In Situ Three-Dimensional Welded Nanofibrous Membranes for Robust Membrane Distillation of Concentrated Seawater

Membrane distillation (MD) is a promising technology for treating the concentrated seawater discharged from the desalination process. Interconnected porous membranes, fabricated by additive manufacturing, have received significant attention for MD technology because of their excellent permeability. However, their poor hydrophobic durability induced by the deformation of pores constrains their water desalination performance. Herein, an in situ three-dimensional (3D) welding approach involving emulsion electrospinning is reported for fabricating robust nanofibrous membranes. The reported method is simple and effective for welding nanofibers at their intersections, and the reinforced membrane pores are uniform in the 3D space. The results show that the in situ 3D welded nanofibrous membrane, with a stability of 170 h and water recovery of 76.9%, exhibits better desalination performance than the nonwelded (superhydrophobic) nanofibrous membrane and the postwelded (superhydrophobic) nanofibrous membrane. Furthermore, the stability mechanism of the in situ 3D welded nanofibrous membrane and the two different wetting mechanisms of the nonwelded and postwelded nanofibrous membranes were investigated in the current work. More significantly, the in situ 3D welded nanofibrous membrane can further concentrate the actual concentrated seawater (121°E, 37°N) to crystallization, demonstrating its potential applications for the desalination of challenging concentrated seawater.

Consistent Thermo-Capillarity and Thermal Boundary Conditions for Single-Phase Smoothed Particle Hydrodynamics

A model for capillary phenomena including temperature-dependency and thermal boundary conditions is presented in the numerical framework of smoothed particle hydrodynamics (SPH). The model requires only a single fluid phase and is therefore computationally more efficient than surface tension schemes which need an explicit fluid-fluid or fluid-gas interface. The model makes use of a surface identification mechanism based on the SPH renormalization tensor. All relevant properties of the continuum surface force (CSF) based approach, i.e., the delta function, normal vector and curvature, are calculated in a consistent manner. The model is parametrized by physical material properties and is successfully validated by means of a large set of analytical test cases. The applicability of the proposed model to more complex scenarios is demonstrated.

Grafted Nanoparticle Surface Wetting during Phase Separation in Polymer Nanocomposite Films

Wetting of polymer-grafted nanoparticles (NPs) in a polymer nanocomposite (PNC) film is driven by a difference in surface energy between components as well as bulk thermodynamics, namely, the value of the interaction parameter, χ. The interplay between these contributions is investigated in a PNC containing 25 wt % polymethyl methacrylate (PMMA)-grafted silica NPs (PMMA-NPs) in poly(styrene-ran-acrylonitrile) (SAN) upon annealing above the lower critical solution temperature (LCST, 160 °C). Atomic force microscopy (AFM) studies show that the areal density of particles increases rapidly and then approaches 80% of that expected for random close-packed hard spheres. A slightly greater areal density is observed at 190 °C compared to 170 °C. The PMMA-NPs are also shown to prevent dewetting of PNC films under conditions where the analogous polymer blend is unstable. Transmission electron microscopy (TEM) imaging shows that PMMA-NPs symmetrically wet both interfaces and form columns that span the free surface and substrate interface. Using grazing-incidence Rutherford backscattering spectrometry (GI-RBS), the PMMA-NP surface excess (Z*) initially increases rapidly with time and then approaches a constant value at longer times. Consistent with the areal density, Z* is slightly greater at deeper quench depths, which is attributed to the more unfavorable interactions between the PMMA brush and SAN segments. The Z* values at early times are used to determine the PMMA-NP diffusion coefficients, which are significantly larger than theoretical predictions. These studies provide insights into the interplay between wetting and phase separation in PNCs and can be utilized in nanotechnology applications where surface-dependent properties, such as wettability, durability, and friction, are important.

