High Water Repellent Properties Research Articles

Obtaining water-repellent coatings based on expanded perlite materials

Superhydrophobic coatings are currently not widely used due to complex scaling problems, high cost and low environmental resistance. One solution is the use of organic coating technology. The paper shows the possibility of obtaining surface coatings with high water-repellent properties based on expanded perlite and regenerated adsorbent. The most effective surface treatment is polymethylhydrogensiloxane. In the work properties of obtained coatings were characterized by contact angles using the sessile droplet technique, optical and electron microscopy and IR-spectroscopy. With polymer content is more than 50 wt% for untreated and more than 40 wt% for the polymethylhydrogensiloxane treated perlite, the Cassie steady state and the water contact angle of more than 140° were reached. The resulting coatings are an example of a good microscale base coat for the further creation of superhydrophobic volumetric hierarchical coatings. It has been shown that the use of an adsorbent for used refined sunflower oil is as effective as the use of freshly ground expanded perlite.

THE USE OF HYDROPHOBIZED PERLITE AS THE BASE LAYER OF SUPERHYDROPHOBIC COATINGS

The development of superhydrophobic materials technology is limited due to low mechanical stability of coatings, complexity of scaling and relatively high cost. One possible way to solve this problem is to use technologies that are used for conventional coatings, such as creating a surface texture by using functionalized fillers. The article considers an example of a method of obtaining such coatings by mechanical grinding of foamed perlite. The geometry of crushed perlite particles, the shape and particle size distribution of their fragments formed during grinding were characterized in the work. An effective surface modifier has been selected to provide superhydrophobic properties and the possibility of forming coatings based on these materials has been established. The structure and water-repellent properties were also characterized. As a result, it is shown that the use of crushed material with hollow particles on the example of expanded perlite after chemical surface treatment is a possible way to obtain coatings with high water-repellent properties. The created systems have a stochastic structure and relatively high values of the wetting angle – up to 140°. The properties of crushed perlite particles were determined – the average particle size is 15 μm, the shape of the fragment and the possibility of modification using siloxane processing agents. In particular, it has been shown that the use of polymethylhydrosiloxane for modification provides its chemical binding on the surface of perlite. The layer of treated particles has a marginal wetting angle of up to 150° and a rolling angle of less than 4°. These particles were successfully bonded with a styrene-acrylic polymer matrix, which led to the formation of coatings with high hydrophobicity at filler levels above 50 wt. %.

A Simple, Long-Lasting Treatment for Concrete by Combining Hydrophobic Performance with a Photoinduced Superhydrophilic Surface for Easy Removal of Oil Pollutants.

Superhydrophobic surfaces present promising applications in the protection of building materials, such as the self-cleaning effect promoted by their high water-repellent properties. However, these surfaces easily lose their properties when exposed to oil contaminants. This is a critical weak point for their application in building facades, which are exposed to environmental pollutants such as hydrocarbons and vandalism (e.g., grafitti). A viable strategy to remove oils is to produce superhydrophilic surfaces, which present underwater superoleophobic behavior. In the case of buildings, the use of this strategy can be considered counterproductive because it promotes their interaction with water, the main vehicle of most decay agents. In this work, we have successfully combined the advantages of a superhydrophilic coating with a hydrophobic impregnation treatment, which prevents water ingress into the porous structure of the substrate. Specifically, a photoinduced superhydrophilic surface was produced on concrete by simple spraying of a starting sol containing TiO2NPs, which create a Cassie-Baxter state, a silica oligomer, producing a compatible matrix promoting good adhesion to the substrate and polydimethylsiloxane as a hydrophobic agent. After being exposed to sunlight, the treated surfaces switched from superhydrophobic (SCA 160°) to superhydrophilic (SCA < 10°). These surfaces presented underwater superoleophobicity (SCA 152° with CHCl3) and oil-contaminated dust was easily cleaned without employing detergents. The photoactivation does not alter the protection against water absorption (>85% reduction). The treatment showed suitable adhesion to the substrate and good resistance to rainfall and outdoor exposure due to the presence of the hydrophobic silica matrix in the concrete pore structure.

