agrichemicals. The present study aims to introduce and apply a new modelling approach to simulate preferential flow and transport in water repellent porous media, and to test the model on basis of an extensive field tracer experiment. The process of preferential flow and transport has been incorporated in the well-known SWAP model and applied to field data of tracer transport through a water repellent sandy soil in the Netherlands. Flow concept and model structure have been outlined, and simulation results presented. Results indicated early arrival times of bromide tracer in the subsoil in the case where preferential flow has been taken into account in the model. Comparison of measured and computed bromide concentration profiles and bromide recovery rates show close resemblances. Several strategies to alleviate soil water repellency and prevent the occurrence of preferential flow and transport processes are highlighted, such as irrigation scheduling, clay additions, and application of surfactants.

Independence of synaptic specificity from neuritic guidance

Neuronal circuits are interconnected with a high degree of specificity. While axonal guidance has been demonstrated to be crucial for the choice of the correct target region, its role in specificity at the level of individual cells remains unclear. Specificity of synapse formation may either result from precise guidance of axonal outgrowth onto the target or depend on a molecular “match” between pre- and postsynapse. To distinguish between these possibilities, an in vitro system was used in which neuritic outgrowth of rat cortical neurons is accurately guided along the narrow pathways of a surface micropattern. The micropattern consisted of a blend of extracellular matrix molecules applied to a cell repellent background of polystyrene by microcontact printing. The system reproduces guidance by attractant and repellent surface cues while no other signals that may influence synapse formation, like gradients of trophic factors or accumulations of signaling molecules, are provided. While the number of contact points between neighboring cells was strongly reduced on patterned substrates due to the geometrical restrictions, frequency of synapse formation was not different from homogeneous cultures. Thus it was unaffected by stringent guidance onto the target cell or by the number of cell-cell contacts. Moreover, a statistically significant enrichment of reciprocal contacts between mixed pairs of excitatory and inhibitory neurons over probabilistic predictions was found, which has similarly been shown by others in dissociated neuronal cultures. Our results indicate that precise axonal guidance is insufficient for target-specific synapse formation and suggest that instead recognition between individual cells is required.

Wettablity of Poly(ethylene terephthalate) Substrates Modified by a Two‐Step Plasma Process: Ultra Water Repellent Surface Fabrication

The fabrication of ultra‐water‐repellent poly(ethylene terephthalate) substrates has been achieved by a two‐step plasma process. First, appropriate nanotextures are prepared on the substrate through an oxygen plasma treatment, and then a hydrophobic layer is coated on the nanotextured surfaces with plasma‐enhanced CVD using tetramethylsilane. The resulting modified substrates show ultra‐water‐repellent characteristics with a water contact angle greater than 150° (Figure).

Morphological and structural study of plasma deposited fluorocarbon films at different thicknesses

The growth of fluorocarbon thin films has been obtained by continuous and modulated r.f. plasmas fed with C 2F 4. The kinetics surface morphology of the coatings has been investigated and analyzed on films of various thicknesses. Such a study has allowed the evolution of structures in size and shape to be followed. Specifically, it has been observed that modulated plasmas with the proper duty cycles (⩽7%) lead to the formation of micrometer-long ribbon-shaped nanostructures. The precursors of the ribbons are nuclei that align into a spiral-mimic. Highly nanostructured films with an optimal thickness and ribbon density exhibit a super-water repellent surface with contact angles up to 170°. The surface roughness and smoothing of fluorocarbon films are strongly affected by the modulated and continuous plasmas, respectively.

Drag Reduction on Super Water Repellent Surface with Air Injection Method. 1st Report. Flow Pattern of Air Film and Stability.

A frictional drag reduction using a specific coating surface (Super Water-Repellent Surface) has been studied. Experiments were carried out by injecting a small amount of air to a rectangular horizontal duct with super water-repellent wall. Three kinds of flow patterns, i.e., bubble, slug and stable air film flow, were defined based on the observation of flow behaviors. It was shown that the friction factors with super water-repellent wall duct were smaller than those of the smooth acrylic wall when the thin air film was formed. The maximum drag reduction ratio was about 32% at Reynolds number around 24000. At higher Reynolds number, the drag reduction ratio decreased due to air film-bubble flow transition occurring.

