Self-healable, Tolerant Superaerophobic Coating for Improving Electrochemical Hydrogen Production.

Gas-evolving electrodes often suffer from the blocking of catalytic active sites-due to unwanted and unavoidable adhesion of generated gas bubbles, which elevates the overpotential for the electrochemical hydrogen evolution reaction (HER)- by raising the resistance of the electrode. Here, a catalyst-free and self-healable superaerophobic coating having ultra-low bubble adhesion is introduced for achieving significantly depleted overpotentials of 209 and 506 mV at both low (50 mA cm-2) and high (500 mA cm-2) current densities, respectively, compared to a bare nickel-foam electrode. The optimized coating ensured an early detachment of the generated tiny (0.8 ± 0.1 mm) gas bubble-and thus, prevented the undesired rise in resistance of the coated electrode. The systematic association of physical (i.e., ionic interactions, H-bonding, etc.) cross-linkage, ß-amino ester type covalent cross-linkage and reinforced halloysite nano clay enables the design of such functional material embedded with essential characteristics-including improved mechanical (toughness of 63.7 kJ m-3, and tensile modulus of 26 kPa) property and chemical (extremes of pH (1 and 14), salinity, etc.) stability, rapid (<10 min) self-healing ability (even at alkaline condition) and desired bubble-wettability (bubble contact angle of 158.2 ± 0.2°) with ultralow force (4.2 ± 0.4 µN) of bubble adhesion.

Resonant coupling of molecular excitons and optical anapoles in silicon nanosphere-J-aggregate heterostructures under vector beam illumination.

Resonant excitation of high-index dielectric nanostructures and their coupling with molecular excitons provide great opportunities for engineering adaptable platforms for hybrid functional optical devices. Here, we numerically calculate resonance coupling of nonradiating anapole states to molecular excitons within silicon nanosphere-J-aggregate heterostructures under illumination with radially polarized cylindrical vector beams. The results show that the resonance coupling is accompanied by a scattering peak around the exciton transition frequency, and the anapole state splits into a pair of anticrossing eigenmodes with a mode splitting energy of ≈200m e V. We also investigate the resonance coupling as a function of the J-aggregate parameters, such as thickness, exciton transition linewidth, and oscillator strength. Resonant coupling of the anapole states and J-aggregate heterostructures could be a promising platform for future nanophotonic applications such as in information processing and sensing.

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.

Design of a Super-Liquid Crystal-Phobic Coating for Immobilizing Liquid Crystal µ-Droplets─Without Affecting Their Sensitivity.

The aqueous interface of nematic liquid crystal (LC) that undergoes a triggered change in ordering transition of mesogens under an appropriate stimulus has emerged as an important tool for various relevant applications. Further, the confinement of LC into a micrometer dimension appeared to be a facile approach for improving their relevant features and performance. However, the optical characterization of ordering transition in a single micrometer-sized, bare, and free-floating LC droplet in the aqueous phase is an extremely challenging task due to unavoidable Brownian motion, which limits its scope for practical applications. Here, we exploited the 1,4-conjugate addition reaction to report a multilayer coating of a reactive nanocomplex that displayed an extreme repellence to beaded LC droplets with tailored adhesive force through the association of adequate orthogonal chemical modifications with glucamine and selected alkyl acrylates. Further, a spatially selective underwater adhesive super-LC-phobic pattern on a hydrophobic background was developed for immobilizing bare and micrometer-sized LC droplets from their aqueous dispersion without having any arbitrary spillage of the aqueous medium. The settled micrometer-sized LC droplets remained efficient for the triggered change in ordering transition from bipolar (having boojum defects at poles) to radial (with a single defect in the center) configuration. Eventually, a simple and fundamentally distinct chemical strategy of immobilizing a soft and functional material by associating bio-inspired wettability allowed to demonstrate the repetitive triggered LC ordering transition in a single and bare LC droplet.

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.

Non-Fluorinated and Robust Superhydrophobic Modification on Covalent Organic Framework for Crude-Oil-in-Water Emulsion Separation.

