Preparation of superhydrophobic paper mulch and study on its anti-UV performance

In order to improve the shortcomings of paper mulch, such as the low water resistance and weather fastness in practical application, the paper mulch with a superhydrophobic structure was prepared by depositing zinc oxide layer and silicon dioxide layer on the surface of paper mulch by the solution impregnation method, the paper mulch surface treatment method is simple and environmentally friendly. The surface chemical composition and surface morphology of paper mulch before and after UV aging were characterized, respectively. The wetting property, bouncing property, and mechanical stability of paper-based film were studied. The results showed that the static contact angle of the superhydrophobic paper mulch was as high as 161.77°, and the average sliding angle was only 3.5°, which also showed excellent droplet bounce performance and mechanical stability. After UV aging experiment, the static contact angle of super-hydrophobic paper mulch was increased to 163.64°, and the sliding angle was reduced to 2.5°. Its excellent performance could still be maintained, showing excellent UV resistance, which improved the weather fastness and water resistance of paper mulch to a certain extent, and laid a foundation for the next large-scale field test.     

Water resistance improvement of paper by superhydrophobic modification with microsized CaCO3 and fatty acid coating

Nanoscaled surface roughness with a hydrophobically modified surface has been widely used for preparation of superhydrophobic materials. However, the complicated procedure, high cost and harmful compounds used in most superhydrophobic surface modifications limited their applications. This research aims at fabricating superhydrophobic cellulosic or semi-superhydrophobic papers with low cost and nontoxic materials. Commercial PCC (precipitated calcium carbonate) particles, hydrophobic stearic acid and polymer latex particles were used for surface roughness control, surface hydrophobic modification agent, and polymer binder, respectively. A simple coating or dipping method was used to produce high contact angle and high water resistance papers. It was found that the surface pretreatment of PCC with fatty acid salt prior mixing with polymer binder plays important role for improving the water contact angle (WCA). The combination of surface coating with dipping treatment will further increase the water contact angle and water resistance of the paper. A WCA near 150° over modified paper surface has been achieved. At the same degree of water resistance, the total cost of the paper can be significantly reduced by our method.     

Preparation of superhydrophobic composite paper mulching film

To study the influence of different concentrations of zinc oxide (ZnO)/silicon dioxide (SiO₂) composite coating on hydrophobic property and mechanical stability of paper mulch film, three kinds of ZnO/SiO₂ composite coating paper mulch films (2%, 4%, 6%) with different coating substance contents were prepared by brush coating method. Through particle size analysis, contact angle, rolling angle and mechanical stability test, combined with scanning electron microscope, three-dimensional morphology and roughness measuring instrument, the optimal concentration of ZnO/SiO₂ composite coated paper mulch film was screened out. Through acid-base salt corrosion test, silver mirror reaction and surface self-cleaning, the optimal concentration of composite coated paper mulch film was compared with the original paper mulch film to prove its excellent chemical stability and hydrophobicity. The results show that the paper mulch film with 4% coating material has excellent hydrophobicity and mechanical stability, can effectively reduce the surface roughness of paper mulch film, and has remarkable effects in resisting acid, alkali and salt and self-cleaning.     

Producing a superhydrophobic paper and altering its repellency through ink-jet printing

A new method for making superhydrophobic (SH) paper based on spraying a nanocomposite film is developed. Furthermore, manipulating the wetting characteristics of SH paper has been demonstrated through a new method, i.e. printing solid grey patterns of different intensities with simple printing technology (home or office grade ink-jet and laser printers). It has been found that for a range of ink intensities (0-85%), water drop mobility can be changed at a different rate (almost independently) from repellency. The repellency of water decreases minimally up to 85% ink intensity with a sharp decrease up to 100% ink intensity. Drop mobility remains constant up to 30% ink intensity with a steady decrease up to 100% ink intensity. It was observed that using ink-jet or laser printing would yield different results for the change of mobility or repellency with higher amounts of ink/toner used. Being able to achieve almost independent control of water drop mobility over water drop repellency on SH paper would allow inexpensive lab-on-paper devices to be used for sampling, mixing and transport of liquids.     