Drag Reduction on Super Water Repellent Surface with Air Injection Method. 2nd Report. Drag Reduction Mechanism.

Experiments were conducted to investigate the slit width effect on the frictional drag reduction using the Super water repellent surface (SWR) and air injection method. The results showed that the friction factor of slit width 2.0 mm was smaller than that of 0.5 mm at low Reynolds number. It was also observed that the stable plane air film was formed for slit width 2.0 mm. The drag reduction mechanism, considering fluid slip at the air/water interface, was also studied both numerically and theoretically. As a result, the drag reduction by the thin air film was maximally 95% at Re=24×104 was obtained.

Low Temperature Deposition of Transparent Ultra Water-Repellent Thin Films by Microwave Plasma Enhanced Chemical Vapor Deposition

ABSTRACTOne of the most common methods for obtaining water repellent surfaces is spreading fluoropolymer or fluoroalkylsilane onto substrates. However, this method is not applicable to low heat-resistant substrates such as plastics, since after spreading, the method requires a heating process which is generally conducted at a temperature of about 600K. The objective of this study is the preparation of ultra water-repellent and optically transparent thin films at low temperatures below 373K. The films were deposited by means of microwave plasma enhanced plasma chemical vapor deposition (MPECVD) using organosilane, that is, trimethylmethoxysilane (TMMOS) as a source with adding Ar, CO2, N2, O2 or air as an excitation gas. Under optimized preparation conditions, films with water contact angles more than 150 degrees and optical transparencies more than 90% were successfully fabricated.

Resistance Tests of Tanker and High Length-to-beam-ratio Ship Models

In the 1 st report, a new technique for reducing frictional drag using a super water repellent surface and air-injection (SWR & A method) was proposed, and its effectiveness for two-dimensional flow was confirmed by carrying out pressure loss tests in a rectangular tube and resistance tests on a horizontal flat plate.This paper presents the results of resistance tests applying the new technique to a tanker model of 7.2 m long and a high length-to-beam-ratio ship model of 12 m long. The results of these tests show that the new technique can significantly reduce frictional drag of the tanker model and the high length-to-beam-ratio ship model, and that frictional drag on the SWR surface of the 12.0 m high length-to-beam-ratio ship model was reduced by 75% at a speed of 6 m/sec, which is the same reduction rate obtained with the flat plate.

ELECTRODEPOSITION AND SURFACE PROPERTIES OF NICKEL-PTFE COMPOSITE FILM

Ni-PTFE composite films with water repellency have been prepared by the electrodeposition in the nickel sulfamate plating bath in which PTFE fine particles are suspended by using a cationic surfactant. The maximum content of PTFE in the composite film was 17wt%. Above the contents of 12wt%, the contact angle of a water drop on the surface reached 156° in maximum. The surfactant was co-deposited with PTFE particles in the electrodeposited Ni-PTFE composite film. This causes that the water repellency on the surface of the film falls after the neutral salt spray test (NSS) and the thermal cycle tests. The heat-treatments above 300°C were effective to maintain the water repellent surface even after the weathering tests, while the surface morphology changed by the heat-treatment.

Hydrophobierung des Betons - Ökologische und ökonomische Aspekte / Water Repellent Treatment of Concrete - ecological and economical aspects

