Hydrophobic Behavior Research Articles

The Influence of Adventitious Carbon Groups on the Wetting of Copper: A Study on the Effect of Microstructure on the Static Contact Angle.

Tuning of the wetting behavior of metallic surfaces by chemical and topographical modification has become popular in recent years. Still, there is a lack in the understanding of fundamental relations between intrinsic properties of the material and its resulting water contact angle. It is widely accepted in the literature that transitions from a hydrophilic to increasingly hydrophobic behavior upon exposure to ambient conditions happen due to the adsorption of adventitious hydrocarbons. In order to investigate the role of metallic bulk microstructure in the wetting behavior and its transition properties, we created three different grain sizes and deformation states on copper by preparation combined with heat treatment. We found that for freshly prepared surfaces, differences in the wetting behavior show a higher static contact angle for mechanically prepared surfaces with a fine-crystalline deformation layer compared to the electropolished cold-rolled copper sheet and the annealed defect-free coarse-grained surface. Already after five days of storage time, most of this difference vanishes, and all surfaces show a wetting behavior with a contact angle in the range of 97-100° after 30 days. Though long-term wetting behavior seems largely independent of microstructure, correlated XPS measurements showed an increased adsorption of organic contaminants of the mechanically polished surface. Preparation-induced near-surface defects seem to accelerate adsorption, while varying grain size and slight bulk deformation from rolling processes did not show significant effects. Complex relations between the amount of adsorbed carbon and the polarity of the adsorption film were found to depend on the sample age and influence the contact angle.

Boron doped graphitic carbon nitride (BN‐g‐C3N4) and palm flower ash reinforced pyrimidinone core‐based polybenzoxazine composites for low‐k and high‐k applications

AbstractThe present work provides a facile process route for the syntheses of pyrimidinone‐based benzoxazines by using stoichiometric quantities of pyrimidinone bisphenol (PBU) and paraformaldehyde, which are separately reacted with various types of amines under suitable experimental conditions. The molecular structure, curing characteristics, thermostability, hydrophobic behavior, and dielectric properties were analyzed using appropriate analytical methods. The polymerization temperature (Tp) of monomers such as PBU‐oda, PBU‐cha, PBU‐ffa, PBU‐a, and PBU‐fa was determined by differential scanning calorimetry (DSC), and the Tp values were noted at 205, 198, 203, 218, and 240°C, respectively. The percentage carbon residue at 850°C for poly(PBU‐oda), poly(PBU‐cha), poly(PBU‐ffa), poly(PBU‐a), and poly(PBU‐fa) were analyzed using thermogravimetric analysis (TGA). The water interface angle values for poly(PBU‐oda), poly(PBU‐cha), poly(PBU‐ffa), poly(PBU‐a), and poly(PBU‐fa) was found to be 141°, 134°, 142°, 136°, and 142°, respectively. The results from the dielectric studies indicate that the benzoxazines (PBU‐ffa and PBU‐a) composites reinforced with palm flower silica (PF‐SiO2) and boron nitride‐g‐C3N4 (BN‐g‐C3N4) were found to be suitable for low and high dielectric applications. From these diverse studies, it can be determined that pyrimidinone‐based benzoxazines to be utilized as high‐performance products in the form of encapsulants, potting agents, and composites for automotive and microprocessor applications.Highlights Pyrimidinone core bisphenol has developed through the efficient method. New pyrimidinone core bisphenol based benzoxazine resins have been developed. BN‐g‐C3N4 filled polybenzoxazine composites have prepared for high‐k applications. Palm flower ash filled polybenzoxazine composites have prepared low‐k applications. Thermal and morphological behavior of composites were studied.

