Tunable Water Adhesion Research Articles

Bioinspired starch nanofibrous films with tunable hydrophobicity and water adhesion via tannic acid-interfacial self-assembly for food packaging

To address the limitations in water resistance and functionality of existing starch-based food packaging materials, this study developed a new sustainable food packaging material—starch nanofibrous films (SNFs) enhanced with an acylated tannic acid (ATA) interfacial self-assembly coating. Inspired by the unique hydrophobicity and water adhesion properties of rose petals, which effectively control surface characteristics to maintain microenvironmental humidity during food processing and storage, this approach significantly enhanced the water resistance, stability, and mechanical strength of the material. Specifically, the obtained SNFs/ATA exhibited a maximum water contact angle of ∼ 134.1°, tensile strength of ∼ 0.86 MPa, and Young’s modulus of ∼ 43.48 MPa. Moreover, SNFs/ATA showed excellent antibacterial and antioxidant properties, UV-blocking capabilities, and degradability, making it an environmentally friendly choice for food packaging. In practical food preservation applications, cherry tomatoes packaged with SNFs/ATA showed a significant extension of shelf life to 15 days, with a 62.5 % reduction in spoilage rate, a 25.4 % decrease in weight loss, and good quality including pulp firmness, pH, titratable acidity, and total soluble solids. This work demonstrates structurally regulated polyphenol assembly in the preparation of all-natural green biomimetic surface, creating new opportunities for the development of sustainable bio-based food packaging systems.

Robust Superhydrophobic Films Based on an Eco-Friendly Poly(l-lactic acid)/Cellulose Composite with Controllable Water Adhesion.

Poly(l-lactic acid) (PLLA) featuring desirable biodegradability and biocompatibility has been recognized as one of the promising eco-friendly biomaterials. However, low crystallization and poor mechanical and chemical performances dramatically hamper its practical application. In this work, we report that functionalized cellulose/PLLA composite superhydrophobic stereocomplex films with controllable water adhesion and protein adsorption can be fabricated by a facile approach for the first time. First, cellulose is surface-modified by means of two silanization modification methods. Then, superhydrophobic cellulose/PLLA composite films are prepared through a solvent-evaporation-induced phase separation method. The two cellulose/PLLA composite films exhibit extreme water repellency but tunable water adhesion from sticky to slippery. The protein adsorption capacity of the cellulose/PLLA composite films can also be regulated. In addition, the stereocomplexation of the composite film provides excellent mechanical properties with an elongation at break of 22.36%, which is 237.8% higher than that of a pure PLLA film, which is more suitable for biomaterials. Furthermore, good biodegradability of the PLLA composite films in nature enables the bio-based composites as alternative materials to replace conventional petroleum-based polymers. The superhydrophobic films have also been demonstrated for many applications, including slippery surfaces, liquid transportation without loss, and antifouling.

Functionalization of Monolithic MOF Thin Films with Hydrocarbon Chains to Achieve Superhydrophobic Surfaces with Tunable Water Adhesion Strength

While the accessible pores render an enormous variety of functionalities to the bulk of metal-organic frameworks (MOFs), the outer surfaces exposed by these crystalline materials also offer unique characteristics not...

Facile one-step spraying preparation of fluorine-free transparent superhydrophobic composite coatings with tunable adhesion for self-cleaning and anti-icing applications

Transparent superhydrophobic coatings are of vital importance for various rising applications, such as photovoltaics, touch panels, smart windows, etc. However, their large-scale practical applications are severely restricted by hazardous fluorinated reagents, multistep preparation procedures, thermal treatment requirements, and poor durability. In this study, a facile one-step spraying method was proposed to fabricate transparent superhydrophobic coatings on various substrates, using an integrated fluorine-free suspension composed of siloxane-containing acrylate copolymers and SiO2 nanoparticles. Thanks to the incorporation of siloxane groups in the copolymers, the prepared coatings can be cured at room temperature without any thermal curing procedure. The resultant coatings exhibit excellent superhydrophobicity and high transparency, with a WCA of 162.2 ± 1.8° and ∼90.83 % transmittance at 550 nm, respectively. Besides, superhydrophobic surfaces with tunable water adhesion can be achieved by adjusting spray pressure. After a series of mechanical durability tests and chemical stability tests, the obtained coatings can still maintain their superhydrophobicity and high transparency. Moreover, the water freezing time on the coated glass can be extended and the ice adhesion strength was significantly reduced, exhibiting excellent anti-icing performance. The facile, fluorine-free, and one-step spraying coating method has scalability and universality, demonstrating the promising prospect of large-scale application in industry.

