Apparent Water Contact Angle Research Articles

Quantitative experimental study on the apparent contact angle of unsaturated loess and its application in soil–water characteristics curve modeling

AbstractAdvancing and receding water contact angles, often denoted as the maximum and minimum apparent water contact angles, are crucial parameters reflecting a soil's water holding capacity. These parameters play an important role in establishing theoretical soil–water characteristic curves (SWCCs) for unsaturated soils. However, pre‐assuming constant advancing and receding contact angles during soil wetting and drying processes may be erroneous due to their close correlations with the water content and void ratio. To address this research gap, systematic laboratory measurements were conducted on a loess with different void ratios and water contents. Apparent water contact angles were acquired using an axisymmetric drop shape analyzer, enabling a comprehensive dataset. Analysis of variance was employed to assess the statistically significant differences between void ratios and water contents. The results reveal a significant increase in the observed water contact angle as the void ratio decreases and a decrease with increasing water content. Although both the void ratio and water content influence the water contact angle, the latter has a more pronounced effect. The relationship between the receding water contact angle and water content/void ratio is observed to be linear. The identification of this linear relationship offers insights into the fitting of the SWCC for loess across varying void ratios. This study serves to enhance theoretical methodologies, particularly in the adaptation of contact angles, thus facilitating the development of more precise SWCC models.

Hierarchical bio-inspired design and fabrication of all-dimensional superhydrophobic ultra-lightweight high-volume fly ash cement foams using novel ultrasonic-assisted siloxane-encapsulated pickering emulsions

Ultra-lightweight foamed cement (ULFC) exhibits super-high porosity and excellent thermal-insulation capabilities. However, the thermodynamic instability and high water-absorptivity of ULFC with high-volume fly ash have restricted its large-scale application. Superhydrophobic technology can significantly improve the substrates’ hydrophobicity, among which the nanocoating is a popular option but the water-repellent layer may be easily destroyed due to the mechanical damage. Therefore, the intrinsic superhydrophobization becomes a promising alternative to the coating scheme. Here, the internal superhydrophobic ULFC was formulated through introducing the ultrasonic-assisted siloxane-encapsulated Pickering emulsions, in which two Pickering structures containing n-dodecyltrimethoxysilane were stabilized by hydrophobic SiO2 and C–S–H nanoparticles, respectively. Compared with the SiO2 nanoparticles-stabilized dispersion, the droplets of C–S–H nanoparticles-stabilized Pickering emulsion were more stable and controlled-release in cement hydration environment. As such, the incorporation of the latter showed no negative impact on the setting times and static yield stress of the interstitial matrix, optimizing the homogeneity, mechanical strength and heat conductivity of ULFC. The combination of nanoscale foam stabilizer and Pickering emulsions could form the hierarchical waterproof structure with low surface free energy at the gas-solid interfaces, and the multiscale siloxane-grafted intertwined hydration products were responsible for the inner superhydrophobicity of ULFC. Therefore, under the water vapor-saturated environment, the water absorption of superhydrophobic samples showed only a slight increase as a function of time and the ULFC was still hydrophobic with a reduction of apparent water contact angle from 154.6° to 137.8°. From energy consumption analysis, the all-dimensional superhydrophobic ULFC had a potential application in heat-insulation building.

Understanding the role of infusing lubricant composition in the interfacial interactions and properties of slippery surface

Liquid-infused surfaces (LISs) have attracted tremendous attention in recent years owing to their excellent surface properties, such as self-cleaning and anti-fouling. Understanding the effect of lubricant composition on LIS performance is of vital importance, which will help establish the criteria to choose suitable infusing lubricants for specific applications. In this work, the role of chemical composition of lubricant in the properties of LISs was investigated. The apparent water contact angle θapp was dependent on the temperature and beeswax/silicone oil ratio. Nevertheless, the trend of moving velocity of water drop on the tilted LISs did not follow that of θapp at 20 °C and 37 °C, which was attributed to the increased lubricant viscosity with beeswax/silicone oil ratio. At 60 °C, the drop velocity and θapp shared the similar variation trend with beeswax/silicone oil ratio, highlighting the significant role of chemistry of the components in beeswax. The alkanes and fatty acids promoted the drop movement, while the fatty acid esters impeded the movement. The interaction forces between water drop and lubricant surfaces were measured using atomic force microscopy. It was demonstrated that the interaction between water drop and lubricant was not the only factor to control the drop movement, while the interaction between lubricant and substrate as well as of lubricant itself also determined the movement. When the adhesions of water-lubricant and lubricant-substrate were similar for different lubricants, the influence of cohesion of lubricant became significant. This work provides useful insights into the fundamental understanding of the interfacial interactions of test drop, infusing lubricant and solid substrate of LISs, and the effect of infusing lubricant composition on the LIS performance.