Abstract The use ofdeicing salts on roads may lead to chloride ion induced corrosion. This deterioration mechanism has become one of the most frequent reasons for repair measures within the planned service-life of concrete structures. One way of reducing the risk of chloride ion induced corrosion is the prevention of the penetration of dissolved chloride into the concrete. By water repellent surface treatment the water and chlorid penetration rate can be substantially slowed down. As the water repellent treatment has a limited service-life and its performance and durability depend on many parameters, no standard performance criteria for the water repellent treatment could be defined yet. This study compares the economical and ecological impact of a water repellent treatment with the impact of repair measures. Results are meant to be used to define standard performance criteria. These criteria must take into consideration not only the performance with respect to the reduction of chloride penetration rate, but also garantee the required durability.The expected life-time of an untreated reinforced concrete element can be estimated by modelling the mechanism of chloride ion induced corrosion. Based on this value the frequency of repair measures within a planned service-life of 100 years can be determined. Comparing the ecological and economical impact of a water repellent treatment with the corresponding impact of repair measures allows us to the formulate performance criteria concerning the durability and the minimum required service-life of a water repellent treatment. The water repellent treatment has to prevent repair measures within the planned service-life of a structural concrete element. Technical criteria concerning the performance of a water repellent treatment within the minimum required service-life can be formulated.

Preparation and Surface Properties of Acrylic Polymers Containing Fluorinated Monomers

A series of novel polymers have been prepared by free radical solution polymerization of a variety of hydrocarbon monomers with the (perfluoroalkyl)ethyl methacrylate monomer H2CC(CH3)CO2(CH2)2(CF2)nF, 1 (n ≈ 7.7). Polymers prepared using two different methods of feeding 1 into the reaction mass are discussed. Through a judicious choice of reaction conditions, some control of polymer architecture was exhibited. The resultant (perfluoroalkyl)ethyl methacrylate-containing acrylic polymers were shown to be quite surface active in the solid state. The magnitude of surface activity depends on the monomer 1 feed method. The polymers were formulated into thin films and applied to a variety of surfaces. With levels at 1.5 wt % of 1, water and oil repellent surfaces were created. Water contact angles (advancing) of ∼80−115° and hexadecane contact angles (advancing) of ∼60−70° were observed routinely. In addition, it was observed that the concentration profile of fluorine in the films exhibited a steep gradient no...

The Chemistry of Paper Preservation: Part 4. Alkaline Paper

The inherent instability of old papers is largely due to the presence of acids which catalyze the hydrolytic degradation of cellulose. The use of alkaline paper can minimize the problem of acidity for new papers. This study focuses on the chemistry involved in the sizing of both acid and alkaline papers and the types of fillers used. The waterproofing agent that is used in acid paper is alum-precipitated rosin size, which tends to spread and create a hydrophobic surfaces over the cellulose fibers. Alkaline paper uses the synthetic sizing agents, alkyl ketene dimers(AKD) and alkyl succinic anhydrides (ASA). These alkaline sizing agents become chemically bound to the cellulose fibers with hydrophobic chains pointing outward, producing a water repellent surface. The sizing reactions take place in a neutral-to-alkaline medium. Calcium carbonate can then be used as a filler to replace expensive titanium dioxide. Finally, the advantages and potential problems in alkaline paper making are discussed.

はっ水性表面への湿雪の付着に関する一検討

はっ水性表面への湿雪の付着に関する一検討

Super Water-repellent Surfaces Resulting from Fractal Structure. II.

A super water-repellent surface with maximum contact angle of 174° was previously obtained by solidifing a wax, alkyl ketene dimer, from a melt. This surface was fractal with dimension of D≈2.3. The surface area magnification factor became quite large due to the fractal structure and then the contact angle of a water droplet also very large. This paper is an extension of the study for clarifying why the alkyl ketene dimer forms a fractal surface. Crystallization of the alkyl ketene dimer from the melt was observed by polarizing optical microscope and DSC measurement. Attempt was also made to develop a super water-repellent paint containing the alkyl ketene dimer. Flake-like crystals of the alkyl ketene dimer were observed on the painted surface following drying of the paint-layer, and super water-repellency of the surface was noted. Through the use of triacylglycerols and dialkyl ketones, the super-water repellent surfaces have been also obtained. It has been experimentally shown that any wax with a contact angle exceeding 90° become super water repellent by making the surface sufficiently rough.