Ultrafast and Eco-Friendly Fabrication Process for Robust, Repairable Superhydrophobic Metallic Surfaces with Tunable Water Adhesion.

Superhydrophobic metallic surfaces with a water contact angle greater than 150° have attracted considerable attention in both fundamental research and industrial applications due to their special properties such as antibiofouling, drag reduction, self-cleaning, anti-icing, anticorrosion, and oil-water separation. Until now, the development of superhydrophobic practical applications is mainly limited by the process complexity, long fabrication time, coating with toxic materials, and easily damaged surface structure. To reduce the fabrication time, and simplify the process for industrial applications, an eco-friendly postprocess has been developed in this research. The superhydrophobic surfaces on the laser-textured titanium, aluminum, copper, stainless steel, and nickel substrates were fabricated extremely rapidly by a simple surface modification of only a 10 min heat treatment with nontoxic silicone oil. Hydrophobic organic group absorption has been accelerated on the silicone oil heat-treated surface and has created a low-energy surface. In addition, we demonstrated the potential of using the laser areal fluence parameter, which could be an alternative to single-laser process parameters such as scanning speed, power, and step size, to fine-tune the water adhesion behavior. Therefore, a surface that integrates different water adhesion behaviors can be easily fabricated for more complex practical applications such as controlled microdroplet transportation, microfluidic systems, and certain biomedical processes. Moreover, the robustness of superhydrophobic surfaces was confirmed by abrasion tests, knife-scratch tests, chemical durability tests, and aging tests, and their repairability was evaluated for product applications in practice.

Superhydrophobic brass surfaces with tunable water adhesion fabricated by laser texturing followed by heat treatment and their anti-corrosion ability

Superhydrophobic metallic surfaces with tunable water adhesion have gained increasing interest due to their significance in both fundamental researches and practical applications. However, the relationship between the water adhesion and the anti-corrosion ability of the superhydrophobic metallic surfaces has been seldom studied. In this work, superhydrophobic brass surfaces with tunable water adhesion were fabricated by laser texturing followed by heat treatment, and the anti-corrosion ability of these surfaces was studied by performing electrochemistry tests. The analyses of surface structures and compositions revealed that the observed superhydrophobicity results from the micro/nanostructures produced by the laser texturing and the adsorption of organic matter from ambient air during the heat treatment; the different water adhesions of these superhydrophobic surfaces are attributed to their different solid–liquid interfacial area fractions. The results of the electrochemistry tests revealed that the anti-corrosion abilities of the investigated surfaces are the following order: the superhydrophobic surface with low water adhesion > the superhydrophobic surface with high water adhesion > the bare brass surface, which stems from the different solid-electrolyte interfacial area fractions of these surfaces.

Near-infrared light accurately controllable superhydrophobic surface from water sticking to repelling

Great attention has been paid to superhydrophobic surface with tunable water adhesion behaviors, but many challenges still remain for developing a surface with accurate regional control of the superwetting behaviors to realize on-demand responses. Herein, a superhydrophobic surface with accurately controllable water adhesion performance for local areas has been developed, by integrating carbonyl iron particles (CIPs) into a shape memory polymer (SMP) to get photothermal-responsive pillar array. The morphologies of the programmed surface can be remotely and accurately regulated through near-infrared (NIR) light irradiation, hence resulting in the accurate control of surface superwetting behaviors. By adjusting the intensity and targeted area of the NIR irradiation, the controllable surface deformation even in a minimal area of ~0.95 mm2 can be achieved. Among those, the surface with bent microstructures demonstrates high water adhesion force (98 μN) with a high water rolling-off angle (even the surface was overturned to 180°), whereas the superhydrophobic surface with the recovered micro/nanostructure arrays exhibits relatively low water adhesion force (25 μN) with an extremely low rolling-off angle (4°). We have proven that these programmable superhydrophobic surfaces can not only accurately adjust the droplet adhesive force in the target area, but also serve as ideal platforms for distinct microfluidic microreactors. These unique characteristics endow the NIR light remotely controlled superhydrophobic surfaces with special advantages for abroad applications in liquid droplet manipulations, micro reactions, biochemical detections, etc.

