Strong Water Adhesion Research Articles

Superhydrophilic Densely‐Packed Gecko‐Like Structures by Soft‐Template Electropolymerization

AbstractBio‐inspired by natural species and previous research works, nanotubes are prepared by soft‐template electropolymerization in micellar solution. Various thiophene‐based and carbazole‐based monomers are designed from a triphenylamine core. With one of the carbazole‐based monomers, which is fully conjugated and with a star‐like structure, gecko‐like surface structures are obtained even if the structure is not perfectly planar. Extremely long and densely packed‐microtubes are reached especially at constant potential. However, the surfaces are not both highly hydrophobic and with strong water adhesion, but are superhydrophilic. These wetting properties can be explained by a high surface energy (γSV)=41.9 mN m−1 compared to gecko foot even if the natural gecko feet are also chemically inhomogeneous, or by differences in the arrangement of the surface structures.

Surfaces displaying high hydrophobicity and strong water adhesion by soft-template electropolymerization using di-substituted benzenes as model

Surfaces displaying high hydrophobicity and strong water adhesion by soft-template electropolymerization using di-substituted benzenes as model

Construction of superhydrophobic surfaces with different water adhesion on the low-temperature steels by picosecond laser processing

Manufacturing superhydrophobic metallic surfaces with desired water adhesion for intended applications such as anti-icing and microdroplets transportation remains a grand challenge. Herein, we demonstrated the fabrication of the superhydrophobic surfaces with different water adhesion on the low-temperature steels including DH36, EH40 and FH36 steels via combined strategies of picosecond laser processing and room-temperature vacuum processing. The laser processing could regulate the dimension of the micro/nanostructures on the low-temperature steel surfaces and the vacuum processing controlled the surface chemical compositions of the laser-processed surfaces, leading to the transition of wetting behaviors from the superhydrophilic states, then to the superhydrophobic Wenzel's states with strong water adhesion and finally to the superhydrophobic Cassie-Baxter's states with weak water adhesion. The superhydrophobic surfaces with the Wenzel's states showed great potential in non-destructive and selective transportation of water droplets, while those with the Cassie-Baxter's states exhibited promising anti-icing performance as well as desirable corrosion, impact, and erosion resistance. This work provides an effective, pollution-free, and stable route for controlling the superwettability of the low-temperature steel surfaces and could find promising applications in surface modifications of metals and alloys.

Directional formation of microtubes by soft-template electropolymerization from fully conjugated triphenylamine-based monomers

Microtubular structures have been prepared by soft-template electropolymerization of conjugated organic monomers with the aim to mimic the strong water-adhesive forces of gecko foot or rose petals. Water-saturated solvent of low water solubility (dichloromethane) was used to form a micellar solution stabilized by tetrabutylammonium perchlorate as the electrolyte and the surfactant, in which case the formation of nanotubes was particularly efficient. The studied monomers were built from a triphenylamine core conjugated with three arms differing by their structure and positions: (i) 2- or 3-positions in the thiophene arms or (ii) carbazole arms attached to para, meta or ortho-positions of the benzene ring of the core. The formation of microtubes is due to preferential growth of polymer films and an aggregation of formed polymers/oligolymers in one direction (1D) facilitated by π–stacking interactions. The key factors influencing on the surface morphologies (monomer structures and reactivity, electrodeposition conditions, etc) are discussed. Impressive results have been obtained in studies of carbazole-containing monomers and the effect of regioisomerism in the monomers (the position of the carbazole attachment to the core). Extremely long microtubes (tens to >100 μm length, diameter ≈ 1.0–1.5 μm) were formed on the electrode surface from the monomer N-Ph-p-Cb with the carbazole attachment in the para-position. Wettability analysis showed highly hydrophobic surfaces with apparent contact angles up to 154.0° and extremely strong water adhesion comparable to rose petals or gecko feet. Such coatings can find applications in water-harvesting systems, sensing platforms or electrochemical analyses.

Unveiling facet-dependent degradation and facet engineering for stable perovskite solar cells.