Revisiting Wetting, Freezing, and Evaporation Mechanisms of Water on Copper

Wetting of metal surfaces plays an important role in fuel cells, corrosion science, and heat-transfer devices. It has been recently stipulated that Cu surface is hydrophobic. In order to address this issue we use high purity (1 1 1) Cu prepared without oxygen, and resistant to oxidation. Using the modern Fringe Projection Phase-Shifting method of surface roughness determination, together with a new cell allowing the vacuum and thermal desorption of samples, we define the relation between the copper surface roughness and water contact angle (WCA). Next by a simple extrapolation, we determine the WCA for the perfectly smooth copper surface (WCA = 34°). Additionally, the kinetics of airborne hydrocarbons adsorption on copper was measured. It is shown for the first time that the presence of surface hydrocarbons strongly affects not only WCA, but also water droplet evaporation and the temperature of water droplet freezing. The different behavior and features of the surfaces were observed once the atmosphere of the experiment was changed from argon to air. The evaporation results are well described by the theoretical framework proposed by Semenov, and the freezing process by the dynamic growth angle model.

Vapor Condensation and Coating Evaporation Are Both Responsible for Soot Aggregate Restructuring

Fresh soot is made of fractal aggregates, which often appear collapsed in atmospheric samples. A body of work has concluded that the collapse is caused by liquid shells when they form by vapor condensation around soot aggregates. However, some recent studies argue that soot remains fractal even when engulfed by the shells, collapsing only when the shells evaporate. To reconcile this disagreement, we investigated soot restructuring under conditions ranging from capillary condensation to full encapsulation, also including condensate evaporation. In these experiments, airborne fractal aggregates were exposed to vapors of wetting liquids, and particle size was measured before and after coating loss, allowing us to isolate the contribution from condensation toward restructuring. We show the existence of three distinct regions along the path connecting the initial fractal and final collapsed aggregates, where minor restructuring occurs already at zero vapor supersaturation due to capillary condensation. Increasing supersaturation increases the amount of condensate, producing a more notable aggregate shrinkage. At even higher supersaturations, the aggregates become encapsulated, and subsequent condensate evaporation leaves behind fully compacted aggregates. Hence, for wetting liquids, minor restructuring begins already during capillary condensation and significant restructuring occurs as the coating volume increases. However, at this time, we cannot precisely quantify the contribution of condensate evaporation to the full aggregate compaction.

Porous Layer-by-Layer Films Assembled Using Polyelectrolyte Blend to Control Wetting Properties

Porous layer-by-layer (LbL) films have been employed for the implementation of superwetting surfaces, but they are limited to the LbL films consisting of only two oppositely charged polyelectrolytes. In this study, LbL films were assembled using a cationic polymer blend of branched poly(ethylene imine) (BPEI) and poly(allylamine hydrochloride) (PAH), and anionic poly(acrylic acid); they were then acid-treated at pH 1.8-2.0 to create a porous structure. The films of 100% BPEI exhibited a relatively smooth surface, whereas those of the 100% PAH exhibited porous surfaces. However, various surface morphologies were obtained when BPEI and PAH were blended. When coated with fluorinated silane, films with 50% and 100% PAH exhibited relatively higher water contact angles (WCAs). In particular, films with 50% PAH exhibited the highest WCA of 140-150° when treated at pH 1.8. These fluorinated films were further infused with lubricant oil to determine their feasibility as slippery surfaces. The water and oil sliding angles were in the range of 10-20° and 5-10°, respectively. Films prepared with the BPEI/PAH blend showed lower water slide angles than those prepared with 100% BPEI or PAH. Acid treatment of LbL films assembled using a polyelectrolyte blend can effectively control surface morphologies and can potentially be applied in superwetting.

Insights into the Control of Drug Release from Complex Immediate Release Formulations

The kinetics of water transport into tablets, and how it can be controlled by the formulation as well as the tablet microstructure, are of central importance in order to design and control the dissolution and drug release process, especially for immediate release tablets. This research employed terahertz pulsed imaging to measure the process of water penetrating through tablets using a flow cell. Tablets were prepared over a range of porosity between 10% to 20%. The formulations consist of two drugs (MK-8408: ruzasvir as a spray dried intermediate, and MK-3682: uprifosbuvir as a crystalline drug substance) and NaCl (0% to 20%) at varying levels of concentrations as well as other excipients. A power-law model is found to fit the liquid penetration exceptionally well (average R2>0.995). For each formulation, the rate of water penetration, extent of swelling and the USP dissolution rate were compared. A factorial analysis then revealed that the tablet porosity was the dominating factor for both liquid penetration and dissolution. NaCl more significantly influenced liquid penetration due to osmotic driving force as well as gelling suppression, but there appears to be little difference when NaCl loading in the formulation increases from 5% to 10%. The level of spray dried intermediate was observed to further limit the release of API in dissolution.