Simple UV-Grafting of PolyAcrylic and PolyMethacrylic Acid on Silicone Breast Implant Surfaces: Chemical and Mechanical Characterizations

Poly(dimethyl siloxane) (PDMS) is one of the most widely used materials in the biomedical field. Despite its numerous advantages, its hydrophobic character promotes bacterial adhesion and biofilm formation. For breast implants, biocompatibility is challenged due to the biofilm formed around the implant that can degenerate to severe capsular contracture over time. Thus, the laboratory has set up strategies to prevent bacterial contamination by grafting covalently hydrophilic bioactive polymers on the surface of implants. In this study, poly(methacrylic acid) (PMAc) and poly(acrylic acid) (PAAc) were chosen as non-toxic and biocompatible bioactive polymers known for reducing bacteria adhesion. These polymers are also good candidates to lend reactivity on the surface for further functionalization. X-ray photoelectron Spectroscopy (XPS) and Fourier-Transform Infrared spectroscopy (FTIR) analysis have highlighted the covalent grafting of these polymers. Apparent water contact angle measurements have shown the change in hydrophilicity on the surface, and a colorimetric assay allowed us to assess the grafting rate of PMAc and PAAc. Tensile strength assays were performed to ensure that the functionalization process does not significantly alter the material’s mechanical properties. Analyses of the surface aspect and roughness by Scanning Electron Microscope (SEM) and optical profilometer allow us to formulate hypotheses to approach the understanding of the behavior of the polymer once grafted.

Trifolium repens L.-Like Periodic Micronano Structured Superhydrophobic Surface with Ultralow Ice Adhesion for Efficient Anti-Icing/Deicing.

Wind turbine blades are often covered with ice and snow, which inevitably reduces their power generation efficiency and lifetime. Recently, a superhydrophobic surface has attracted widespread attention due to its potential values in anti-icing/deicing. However, the superhydrophobic surface can easily transition from Cassie-Baxter to Wenzel at low temperature, limiting its wide applications. Herein, inspired by the excellent water resistance and cold tolerance of Trifolium repens L. endowed by its micronano structure and low surface energy, a fresh structure was prepared by combining femtosecond laser processing technology and a boiling water treatment method. The prepared icephobic surface aluminum alloy (ISAl) mainly consists of a periodic microcrater array, nonuniform microclusters, and irregular nanosheets. This three-scale structure greatly promotes the stability of the Cassie-Baxter state. The critical Laplace pressure of ISAl is up to 1437 Pa, and the apparent water contact angle (CA) is higher than 150° at 0 °C. Those two factors contribute to its excellent anti-icing and deicing performances. The results show that the static icing delay time reaches 2577 s, and the ice adhesion strength is only 1.60 kPa. Furthermore, the anti-icing and deicing abilities of the proposed ISAl were examined under the environment of low temperature and high relative humidity to demonstrate its effectiveness. The dynamic anti-icing time of ISAl in extreme environments is up to 5 h, and ice can quickly fall with a speed of 34 r/min when it is in a horizontal rotational motion. Finally, ISAl has excellent reusability and mechanical durability, with the ice adhesion strength still being less than 6 kPa and the CA greater than 150° after 15 cycles of icing-deicing tests. The proposed structure would offer a promising strategy for the efficient anti-icing and deicing of wind turbine blades.