Highly conjugated carbazole-based monomers for the control of nanotubular surface structures by soft template electropolymerization

Abstract In this work, a bioinspired approach is used to prepare nanotubular structures with tunable hydrophobicity and water adhesion by a soft template surfactant-free electropolymerization in organic solvent. Various highly conjugated carbazole-based molecules are used as monomer. The presence of water in the organic solvent enables the formation of porous and rough nanostructures. Their shapes depend essentially on the nature of the monomer and the way it polymerizes. Various morphologies were obtained from nanoparticles network to horizontally or vertically aligned nanotubes. The nanostructured surfaces reach superhydrophobic properties and their dynamical behavior varies with the monomer from sticky to slippery. For example, using 9,3′:6′,9″-tercarbazole (TC) very long nanotubes are observed but their number is higher at constant potential. At high deposition charge, it is observed that most of the tubes are even collapsed leading to a strong increase of surface hydrophobicity with apparent contact angle up to 143° with strong water adhesion comparable to rose petals or gecko foot.

Controllable superhydrophobic surfaces with tunable adhesion on Mg alloys by a simple etching method and its corrosion inhibition performance

Through a simple chemical etching and surface modification, superhydrophobic surfaces with tunable water adhesion were prepared on rolled Mg-3Al-1Zn (AZ31) and Mg-9Al-1Zn (AZ91) alloy sheets. The different water adhesion is described by three different wetting model, i.e. Wenzel, Cassie impregnating, and Cassie model. An in-depth investigation on anti-corrosion performances of low adhesive superhydrophobic AZ31 and AZ91 surfaces reveals that dense microstructure can effectively improve the stability of Cassie state, thus facilitating durable anti-corrosion ability. Simultaneously, the superhydrophobic surfaces with tunable water adhesion are demonstrated to be feasible in the application of low-loss transport of microdroplet. In addition, the as-fabricated superhydrophobic surfaces show high-temperature stability and chemical stability in a large range of temperature and pH, respectively. It is expected that this research can shed light on designing new anti-corrosion and tunable adhesive superhydrophobic surfaces, and as-fabricated superhydrophobic Mg alloys are promising in medical instruments, transport systems, micro-fluidic devices, and so on.

Single-step plasma-induced hierarchical structures for tunable water adhesion

Smart surfaces in nature have been extensively studied to identify their hierarchical structures in micro-/nanoscale to elucidate their superhydrophobicity with varying water adhesion. However, mimicking hybrid features in multiscale requires complex, multi-step processes. Here, we proposed a one-step process for the fabrication of hierarchical structures composed in micro-/nanoscales for superhydrophobic surfaces with tunable water adhesion. Hierarchical patterns were fabricated using a plasma-based selective etching process assisted by a dual scale etching mask. As the metallic mesh is placed above the substrate, it serves the role of dual scale etching masks on the substrate: microscale masks to form the micro-wall network and nanoscale masks to form high-aspect-ratio nanostructures. The micro-walls and nanostructures can be selectively hybridized by adjusting the gap distance between the mesh and the target surface: single nanostructures on a large area for a larger gap distance and hybrid/hierarchical structures with nanostructures nested on micro-walls for a shorter gap distance. The hierarchically nanostructured surface shows superhydrophobicity with low water adhesion, while the hybrid structured surface becomes become superhydrophobic with high adhesion. These water adhesion tunable surfaces were explored for water transport and evaporation. Additionally, we demonstrated a robust superhydrophobic surface with anti-reflectance over a large area.

Pillararene-based supramolecular membranes with the rose-petal effect and nanostructure-modulated tunable water adhesion

Pillararene-based supramolecular membranes with the rose-petal effect and nanostructure-modulated tunable water adhesion was fabricated via integrating electrospraying with the breath figure approach.