Determination of Hydrophobic Contact Angle of Epoxy Resin Compound Silicon Rubber and Silica

Epoxy resin is a thermosetting polymeric material which is very good for application of high voltage outdoor insulator in electrical power system. This material has several advantages, i.e. high dielectric strength, light weight, high mechanical strength, easy to blend with additive, and easy maintenance if compared to that of porcelain and glass outdoor insulators which are commonly used. However, this material also has several disadvantages, i.e. hydrophilic property, very sensitive to aging and easily degraded when there is a flow of contaminants on its surface. The research towards improving the performance of epoxy resin insulation materials were carried out to obtain epoxy resin insulating material with high water repellent properties and high surface tracking to aging. In this work, insulating material was made at room temperature vulcanization, with material composition: Diglycidyl Ether Bisphenol A (DGEBA), Metaphenylene Diamine (MPDA) as hardener with stoichiometric value of unity, and nanosilica mixed with Silicon Rubber (SiR) with 10% (RTV21), 20% (RTV22), 30% (RTV23), 40% (RTV24) and 50% (RTV25) variation. The usage of nanosilica and Silicon Rubber (SIR) as filler was expected to provide hydrophobic properties and was able to increase the value of surface tracking of materials. The performance of the insulator observed were contact angle of hydrophobic surface materials. Tests carried out using Inclined Plane Tracking procedure according to IEC 60-587: 1984 with Ammonium Chloride (NH4Cl) as contaminants flowed using peristaltic pumps. The results show that hydrophobic contact angle can be determined from each sample, and RTV25 has maximum contact angle among others.

Determination of Hydrophobic Contact Angle of Epoxy Resin Compound Silicon Rubber and Silica

Epoxy resin is a thermosetting polymeric material which is very good for application of high voltage outdoor insulator in electrical power system. This material has several advantages, i.e. high dielectric strength, light weight, high mechanical strength, easy to blend with additive, and easy maintenance if compared to that of porcelain and glass outdoor insulators which are commonly used. However, this material also has several disadvantages, i.e. hydrophilic property, very sensitive to aging and easily degraded when there is a flow of contaminants on its surface. The research towards improving the performance of epoxy resin insulation materials were carried out to obtain epoxy resin insulating material with high water repellent properties and high surface tracking to aging. In this work, insulating material was made at room temperature vulcanization, with material composition: Diglycidyl Ether Bisphenol A (DGEBA), Metaphenylene Diamine (MPDA) as hardener with stoichiometric value of unity, and nanosilica mixed with Silicon Rubber (SiR) with 10% (RTV21), 20% (RTV22), 30% (RTV23), 40% (RTV24) and 50% (RTV25) variation. The usage of nanosilica and Silicon Rubber (SIR) as filler was expected to provide hydrophobic properties and was able to increase the value of surface tracking of materials. The performance of the insulator observed were contact angle of hydrophobic surface materials. Tests carried out using Inclined Plane Tracking procedure according to IEC 60-587: 1984 with Ammonium Chloride (NH4Cl) as contaminants flowed using peristaltic pumps. The results show that hydrophobic contact angle can be determined from each sample, and RTV25 has maximum contact angle among others.

Ultralight and hydrophobic nanofibrillated cellulose aerogels from coconut shell with ultrastrong adsorption properties

ABSTRACTUltralight aerogels based on nanofibrillated cellulose (NFC) isolated from coconut shell were successfully prepared via a mild fast method, which included chemical pretreatment, ultrasonic isolation, solvent exchange, and tert‐butanol freeze drying. The as‐prepared NFC aerogels with complex three‐dimensional fibrillar networks had a low bulk density of 0.84 mg/cm3 (specific surface area = 9.1 m2/g and pore volume = 0.025 cm3/g), maintained a cellulose I crystal structure, and showed more superior thermal stability than the coconut shell raw materials. After the hydrophobic modification by methyl trichlorosilane (MTCS), the NFC aerogels exhibited high water repellency properties, an ultrastrong oil‐adsorption capacity (542 times that of the original dry weight of diesel oil), and superior oil–water separation performance. Moreover, the absorption capabilities of the MTCS‐treated NFC aerogels were as high as 296−669 times their own weights for various organic solvents and oil. Thus, this class of high‐performance adsorbing materials might be useful for dealing with chemical leaks and oil spills. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42037.

Simple treatment of cotton textile to impart high water repellent properties

We describe two methods to impart the water repellency for the surface of cotton fabric, using a commercially available and a laboratory synthesized fluoroalkylsiloxanes. To characterize the wettability and the durability of water repellent properties of hydrophobic coating produced, we have studied the advancing water contact angles, rolling angles and the evolution of water contact angle in time during a continuous contact of the surface with the water drop. The quality of the coatings was also assessed after the washing procedure. The analysis of the wettability of hydrophobized fabrics indicated that a better effect, leading to the superhydrophobic state of the surface, was observed when the surface relief of the fabric with the coating is determined by not only the structure and braiding of the fabric, but also the additional elements of texture created by the aggregates of molecules of hydrophobic agent.