Facile and eco-friendly fabrication of superhydrophilic and superhydrophobic SiC surfaces by nanosecond laser treatment

Superhydrophobic silicon carbide surfaces have garnered substantial attention for their potential applications in aerospace, ship domain, military, etc., fields. In this work, we used a nanosecond laser (λ = 1065 nm) and fluorine-free N-octyltriethoxysilane (OcTES) to fabricate SiC surfaces capable of transitioning from superhydrophilic to superhydrophobic. Superhydrophilic surfaces were produced within minutes through laser treatment, and the time required to convert it to superhydrophobic surfaces is only 1 h. The apparent water contact angle (WCA) of superhydrophilic SiC could reach the saturated Wenzel regime. The number of hydrophilic polar bonds on SiC surfaces increased while nonpolar bonds of hydrophobicity decreased due to oxidation during laser treatment. After OcTES treatment, the SiC surface transformed from superhydrophilic to superhydrophobic (WCA of 153° and roll-off angle of 0°). These results indicate that surface roughness and chemical compositions are critical for superhydrophobicity. It was discovered that Si–O–Si groups were formed on SiC surfaces in the atmosphere, thereby enhancing the material surface's hydrophobicity. Superhydrophobic SiC surfaces also have excellent low-adhesion and anti-icing properties, making them of potential interest for functional ceramic surface applications.

Superhydrophilicity and Antifouling Behavior in Electrochemically Oxidized Nanocrystalline Pseudographite

Electrochemical oxidation of GUITAR (pseudoGraphite from the University of Idaho Thermolyzed Asphalt Reaction) produces a surface that exhibits superhydrophilic properties. This surface contains 20.7% relative oxygen abundance, giving it a heightened affinity for water relative to the pristine material. Scanning electron and atomic force micrographs reveal spherical, bubble-like structures on GUITAR, indicating a higher surface roughness (Rq = 300–400 nm) over the predominantly smooth titanium substrate (Rq = 94.5 nm). Combining an intrinsic affinity toward water with a heightened surface roughness produces a material with an apparent water contact angle of 0°. The synergistic effects of a superhydrophilic surface that can function as an electrode result in an electrocatalyst material that is highly resistant to fouling. When stored in water, oxidized GUITAR (Ox-GUITAR) completely resists fouling by volatile organic compounds for the duration of testing (72 h). When fouled directly with a drop of oil, the residue can be removed using a simple water rinse. The removal of oil residues from carbon surfaces is typically not possible without the use of solvents, surfactants, or mechanical exfoliation. This combination of properties opens Ox-GUITAR to a broad array of possible applications, such as implantable electrodes, field sensors, or water-quality monitoring.

Electrospun Multilayered Films Based on Poly(3-hydroxybutyrate-co-3-hydroxyvalerate), Copolyamide 1010/1014, and Electrosprayed Nanostructured Silica

In this research, bio-based electrospun multilayered films for food packaging applications with good barrier properties and close to superhydrophobic behavior were developed. For this purpose, two different biopolymers, a low-melting point and fully bio-based synthetic aliphatic copolyamide 1010/1014 (PA1010/1014) and the microbially synthesized poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and food-contact-complying organomodified silica (SiO2) nanostructured microparticles, were processed by electrospinning. The production of the multilayer structure was finally obtained by means of a thermal post-treatment, with the aim to laminate all of the components by virtue of the so-called interfiber coalescence process. The so developed fully electrospun films were characterized according to their morphology, their permeance to water vapor and oxygen, the mechanical properties, and their water contact angle properties. Interestingly, the annealed electrospun copolyamide did not show the expected improved barrier behavior as a monolayer. However, when it was built into a multilayer form, the whole assembly exhibited a good barrier, an improved mechanical performance compared to pure PHBV, an apparent water contact angle of ca. 146°, and a sliding angle of 8°. Consequently, these new biopolymer-based multilayer films could be a bio-based alternative to be potentially considered in more environmentally friendly food packaging strategies.

