Superamphiphobic Silicon-Nanowire-Embedded Microsystem and In-Contact Flow Performance of Gas and Liquid Streams

Transferrable Electrospinning Nanofiber Meshes as Strongly Adhered Scaffolds for Slippery Liquid-Infused Porous Surfaces

Slippery liquid-infused porous surfaces (SLIPS) are self-healing protective coatings that can be made by infiltration of a porous scaffold with a chemically resistant oil. A popular method to apply a SLIPS coating is using electrospinning to deposit a nanofiber mesh onto the intended substrate. However, electrospinning only lightly deposits the nanofibers onto the intended substrate, so the coating detaches easily even when unintended. We report a simple, yet effective, solution to the adhesion problem. Electrospun nanofiber meshes are typically well entangled and cohesive, so they can be detached from the electrospinning target and transferred onto the final target. Using a thin layer of adhesive on the intended surface, the electrospinning mesh can be securely attached and infiltrated with protective oil to yield a more stable SLIPS coating. An adhered coating can be submerged under corrosive solution and repeatedly self-heal from damage to the same spot. With the electrospun nanofiber meshes' flexibility and stretchability, the meshes can be fitted around a wide range of targets including ones that are otherwise difficult to apply a nanofiber mesh on. The use of an adhesive interlayer between the nanofiber mesh and substrate is a simple solution to improve coating stability, and the solution facilitates application of SLIPS onto a broader range of substrates.

Block-Copolymers Enable Direct Reduction and Structuration of Noble Metal-Based Films

Noble metal nanostructured films are of great interest for various applications including electronics, photonics, catalysis, and photocatalysis. Yet, structuring and patterning noble metals, especially those of the platinum group, is challenging by conventional nanofabrication. Herein, an approach based on solution processing to obtain metal-based films (rhodium, ruthenium (Ru) or iridium in the presence of residual organic species) with nanostructuration at the 20 nm-scale is introduced. Compared to existing approaches, the dual functionality of block-copolymers acting both as structuring and as reducing agent under inert atmosphere is exploited. A set of in situ techniques has allowed for the capturing of the carbothermal reduction mechanism occurring at the hybrid organic/inorganic interface. Differently from previous literature, a two-step reduction mechanism is unveiled with the formation of a carbonyl intermediate. From a technological point of view, the materials can be solution-processed on a large scale by dip-coating as polymers and simultaneously structured and reduced into metals without requiring expensive equipment or treatments in reducing atmosphere. Importantly, the metal-based films can be patterned directly by block-copolymer lithography or by soft-nanoimprint lithography on various substrates. As proof-of-concept of application, the authors demonstrate that nanostructured Ru films can be used as efficient catalysts for H₂ generation into microfluidic reactors.

Replacing Metals with Oxides in Metal-Assisted Chemical Etching Enables Direct Fabrication of Silicon Nanowires by Solution Processing

Metal-assisted chemical etching (MACE) has emerged as an effective method to fabricate high aspect ratio nanostructures. This method requires a catalytic mask that is generally composed of a metal. Here, we challenge the general view that the catalyst needs to be a metal by introducing oxide-assisted chemical etching (OACE). We perform etching with metal oxides such as RuO₂ and IrO₂ by transposing materials used in electrocatalysis to nanofabrication. These oxides can be solution-processed as polymers exhibiting similar capabilities of metals for MACE. Nanopatterned oxides can be obtained by direct nanoimprint lithography or block-copolymer lithography from chemical solution on a large scale. High aspect ratio silicon nanostructures were obtained at the sub-20 nm scale exclusively by cost-effective solution processing by halving the number of fabrication steps compared to MACE. In general, OACE is expected to stimulate new fundamental research on chemical etching assisted by other materials, providing new possibilities for device fabrication.

Reaction study of α-phase NaYF4:Yb,Er generation via a tubular microreactor: discovery of an efficient synthesis strategy

α-Phase NaREF4 is the necessary intermediate to obtain β-phase NaREF4, which is good at upconversion luminescence. We herein report microreaction research on the generation of α-NaYF4:Yb,Er nanoparticles. Owing to the fast heating and cooling ability of a quartz microreactor, α-NaYF4:Yb,Er was successfully generated within a reaction time of <10 min. The results showed that it was difficult to complete the α-NaYF4:Yb,Er generation reaction in such a short reaction time by using the traditional synthetic route with a precursor solution containing NaF. However, as we changed the precursor to a solution containing amorphous NaREF4, the yield of α-NaYF4:Yb,Er increased to 95%. By focusing on applying the new precursor solution, we investigated the influence of the reaction temperature on the morphology of α-NaYF4:Yb,Er and exhibited the effects of size and crystallinity of α-NaYF4:Yb,Er on the generation of β-NaYF4:Yb,Er. Finally, an improved microreaction system with an in-line mixing of NH4REF4 and NaOA solutions was developed, whose products were successfully converted to uniform β-NaYF4:Yb,Er nanocrystals through the Ostwald-ripening process. The new reaction path and the reaction device further opened a door for the highly efficient synthesis of upconversion luminescent nanoparticles.