Covalent organic frameworks (COFs) having high specific surface area, tunable pore size and high crystallinity are mostly post modified following fluorine-based and complex synthetic approaches to achieve a bio-inspired liquid wettability, i.e. superhydrophobicity. Herein, a facile, non-fluorinated and robust chemical approach is introduced for tailoring the water wettability of a new COF-which was prepared through Schiff-base condensation reaction. A silane precursor was readily reacted with selected alkyl acrylates through 1,4-conjugate addition reaction, prior to grafting on the prepared C4-COF for tailoring different water wettability-including robust superhydrophobicity. The superhydrophobic C4-COF (SH-C4-COF) that displayed significantly enhanced (>5 times; from 220 wt. % to 1156 wt. %) oil-absorption capacity, was extended to address the relevant challenges of "oil-in-water" emulsion separation, rapidly (<1 minute) and repetitively (50 times) at diverse and harsh conditions.

Excitation of Nonradiating Anapoles in Dielectric Nanospheres.

Although the study of nonradiating anapoles has long been part of fundamental physics, the dynamic anapole at optical frequencies was only recently experimentally demonstrated in a specialized silicon nanodisk structure. We report excitation of the electrodynamic anapole state in isotropic silicon nanospheres using radially polarized beam illumination. The superposition of equal and out-of-phase amplitudes of the Cartesian electric and toroidal dipoles produces a pronounced dip in the scattering spectra with the scattering intensity almost reaching zero-a signature of anapole excitation. The total scattering intensity associated with the anapole excitation is found to be more than 10 times weaker for illumination with radially vs linearly polarized beams. Our approach provides a simple, straightforward alternative path to realizing nonradiating anapole states at the optical frequencies.

Block-copolymer assisted fabrication of anisotropic plasmonic nanostructures.

The anisotropic nanostructures of noble metals are of great interest for plasmonic applications, due to the possibility of tuning the localized surface plasmon resonance (LSPR) across the UV-visible-near infrared (UV-vis-NIR) without sacrificing the linewidth, as well as achieving larger local field enhancement. Here, we report a simple and promising fabrication method of anisotropic gold nanostructures film using polystyrene-b-poly(2vinylpyridine) (PS-b-P2VP) block copolymers (BCPs) as a template. In this approach, PS-b-P2VP spherical micelles were first synthesized as a template, followed by selective deposition of an Au precursor inside the P2VP core of the micelles, using an ethanol solution of Au salt. Subsequently, heat treatment of the precursor deposited BCP films followed by the removal of the BCP template produced anisotropic gold nanostructures of various shapes, such as octahedron, decahedron, tetrahedron, triangles, and triangular prism. A temperature and time dependent study during heat treatment shows the formation of clusters at a higher temperature. Furthermore, measurements of the ensemble extinction spectra of the anisotropic Au nanoparticle films showed two broad distinct LSPR peaks; one in the visible range (∼660 nm), and the other in the NIR range (∼875 nm). The electrodynamic simulation showed that octahedron and decahedron nanoparticles are responsible for the LSPR response in the visible; whereas the triangular shapes are responsible for the LSPR response in the NIR. Our work is expected to open up a new direction for the synthesis of anisotropic nanostructures of noble metals, that can be utilized to tune the LSPR response across the UV-vis-NIR range, using a simple BCP template-based method.

Selective Induction of Optical Magnetism.

An extension of the Maxwell-Faraday law of electromagnetic induction to optical frequencies requires spatially appropriate materials and optical beams to create resonances and excitations with curl. Here we employ cylindrical vector beams with azimuthal polarization to create electric fields that selectively drive magnetic responses in dielectric core-metal nanoparticle "satellite" nanostructures. These optical frequency magnetic resonances are induced in materials that do not possess spin or orbital angular momentum. Multipole expansion analysis of the scattered fields obtained from electrodynamics simulations show that the excitation with azimuthally polarized beams selectively enhances magnetic vs electric dipole resonances by nearly 100-fold in experiments. Multipolar resonances (e.g., quadrupole and octupole) are enhanced 5-fold by focused azimuthally versus linearly polarized beams. We also selectively excite electric multipolar resonances in the same identical nanostructures with radially polarized light. This work opens new opportunities for spectroscopic investigation and control of "dark modes", Fano resonances, and magnetic modes in nanomaterials and engineered metamaterials.

Slippery Liquid-Infused Porous Surfaces that Prevent Microbial Surface Fouling and Kill Non-Adherent Pathogens in Surrounding Media: A Controlled Release Approach.