Shape memory superhydrophobic surface with switchable transition between “Lotus Effect” to “Rose Petal Effect”

Superhydrophobic surface with tunable water adhesion has attracted great interests due to its unique performances in manipulating the status of water stay and roll-off. Herein, inspired by two typical superhydrophobic models of rose petal and lotus leaves, a superhydrophobic surface that can reversibly transform between the Cassie-Baxter state and the Cassie impregnating state has been developed by regulating the shape memory polymer SMP micro/nanostructures. The superhydrophobic surface with intact micro/nanostructure arrays exhibits excellent self-cleaning properties with extraordinary low water adhesive force, whereas the superhydrophobic surface with compressed microstructure arrays demonstrates high water adhesion. In response to the heating triggered deforming-restoring action, the switchable superwetting transition between those two models can be easily realized by their transformed morphologies. Due to the good shape memory effect of the polymer, the structured SMP assay surfaces can display a multiply switchable transition between the “lotus-effect” and the “rose-petal effect”, revealing a great potential for rewritable liquid patterns, controlled droplet transportation.

Dynamic Wetting Properties of Mesh Substrates with Tunable Water Adhesion

AbstractThe front cover artwork is provided by the NICE Lab and InPhyNi from University Côte d′Azur (France). The image shows how to better characterize complex surfaces such as mesh substrates with tunable water adhesion using a catapult‐like process. Read the full text of the Article at 10.1002/cphc.201900443.

Temperature-based adhesion tuning and superwettability switching on superhydrophobic aluminum surface for droplet manipulations

Superhydrophobic surfaces with tunable water adhesion and adjustable wettability have the capacity to manipulate water droplets under complicated conditions and, therefore, have great prospects in various domains. Hence, developing a facile method to prepare highly stable superhydrophobic surfaces with tunable water adhesion and adjustable wettability is of great importance. Herein, we prepare the superhydrophobic aluminum surface by combining laser etching and stearic acid modification. The variations of water contact angle, water sliding angle and water adhesive force with temperature of the prepared surface are characterized during the adhesion tuning process to investigate its temperature-responsive characteristics. A low/high adhesion switching of water on the prepared surface is subsequently achieved under alternating temperature. In addition, a facile approach is designed to achieve the superwettability switching process (from superhydrophobic state to superhydrophilic state) on the prepared surface. The prepared superhydrophobic surface displays excellent recoverability, stability and repeatability in the adhesion switching process and the superwettability switching process, even after being cycled for 10 times.

Dynamic Wetting Properties of Mesh Substrates with Tunable Water Adhesion.

In nature, wetting phenomena are present nearly everywhere and are a source of inspiration for liquid transportation. A good understanding of the underlying dynamic phenomena that governs wettability is therefore extremely important for researchers involved in bio-inspired surfaces. Herein, we study the adhesive behavior with water of mesh substrates modified with structured copolymers in order to tune the surfaces from parahydrophobic states (high water adhesion) to superhydrophobic states (low water adhesion). Using the ejection test method (ETM), a new technique that consists of the ejection of water droplets deposited onto a substrate with the aid of a catapult system, we experimentally demonstrate that the elasticity of the mesh substrate can be exploited for efficient vertical actuation of droplets.

Superhydrophobic polytetrafluoroethylene surfaces with accurately and continuously tunable water adhesion fabricated by picosecond laser direct ablation

Superhydrophobic polytetrafluoroethylene (PTFE) surfaces with accurately and continuously tunable water adhesion were fabricated by a simple and rapid method of picosecond (ps) laser direct ablation. By simply changing laser scan intervals (LSIs) from 5 to 140 μm, three laser-ablated PTFE surfaces, i.e., the two superhydrophobic surfaces with ultralow water adhesion and with tunable water adhesion, and the ordinary hydrophobic surface with ultrahigh water adhesion, could be obtained. Here, the sliding angles of water droplets on these surfaces could be continuously varied from about 1° to about 90°. XPS analysis suggested that the continuous variations of water adhesion and wettability were probably attributed to the change of surface microstructure and not to that of chemical composition. SEM analysis showed that different LSIs resulted in different surface microstructures and different area ratios of the laser-ablated regions to the pristine regions. This was because of the composite ablation process of photothermal and photochemical effects of the special ps laser wavelength (355 nm) and pulse duration (about 10 ps). The tunable water adhesion was verified by the coalescence-induced droplets jumping behavior. This study will provide a novel and versatile method for the rapid fabrication of superhydrophobic material surfaces with accurately and continuously tunable adhesion.