Fabrication of a flexible transparent superomniphobic polydimethylsiloxane surface with a micropillar array

Although superomniphobic surfaces have attracted extensive interest owing to many important applications, successful fabrication of such surfaces still remains a critical challenge. Herein, we present a flexible transparent superomniphobic polydimethylsiloxane (PDMS) surface with a micropillar array using Si nanowires as the mould. The as-obtained PDMS not only exhibits excellent liquid-repellent performance with a static contact angle of over 150° and sliding angle of less than 6° against a wide range of liquids, but also maintains the super-repellency even under acid/base corrosion, mechanical damage, and unidirectional stretching.

A flexible transparent superomniphobic polydimethylsiloxane (PDMS) surface with a micropillar array has been fabricated using Si nanowires as the mould.

Inorganic Polymer Micropillar-Based Solution Shearing of Large-Area Organic Semiconductor Thin Films with Pillar-Size-Dependent Crystal Size

It is demonstrated that the crystal size of small-molecule organic semiconductors can be controlled during solution shearing by tuning the shape and dimensions of the micropillars on the blade. Increasing the size and spacing of the rectangular pillars increases the crystal size, resulting in higher thin-film mobility. This phenomenon is attributed as the microstructure changing the degree and density of the meniscus line curvature, thereby controlling the nucleation process. The use of allylhybridpolycarbosilane (AHPCS), an inorganic polymer, is also demonstrated as the microstructured blade for solution shearing, which has high resistance to organic solvents, can easily be microstructured via molding, and is flexible and durable. Finally, it is shown that solution shearing can be performed on a curved surface using a curved blade. These demonstrations bring solution shearing closer to industrial applications and expand its applicability to various printed flexible electronics.

Dynamic Shaping of Femtoliter Dew Droplets

Herein, we show that wetting properties such as giant wetting anisotropy and dynamic shaping can be observed when femtoliter (submicron scale) dew droplets are condensed on nanopatterned mildly hydrophilic surfaces. Large-scale, optically transparent, nanopatterned TiO₂ surfaces were fabricated by direct nanoimprinting lithography of sol-gel-derived films. Square, infinitely elongated, or circular droplets were obtained with square, line, or concentric patterns, respectively, and were visualized in situ during formation and recession using optical microscopy and environmental scanning electronic microscopy. We first describe how extremely elongated droplets could form on mildly hydrophilic surfaces, naturally contaminated in real environmental conditions. In this configuration, the dew droplet shape can be dynamically and reversibly varied by controlling the out-of-equilibrium conditions associated with condensation/evaporation kinetics. As an example of the application, we propose a "morphological" sensor that exploits the shape of the dew droplets as a transduction mode for detecting organic vapors in the outer atmosphere. Importantly, this study is underlining that environmentally stable, purely hydrophilic surfaces can be smartly engineered to induce wetting phenomena at very small scale never observed so far for hydrophobic or heterogeneous surfaces. Our versatile approach based on nanoimprinted, transparent sol-gel films could open great perspectives for the implementation of environmentally stable, mildly hydrophilic materials for "dew engineering" applications such as open microfluidics, fuming for fingerprints, vapor sensing, or water harvesting on glass windows, for instance.

Salvinia-Effect-Inspired "Sticky" Superhydrophobic Surfaces by Meniscus-Confined Electrodeposition

Inspired by the Salvinia effect, we report the fabrication and characterization of a novel "sticky" superhydrophobic surface sustaining a Cassie-Baxter wetting state for water droplets with high contact angles but strong solid-liquid retention. Unlike superhydrophobic surfaces mimicking the lotus or petal effect, whose hydrophobicity and droplet retention are typically regulated by hierarchical micro- and nanostructures made of a homogeneous material with the same surface energy, our superhydrophobic surface merely requires singular microstructures covered with a hydrophobic coating but creatively coupled with hydrophilic tips with different surface energy. Hydrophilic tips are selectively formed by meniscus-confined electrodeposition of a metal (e.g., nickel) layer on top of hydrophobic microstructures. During the electrodeposition process, the superhydrophobic surface retains its plastron so that the electrolyte cannot penetrate into the cavity of hydrophobic microstructures, consequently making the electrochemical reaction between solid and electrolyte occur only on the tip. In contrast to typical superhydrophobic surfaces where droplets are highly mobile, the "sticky" superhydrophobic surface allows a water droplet to have strong local pinning and solid-liquid retention on the hydrophilic tips, which is of great significance in many droplet behaviors such as evaporation.