Interaction of porous substrate and vegetable oil-based hydrophobic thermoset coatings during UV-polymerization

In the current study, we report the progress in developing new UV polymerizable hydrophobic biobased coatings from modified vegetable oil for porous substrates like paper and wood. The aim was to produce novel hydrophobic coatings on porous substrates and investigate how the porous nature of the substrates will be affected by different chemical formulations that penetrate into the interior of the substrate during the exposure to different intensities of UV light, and what hydrophobic properties that interaction will result in. The curing formulations were based on acrylated epoxidized linseed oil (AELO) as a prepolymer. For the UV polymerization, 1-hydroxycyclohexyl phenyl ketone (Irgacure 184) was used as a photoinitiator; isobornyl acrylate (IBA) and isosorbide methacrylate (IM) were used as bio-based diluents; hexadecyltrimethoxysilane (HDTMS), vinyl-polydimethylsiloxane (v-PDMS), triethoxyoctylsilane (TEOS) were used as hydrophobic additives and they were added in different concentrations to the AELO curing formulations. The formulations were then cured under UV light on wood and paper substrates. FT-IR analysis showed that the AELO resin was successfully polymerized on both paper and wood substrates, and by contact angle measurements it was found that the highest hydrophobicity was achieved for the coatings that contain HDTMS (108° in average). The layer thickness on wood substrates was in between 9 and 20 µm, and on paper substrates between 8 and 24 µm. Only about a 5° difference in contact angle was observed between the coatings with respect to change in diluents and different UV light intensity. All cured samples showed a good chemical resistance to acetic acid, citric acid and ethyl alcohol after 1 hour exposure; to acetone and ethylbutyl acetate after 10 s, and to benzine after 2 minutes. Outstanding hydrophobic behavior was observed for the HDTMS coatings, however, better physical properties were determined for the coatings containing v-PDMS and TEOS, on which the scratching was observed after the applied force of 1.5 and 0.6 N in comparison to HDTMS coatings (0.4 N). The resulting properties achieved for the AELO coatings indicated that it has a potential to be used for wood coating and packaging application.

Functionalization, protonation and ligand extension on MIL-53 (Al) MOFs to boost water adsorption and thermal energy storage for heat transformations

Understanding the relationship between the geometry of metal–organic frameworks (MOFs) and the shape of H2O adsorption isotherms is of utmost importance to control the hydrophilic and hydrophobic behaviors of water in MOFs with adsorption/desorption kinetics to realize their applications in thermal energy storage (TES). The MOFs are potential candidates for TES through water adsorption process. The TES can be used as a pivot for heat transformations related to cooling, heat pump, desalination, power generation, water harvesting and dehumidification. The TES performances are mainly determined by water adsorption characteristics such as water uptake/offtake loadings, kinetics and adsorbents-water interaction energy. Therefore, this paper presents a comprehensive analysis on the restructuring of MIL-53 (Al) MOFs for heat transformation applications. In this work, the original MOF is first functionalized with amino or hydroxyl functional groups. Next, the functionalized MOF is protonated with hydrochloric acid. In addition, ligand extension is applied on the original MOF by replacing the original organic linker with the progressively longer linkers. The surface properties of these restructured MOFs are measured by XRD, FTIR, TGA and N2 adsorption analysis. The water uptakes under equilibrium and dynamic conditions are presented in the form of isotherms and kinetic plots. The structural, thermal and cyclic water transfer stabilities of these MOFs are also presented. It is found that the tailored MIL-53 (Al) MOFs modify both the hydrophilicity and hydrophobicity of the original MOFs and improve the water loadings up to 0.9 g/g. The functionalized and protonated MIL-53 (Al) MOFs show higher water transfer with faster kinetics as compared to the parent MIL-53(Al) MOFs. The ligand extended MIL-53 (Al) MOFs provide higher water transfer between humid (relative humidity RH of 80% to 90%) and regenerated (RH of 30%) conditions with promising thermal energy storage density (TESD, up to 1.54 MJ/L).