Internal erosion in hydrophobic and hydrophilic soils

The water repellency of soil occurs when organic matter coats the soil particle surface; this can either happen naturally due to wildfire and fungal growth or be induced by chemical treatments. The internal stability of water-repellent soils subjected to seepage has not been explored in the literature. In this study, the mechanical responses to internal erosion in three synthetic water-repellent soils, treated by different organic matters, were first investigated using a modified stress-controlled triaxial apparatus. The degree of hydrophobicity of the test soils was assessed through the measurement of apparent water contact angle. In each internal erosion test, the cumulative particle loss, deformation and hydraulic conductivity were evaluated. The water-repellent coatings efficiently suppressed the progression of internal erosion at practical hydraulic gradients because of their smaller fluid–solid adhesion. Continuously increasing the hydraulic gradient would finally result in a breakthrough of internal erosion due to the saturation of the hydrophobic soils under high pore-water pressures. Post-erosion contact angle measurements and scanning electron microscopy images confirmed the durability of the three water-repellent coatings against seepage erosion. The findings of this study confirm the potential of applying hydrophobic soils to mitigate internal erosion under normal hydraulic loading conditions.

Modelling for effects of surface chemical composition on contact angle and applications in membrane flux control

Surface wettability is related to the chemical composition of the surfaces; however, their mathematical connections are not well understood. An accurate and concise equation was derived to relate the contact angle and chemical composition of a composite surface, and subsequently verified by measuring the apparent water contact angle (WCA) on a special uniform surface with an increasing modification ratio. This surface was fabricated using the layer-by-layer method and modified using the ion exchange method. Excellent correlation (R2 = 0.9985) of the linear fit between the WCA cosine value and modification ratio verified the theoretical correlation. This conclusion was further applied to the study of membrane separation performance. The water flux of two cellulose membranes modified by chlorosulfonic acid had a good linear relationship (R2 = 0.9875) with the modification ratio. This result provides insight into precise wettability control, which is significant for the study of surfaces, membranes, and other fields.

Formation of Nanotubular Structures with Petal Effect by Soft-Template Electropolymerization of Benzotrithiophene with Hydrophilic Carboxyl Group

The bioinspiration is one of the best ways to make a breakthrough in a field, and particularly in the wetting properties. Bioinspired by natural species, such as rose petals and gecko foot, and previous researches, nanotubular structures are prepared here by soft-template electropolymerization in organic solvent and using an original benzotrithiophene with a hydrophilic carboxyl group, as the monomer. The best results are obtained by cyclic voltammetry because of a much higher amount of gas bubbles released with this deposition method. Both nanoparticles and nanotubes are observed while the water content has an influence on the number of nanotubes. Even if the monomer has hydrophilic carboxyl group, the best films have both high hydrophobicity (apparent water contact angle up to 130.7°) and strong water adhesion (petal effect). These surfaces could be used in future in applications such as water harvesting systems.

Cooperative construction of oil/water separator using renewable lignin and PDMS

Super-hydrophobic materials have played a significant role in the oil/water separation field. The traditional super-hydrophobic materials are prepared by fluorine-containing materials. However, although fluorine-containing materials have lower surface energy, they are expensive and difficult to degrade. Therefore, it's a great challenge for the designed and prepared the super-hydrophobic porous materials with super-oleophilicity to explore an environmentally friendly, easy-to-operate, low-cost, and renewable separator for oil/water mixtures separation. In this work, taking advantage of the microscale of renewable lignin and the low surface energy of polydimethylsiloxane （PDMS）, the porous super-hydrophobic sponge material with super-oleophilicity was prepared by the synergy of polydimethylsiloxane (PDMS) and lignin. After soaking and curing, the porous super-hydrophobic sponge showed a high apparent water contact angle which is up to 160°. The designed porous sponge materials can effectively absorb heavy oil in oil-water mixtures separation. Moreover, the porous sponge materials possess temperature stability, acid and alkali stability, and are easy easily recyclable. As high-efficiency oil-water separation material prepared by the synergy between renewable natural polymers and fluorine-free materials, this technique is not only conducive to remediate environmental problems but also helpful to explore the potentiality of lignin that seemingly bio-waste. At the same time, valuable oil can also be recycled.