はっ水性表面に対する氷の付着力と表面粗さに関する一検討

はっ水性表面に対する氷の付着力と表面粗さに関する一検討

Seed Selection by the Red Imported Fire Ant (Hymenoptera: Formicidae) in the Laboratory

Ninety–sixspecies and varieties of seeds in 28 families were presented to laboratory colonies of Solenopsis invicta Buren. Small seeds were moved and subsequently damaged more often than large seeds. Although generally more resistant to damage, some species with large seeds such as com, Zea mays L., were susceptible to S. invicta damage. Seed coats protected some seed species from ant damage. Presence of repellent and attractant surface chemical swas also demonstrated for some seeds. Although chemicals could be extracted from seeds that could be considered attractive, some seeds appeared to be protected from S. invicta predation by repellents (predation means the seed is damaged so extensively that it can no longer germinate). Many species of seeds were susceptible to some degree of S. invicta predation, and most were transported to new locations. We also soaked seeds, which in general increased their susceptibility to predation, although seed removal was reduced. Seeds that were beginning to germinate were difficult to characterize: some germinated seeds were more susceptible to predation, but other germinated seeds were less susceptible to predation. Of resistant and susceptible seeds, Fabaceae seeds were most resistant and Labiatae seeds were most susceptible to S. invicta movement and damage. Seeds may play an important role as a food resource for S. invicta , and, as a result, S. invicta may be serious seed predators and competitors of animals for which seeds represent an important resource.

The effects of fire and water repellency on infiltration and runoff under Mediterranean type forest

An investigation is being made into the relationship between forest fire and hillslope hydrology in the Selva region of Catalonia over a three year period at sites with a known fire history. The major sites are on granite, granodiorite or on sediments derived from these rocks at locations between Santa Christina d'Aro and Santa Coloma de Farnes. It appears that there is a general relationship between the type of organic profile found in a forest and the impact of fire in terms of loss of organic matter, soil erosion hillslope hydrology and on the regeneration of the forest. This paper summarises the results of about 150 rainfall simulation experiments and presents an overview of work carried out so far. A major conclusion is that runoff processes are discontinuous and spatially structured due mainly to the effects of water repellency. As a result of surface properties (macropores, hydrophobic behaviour and swelling), four types of infiltration curve can be recognised. At many locations infiltration increases with time during the early part of an experiment, reaches a maximum value after about 30 minutes therupon subsequently decreasing. This type of relationship can not be modelled with standard infiltration equations. Illustrations are given of sections through both burnt and unburnt soils to show how the hydrophobic effect influences water penetration. It can be seen that infiltration patterns are similar for both burnt and unburnt soils and that micropores filled with organic matter are very important in conducting water through a water repellent surface layer. The hydrophobic layer traps water in the BC horizon and prevents evaporation and loss by upwards capillary movement. Although the hydrophobic effects mean that small areas sometimes have a high runoff coefficient, on larger areas there are many macropores and shrubs, beneath which the soil is permeable, and these trap runoff generated on the water repellent areas. The main effect of fire is to illiminate the storage of water in the organic horizons (several cm). At first infiltration rates remain high but later these decrease as there is a reduction in porosity. The sites having a moder type profile have better water retention properties, more organic matter that survives the fire and a faster rate of vegetation recovery. Sites with a mor type profile can be degraded and erode if they are subject to disturbance. The study provides another example of how, on seemingly uniform slopes, hydrological processes are structured by interactions with vegetation. The patterns produced by these interactions survive the effects of fire.

Evaluation of electrical contact materials for mercury switches designed to detect angular rotation

The adherence of mercury to a variety of materials was evaluated for various surface treatments in terms of contact angle and maximum meniscus height on separation. It was found that arcing markedly increased wettability and that roughening produced mercury repellent surfaces.

Synthesis and application of fluorine containing graftcopolymers

Well-defined graftcopolymers were prepared by radical copolymerization of methyl methacrylate macromonomer with perfluoroalkyl acrylate. Contact angle of the solvent cast films of poly(methyl methacrylate) containing various amount of the graftcopolymer was measured against water droplet. Addition of 0.2 wt% of the graftcopolymer was sufficient to improve the polymer films to water repellent surfaces, while 10 wt% was necessary to modify the polymer surfaces to the same level of water repellency.