Mechanical wear and hydrophobicity behaviour of Digitaria ischaemum fibre-reinforced finger millet husk biosilica toughened epoxy composites

Mechanical wear and hydrophobicity behaviour of Digitaria ischaemum fibre-reinforced finger millet husk biosilica toughened epoxy composites

Design for disassembly of composites and thermoset by using cleavable ionic liquid monomers as molecular building blocks

Aircraft, automotive industries and the increasing numbers of wind turbine blade lead to a huge amount of carbon fiber reinforced polymers requiring to be recycled and/or reused in a closed loop supply chain or circularity of materials. Herein, we have designed and synthesized a tetra-epoxidized imidazolium ionic liquid (Tetra-IL) monomer containing ester-cleavable groups. This monomer was incorporated as a molecular brick platform into conventional epoxy-amine networks in order to tailor the physical properties as well as the end-of-life of the resulting networks. Thus, the introduction of only 10% of IL-based comonomers significantly reduced the gel time by 85% opening perspectives in the field of fast-cure epoxy resins. Overall, all the networks designed in this work presented high thermal stability (>350 °C), higher Tg included between 180 and 230 °C combined with hydrophobic behavior. Increasing the amount of IL monomer in the networks improved the homogeneity of thermosets and wettability of the epoxy resins with the carbon fibers (CF). Most importantly, the use of Tetra-IL led to the development of degradable networks under mild conditions within a brief timeframe (4.5 h) and allowing to recover the carbon fibers. In summary, this study highlighted the great potential of IL-based comonomers as molecular brick into conventional epoxy thermosets as a promising strategy to tailor the physical properties versus sustainability/degradability for the development of high-performance thermosets and composites.

Origin of the Hydrophobic Behaviour of Hydrophilic CeO2

Origin of the Hydrophobic Behaviour of Hydrophilic CeO₂

Cover Picture: Origin of the Hydrophobic Behaviour of Hydrophilic CeO2 (Angew. Chem. Int. Ed. 35/2023)

Cover Picture: Origin of the Hydrophobic Behaviour of Hydrophilic CeO₂ (Angew. Chem. Int. Ed. 35/2023)

Tailoring the wettability of surface-textured copper using sub-THz bursts of femtosecond laser pulses

In this work, copper surfaces were textured with sub-Terahertz bursts of femtosecond pulses. The wettability of Cu textured surfaces was investigated by measuring the static water contact angle (WCA) as a function of the number of sub-pulses and the intra-burst frequency. A superhydrophobic, antiadhesive response was observed when using bursts with a high number of sub-pulses (equal to or higher than 16) or a high intra-burst frequency (equal to or higher than 0.09 THz). Such trend was ascribed to the generation, under specific laser irradiation conditions, of a double-scale hierarchical texture on the sample surface, formed by sub-micro patterns with fine periodic ripples (LIPSS, Laser-Induced Periodic Surface Structures) and random nanoparticle decoration. Such texture enhances the hydrophobic behavior given by inherent adsorption of adventitious hydrocarbons on laser-processed and thermally-treated metal targets.

Sorption Capacity of Polydimethylsiloxane Foams Filled with Thermal-Treated Bentonite-Polydimethylsiloxane Composite Foams for Oil Spill Remediation.

The spillage of oil causes severe and long-lasting impacts on both the environment and human life. It is crucial to carefully reconsider the methods and techniques currently employed to recover spilled oil in order to prevent any possible secondary pollution and save time. Therefore, the techniques used to recover spilled oil should be readily available, highly responsive, cost-effective, environmentally safe, and, last but not least, they should have a high sorption capacity. The use of sorbents obtained from natural materials is considered a suitable approach for dealing with oil spills because of their exceptional physical characteristics that support sustainable environmental protection strategies. This article presents a novel sorbent material, which is a composite siloxane foam filled with bentonite clay, aimed at enhancing the hydrophobic and oleophilic behavior of the material. The thermal treatment of bentonite optimizes its sorption capacity by eliminating water, and increasing the surface area, and, consequently, its interaction with oils. In particular, the maximum sorption capacity is observed in kerosene and naphtha for the bentonite clay thermally treated at 600 °C, showing an uptake at saturation of 496.8% and 520.1%, respectively. Additionally, the reusability of the composite foam is evaluated by squeezing it after reaching its saturation point to determine its sorption capacity and reusability.