Tunable Hydrophobicity via Dimensionally Confined Polymerization of Organometallic Adducts

Fabrication of tunable fine textures on solid metal surfaces often demands sophisticated reaction/processing systems. By exploiting in situ polymerization and self-assembly of inorganic adducts derived from liquid metals (the so-called HetMet reaction) with concomitant solidification, solid metal films with tunable texture are readily fabricated. Serving as a natural dimensional confinement, interparticle pores and capillary-adhered thin liquid films in a pre-packed bed of undercooled liquid metal particles lead to the expeditious surface accumulation of organometallic synthons, which readily oligomerize and self-assemble into concentration-dictated morphologies/patterns. Tuning particle size, particle packing (flat or textured), and reactant concentration generates diverse, autonomously organized organometallic structures on a metal particle bed. Concomitant solidification and sintering of the underlying undercooled particle bed led to a multiscale patterned solid metal surface. The process is illustrated by creating tunable features on pre-organized metal particle beds with concomitant tunable wettability as illustrated through the so-called petal and lotus effects.

Analysis of Polyvinylidene Fluoride Membranes Fabricated for Membrane Distillation

The optimization of the properties for MD membranes is challenging due to the trade-off between water productivity and wetting tendency. Herein, this study presents a novel methodology to examine the properties of MD membranes. Seven polyvinylidene fluoride (PVDF) membranes were synthesized under different conditions by the phase inversion method and characterized to measure flux, rejection, contact angle (CA), liquid entry pressure (LEP), and pore sizes. Then, water vapor permeability (B_w), salt leakage ratio (L_w), and fiber radius (R_f) were calculated for the in-depth analysis. Results showed that the water vapor permeability and salt leakage ratio of the prepared membranes ranged from 7.76 × 10⁻⁸ s/m to 20.19 × 10⁻⁸ s/m and from 0.0020 to 0.0151, respectively. The R_f calculated using the Purcell model was in the range from 0.598 μm to 1.690 μm. Since the R_f was relatively small, the prepared membranes can have high LEP (more than 1.13 bar) even at low CA (less than 90.8°). The trade-off relations between the water vapor permeability and the other properties could be confirmed from the results of the prepared membranes. Based on these results, the properties of an efficient MD membrane were suggested as a guideline for the membrane development.

Biomimetic Approach for the Elaboration of Highly Hydrophobic Surfaces: Study of the Links between Morphology and Wettability

This investigation of morphology-wetting links was performed using a biomimetic approach. Three natural leaves' surfaces were studied: two bamboo varieties and Ginkgo Biloba. Multiscale surface topographies were analyzed by SEM observations, FFT, and Gaussian filtering. A PDMS replicating protocol of natural surfaces was proposed in order to study the purely morphological contribution to wetting. High static contact angles, close to 135∘, were measured on PDMS replicated surfaces. Compared to flat PDMS, the increase in static contact angle due to purely morphological contribution was around 20∘. Such an increase in contact angle was obtained despite loss of the nanometric scale during the replication process. Moreover, a significant decrease of the hysteresis contact angle was measured on PDMS replicas. The value of the contact angle hysteresis moved from 40∘ for flat PDMS to less than 10∘ for textured replicated surfaces. The wetting behavior of multiscale textured surfaces was then studied in the frame of the Wenzel and Cassie-Baxter models. Whereas the classical laws made it possible to describe the wetting behavior of the ginkgo biloba replications, a hierarchical model was developed to depict the wetting behavior of both bamboo species.

