'Rewritable' and 'liquid-specific' recognizable wettability pattern.

Bio-inspired surfaces with wettability patterns display a unique ability for liquid manipulations. Sacrificing anti-wetting property for confining liquids irrespective of their surface tension (γLV), remains a widely accepted basis for developing wettability patterns. In contrast, we introduce a 'liquid-specific' wettability pattern through selectively sacrificing the slippery property against only low γLV (<30 mN m-1) liquids. This design includes a chemically reactive crystalline network of phase-transitioning polymer, which displays an effortless sliding of both low and high γLV liquids. Upon its strategic chemical modification, droplets of low γLV liquids fail to slide, rather spill arbitrarily on the tilted interface. In contrast, droplets of high γLV liquids continue to slide on the same modified interface. Interestingly, the phase-transition driven rearrangement of crystalline network allows to revert the slippery property against low γLV liquids. Here, we report a 'rewritable' and 'liquid-specific' wettability pattern for high throughput screening, separating, and remoulding non-aqueous liquids.

Covalent crosslinking chemistry for controlled modulation of nanometric roughness and surface free energy.

Smooth interfaces embedded with low surface free energy allow effortless sliding of beaded droplets of selected liquids-with homogeneous wettability. Such slippery interfaces display low or moderate contact angles, unlike other extremely liquid repellent interfaces (e.g. superhydrophobic). These slippery interfaces emerged as a promising alternative to extremely liquid repellent hierarchically rough interfaces that generally suffer from instability under severe conditions, scattering of visible light because of the hierarchically rough interface, entrapment of fine solid particulates in their micro-grooves and so on. However, a controlled and precise modulation of surface free energy and nanometric roughness is essential for designing a more compelling solid and dry antifouling interface. Here, we have unprecedentedly demonstrated the ability of covalent cross-linking chemistry for precise and simultaneous modulation of both essential surface free energy (∼49 mN m-1 to ∼22 mN m-1) and roughness (root mean square roughness from 30 nm to 3 nm) of a solid interface for achieving liquid, substrate, and process independent, robust slippery properties. The strategic selection of ß-amino-ester linkage through a 1,4-conjugated addition reaction between amine and acrylate groups of a three component reaction mixture (dominated by a 61% (w/w) crosslinker) under ambient conditions provided a facile basis for associating various important and relevant properties-including self-cleaning ability, anti-smudge properties (against both water and oil-based inks), thermal stability (>300 °C), chemical stability, physical durability, optical transparency (∼95%) and so on. The embedded slippery properties of the coating remained unaffected at both low (0 °C) and high (100 °C) temperatures. Thus, the prepared coating would be appropriate to maintain the unperturbed performance of commercially available solar cell modules and other relevant objects under outdoor conditions.

Polymerization of monomer aggregates for tailoring and patterning water wettability.

An approach of 'polymerization of monomers in its aggregated form' is unprecedentedly introduced to (i) tailor the water wettability of fibrous and porous substrates from hydrophobicity to superhydrophobicity, and (ii) associate patterned wettability. A solution of selected monomers-i.e., alkyl acrylate in a good solvent (indicating high solubility; ethanol) was transferred into a bad solvent (refers to poor solubility; water) to achieve a stable dispersion of monomer aggregates of size <1 µm for deposition on fibrous and porous substrates. Its photopolymerization provided a durable coating with the ability to tailor the water wettability from 134° to 153°. Furthermore, a spatially selective photopolymerization process yielded a patterned interface of superhydrophilicity and superhydrophobicity. Such a facile chemical approach with the ability to provide a durable coating embedded with tailored and patterned wettability would be useful for various potential applications.

Design of a self-cleanable multilevel anticounterfeiting interface through covalent chemical modulation.