A multifunction superhydrophobic surface with excellent mechanical/chemical/physical robustness

Superhydrophobic surfaces have many advantages in wetting fields. However, the lack of easyily production methods and limited mechanical/chemical/physical robustness remain the two most pertinent barriers to the scalability, large-area production, and widespread use of superhydrophobic materials. In this work, a mechanical/chemical/physical robustness superhydrophobic coating sample consisting of a regular array of square Cu mesh with secondary nano structures of polytetrafluoroethylene (PTFE) and SiO2 powders on the sidewalls is produced through a scalable and easyily production technique of the combination of hot-press sintering and subsquent spray-coating. The Cu mesh is used as a template to fabricate the grooves and bulges as the first-level roughness, and the SiO2 powder is maintained on the surface of the coatings to form two-level hierarchical structures, with both micro and nano structures firmly affixed by low-surface energy polymer binder (PTFE). For comparison, Cu mesh and Cu mesh/Cu sample are also produced. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and time-dependent apparent contact angle are used to examine the as-prepared materials. The corrosive solution, high temperature, UV irradiation, ultrasonic treatment, water drop hitting, sand drop impacting, multi-cycled sandpaper abrasion, tape-peeling test, and self-cleaning test was conducted to simulate the real-world damages. All of the armored superhydrophobic coating samples have an apparent water contact angle of more than 150°, as well as outstanding mechanical and chemical resilience. The salt spray test and mechanical behavior of the as-prepared samples revealed that the armored superhydrophobic coating sample has the lowest corrosion rate, the highest tensile strength, and the greatest elongation among these threee as-prepared samples, implying that it has the best anti-corrosion ability and mechanical property. This strategy might give guidance for the development of composite materials that need to retain mechanical/chemical/physical robustness in severe working conditions.

Fabrication and Characterization of Superhydrophobic Graphene/Titanium Dioxide Nanoparticles Composite.

Materials with superhydrophobic surfaces have received vast attention in various industries due to their valuable properties, such as their self-cleaning and antifouling effects. These promising superhydrophobic properties are taken into high priority, particularly for medical devices and applications. The development of an ideal superhydrophobic surface is a challenging task and is constantly progressing. Various strategies have been introduced; however, a minority of them are cost-effective. This work presents a facile fabrication of the superhydrophobic surface by using graphene and titanium dioxide (TiO2) nanoparticles. The graphene and TiO2 hybrid nanoparticles are dip-coated on a biodegradable thermoplastic poly(lactic acid) (PLA) substrate. The thermoplastic PLA is approved by the Food and Drug Administration (FDA), and is widely utilized in medical devices. The graphene/TiO2 coating is substantiated to transform the hydrophilic PLA film into superhydrophobic biomaterials that can help to reduce hazardous medical-device complications. The surface wettability of the graphene/TiO2 nanoparticle-coated PLA surface was evaluated by measuring the apparent water contact angle. The surface chemical composition and surface morphology were analyzed via Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The graphene/TiO2-coated PLA film achieved superhydrophobic properties by demonstrating a water contact angle greater than 150°. The water contact angle of the graphene/TiO2 coating increased along with the concentration of the nanoparticles and the ratio of TiO2 to graphene. Moreover, the graphene/TiO2 coating exhibited excellent durability, whereby the contact angle of the coated surface remained unchanged after water immersion for 24 h. The duration of the effectiveness of the superhydrophobic coating suggests its suitability for medical devices, for which a short duration of administration is involved. This study reports an easy-to-replicate and cost-effective method for fabricating superhydrophobic graphene/TiO2-coated surfaces, which additionally substantiates a potential solution for the manufacturing of biomaterials in the future.

Super-Repellent Paper Coated with Electrospun Biopolymers and Electrosprayed Silica of Interest in Food Packaging Applications.