One-Step Synthesis of a Durable and Liquid-Repellent Poly(dimethylsiloxane) Coating

Coatings with low sliding angles for liquid drops have a broad range of applications. However, it remains a challenge to have a fast, easy, and universal preparation method for coatings that are long-term stable, robust, and environmentally friendly. Here, a one-step grafting-from approach is reported for poly(dimethylsiloxane) (PDMS) brushes on surfaces through spontaneous polymerization of dichlorodimethylsilane fulfilling all these requirements. Drops of a variety of liquids slide off at tilt angles below 5°. This non-stick coating with autophobicity can reduce the waste of water and solvents in cleaning. The strong covalent attachment of the PDMS brush to the substrate makes them mechanically robust and UV-tolerant. Their resistance to high temperatures and to droplet sliding erosion, combined with the low film thickness (≈8 nm) makes them ideal candidates to solve the long-term degradation issues of coatings for heat-transfer surfaces.

Atomic Level Insight into Wetting and Structure of Ag Droplet on Graphene Coated Copper Substrate-Molecular Dynamics versus Experiment

Understanding the atomic-level phenomena occurring upon the wetting of graphene-coated Cu with liquid Ag is pivotal for the description of the wetting phenomenon and the role of graphene as a diffusion barrier. We have performed molecular dynamics (MD) simulations and confronted with our present experimental results to characterize wetting behavior of graphene coated Cu surfaces. Perfect and defected graphene layers covering Cu surface were wetted with liquid Ag droplet at 1273 K. Structural and topological aspects are discussed to characterize structure of the liquid Ag droplet and a product of wetting reaction occurring on Cu/Gn and Cu/Gndef substrates, also including perfect graphene layer and a pure Cu surface. The obtained results reveal the importance of defects in graphene structure, which play a key role in wetting mechanism and the formation of AgCu alloy. As a consequence, we observe a change of the wetting behavior and topology of both bulk and adsorbed Ag atoms by using Voronoi analysis (VA). Despite the differences in time scale, atomistic simulations allowed us to catch the early stages of wetting, which are important for explaining the final stage of wetting delivered from experiment. Our findings reveal also graphene translucency to metal-metal interactions, observed in previous papers.

The Tuning of LIPSS Wettability during Laser Machining and through Post-Processing

In this work, we investigate the fabrication of stainless-steel substrates decorated with laser-induced periodic surface structures (LIPSS) of both hydrophilic and hydrophobic wettability through different post-processing manipulation. In carrying out these experiments, we have found that while a CO₂-rich atmosphere during irradiation does not affect final wettability, residence in such an atmosphere after irradiation does indeed increase hydrophobicity. Contrarily, residence in a boiling water bath will instead lead to a hydrophilic surface. Further, our experiments show the importance of removing non-sintered nanoparticles and agglomerates after laser micromachining. If they are not removed, we demonstrate that the nanoparticle agglomerates themselves become hydrophobic, creating a Cassie air-trapping layer on the surface which presents with water contact angles of 180°. However, such a surface lacks robustness; the particles are removed with the contacting water. What is left behind are LIPSS which are integral to the surface and have largely been blocked from reacting with the surrounding atmosphere. The actual surface presents with a water contact angle of approximately 80°. Finally, we show that chemical reactions on these metallic surfaces decorated with only LIPSS are comparatively slower than the reactions on metals irradiated to have hierarchical roughness. This is shown to be an important consideration to achieve the highest degree of hydro-philicity/phobicity possible. For example, repeated contact with water from goniometric measurements over the first 30 days following laser micromachining is shown to reduce the ultimate wettability of the surface to approximately 65°, compared to 135° when the surface is left undisturbed for 30 days.

Should I bend or should I grow: the mechanisms of droplet-mediated autophagosome formation

Phase-separated droplets with liquid-like properties can be degraded by macroautophagy/autophagy, but the mechanism underlying this degradation is poorly understood. We have recently derived a physical model to investigate the interaction between autophagic membranes and such droplets, uncovering that intrinsic wetting interactions underlie droplet-membrane contacts. We found that the competition between droplet surface tension and the increasing tendency of growing membrane sheets to bend determines whether a droplet is completely engulfed or isolated in a piecemeal fashion, a process we term fluidophagy. Intriguingly, we found that another critical parameter of droplet-membrane interactions, the spontaneous curvature of the membrane, determines whether the droplet is degraded by autophagy or - counterintuitively - serves as a platform from which autophagic membranes expand into the cytosol. We also discovered that the interaction of membrane-associated LC3 with the LC3-interacting region (LIR) found in the autophagic cargo receptor protein SQSTM1/p62 and many other autophagy-related proteins influences the preferred bending directionality of forming autophagosomes in living cells. Our study provides a physical account of how droplet-membrane wetting underpins the structure and fate of forming autophagosomes.