A myriad of studies and strategies have already been devoted to improving the stability of perovskite films; however, the role of the different perovskite crystal facets in stability is still unknown. Here, we reveal the underlying mechanisms of facet-dependent degradation of formamidinium lead iodide (FAPbI3) films. We show that the (100) facet is substantially more vulnerable to moisture-induced degradation than the (111) facet. With combined experimental and theoretical studies, the degradation mechanisms are revealed; a strong water adhesion following an elongated lead-iodine (Pb-I) bond distance is observed, which leads to a δ-phase transition on the (100) facet. Through engineering, a higher surface fraction of the (111) facet can be achieved, and the (111)-dominated crystalline FAPbI3 films show exceptional stability against moisture. Our findings elucidate unknown facet-dependent degradation mechanisms and kinetics.

Directional growth of nanotubes on micelles by soft-template electropolymerization with varying hydrophobicity and strong water adhesion

Inspired by the strong water adhesion found in gecko feet and rose petals, surfaces with nanotubes are prepared by soft-template electropolymerization.

Advance of the Biocompatible Hydrogels in Medical Applications

Hydrogels are widely used because of their strong water absorption, adhesion and biocompatibility. This article briefly analyzes the application of hydrogel dressing, type I collagen hydrogel and hydrogel in oral and bone tissues, and puts forward the existing problems, the future development trend and the prospect of its development.

Laser-Induced Fast Assembly of Wettability-Finely-Tunable Superhydrophobic Surfaces for Lossless Droplet Transfer.

Rose-petal-like superhydrophobic surfaces with strong water adhesion are promising for microdroplet manipulation and lossless droplet transfer. Assembly of self-grown micropillars on shape-memory polymer sheets with their surface adhesion finely tunable was enabled using a picosecond laser microprocessing system in a simple, fast, and large-scale manner. The processing speed of the wettability-finely-tunable superhydrophobic surfaces is up to 0.5 cm2/min, around 50-100 times faster than the conventional lithography methods. By adjusting the micropillar height, diameter, and bending angle, as well as superhydrophobic chemical treatment, the contact angle and adhesive force of water droplets on the micropillar-textured surfaces can be tuned from 117.1° up to 165° and 15.4 up to 200.6 μN, respectively. Theoretical analysis suggests a well-defined wetting-state transition with respect to the micropillar size and provides a clear guideline for microstructure design for achieving a stabilized superhydrophobic region. Droplet handling devices, including liquid handling tweezers and gloves, were fabricated from the micropillar-textured surfaces, and lossless liquid transfer of various liquids among various surfaces was demonstrated using these devices. The superhydrophobic surfaces serve as a microreactor platform to perform and reveal the chemical reaction process under a space-constrained condition. The superhydrophobic surfaces with self-assembled micropillars promise great potential in the fields of lossless droplet transfer, biomedical detection, chemical engineering, and microfluidics.

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.

Tunable Nanoporous Structures with Rose Petal Effect by Soft‐Template Electropolymerization of Benzotrithiophene Monomers

AbstractHere, various original benzotrithiophene‐based monomers are synthesized and studied for their capacity to form nanoporous structures by soft‐template electropolymerization in organic solvent while studying the influence of water (H2O). Here, nanoporous structures are especially observed in solvent saturated with H2O, while the substituent has in influence especially on the size of the porous structures. The highest hydrophobic properties Θw=141.1° are obtained with perfluorooctyl chains (BTT‐F8), which leads to a huge number of nanoporous structures of extremely small size. Moreover, the surfaces have also strong water adhesion comparable to rose petals or gecko foot and could be used in future applications in water harvesting systems.

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.

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.

Biocompatible Catechol‐Functionalized Cellulose‐Based Adhesives with Strong Water Resistance

AbstractNumerous traditional adhesives have good adhesion in dry environments. However, non‐environmental‐friendliness and poor water resistance largely limit their practical applications. To prepare biocompatible adhesives with strong water resistance and adhesion strength, in this paper, catechol‐functionalized cellulose‐based adhesive polymers are synthesized by grafting N‐(3,4‐dihydroxyphenethyl)methacrylamide and methyl methacrylate onto cellulose chain through atom transfer radical polymerization (ATRP). The successful synthesis of the catechol‐functionalized cellulose‐based adhesive polymers is confirmed by FTIR and 1H NMR. The different characteristics of the adhesive polymers, such as thermal stability, swelling ratio, biocompatibility, and adhesion strength are investigated. Strong water resistance on various substrates is realized in underwater environment for the catechol‐functionalized cellulose‐based adhesive with addition of Fe3+. The adhesion strength and thermal stability are enhanced when the catechol content is increased. The adhesive with catechol content of 25.4% shows the adhesion strength of 0.45 MPa for iron substrate in underwater environment. In addition, the adhesive with addition of Fe3+ exhibits excellent adhesion in dry environment, with maximum adhesion strength of 3.50 MPa for iron substrate. The cell culture test shows that the adhesive polymers have excellent biocompatibility. The biocompatible adhesives with strong water resistance have potential application in electronic, wood, and building fields.