In the current work, a super-repellent biopaper suitable for food contact applications was developed. To do this, three different kinds of biopolymers, namely polylactide (PLA), poly(ε-caprolactone) (PCL), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), and hydrophobic silica microparticles (SiO2), were sequentially processed by electrohydrodynamic processing (EDHP). As a first step, the ultrathin biopolymer fibers were deposited onto a commercial food contact cellulose paper by electrospinning and, thereafter, the nanostructured silica was sequentially electrosprayed. The multilayer coated papers were annealed at different temperatures to promote adhesion between the layers and enhance the super-repellent properties. The developed coatings were characterized in terms of morphology, permeance to water vapor, adhesion, mechanical resistance, and contact and sliding angle. The resultant multilayer biopapers presented a hierarchical micro/nanostructured surface with an apparent water contact angle (WCA) higher than 155° and sliding angle (SA) lower than 10° for all the tested biopolymers used. Among the different multilayer approaches, it was observed that the paper/PHBV/SiO2 showed the best performance, in terms of water vapor permeance; resistance after the tape peeling-off test; and food super-repelling properties to water, yogurt, and custard. Overall, this study presents the successful generation of super-repellent biopapers coated with PLA, PCL, or PHBV along with hydrophobic silica microparticles and its effectiveness for easy emptying food packaging applications to reduce food waste.

A bioinspired approach to fabricate fluorescent nanotubes with strong water adhesion by soft template electropolymerization and post-grafting

HypothesisIn this original work, we aim to control both the surface wetting and fluorescence properties of extremely ordered and porous conducting polymer nanotubes prepared by soft template electropolymerization and post-grafting. For reaching this aim, various substituents of different hydrophobicity and fluorescence were post-grafted and the post-grafting yields were evaluated by surface analyses. We show that the used polymer is already fluorescent before post-grafting while the post-grafting yield and as a consequence the surface hydrophobicity highly depend on the substituent. ExperimentsHere, we have chosen to chemically grafting various fluorinated and aromatic substituents using a post-grafting in order to keep the same surface topography. Flat conducting polymer surfaces with similar properties have been also prepared for determining the surface energy with the Owens-Wendt equation and estimating the post-grafting yield by X-ray Photoemission Spectroscopy (XPS) and Time of Flight Secondary Emission Spectrometry (ToF-SIMS). For example, using fluorinated chains of various length (C4F9, C6F13 and C8F17), it is demonstrated that the surface hydrophobicity and oleophobicity do not increase with the fluorinated chain length due to the different post-grafting yields and because of the presence of nanoroughness after post-grafting. FindingsThese surfaces have high apparent water contact angle up to 130.5° but also strong water adhesion, comparable to rose petal effect even if there are no nanotubes on petal surface. XPS and ToF-SIMS analyses provided a detailed characterisation of the surface chemistry with a qualitative classification of the grafted surfaces (F6 > F4 > F8). SEM analysis shows that grafting does not alter the surface morphology. Finally, fluorescence analyses show that the polymer surfaces before post-treatment are already nicely fluorescent. Although the main goal of this paper was and is to understand the role of surface chemistry in tailoring the wetting properties of these surfaces rather than provide specific application examples, we believe that the obtained results can help the development of specific nanostructured materials for potential applications in liquid transport, or in stimuli responsive antimicrobial surfaces.

Macroporous Superhydrophobic Coatings with Switchable Wettability Enabled by Smart Shape Memory Polymers

AbstractHere, a facile bottom‐up nanofabrication technology for making smart superhydrophobic coatings with switchable wettability and tunable optical properties by integrating shape memory polymers (SMPs) with templated macroporous photonic crystals is reported. Thermoresponsive shape memory efforts exhibited by a polyurethane‐based shape memory copolymer enable reversible microstructural transitions between a “memorized” permanent configuration composing of highly ordered arrays of macropores and a temporary deformed structure with collapsed macropores. The unique macroporous SMP photonic crystal arrays with large surface roughness can entrap a large portion of air in the interconnecting macropores, resulting in superior superhydrophobic properties including high apparent water contact angle (CA > 160°) and low CA hysteresis. Importantly, the shape memory‐enabled microstructural transitions lead to drastic wettability switching from superhydrophobic (CA > 160°) to hydrophobic (CA ≈ 110°) or from oleophobic (CA ≈139° for hexadecane) to oleophilic (CA ≈ 80°). The large CA tunability (>50°) coupled with the simultaneous color change from shining iridescence to colorless associated with the same microstructural transition can not only provide a noninvasive means for visually indicating the surface wetting states, this favorable coupling between the wetting and optical behaviors of macroporous SMP photonic crystal membranes can also pave the way for developing new tunable nanooptical devices.