Unlocking the Stability of Reduced Graphene Oxide Nanosheets in Biological Media via Use of Sodium Ascorbate

AbstractGraphene oxide and reduced graphene oxide (RGO) are carbon bidimensional nanomaterials largely exploited in biomedicine. Their unique interactions with eukaryotic and prokaryotic cells are used to obtain precise intracellular delivery, to create device coatings, and to design theranostic materials for both therapeutic and imaging applications, mainly in the cancer research field. It is known, however, that the hydrophobic behavior of RGO limits its stability in biological media. Here, the employment of sodium ascorbate (NaA) as a reducing agent for the preparation of RGO to provide a nanomaterial with remarkable suitability for applications in cell culture media is proposed. It is demonstrated via a combined experimental and theoretical approach that NaA is able to yield a peculiar RGO derivative, exerting a twofold effect, that is, C sp2 network restoration upon epoxide reduction and RGO edge functionalization via H‐bonding, lending RGO a so far unexampled dispersibility in aqueous‐based media. The kinetic stability of the bidimensional layers of RGO obtained from NaA is demonstrated together with its superior biocompatibility for drug delivery, unlocking outstanding potentialities for biological applications.

SiO2/PDMS functionalized hybrid ceramics: effect of functional group on hydrophobic behavior

In this paper, the hydrophobic effect of the functional group in a hybrid ceramic synthesized from tetraethyl orthosilicate (TEOS) and polydimethylsiloxane (PDMS) is investigated. The hybrid ceramics were synthesized using di-butyl-di-di-tin laurate (DBTL) as a polycondensation catalyst and different concentrations of the polysiloxane chain varying from 20-40%w. Infrared spectroscopy confirmed the formation of the hybrid material, observing the corresponding signals for the siloxane bond (Si–O–Si) corresponding to the silica network, inorganic fragment (1100 cm–1 ) and those corresponding to the polymer chain (785 cm–1 ) besides, the Si–C bond of the polymer is presented at 1250 cm–1 . The amino functional group was identified as a low intensity signal at 1300 cm–1 (N–C) and 1204 cm–1 (Si– N); on the other hand, the phenyl group was present at 3080 cm–1 for the C–H group of the aromatic ring and with the C=C bond of the ring at 1429, 794 and 845 cm–1 . While the hydrophobic character was evaluated with the contact angle  obtaining a hydrophobic to superhydrophobic behavior with  de 110-130º.

Effect of cassava tuber nanocellulose and satin weaved bamboo fiber addition on mechanical, wear, hydrophobic, and thermal behavior of unsaturated polyester resin composites

Effect of cassava tuber nanocellulose and satin weaved bamboo fiber addition on mechanical, wear, hydrophobic, and thermal behavior of unsaturated polyester resin composites

Co-Electrospun Poly(ε-Caprolactone)/Zein Articular Cartilage Scaffolds.

Osteoarthritis scaffold-based grafts fail because of poor integration with the surrounding soft tissue and inadequate tribological properties. To circumvent this, we propose electrospun poly(ε-caprolactone)/zein-based scaffolds owing to their biomimetic capabilities. The scaffold surfaces were characterized using Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, static water contact angles, and profilometry. Scaffold biocompatibility properties were assessed by measuring protein adsorption (Bicinchoninic Acid Assay), cell spreading (stained F-actin), and metabolic activity (PrestoBlue™ Cell Viability Reagent) of primary bovine chondrocytes. The data show that zein surface segregation in the membranes not only completely changed the hydrophobic behavior of the materials, but also increased the cell yield and metabolic activity on the scaffolds. The surface segregation is verified by the infrared peak at 1658 cm-1, along with the presence and increase in N1 content in the survey XPS. This observation could explain the decrease in the water contact angles from 125° to approximately 60° in zein-comprised materials and the decrease in the protein adsorption of both bovine serum albumin and synovial fluid by half. Surface nano roughness in the PCL/zein samples additionally benefited the radial spreading of bovine chondrocytes. This study showed that co-electrospun PCL/zein scaffolds have promising surface and biocompatibility properties for use in articular-tissue-engineering applications.