Controlling water adhesion on superhydrophobic surfaces with bi-functional polymers

With an aim to control the surface hydrophobicity and water adhesion, as observed on various natural surfaces, novel 3,4-propylenedioxythiophene (ProDOT) monomers having one and two 3-trimethylsilylpropyl (TMS) groups were synthesized and subjected to electropolymerization to form surface coatings. The monomer ProDOT is employed owing to its tendency to form fibrous structures by electropolymerization [T. Darmanin, F. Guittard, Mater. Chem. Phys. 146 (2014) 6–11], whereas the TMS groups generate very low surface energies comparable to short chain fluorocarbons [N. M. Kovalchuk, et al., Colloids Surfaces A 604 (2020) 125277.]. It is shown that even though these two types of monomer lead to fibrous structures, the dimensions of the fibers as well as the wetting properties are different. The monomer with only a single TMS group (ProDOTSiMe3) generates extremely long nanofibers with only low surface roughness. The resulting surfaces have extremely high apparent contact angles (θw) up to 141.7° and strong water adhesion, similar to rose petals or gecko feet. On the other hand, the analogue with two TMS groups (ProDOT(SiMe3)2) forms short nanofibers but with extremely high surface roughness. The resulting surfaces are superhydrophobic with θw > 160° and ultra-low water adhesion (hysteresis and sliding angles < 1°), similar to lotus leaves. These results point to interesting applications offering control over water adhesion whilst maintaining high hydrophobicity.

Bioinspired surfaces with strong water adhesion from electrodeposited poly(thieno[3,4-b]thiophene) with various branched alkyl chains

In this original work, we wanted to prepare surfaces with both high hydrophobicity and strong water adhesion, as observed on rose petals or gecko foot. The surfaces are prepared by electropolymerization and using thieno[3,4-b]thiophene monomers with various branched alkyl chains. Here, branched alkyl chains are used to their lower hydrophobic properties compared to linear alkyl chains and fluorinated chains. It is observed a change from structured to smooth when the branched alkyl chain length increases. Using short branched alkyl chains, the surfaces are mainly composed of wrinkles and nanoparticles displaying high hydrophobicity ( $${\theta }_{\mathrm{w}}$$ up to 134.9°) combined with strong water adhesion, as observed on rose petals even if $${\theta }_{\mathrm{w}}$$ is less important. Dynamic contact angle measurements show that their water adhesion is extremely strong and water droplets remain stuck on them. By adding H2O in the solvent (CH2Cl2 + H2O), it is possible to release gas bubbles (H2 and/or O2) in-situ leading to more porous surfaces but here it is observed an increase of surface hydrophilicity. These original polymer surfaces have potential applications in water harvesting systems or oil/water separation membranes, for example.

Cellulose-Based Superhydrophobic Surface Decorated with Functional Groups Showing Distinct Wetting Abilities to Manipulate Water Harvesting.

Inspired by the distinct functions of desert beetles with efficient droplet nucleation and lotus leaves with excellent droplet removal, an integrated method is presented for the design of a superhydrophobic surface decorated with hydrophilic groups that can efficiently nucleate and remove water droplets. We constructed a cellulose-based superhydrophobic surface containing numerous olefin terminal groups by solvent exchange and spray coating. This surface is different from most of the reported biomimicking water harvesting surfaces that rely on complicated lithography and micropatterning techniques requiring special instruments. The obtained superhydrophobic surface was further modified using various thiol compounds via a thiol-ene reaction to manipulate the water harvesting property. The modified surfaces containing hydrophobic groups (e.g., 1-octadecanethiol and 1H,1H,2H,2H-perfluorodecanethiol) or a strong hydrophilic group (e.g., 3-mercaptopropionic acid and 6-mercapto-1-hexanol) exhibited insufficient fog collecting abilities due to poor water droplet nucleation or strong water adhesion. By contrast, the modified surface decorated with moderately hydrophilic amino groups combines the advantages of biological surfaces with distinct wetting features (such as fog-harvesting beetles and water-repellent lotus leaves), resulting in accelerated water nucleation and less compromise of the water removal efficiency. Molecular dynamic simulations revealed that the efficient droplet nucleation is attributed to the hydrophilic amino groups whereas the rapid droplet removal is due to the maintained superhydrophobicity of the amino group-modified surface. This strategy of decorating a superhydrophobic surface with moderately hydrophilic functional groups provides insight into the manipulation of droplet nucleation and removal for water collection efficiency.