Counterfeit products have posed a significant threat to consumers safety and the global economy. To address this issue, extensive studies have been exploring the use of coatings with unclonable, microscale features for authentication purposes. However, the ease of readout, and the stability of these features against water, deposited dust, and wear, which are required for practical use, remain challenging. Here we report a novel class of chemically functionalizable coatings with a combination of a physically unclonable porous topography and distinct physiochemical properties (e.g., fluorescence, water wettability, and water adhesion) obtained through orthogonal chemical modifications (i.e., 1,4-conjugate addition reaction and Schiff-base reaction at ambient conditions). Unprecedentedly, a self-cleanable and physically unclonable coating is introduced to develop a multilevel anticounterfeiting interface. We demonstrate that the authentication of the fluorescent porous topography can be verified using deep learning. More importantly, the spatially selective chemical modifications can be read with the naked eye via underwater exposure and UV light illumination. Overall, the results reported in this work provide a facile basis for designing functional surfaces capable of independent and multilevel decryption of authenticity.

Reactive Multilayer Coating As Versatile Nanoarchitectonics for Customizing Various Bioinspired Liquid Wettabilities.

In last few decades, multilayer coatings have achieved enormous attention owing to their unique ability to tune thickness, topography, and chemical composition for developing various functional materials. Such multilayer coatings were mostly and conventionally derived by following a simple layer-by-layer (LbL) deposition process through the strategic use of electrostatic interactions, hydrogen bonding, host-guest interactions, covalent bonding, etc. In the conventional design of multilayer coatings, the chemical composition and morphology of coatings are modulated during the process of multilayer constructions. In such an approach, the postmodulations of the porous multilayers with different and desired chemistries are challenging to achieve due to the lack of availability of readily and selectively reactive moieties. Recently, the design of readily and selectively reactive multilayer coatings (RMLCs) provided a facile basis for postmodulating the prepared coating with various desired chemistries. In fact, by taking advantage of the inherent ability of co-optimizing the topography and various chemistries in porous RMLCs, different durable bioinspired liquid wettabilities (i.e., superhydrophobicity, underwater superoleophobicity, underwater superoleophilicity, slippery property, etc.) were successfully derived. Such interfaces have enormous potential in various prospective applications. In this review, we intend to give an overview of the evolution of LbL multilayer coatings and their synthetic strategies and discuss the key advantages of porous RMLCs in terms of achieving and controlling wettability properties. Recent attempts toward various applications of such multilayer coatings that are strategically embedded with different desired liquid wettabilities will be emphasized.

Role of chemistry in bio-inspired liquid wettability.

Chemistry and topography are the two distinct available tools for customizing different bio-inspired liquid wettability including superhydrophobicity, superamphiphobicity, underwater superoleophobicity, underwater superoleophilicity, and liquid infused slippery property. In nature, various living species possessing super and special liquid wettability inherently comprises of distinctly patterned surface topography decorated with low/high surface energy. Inspired from the topographically diverse natural species, the variation in surface topography has been the dominant approach for constructing bio-inspired antiwetting interfaces. However, recently, the modulation of chemistry has emerged as a facile route for the controlled tailoring of a wide range of bio-inspired liquid wettability. This review article aims to summarize the various reports published over the years that has elaborated the distinctive importance of both chemistry and topography in imparting and modulating various bio-inspired wettability. Moreover, this article outlines some obvious advantages of chemical modulation approach over topographical variation. For example, the strategic use of the chemical approach has allowed the facile, simultaneous, and independent tailoring of both liquid wettability and other relevant physical properties. We have also discussed the design of different antiwetting patterned and stimuli-responsive interfaces following the strategic and precise alteration of chemistry for various prospective applications.

Designing a Network of Crystalline Polymers for a Scalable, Nonfluorinated, Healable and Amphiphobic Solid Slippery Interface.