Functional and versatile superhydrophobic coatings via stoichiometric silanization

Superhydrophobic coatings have tremendous potential for applications in different fields and have been achieved commonly by increasing nanoscale roughness and lowering surface tension. Limited by the availability of either ideal nano-structural templates or simple fabrication procedures, the search of superhydrophobic coatings that are easy to manufacture and are robust in real-life applications remains challenging for both academia and industry. Herein, we report an unconventional protocol based on a single-step, stoichiometrically controlled reaction of long-chain organosilanes with water, which creates micro- to nano-scale hierarchical siloxane aggregates dispersible in industrial solvents (as the coating mixture). Excellent superhydrophobicity (ultrahigh water contact angle >170° and ultralow sliding angle <1°) has been attained on solid materials of various compositions and dimensions, by simply dipping into or spraying with the coating mixture. It has been demonstrated that these complete waterproof coatings hold excellent properties in terms of cost, scalability, robustness, and particularly the capability of encapsulating other functional materials (e.g. luminescent dyes).

What Can Probing Liquid-Air Menisci Inside Nanopores Teach Us About Macroscopic Wetting Phenomena?

Solid surfaces with excellent nonwetting ability have drawn significant interest from interfacial scientists and engineers. While much effort was devoted to investigating macroscopic wetting phenomena on nonwetting surfaces, the otherwise microscopic wetting has received less attention, and the surface/interface properties at the microscopic scale are not well resolved and correlated with the macroscopic wetting behavior. Herein, we first characterize the nanoscopic morphology and effective stiffness of liquid-air interfaces inside nanopores (nanomenisci) on diverse nonwetting nanoporous surfaces underneath water droplets using atomic force microscopy. Detailed three-dimensional imaging of the droplet-surface contact region reveals that water only slightly penetrates into the nanopores, allowing for quantitative prediction of the macroscopic contact angle using the Cassie-Baxter model. By gradually increasing the scanning force, we observe incrementally wetting of nanopores by water, and dewetting occurs when the force is lowered again, exhibiting reversible wetting-dewetting transitions. Further, nanoindentation measurements demonstrate that the nanomenisci show apparent elastic deformation and size-dependent effective stiffness at small indenting forces. Finally, we correlate the effective stiffness of the nanomenisci with the transition from complete rebound to partial rebound for impinging droplets on nanoporous surfaces. Our study suggests that probing the physical properties of the liquid-air menisci at the nanoscale is essential to rationalize macroscopic static and dynamic wetting phenomena on structured surfaces.

How ice grows from premelting films and water droplets

Close to the triple point, the surface of ice is covered by a thin liquid layer (so-called quasi-liquid layer) which crucially impacts growth and melting rates. Experimental probes cannot observe the growth processes below this layer, and classical models of growth by vapor deposition do not account for the formation of premelting films. Here, we develop a mesoscopic model of liquid-film mediated ice growth, and identify the various resulting growth regimes. At low saturation, freezing proceeds by terrace spreading, but the motion of the buried solid is conveyed through the liquid to the outer liquid-vapor interface. At higher saturations water droplets condense, a large crater forms below, and freezing proceeds undetectably beneath the droplet. Our approach is a general framework that naturally models freezing close to three phase coexistence and provides a first principle theory of ice growth and melting which may prove useful in the geosciences.