Fabrication of PCL/CMARX/GO Composite Nanofibrous Mats for Dye Adsorption: Wastewater Treatment.

The effluents of industrial wastewater contain several toxic organic and inorganic pollutants that may contaminate clean and freshwater sources if untreated or poorly treated. These toxic pollutants include colors; hazardous compounds; surfactants; cosmetics; agrochemicals; pharmaceutical by-products; and agricultural, pharmaceutical, and medical contaminants. Treating wastewater has become a global problem. Many projects have been started in the last two decades to treat wastewater, resultant water pollution, and associated waste management problems. Adsorbants based on graphene oxide (GO) are viable wastewater treatment materials due to their adaptability, photocatalytic action, and capacity for self-assembly. Here, we report the fabrication of nanofibrous mats from polycaprolactone (PCL), carboxymethyl arabinoxylan (CMARX), and carboxyl-functionalized-graphene oxide using an electrospinning technique. The silver nanoparticles were loaded onto the mat to enhance their photocatalytic activity. These mats were characterized using different techniques, including Fourier transform infrared (FTIR), scanning electron microscope (SEM), and transmission electron microscope (TEM). The water contact angles were used to study their hydrophilic and hydrophobic behavior. The Langmuir isotherm model and adsorption kinetics were studied to evaluate their adsorption capabilities against methylene blue (MB). Sample 2 followed the Langmuir isotherm model (R2 = 0.9939). Adsorption kinetics exhibited pseudo-second order behavior (R2 = 0.9978) due to their maximum correlation coefficient values. MB has excellent adsorption at room temperature and the formation of the monolayer at the surface of the adsorption mat. An enhanced PO43- and MB adsorption was observed, providing recyclability up to 4-5 times. Hence, the fabricated nanofibrous mat would be a potential candidate for more effective wastewater treatment applications.

Enhancing Fines Recovery by Hybrid Flotation Column and Mixed Collectors

The froth flotation technique can be considered one of the most efficient methods for the separation of minerals. Prior to utilizing any physicochemical separation method, the size of the mined ore must be decreased to facilitate the release of the valuable materials. This practice, along with the increased exploitation of ores that carry fine mineral particles caused the production of fine and ultrafine particles which are difficult to recover with classical enrichment methods, due to their different characteristics compared to coarser particles. It is established that fine and ultrafine particles are difficult to float, leading to losses of valuable minerals, mainly due to their low collision efficiency with bubbles. Moreover, fine particles require higher reagent consumption due to the fact that have a higher specific area, and finally, their flotation is limited by low kinetic energy. Flotation of fines can be enhanced by either decreasing bubble diameter or increasing their apparent size, or moreover, by enhancing the collector’s adsorption (their hydrophobic behavior) using alternative reagents (non-ionic co-collectors). In the present research, flotation experiments on a hybrid electrolytic flotation column that can produce microbubbles (−50 μm), were carried out for recovering fine magnesite (−25 μm) particles. In addition, the synergistic effect of anionic/non-ionic collectors were studied for the enhancement of fines recovery. Experimental flotation results so far designate the enhancement of fine magnesite particle recovery by approximately 8% with the addition of microbubbles. Finally, the synergistic effect of anionic/non-anionic collectors led to the improvement of flotation recovery by almost 12%.

Synthesis, characterization and tribological properties of solid lubricant graphite films produced by PECVD

Graphite, which is one of the mostly used solid lubricants, is commonly used in different industrial applications due to its low friction coefficient. However, the synthesis of graphite films can be a challenging process in some cases, where durable coatings are needed. Therefore, the aim of this study is to obtain graphite films with low friction coefficients and investigate their tribological properties. In order to achieve this, graphite films were synthesized on glass substrates by using Plasma Enhanced Chemical Vapor Deposition (PECVD) technique for different process times (30, 60 and 90 min). Reciprocating wear tests were performed to determine the tribological properties of the obtained graphite films. Afterwards, Raman, FT-IR, SEM and surface wettability analyzes were carried out to characterize the films. The results showed that the graphite film synthesized for 90 min exhibited higher wear resistance and lower friction coefficient than untreated and other treated samples because it had high film thickness and hydrophobicity. Also, it was seen that the thicknesses of the coatings increased depending on the treatment time and the contact angle measurements showed that all the graphite films exhibited hydrophobic behaviour.