The fluorinated-liquid infused amphiphobic slippery interfaces exhibiting superior sliding of the beaded oil/water droplets, often suffer from durability and contamination issues. Here, the ability of 1) hexagonal packing of hydrocarbon sides in a selected "comb-like" polymer and 2) its reversible phase transition at 51 °C was rationally exploited to achieve temperature-assisted rapid (<1 minute) and repetitive (50 times) self-healable amphiphobic solid-slippery coating on both planar and geometrically-complex substrates. The selected "comb-like" polymer was strategically infused in a porous, hydrophilic and thick (≈4.8 µm) polymeric coating. The resultant solid and smooth interface exhibited sliding of beaded droplets of various liquids, including droplets of water, polar (ethanol, 1-propanol, 1-hexanol, DMSO, DMF), and non-polar (decane, dodecane, diiodomethane) organic solvents, edible (vegetable oil), motor, engine (petrol, diesel, kerosene) and crude oils.

Design of 'tolerant and hard' superhydrophobic coatings to freeze physical deformation.

While the development of mechanically durable and abrasion tolerant superhydrophobicity on a rigid substrates itself remains a highly challenging task, the design of superhydrophobic coatings that can restrict both the tensile and compressive deformations of soft and deformable substrates is unprecedented-and such an approach would be of potential interest in various applied and fundamental contexts. In this communication, a reaction mixture was developed following a simple 1,4-conjugate addition reaction between selected small molecules and appropriate crosslinkers for achieving 'tolerant and hard' superhydrophobicity-which is not just capable of surviving under severe conditions-but also restricts both the tensile and compressive deformations of the selected soft substrates. The compressive and tensile moduli of the selected soft substrates increased by 2.2 × 104% and 1.8 × 104%, respectively, after the deposition of the appropriate reaction mixtures. Moreover, the integration of the crosslinkers in the reaction mixture provided a facile basis to resist the physical erosion/rupture of the selected soft substrates under severe abrasive conditions. Thus, a simple and elegant chemical approach not only controlled the mechanical properties of the porous and fibrous soft substrates under ambient conditions-but also provided highly tolerant superhydrophobicity-which likely leads to various outdoor applications.

Rapid and Scalable Synthesis of a Vanillin-Based Organogelator and Its Durable Composite for a Comprehensive Remediation of Crude-Oil Spillages.

Phase-selective organogelators (PSOGs) that have immense potential in effective oil/water separation, antifouling coating, ice-repellent coating, and so on are often synthesized by following complex and multistep synthesis procedures that involve additional and tedious purification steps. On the other side, a comprehensive, selective, environmentally friendly, and energy-efficient separation of different and complex forms of oil spillages (e.g., floating oil or oil-in-water emulsions) from contaminated aqueous phase is challenging to achieve based on earlier-reported PSOGs and their composites. Here, vanillin, a naturally abundant molecule, is unprecedentedly exploited to synthesize a purified PSOG (with a yield of 97%) by adopting a catalyst-free, single-step, and rapid (<2 min) synthesis process under ambient conditions. The Schiff's base reaction between the aldehyde group of vanillin and the primary amine group of octadecylamine provided the desired and purified PSOG-without demanding any additional purification processes (e.g., column chromatography). The appropriate coexistence of the imine linkage, hydrocarbon tail, and hydroxyl group in the vanillin-derived organogelator (VDOG) played an important role in achieving a self-standing organogel that sustained ∼60 times the external load of its weight-without having any noticeable physical deformation. Further, an appropriate and facile integration of the synthesized VDOG with a commercially available biodegradable porous and spongy matrix (i.e., polyurethane sponge) allowed us to develop an oil-selective absorbent with (1) enhanced water repellency (140°) and (2) superior oil-absorption capacity (i.e., 55.2 times its own weight). Such composite material remained durable for repetitive (at least for 50 cycles) and distillation-free separation/recovery of crude oil at practically relevant severe and diverse settings. Thereafter, the synthesized VDOG was successfully and unprecedentedly extended to demonstrate rapid, facile, and efficient separation of surfactant-stabilized oil-in-water emulsions.