Bacteria Adhesion of Textiles Influenced by Wettability and Pore Characteristics of Fibrous Substrates

Bacteria adhesion on the surface is an initial step to create biofouling, which may lead to a severe infection of living organisms and humans. This study is concerned with investigating the textile properties including wettability, porosity, total pore volume, and pore size in association with bacteria adhesion. As model bacteria, Gram-negative, rod-shaped Escherichia coli and the Gram-positive, spherical-shaped Staphylococcus aureus were used to analyze the adhesion tendency. Electrospun webs made from polystyrene and poly(lactic acid) were used as substrates, with modification of wettability by the plasma process using either O2 or C4F8 gas. The pore and morphological characteristics of fibrous webs were analyzed by the capillary flow porometer and scanning electron microscopy. The substrate's wettability appeared to be the primary factor influencing the cell adhesion, where the hydrophilic surface resulted in considerably higher adhesion. The pore volume and the pore size, rather than the porosity itself, were other important factors affecting the bacteria adherence and retention. In addition, the compact spatial distribution of fibers limited the cell intrusion into the pores, reducing the total amount of adherence. Thus, superhydrophobic textiles with the reduced total pore volume and smaller pore size would circumvent the adhesion. The findings of this study provide informative discussion on the characteristics of fibrous webs affecting the bacteria adhesion, which can be used as a fundamental design guide of anti-biofouling textiles.

Subcompartmentalization and Pseudo-Division of Model Protocells

Membrane enclosed intracellular compartments have been exclusively associated with the eukaryotes, represented by the highly compartmentalized last eukaryotic common ancestor. Recent evidence showing the presence of membranous compartments with specific functions in archaea and bacteria makes it conceivable that the last universal common ancestor and its hypothetical precursor, the protocell, may have exhibited compartmentalization. To the authors' knowledge, there are no experimental studies yet that have tested this hypothesis. They report on an autonomous subcompartmentalization mechanism for protocells which results in the transformation of initial subcompartments to daughter protocells. The process is solely determined by the fundamental materials properties and interfacial events, and does not require biological machinery or chemical energy supply. In the light of the authors' findings, it is proposed that similar events may have taken place under early Earth conditions, leading to the development of compartmentalized cells and potentially, primitive division.

Direct Fluorination as Method of Improvement of Operational Properties of Polymeric Materials

Direct fluorination of polymers is a widely utilized technique for chemical modification. Such introduction of fluorine into the chemical structure of polymeric materials leads to laminates with highly fluorinated surface layer. The physicochemical properties of this layer are similar to those of perfluorinated polymers that differ by a unique combination of chemical resistance, weak adhesion, low cohesion, and permittivity, often barrier properties, etc. Surface modification by elemental fluorine allows one to avoid laborious synthesis of perfluoropolymers and impart such properties to industrial polymeric materials. The current review is devoted to a detailed consideration of wetting by water, energy characteristics of surfaces, adhesion, mechanical and electrical properties of the polymers, and composites after the direct fluorination.

Nanoparticle Wetting Agent for Gas Stream-Assisted Blade-Coated Inverted Perovskite Solar Cells and Modules

Lab-scale perovskite solar cells (PSCs) have recently reached power conversion efficiencies (PCEs) of up to 25.2%. However, a reliable transfer of solution processing from spin coating to scalable printing techniques and a homogeneous deposition on large substrate sizes is challenging also caused by dewetting of the perovskite precursor solution on highly hydrophobic subjacent materials. In this work, we report the utilization of blade-coated nonconductive silicon oxide (SiO₂) nanoparticles (NPs) as wetting agent for the precursor solution to enable the deposition of a homogeneous perovskite layer on the nonwetting hole transport layer (HTL). The NPs enhance the HTL surface energy, thus, wetting and homogeneous spreading of the precursor solution is strongly improved so that pinholes in the perovskite layer are avoided. In addition, we apply this concept for the first time for gas stream-assisted blade coating of PSCs and modules in the inverted (p-i-n) device architecture with poly(triaryl amine) (PTAA) as HTL on large-area substrates. To prevent void formation at the HTL interface of gas stream-assisted blade coated perovskite layers, the effect of blending small amounts of lead chloride (PbCl₂) in the perovskite precursor solution is investigated, which also improves reproducibility and device performance. Following these optimizations, blade coated PSCs with 0.24 cm² active area achieve up to 17.9% PCE. Furthermore, to prove scalability, we show enlarged substrates of up to 9 × 9 cm² and analyze the homogeneity of the perovskite layer in blade coating direction. Moreover, by implementing the blade coated NP wetting agent, we fabricate large-area modules with a maximum PCE of 9.3% on 49.60 cm² aperture area. This represents a further important step bringing solution-processed inverted PSCs closer to application.