Facile preparation of diverse alumina surface structures by anodization and superhydrophobic surfaces with tunable water droplet adhesion

Hierarchical alumina superhydrophobic surfaces with a series of different morphologies were obtained by anodization method, and then modified with stearic acid (STA). The effects of anodization parameters including time and voltage on surface morphology and the wettability of surface were investigated in detail. The diverse alumina surface architectures including nanoporous, nanowire clusters and nanorods were obtained by the anodization parameter modulation via a self-assembly process. The results demonstrated that these structures were able to achieve to superhydrophobic. More interestingly, the superhydrophobic alumina surfaces shown a high contrast water droplet adhesion, which conferred with a higher water contact angle of ∼156° and a sliding angle as low as ∼2.1° as well as a strongly sticky water adhesion. However, this paper provides a simple and effective approach to fabricate the superhydrophobic surfaces with tunable water adhesion, which has an important for designing advanced functional materials for application.

Bioinspired silica-containing polyurethane-acrylate films: Towards superhydrophobicity with tunable water adhesion

In this paper, a convenient, straightforward, and large-scale transferable approach for the preparation of fluorine-free bioinspired superhydrophobic silica-filled photo-crosslinked polyurethane-acrylate (PUA) nanocomposite films is reported. The enrichment of the hydrophobic fumed silica at the film surface and especially its inherent dual scale dimension, related to its synthesis, enables to endow the film with super water-repellent features. Particularly, the effect of the silica content from 0 to 60 wt% is studied and the wettability properties of the resulting nanocomposite films are investigated in link with the chemical composition and the surface morphology at different scales. It is shown that different wetting states can be achieved from Wenzel to Cassie impregnating and then Cassie-Baxter regime, dictated by the silica content present at the air surface. Thus, by simply varying the silica content, the water adhesion can be adjusted from very high for a silica content equal to 50 wt% to extremely low for a silica content equal to 60 wt%, imparting the film with “Lotus” or “rose petal” effect, respectively. The as-prepared slippery or sticky nanocomposite films are shown to exhibit long-lasting wettability performances.

Multiple Liquid Manipulations on Patterned Surfaces with Tunable Adhesive Property

AbstractMicro/nanostructured surfaces with designable wettability show great promise in many fields. This paper reports a new strategy for fabricating superhydrophobic surfaces with tunable water adhesion force by combining multiscale surface structures and mussel‐inspired surface chemistry, which can be used for multiple liquid manipulations. Highly ordered porous films prepared by the breath figure method enable convenient construction of surfaces with honeycomb‐patterned or nanosized pincushion‐like structures. Multiple liquid manipulations including no‐loss transportation of water droplets, water collection, programmable movement of water droplets, and chemical reaction monitoring are demonstrated on the micro/nanostructured surfaces. The proposed method is facile, energy‐efficient, and can be conducted for the preparation of superhydrophobic surfaces with high contrast adhesion patterns.

Tunable rose petal effect of cobalt coated zinc surfaces via a facile electroless galvanic deposition process

The rose petal effect (large apparent contact angles accompanied by high affinity to water) has greatly inspired researchers recently. In this paper, the rose-petal surfaces with tunable high water adhesion have been prepared successfully via a facile electroless galvanic deposition process as well as the subsequent modification with stearic acid on zinc substrates. We have regulated the concentration of CoSO4 solution in the process of electroless galvanic deposition to control the surface topography. After being modified with stearic acid, the as-prepared cobalt coated films showed similar apparent contact angles larger than 150° but contrast high water adhesion. To the best of our knowledge, the fabrication of rose petal surfaces with tunable water adhesion is still scarce. The largest water droplet volumes suspended on the tunable rose petal surfaces were 8, 24 and 28 μL, respectively. In addition, based on the different water adhesion on the rose petal surfaces, the selective transportation of microdroplets with different volumes has been demonstrated. We believe that these tunable adhesive rose petal surfaces would have great potential in the droplet-based microreactors.