Surface Properties of Honeycomb and Pincushion Structures of Various Hydrophobic Polymer Materials Prepared by Self-Organization

Surface wettability is a significant factor in determining the physical and chemical properties of materials. It is known that both the chemical properties of the surface and its topography play important roles. A honeycomb-structured polymer film can be prepared by casting a hydrophobic polymer solution under humid conditions. Here, we measured water repellency on the honeycomb- and pincushion-structured films of various kinds of hydrophobic polymers. We show that the honeycomb- and pincushion-structured films of hydrophobic polymers have high water repellent properties. Especially, the water contact angles on pincushion-structured films are over 130°. From the results of these experiments, it appears that the surface structures prepared by self-organization process enhance the hydrophobicity of the surface. An easy process for creating highly water repellent surfaces is required to utilize these surfaces in industrial applications. Thus, the simple self-organization process has advantages from the standpoint of application.

Fabrication of Spatially Periodic Double Roughness Structures by Directional Viscous Fingering and Spinodal Dewetting for Water-Repellent Surfaces

Water-repellent and self-cleaning properties of lotus leaves are considered to be due to its double roughness structure, protrusion structure (approximately 20 microm) and hairy structure (0.2-1.0 microm). In this study, attempts to fabricate a spatially periodic double roughness structure by two far-from-equilibrium self-organization phenomena, a directional viscous fingering and a spinodal dewetting, were made. A mixture of an octylsilyl titanium dioxide particle having an average diameter of 35 nm suspended in volatile silicone, decamethyl cyclopentasiloxane, and octyl p-methoxycinnamate was spread on a glass plate by dragging an applicator across the top. Formation of a stripe pattern parallel to the direction of dragging, called directional viscous fingering, was sometimes observed. Influences of spreading conditions on the pattern formation were analyzed. In addition, attempts were made to apply the stripe pattern formation to the preparation of a water repellent surface. We have succeeded in preparing a highly water-repellent surface by immersing a glass plate, on which a spatially periodic stripe pattern having a characteristic wavelength of 200-700 microm was formed, in water, after the completion of evaporation of decamethyl cyclopentasiloxane. In this case, dewetting patterns having a characteristic wavelength at around 5 microm were formed at the bottom part of the stripe patterns. Neither the surface on which only the mesoscopic spatially periodic stripe pattern was formed nor the one on which only the microscopic dewetting pattern was formed showed high water-repellent properties, indicating that the coexistence of the two different scales of patterns increased the water-repellent properties of the hydrophobic surface.

Hydraulic functions and water repellency of forest floor horizons on sandy soils

For a better understanding of water flow phenomena in pine ecosystems, we characterized hydraulic functions as well as water repellency behaviour of forest floor horizons. The investigations covered 11 pine stands ( Pinus sylvestris) on sandy soil in northeast Germany. All sites were classified as Haplic Arenosol. Two kinds of forest floor horizons were analysed: the slightly mineralised Of horizon under the soil surface and the more or less strongly humified Oh horizon which underlies directly the Of horizon. Data analysis shows a good correlation between soil organic matter, bulk density and water characteristics which can be easily used to predict soil available water. The soil available water (pF 1.8–4.2) of the forest floor horizons ranges from 22 vol.% (Of) up to 26 vol.% (Oh) with high spatial variability. However, the maximum of water storage capacity is available only in short time in spring after total rewetting. The unsaturated hydraulic conductivity of the Of horizon was slightly lower than that of the Oh horizon. Water repellency was studied using the water drop penetration time test (wdpt). Results show a strong dependency of water repellency on pressure head and soil water content. At pF 2.0 both organic horizons exhibited considerable portions of water repellency causing wdpt of up to 10 min. Extremely high water repellency of > 6 h occurred at pF > 3.6. Field transect measurements over a 2 year period show that water repellency was found throughout the year, being less developed at high water contents during winter time and being most pronounced at low water contents in summer. Even during winter time the soil profile rewetted only partly because of its high water repellent properties. Water repellency occurs whenever soil moisture reaches thresholds of a critical content of about 14–16 vol.% in the forest floor horizons, 5–6 vol.% in the humus enriched horizons and about 3 vol.% in the sandy mineral subsoil.