Many types of slippery liquid-infused porous surfaces (or 'SLIPS') can resist adhesion and colonization by microorganisms. These 'slippery' materials thus offer new approaches to prevent fouling on a range of commercial and industrial surfaces, including biomedical devices. However, while SLIPS can prevent fouling on surfaces to which they are applied, they can currently do little to prevent the proliferation of non-adherent (planktonic) organisms, stop them from colonizing other surfaces, or prevent them from engaging in other behaviors that could lead to infection and associated burdens. Here, we report an approach to the design of multi-functional SLIPS that addresses these issues and expands the potential utility of slippery surfaces in antimicrobial contexts. Our approach is based on the incorporation and controlled release of small-molecule antimicrobial agents from the porous matrices used to host infused slippery oil phases. We demonstrate that SLIPS fabricated using nanoporous polymer multilayers can prevent short- and longer-term colonization and biofilm formation by four common fungal and bacterial pathogens (Candida albicans, Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus), and that the polymer and oil phases comprising these materials can be exploited to load and sustain the release of triclosan, a model hydrophobic and broad-spectrum antimicrobial agent, into surrounding media. This approach both improves the inherent anti-fouling properties of these materials and endows them with the ability to efficiently kill planktonic pathogens. Finally, we show that this approach can be used to fabricate dual-action SLIPS on complex surfaces, including the luminal surfaces of flexible catheter tubes. This strategy has the potential to be general; we anticipate that the materials, strategies, and concepts reported here will enable new approaches to the design of slippery surfaces with improved anti-fouling properties and open the door to new applications of slippery liquid-infused materials that host or promote the release of a variety of other active agents.

Enhancing nanoparticle electrodynamics with gold nanoplate mirrors.

Mirrors and optical cavities can modify and enhance matter-radiation interactions. Here we report that chemically synthesized Au nanoplates can serve as micrometer-size mirrors that enhance electrodynamic interactions. Because of their plasmonic properties, the Au nanoplates enhance the brightness of scattered light from Ag nanoparticles near the nanoplate surface in dark-field microscopy. More importantly, enhanced optical trapping and optical binding of Ag nanoparticles are demonstrated in interferometric optical traps created from a single laser beam and its reflection from individual Au nanoplates. The enhancement of the interparticle force constant is ≈20-fold more than expected from the increased intensity due to standing wave interference. We show that the additional stability for optical binding arises from the restricted axial thermal motion of the nanoparticles that couples to and reduces the fluctuations in the lateral plane. This new mechanism greatly advances the photonic synthesis of ultrastable nanoparticle arrays and investigation of their properties.

Surfactant-induced ordering and wetting transitions of droplets of thermotropic liquid crystals "caged" inside partially filled polymeric capsules.

We report a study of the wetting and ordering of thermotropic liquid crystal (LC) droplets that are trapped (or "caged") within micrometer-sized cationic polymeric microcapsules dispersed in aqueous solutions of surfactants. When they were initially dispersed in water, we observed caged, nearly spherical droplets of E7, a nematic LC mixture, to occupy ∼40% of the interior volume of the polymeric capsules [diameter of 6.7 ± 0.3 µm, formed via covalent layer-by-layer assembly of branched polyethylenimine and poly(2-vinyl-4,4-dimethylazlactone)] and to contact the interior surface of the capsule wall at an angle of ∼157 ± 11°. The internal ordering of LC within the droplets corresponded to the so-called bipolar configuration (distorted by contact with the capsule walls). While the effects of dodecyltrimethylammonium bromide (DTAB) and sodium dodecyl sulfate (SDS) on the internal ordering of "free" LC droplets are similar, we observed the two surfactants to trigger strikingly different wetting and configurational transitions when LC droplets were caged within polymeric capsules. Specifically, upon addition of SDS to the aqueous phase, we observed the contact angles (θ) of caged LC on the interior surface of the capsule to decrease, resulting in a progression of complex droplet shapes, including lenses (θ ≈ 130 ± 10°), hemispheres (θ ≈ 89 ± 5°), and concave hemispheres (θ < 85°). The wetting transitions induced by SDS also resulted in changes in the internal ordering of the LC to yield states topologically equivalent to axial and radial configurations. Although topologically equivalent to free droplets, the contributions that surface anchoring, LC elasticity, and topological defects make to the free energy of caged LC droplets differ from those of free droplets. Overall, these results and others reported herein lead us to conclude that caged LC droplets offer a platform for new designs of LC-droplet-based responsive soft matter that cannot be realized in dispersions of free droplets.

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.

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.

Sequential Infiltration Synthesis of Silicon Dioxide in Polymers with Ester Groups-Insight from In Situ Infrared Spectroscopy.