Chemical and Wetting Analysis of the Ni-Ti Coating on SiC Improved by a 2-Step Coating-Sintering Process

A two-stepped coating-sintering process to prepare the qualified Ni-Ti transition applied in metal-ceramic bonding proved to be effective to improve the wetting abilities. The method was introduced in detail and compared with 2 control groups. To analyze the benefits, the morphology and composition were captured by field emission scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The comparisons of different coating depths and different sintering conditions were also recorded and analyzed. The influence of the EDS detecting depth was a concern in the discussions. Finally, the contact angle tests and surface energies were also estimated to verify the reliability of the transition layer. The results indicated that the coating-sintering process combined with protective sintering was preferred and necessary to increase the activeness.

Ionotronic Luminescent Fibers, Fabrics, and Other Configurations

A family of recently developed devices, hydrogel ionotronics, uses hydrogels as ionic conductors, and uses hydrophobic elastomers as dielectrics. This development has posed a challenge: integrate hydrogels and hydrophobic elastomers-in various manufacturing processes-with strong, stretchable, and transparent adhesion. Here, a multistep dip-coating process is described to enable hydrogel ionotronics of diverse configurations. In doing so, a hydrophobic surface is primed to let a hydrophilic precursor wet it, and then polymers of different layers are interlinked with covalent bonds. As a representative example, an ionotronic luminescent fiber that can be lengthened to ≈2.5 times its original length and keeps functioning after 10 000 cycles of stretching is fabricated. A luminescent fabric that displays movable pixels and other configurations is also demonstrated. The proposed method of fabrication expands the design space for hydrogel ionotronics.

Superhydrophobic surfaces for extreme environmental conditions

Superhydrophobic surfaces for repelling impacting water droplets are typically created by designing structures with capillary (antiwetting) pressures greater than those of the incoming droplet (dynamic, water hammer). Recent work has focused on the evolution of the intervening air layer between droplet and substrate during impact, a balance of air compression and drainage within the surface texture, and its role in affecting impalement under ambient conditions through local changes in the droplet curvature. However, little consideration has been given to the influence of the intervening air-layer thermodynamic state and composition, in particular when departing from standard atmospheric conditions, on the antiwetting behavior of superhydrophobic surfaces. Here, we explore the related physics and determine the working envelope for maintaining robust superhydrophobicity, in terms of the ambient pressure and water vapor content. With single-tier and multitier superhydrophobic surfaces and high-resolution dynamic imaging of the droplet meniscus and its penetration behavior into the surface texture, we expose a trend of increasing impalement severity with decreasing ambient pressure and elucidate a previously unexplored condensation-based impalement mechanism within the texture resulting from the compression, and subsequent supersaturation, of the intervening gas layer in low-pressure, humid conditions. Using fluid dynamical considerations and nucleation thermodynamics, we provide mechanistic understanding of impalement and further employ this knowledge to rationally construct multitier surfaces with robust superhydrophobicity, extending water repellency behavior well beyond typical atmospheric conditions. Such a property is expected to find multifaceted use exemplified by transportation and infrastructure applications where exceptional repellency to water and ice is desired.

Quantifying Surface Wetting Properties Using Droplet Probe Atomic Force Microscopy

The functional properties of a surface, such as its anti-fogging or anti-fouling performance, are influenced by its wettability. To quantify surface wettability, the most common approach is to measure the contact angles of a liquid droplet on the surface. While well established and relatively easy to perform, contact angle measurements were developed to describe macroscopic wetting properties and are difficult to perform for submillimetric droplets. Moreover, they cannot spatially resolve surface heterogeneities that can contribute to surface fouling. To address these shortcomings, we report on using an atomic force microscopy technique to quantitatively measure the interaction forces between a microdroplet and a surface with piconewton force resolution. We show how our technique can be used to spatially map topographical and chemical heterogeneities with micron resolution.