Patterned superhydrophobic paper for microfluidic devices obtained by writing and printing

This work outlines inexpensive patterning methodologies to create open-air microfluidic paper-based devices. A phase-separation methodology was used to obtain biomimetic superhydrophobic paper, hierarchically composed by micro and nano topographies. Writing and printing are simple actions that can be used to pattern flat superhydrophobic paper with more wettable channels. In particular, inkjet printing permits controlling the wettability of the surface by changing the darkness of the printed regions. The difference between capillary forces provides the possibility to control and drive liquid flows through the open path lines, just by titling the piece of paper. Additionally, maintaining a continuous flow, it is possible to direct the liquid at different volumetric rates in a horizontal position along non-linear channel paths printed/written over the surface.     

Underwater saturation resistance and electrolytic functionality for superhydrophobic nanocomposites

In the current study, water immersion saturation characterization and saturation resistance are investigated for various superhydrophobic polymer nanocomposite coatings. Two different diagnostic methods are used to characterize superhydrophobic performance longevity under continuous water contact: optical reflectivity (associated with captured air layer) and static contact angle (measured immediately after an immersion period). The results indicate that retention of optical reflectivity and superhydrophobicity vary significantly among coatings, and that superhydrophobicity can be lost within a few minutes whereas optical reflectivity can be maintained for hours. Novel electrolytic reactions on electroconductive polymeric nanocomposites can extend superhydrophobic duration by 400 %.     

Creation of low hysteresis superhydrophobic paper by deposition of hydrophilic diamond-like carbon films

The creation of low hysteresis superhydrophobic paper is reported using a combination of oxygen plasma etching and plasma deposition of an 80 nm non-fluorinated, hydrophilic diamond-like carbon (DLC) coating. The DLC has an equilibrium (flat surface) contact angle (θ _e ) of 68.2° ± 1.5°, which is well below the 90° contact angle that is typically believed to be a prerequisite for superhydrophobicity. Coating of paper substrates with the DLC film yields an advancing contact angle of 124.3° ± 4.1°, but the surface remains highly adhesive, with a receding contact angle <10°. After 60 min of plasma etching and DLC coating, a low hysteresis, superhydrophobic surface is formed with an advancing contact angle of 162.0° ± 6.3° and hysteresis of 8.7° ± 1.9°. To understand the increase in contact angle and decrease in hysteresis, atomic force microscopy and optical profilometry studies were performed. The data demonstrates that while little additional nanoscale roughness is imparted beyond the first 5 min of etching, the roughness at the microscale continually increases. The hierarchical structure provides the appropriate roughness to create low hysteresis superhydrophobic paper from a hydrophilic coating.     

Formation of superhydrophobic cerium oxide surfaces on aluminum substrate and its corrosion resistance properties

Superhydrophobic cerium oxide film was introduced to aluminum substrate by an in‐situ growth process and surface modification. Different molar ratios between Ce(NO₃)₃ · 6H₂O and C₆H₁₂N₄ were involved in this research. The morphologies, chemical compositions and wetting properties of the films were analyzed by scanning electron microscopy (SEM), energy dispersive X‐ray detector, Fourier transfer infrared spectrometer and water contact angle (WCA) measurement, respectively. A great WCA of 158.8^o with a low angle hysteresis of about 3^o was obtained. Combination of uniform hierarchical micro‐nanostructure as revealed by SEM together with the hydrophobic alkyl groups from stearic acid was found to be responsible for the superior superhydrophobic property. The corrosion resistance performance of the superhydrophobic surface was evaluated by immersing in sodium chloride aqueous solution, the WCA kept as high as 152.1^o after immersion for 21 days, indicating our superhydrophobic surfaces had high chemical stability and durability in corrosive medium. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis and thermal decomposition of acid alkali metal hexafluoroaluminates

Acid alkali hexafluoroaluminates of K and Rb were prepared by precipitation of alkali fluoride containing H₃AlF₆ solutions with ethanol. Compounds were characterized by X-ray diffraction, IR spectroscopy,¹H-NMR and chemical analysis. The constitution is M^I(H₃O)₂AlF₆. Lattice parameters were determined.Dehydration and thermal decomposition were investigated by thermal analysis (TG, DTG, DTA) on a derivatograph-Q and by high temperature X-ray diffraction. Thermal decomposition is accompanied by liberation of H₂O and HF and a condensation of [AlF₆]^3– octahedra forming layer structures. Stable intermediate products are M^IAlF₄·0.5H₂O and M^IAlF₄. At higher temperatures hydrolysis occurs.