Bioinspired surfaces with strong water adhesion by electropolymerization of thieno[3,4-b]thiophene with mixed hydrocarbon/short fluorocarbon chains

Here, in the aim to replace long perfluorinated chains (C8F17) in polymer we use both a short C4F9 perfluorinated chain and a hydrocarbon chain a various length (from C2 to C12). These chains are grafted to thieno[3,4-b]thiophene monomers to perform electrodeposited conducting polymer films with high hydrophobic properties. Two solvents are used: dichloromethane (CH2Cl2) and dichloromethane saturated with water (CH2Cl2 + H2O) in order to release also in-situ O2 and/ or H2 gas bubbles. In CH2Cl2, spherical particles covering the surface are observed with short alkyl chains and large wrinkles with long alkyl chains. The highest hydrophobicity θw = 139.3° are obtained with Thieno-F4-C6 after 5 deposition scans, which presents also strong water adhesion. In CH2Cl2 + H2O, the surfaces are smoother and traces of very large bubbles are present but only with short alkyl chains. However, the polymer growth is inhomogeneous because the substituents are too flexible to stabilize the released gas bubbles. The preliminary results are encouraging and more rigid substituents or spacers could be envisaged in the future to induce homogenous porous structures.

A bioinspired strategy for poly(3,4-ethylenedioxypyrrole) films with strong water adhesion

Abstract Using a bioinspired approach, we prepare poly(3,4-ethylenedioxypyrrole) (PEDOP) films with parahydrophobic properties, characterized by high apparent water contact angle and strong water adhesion. The films are made by electropolymerization and the influence of substitution by an alkyl chain of various length (from C4H9 to C14H29) on the 3,4-ethylenedioxy-bridge is reported. More precisely, the best properties are obtained from a length of C12H25 due to the formation of spherical nanoparticles.

Variations in surface structures and wettability in the genus Pachnoda Burmeister

In order to grow and live, all species need access to water and often the ability to control their intake thereof. Among species throughout the world, several animals and plants are known for unique surface patterns and features that influence their wettability in such a way that water is always readily accessible, even in arid and hot climates. In this work, the authors report a journey into the genus Pachnoda, studying 12 species or subspecies to compare their surface properties and wettabilities. This work reveals exceptional natural surface morphologies based on a honeycomb structure with significant variations depending on the Pachnoda genus. Even if the materials present on their surface are intrinsically hydrophilic, some of the species have parahydrophobic properties with apparent contact angles of up to 145° and extremely strong water adhesion. Only the Cassie–Baxter equation can explain these results indicating the presence of trapped air within these surface structures when a liquid, such as water, makes contact. Among the species explored here, water hydrophobicity and adhesion are controlled by the dimensions of the honeycombs, the presence of lamellar structures on the border of these features and the presence of roughness in their internal structures.

Bioinspired superhydrophobic–superhydrophilic convertible film based on anisotropic red blood cell-like particles with protuberances

A novel morphology structure of red blood cell-like (RBC) particles with protuberances (P-RBC) was prepared through dispersion polymerization process. Based on these particles, a superhydrophobic coating film with strong water adhesion and a superhydrophilic film was fabricated depending on orientation of particles during self-assembly progress. The superhydrophobic coating film with water contact angle (CA) of 163.6° was fabricated when the direction of particle cavity was facing-down. Strong water adhesion was resulted from the larger micro-nano structure of particles. Waterdrop tightly attached to the surface of the coating film even if it was taken upside down. Whilst if the cavity of particles was upward, the coating film was transferred to be superhydrophilic of CA of 3.8° under co-efforts of storage ability of cavities, penetration capacity of channel formed by well-ordered particles, and increased surface roughness. This work gives that anisotropy colloidal particles have potential application with their superior wetting characteristics in many fields, such as material transfer process, waterproof protection and oil-water separation.