Fast and environmentally friendly fabrication of superhydrophilic-superhydrophobic patterned aluminum surfaces

The superwettability patterned aluminum surface has been shown considerable attention for emerging applications. However, the available techniques are time-consuming and require hazardous chemicals, especially toxic fluoride. In this work, the superhydrophilic-superhydrophobic patterned surface of aluminum was successfully fabricated by using nanosecond laser (λ=1065 nm) and fluorine-free N-Octyltriethoxysilane (OcTES). The time required to make superhydrophilic surfaces is only a few minutes and switch it into superhydrophobic is only 30 min. The patterned surface had both superhydrophilicity (apparent water contact angle (WCA) closed to 0°) and superhydrophobicity (WCA of 156° and roll-off angle of 2.9°), which achieved the droplet arrays and the fluid channels with special patterns. The results indicated that the synergy between the rough surface and the dominant presence of polar Al-OH groups induced by laser ablation was critical for superhydrophilicity. The OcTES molecules containing non-polar C-C(H) groups were assembled on the rough surface by the formation of Si-O-Al bonds, which transformed the laser-treated surface from superhydrophilic into superhydrophobic. This work is of significance for the eco-friendly fabrication of superwettability patterned aluminum surface and shows potential applications in fluidic systems and liquid controls.

Investigation of Surface Modification of Polystyrene by a Direct and Remote Atmospheric-Pressure Plasma Jet Treatment.

Localized functionalization of polymer surface with an atmospheric-pressure plasma jet was investigated at various treatment conditions. Polystyrene samples were treated with the plasma jet sustained in argon under direct or remote conditions. The two-dimensional evolution of surface wettability and the spot size of the treated area was determined systematically by measuring apparent water contact angles. Modification of surface chemistry and the formation of functional groups were investigated by X-ray photoelectron spectroscopy (XPS). The saturation of surface wettability and functional groups was observed even after a second of treatment providing the sample was placed close to the exhaust of the discharge tube. The spot diameter of the modified area increased logarithmically with increasing treatment time. However, it decreased linearly when increasing the distance. At the edge of the glowing plasma, however, the modification of surface properties was more gradual, so even 30 s of treatment caused marginal effects. With a further increase in the distance from the edge of the glowing plasma, however, there were no further treatment effects. The results are explained by significant axial as well as radial gradients of reactive species, in particular hydroxyl radicals.

Preparation of TiO₂-SiO₂ Hybrid Nanosols Coated Flame-Retardant Polyester Fabric Possessing Dual Contradictory Characteristics of Superhydrophobicity and Self Cleaning Ability.

TiO₂, SiO₂ and their hybrid nanocoatings are prepared on inherent flame retardant textile substrates from titanium(IV)iso-proproxide (TTIP) and tetraethoxysilane (TEOS) precursors using a sol-gel process followed by hydrothermal treatment. The coated samples are further functionalized by hexadecyltrimethoxysilane (HDTMS) to impart superhydrophobicity. Sample characterization of the nanosols, nanoparticles and coated samples are investigated using, X-ray diffractometer, transmission electron microscopy, scanning electron microscopy, UV-Vis spectroscopy, contact angle measurement. Stain degradation test under mild UV irradiation shows almost 54% degradation of coffee stain within 4 hours measured by Spectrophotometer. UV-Vis Absorption Spectroscopy demonstrates complete degradation of methyl orange colorant within 3 hours. Hybrid nanosol coated and HDTMS modified inherent flame retardant polyester surfaces show apparent water contact angle as ~145°, which is much closer to proximity of superhydrophobic surfaces. Thus, the novelty of present work is, by using sol-gel technique, a bi-functional textile surface has been developed which qualifies the very specific requirements of protective clothing like self-cleaning property (imparted by TiO₂ nanoparticles) and superhydrophobicity (imparted by SiO₂ nanoparticles and further surface modification by HDTMS), which are entirely contradictory in nature, in a single fabric itself. Thus developed textile surfaces also possess the other attributes of protective clothing like flame retardancy and air permeability.