Why microfluidics? Merits and trends in chemical synthesis

The intrinsic limitations of conventional batch synthesis have hindered its applications in both solving classical problems and exploiting new frontiers. Microfluidic technology offers a new platform for chemical synthesis toward either molecules or materials, which has promoted the progress of diverse fields such as organic chemistry, materials science, and biomedicine. In this review, we focus on the improved performance of microreactors in handling various situations, and outline the trend of microfluidic synthesis (microsynthesis, μSyn) from simple microreactors to integrated microsystems. Examples of synthesizing both chemical compounds and micro/nanomaterials show the flexible applications of this approach. We aim to provide strategic guidance for the rational design, fabrication, and integration of microdevices for synthetic use. We critically evaluate the existing challenges and future opportunities associated with this burgeoning field.

Two-Step Process To Create "Roll-Off" Superamphiphobic Paper Surfaces

Surface modification of cellulose-based paper, which displays roll-off properties for water and oils (surface tension ≥23.8 mN·m^-1) and good repellency toward n-heptane (20.1 mN·m^-1), is reported. Droplets of water, diiodomethane, motor oil, hexadecane, and decane all "bead up", i.e., exhibit high contact angles, and roll off the treated surface under the influence of gravity. Unlike widely used approaches that rely on the deposition of nanoparticles or electrospun nanofibers to create superamphiphobic surfaces, our method generates a hierarchical structure as an inherent property of the substrate and displays good adhesion between the film and substrate. The two-step combination of plasma etching and vapor deposition used in this study enables fine-tuning of the nanoscale roughness and thereby facilitates enhanced fundamental understanding of the effect of micro- and nanoscale roughness on the paper wetting properties. The surfaces maintain their "roll-off" properties after dynamic impact tests, demonstrating their mechanical robustness. Furthermore, the superamphiphobic paper has high gas permeability due to pore-volume enhancement by plasma etching but maintains the mechanical flexibility and strength of untreated paper, despite the presence of nanostructures. The unique combination of the chemical and physical properties of the resulting superamphiphobic paper is of practical interest for a range of applications such as breathable and disposable medical apparel, antifouling biomedical devices, antifingerprint paper, liquid packaging, microfluidic devices, and medical testing strips through a simple surface etching plus coating process.

Integrated CO2 capture-fixation chemistry via interfacial ionic liquid catalyst in laminar gas/liquid flow

Simultaneous capture of carbon dioxide (CO₂) and its utilization with subsequent work-up would significantly enhance the competitiveness of CO₂-based sustainable chemistry over petroleum-based chemistry. Here we report an interfacial catalytic reaction platform for an integrated autonomous process of simultaneously capturing/fixing CO₂ in gas–liquid laminar flow with subsequently providing a work-up step. The continuous-flow microreactor has built-in silicon nanowires (SiNWs) with immobilized ionic liquid catalysts on tips of cone-shaped nanowire bundles. Because of the superamphiphobic SiNWs, a stable gas–liquid interface maintains between liquid flow of organoamines in upper part and gas flow of CO₂ in bottom part of channel. The intimate and direct contact of the binary reagents leads to enhanced mass transfer and facilitating reactions. The autonomous integrated platform produces and isolates 2-oxazolidinones and quinazolines-2,4(1H,3H)-diones with 81–97% yields under mild conditions. The platform would enable direct CO₂ utilization to produce high-valued specialty chemicals from flue gases without pre-separation and work-up steps.

Microfluidics is an attractive route for synthesis, but can suffer from poor reactivity with gaseous reagents. Here the authors report a microfluidic system catalysing an interfacial reaction between CO₂ and liquid phase reagents by modifying silicon nanowires with immobilized ionic liquid catalysts.

Preparation of stable superamphiphobic surfaces on X80 pipeline steel substrates

Micro/nano multi-scale superamphiphobic surfaces with excellent stability were prepared via facile electrochemical-deposition, alkaline etching and fluorination treatment processes.