Origin of the Hydrophobic Behaviour of Hydrophilic CeO2.

The nature of the hydrophobicity found in rare-earth oxides is intriguing. The CeO2(100) surface, despite its strongly hydrophilic nature, exhibits hydrophobic behaviour when immersed in water. In order to understand this puzzling and counter-intuitive effect we performed a detailed analysis of the water structure and dynamics. We report here an ab-initio molecular dynamics simulation (AIMD) study which demonstrates that the first water layer, in immediate contact with the hydroxylated CeO2 surface, is responsible for the effect behaving as a hydrophobic interface with respect to the rest of the liquid water. The hydrophobicity is manifested in several ways:a considerable diffusion enhancement of the confined liquid water as compared with bulk water at the same thermodynamic condition, a weak adhesion energy and few H-bonds above the hydrophobic water layer, which may also sustain a water droplet. These findings introduce a new concept in water/rare-earth oxide interfaces: hydrophobicity mediated by specific water patterns on a hydrophilic surface.

Origin of the Hydrophobic Behaviour of Hydrophilic CeO2

AbstractThe nature of the hydrophobicity found in rare‐earth oxides is intriguing. The CeO2 (100) surface, despite its strongly hydrophilic nature, exhibits hydrophobic behaviour when immersed in water. In order to understand this puzzling and counter‐intuitive effect we performed a detailed analysis of the water structure and dynamics. We report here an ab‐initio molecular dynamics simulation (AIMD) study which demonstrates that the first water layer, in immediate contact with the hydroxylated CeO2 surface, is responsible for the effect behaving as a hydrophobic interface with respect to the rest of the liquid water. The hydrophobicity is manifested in several ways: a considerable diffusion enhancement of the confined liquid water as compared with bulk water at the same thermodynamic condition, a weak adhesion energy and few H‐bonds above the hydrophobic water layer, which may also sustain a water droplet. These findings introduce a new concept in water/rare‐earth oxide interfaces: hydrophobicity mediated by specific water patterns on a hydrophilic surface.

Ultralight and highly efficient oil-water selective aerogel from carboxymethyl chitosan and oxidized β-cyclodextrin for marine oil spill cleanup

Biomass-based aerogels for oil spill cleanup have attracted tremendous research interests due to their feasibility in oil-water separation. However, the cumbersome preparation process and toxic cross-linking agents hinder their application. In this work, a facile and novel method to prepare hydrophobic aerogels is reported for the first time. Da-β-CD/CMCS aerogel (DCA), Da-β-CD/CMCS/PVA aerogel (DCPA), and hydrophobic Da-β-CD/CMCS/PVA aerogel (HDCPA) were successfully synthesized via the Schiff base reaction between carboxymethyl chitosan (CMCS) and dialdehyde β-cyclodextrin (Da-β-CD). Meanwhile, polyvinyl alcohol (PVA) acted as reinforcement and hydrophobic modification was conducted via chemical vapor deposition (CVD). The structure, mechanical properties, hydrophobic behaviors and absorption performance of aerogels were comprehensively characterized. The results indicated that the DCPA containing 7 % PVA exhibited excellent compressibility and elasticity even at a compressive strain of ε = 60 %, however, the DCA without PVA showed incompressibility, suggesting that the important role played by PVA in improving compressibility. Moreover, HDCPA possessed excellent hydrophobicity (water contact angle up to 148.4°), which could be well maintained after experiencing wear and corrosion in harsh environments. HDCPA also possesses high absorption capacities (24.4–56.5 g/g) towards different oils with satisfied recyclability. These advantages endow HDCPA with great potential and application prospects in offshore oil spill cleanup.