New strategies to synthesize nanometer-scale silicon dioxide (SiO2) patterns have drawn much attention in applications such as microelectronic and optoelectronic devices, membranes, and sensors, as we are approaching device dimensions shrinking below 10 nm. In this regard, sequential infiltration synthesis (SIS), a two-step gas-phase molecular assembly process that enables localized inorganic material growth in the targeted reactive domains of polymers, is an attractive process. In this work, we performed in situ Fourier transform infrared spectroscopy (FTIR) measurements during SiO2 SIS to investigate the reaction mechanism of trimethylaluminum (TMA) and tri(tert-pentoxy) silanol (TPS) precursors with polymers having ester functional groups (poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA), polycaprolactone (PCL), and poly(t-butyl methacrylate) (PBMA)), for the purpose of growing patterned nanomaterials. The FTIR results show that for PMMA and PEMA, a lower percentage of functional groups participated in the reactions and formed weak and unstable complexes. In contrast, almost all functional groups in PCL and PBMA participated in the reactions and showed stable and irreversible interactions with TMA. We discovered that the amount of SiO2 formed is not directly correlated with the number of interacting functional groups. These insights into the SiO2 SIS mechanism will enable nanopatterning of SiO2 for low-dimensional applications.

Azolla Pinnata: Sustainable Floating Oil Cleaner of Water Bodies.

Various plant-based materials effectively absorb oil contaminants at the water/air interface. These materials showcase unparalleled efficiency in purging oil contaminants, encompassing rivers, lakes, and boundless oceans, positioning them as integral components of environmental restoration endeavors. In addition, they are biodegradable, readily available, and eco-friendly, thus making them a preferable choice over traditional oil cleaning materials. This study explores the phenomenal properties of the floating Azolla fern (Azolla pinnata), focusing on its unique hierarchical leaf surface design at both the microscale and nanoscale levels. These intricate structures endow the fern with exceptional characteristics, including superhydrophobicity, high water adhesion, and remarkable oil or organic solvent absorption capabilities. Azolla's leaf surface exhibits a rare combination of dual wettability, where hydrophilic spots on a superhydrophobic base enable the pinning of water droplets, even when positioned upside-down. This extraordinary property, known as the parahydrophobic state, is rare in floating plants, akin to the renowned Salvinia molesta, setting Azolla apart as a natural wonder. Submerged in water, Azolla leaves excel at absorbing light oils at the air-water interface, demonstrating a notable ability to extract high-density organic solvents. Moreover, Azolla's rapid growth, doubling in the area every 4-5 days, especially in flowing waters, positions it as a sustainable alternative to traditional synthetic oil-cleaning materials with long-term environmental repercussions. This scientific lead could pave the way for more environmentally friendly approaches to mitigate the negative impacts of oil spills and promote a cleaner water ecosystem.

Chemically selective raising and rolling of oil-droplets underwater: an equipment-free chemical sensing method.

A dual chemically reactive multilayer coating is rationally subjected to mono- and dual-functionalization through a 1,4-conjugate addition reaction at ambient conditions to depict the raising of the oil contact angle and rolling of a beaded oil-droplet underwater, respectively, only in the presence of targeted toxic chemicals (e.g. nitrite ion and hydrazine). Rational switching of the hydrophobic aromatic moiety into a hydrophilic moiety in the modified multilayer coatings via selected modified Griess reaction and Schiff base reaction contributed to the desired change in underwater oil-wettability and oil-adhesion. Eventually, this approach allowed equipment-free and naked-eye chemical sensing with high selectivity and sensitivity.

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.

Lubricated Interfaces Enabling Simultaneous Pulsatile and Continuous Chemical Release Modes.

The release of chemicals following either pulsatile or continuous release modes is important for various potential applications, including programmed chemical reactions, mechanical actuation, and treatments of various diseases. However, the simultaneous application of both modes in a single material system has been challenging. Here, two chemical loading methods are reported in a liquid-crystal-infused porous surface (LCIPS) that enables both a pulsatile and continuous release of chemicals simultaneously. Specifically, chemicals loaded in the porous substrate exhibit a liquid crystal (LC) mesophase-dependent continuous release, whereas the chemicals dissolved in micrometer-sized aqueous droplets dispersed in the LC surface follow a pulsatile release activated by a phase transition. Moreover, the loading method of distinct molecules can be controlled to program their release mode. Finally, the pulsatile and continuous release of two distinct bioactive small molecules, tetracycline and dexamethasone, are demonstrated which display antibacterial and immunomodulatory activities for applications such as chronic wound healing and biomedical implant coating.

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.