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Zusammenfassung Es wurden saure Kalium- und Rubidiumhexafluoroaluminate durch Fällung aus Alkalifluorid enthaltenden H₃AlF₆-Lösungen mit Ethanol dargestellt. Die erhaltenen Verbindungen wurden chemisch, röntgenographisch, IR- sowie¹H-NMR-spektroskopisch charakterisiert. Die Konstitution der Verbindungen ist M^I(H₃O)₂AlF₆. Die Gitterkonstanten wurden aus Röntgendiffraktionsdaten bestimmt. Entwässerung und thermische Zersetzung wurden mittels Heizguiniertechnik und Thermoanalyse (TG, DTG, DTA) an einem Derivatograph-Q untersucht. Bei der thermischen Zersetzung erfolgt eine HF- und H₂O-Abgabe sowie eine Kondensation von AlF ₆ ^3– -Oktaedern unter Ausbildung von Schichtstrukturen. Als stabile Zwischenprodukte wurden M^IAlF₄·0.5H₂O und M^IAlF₄ nachgewiesen. Bei höheren Temperaturen werden Hydrolysereaktionen beobachtet.

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, H₃AlF₆, . M¹(H₃O)₂AlF₆ , - - . . (, , ) Q- , . [AlF₆]^3– . M¹AlF₄·0.5H₂O M¹AlF₄. .

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Presented at the Microsymposium on Halogen Chemistry held in Budapest, 1987.     

Analysis of droplet evaporation on a superhydrophobic surface

The evaporation process for small, 1-2-mm-diameter droplets of water from patterned polymer surfaces is followed and characterized. The surfaces consist of circular pillars (5-15 microm diameter) of SU-8 photoresist arranged in square lattice patterns such that the center-to-center separation between pillars is 20-30 microm. These types of surface provide superhydrophobic systems with theoretical initial Cassie-Baxter contact angles for water droplets of up to 140-167 degrees, which are significantly larger than can be achieved by smooth hydrophobic surfaces. Experiments show that on these SU-8 textured surfaces water droplets initially evaporate in a pinned contact line mode, before the contact line recedes in a stepwise fashion jumping from pillar to pillar. Provided the droplets of water are deposited without too much pressure from the needle, the initial state appears to correspond to a Cassie-Baxter one with the droplet sitting upon the tops of the pillars. In some cases, but not all, a collapse of the droplet into the pillar structure occurs abruptly. For these collapsed droplets, further evaporation occurs with a completely pinned contact area consistent with a Wenzel-type state. It is shown that a simple quantitative analysis based on the diffusion of water vapor into the surrounding atmosphere can be performed, and estimates of the product of the diffusion coefficient and the concentration difference (saturation minus ambient) are obtained.     

Simple method for preparing superhydrophobic paper: spray-deposited hydrophobic silica nanoparticle coatings exhibit high water-repellency and transparency

Superhydrophobic and transparent coatings are deposited onto paper by spraying alcohol suspensions of SiO(2) nanoparticles. Superhydrophobicity depends on the aggregation states of nanoparticles, which are determined by the type of alcohol used in the suspensions. The superhydrophobicity of the paper is maintained after touching the paper with a bare finger.     

Microbial reverse-electrodialysis chemical-production cell for acid and alkali production

A new type of bioelectrochemical system, called a microbial reverse-electrodialysis chemical-production cell (MRCC), was developed to produce acid and alkali using energy derived from organic matter (acetate) and salinity gradients (NaCl solutions representative of seawater and river water). A bipolar membrane (BPM) was placed next to the anode to prevent Cl⁻ contamination and acidification of the anolyte, and to produce protons for HCl recovery. A 5-cell paired reverse-electrodialysis (RED) stack provided the electrical energy required to overcome the BPM over-potential (0.3–0.6 V), making the overall process spontaneous. The MRCC reactor produced electricity (908 mW/m²) as well as concentrated acidic and alkaline solutions, and therefore did not require an external power supply. After a fed-batch cycle, the pHs of the chemical product solutions were 1.65 ± 0.04 and 11.98 ± 0.10, due to the production of 1.35 ± 0.13 mmol of acid, and 0.59 ± 0.14 mmol of alkali. The acid- and alkali-production efficiencies based on generated current were 58 ± 3% and 25 ± 3%. These results demonstrated proof-of-concept acid and alkali production using only renewable energy sources.