Capillarity and Wetting Phenomena: Drops, Bubbles, Pearls, Waves

Studying nature to reveal the mechanisms of special wetting phenomena in biological systems can effectively inspire the design and fabrication of functional interfacial materials with superwettability. In this Review, the historical development, new phenomena and emerging applications of superwettability systems are discussed.

Nature-inspired superwettability systems

Ionic liquids are remarkable chemical compounds, which find applications in many areas of modern science. Because of their highly tunable nature and exceptional properties, ionic liquids have become essential players in the fields of synthesis and catalysis, extraction, electrochemistry, analytics, biotechnology, etc. Apart from physical and chemical features of ionic liquids, their high biological activity has been attracting significant attention from biochemists, ecologists, and medical scientists. This Review is dedicated to biological activities of ionic liquids, with a special emphasis on their potential employment in pharmaceutics and medicine. The accumulated data on the biological activity of ionic liquids, including their antimicrobial and cytotoxic properties, are discussed in view of possible applications in drug synthesis and drug delivery systems. Dedicated attention is given to a novel active pharmaceutical ingredient-ionic liquid (API-IL) concept, which suggests using traditional drugs in ...

Biological Activity of Ionic Liquids and Their Application in Pharmaceutics and Medicine.

DOI: 10.1002/aenm.201702884 during desalination process and block the channels for vapor escape, resulting in the reduction of energy transfer efficiency, pure water yield, and unstable performance. Therefore, long-term stability becomes critical issues that need to be addressed. Recently, Janus membrane is emerging as a novel class of materials comprised of a two-layer structure with opposing properties and different functions.[26,27] Since the first study of Janus particle by Cho and Lee in 1985,[28] various Janus such as micelles,[29] rods,[30] and sheets[31] have been fabricated, with wide applications in oil/water separation,[32] switchable ion transport,[33] interfacial mass transfer,[34] and fog collection.[35] Here we demonstrate that a flexible Janus absorber fabricated by convenient electrospinning process can enable stable and efficient solar desalination. Taking advantage of the unique structures of Janus absorbers, two functions of solar steam generation, solar absorption and water pumping, are decoupled into different layers, with upper hydrophobic carbon black nanoparticles (CB) coating polymethylmethacrylate (PMMA) layer for light absorption and water evaporation, and bottom hydrophilic polyacrylonitrile (PAN) layer for pumping water. Therefore, salt may only be deposited in the hydrophilic PAN layer and quickly be dissolved because of continuous water pumping. Under 1-sun illumination, the Janus absorber demonstrates efficient solar steam generation (72%) and stable water output (1.3 kg m−2 h−1, over 16 d, with 45 min each day), not achieved in most of previous absorbers. With unique structure design achieved by scalable process, our flexible Janus absorber provides an efficient, stable, and portable solar steam generator for direct solar desalination. Figure 1 presents the illustration of solar steam generation (Figure 1a), and structures of Janus absorber (Figure 1b) in sea water. Porous absorbers naturally float on the water surface, absorbing solar energy to generate steam, without heating the bulk water. CB coating PMMA (CB/PMMA) layer stays above the water surface due to its hydrophobic property while PAN layer is immersed in water for efficient water supply. During the solar steam generation process, the CB/PMMA layer harvests solar energy and converts light to heat, generating vapor from the interfacial region of CB/PMMA and PAN. Thus, the With recent progress in interfacial solar steam generation, direct solar desalination is considered a promising technology for providing a clean water solution through a cost effective and environmental-friendly pathway. As a high and stable water production rate is the key to enable widespread applications, salt deposition becomes a critical issue that needs to be addressed. Herein, the authors demonstrate that a flexible Janus absorber fabricated by sequential electrospinning can enable stable and efficient solar desalination. Taking advantage of the unique structure of Janus, two functions of steam generation, solar absorption and water pumping, are decoupled into different layers, with an upper hydrophobic carbon black nanoparticles (CB) coating poly methylmethacrylate (PMMA) layer for light absorption, and a lower hydrophilic polyacrylonitrile (PAN) layer for pumping water. Therefore, salt can only be deposited in the hydrophilic PAN layer and quickly be dissolved because of continuous water pumping. Janus absorber demonstrates high efficiency (72%) and stable water output (1.3 kg m–2 h–1, over 16 days) under 1-sun, not achieved in most previous absorbers. With a unique structure design achieved by scalable process, this flexible Janus absorber provides an efficient, stable and portable solar steam generator for direct solar desalination.

Flexible and Salt Resistant Janus Absorbers by Electrospinning for Stable and Efficient Solar Desalination

Engineered wettability is a traditional, yet key issue in surface science and attracts tremendous interest in solving large-scale practical problems. Recently, different super-wettability systems have been discovered in both nature and experiments. In this Review we present three types of super-wettability, including the three-dimensional, two-dimensional, and one-dimensional material surfaces. By combining different super-wettabilities, novel interfacial functional systems could be generated and integrated into devices for use in tackling current and the future problems including resources, energy, environment, and health.

Bioinspired Super-Wettability from Fundamental Research to Practical Applications

Inspired by the efficient fog collection on cactus spines, conical copper wires with gradient wettability are fabricated through gradient electrochemical corrosion and subsequent gradient chemical modification. These dual-gradient copper wires' fog-collection ability is demonstrated to be higher than that of conical copper wires with pure hydrophobic surfaces or pure hydrophilic surfaces, and the underlying mechanism is also analyzed.

Bioinspired Conical Copper Wire with Gradient Wettability for Continuous and Efficient Fog Collection

Engineered asymmetric membranes for intelligent molecular and ionic transport control at the nanoscale have gained significant attention and offer prospects for broad application in nanofluidics, energy conversion, and biosensors. Therefore, it is desirable to construct a high-performance heterogeneous membrane capable of coordinating highly selective and rectified ionic transport with a simple, versatile, engineered method to mimic the delicate functionality of biological channels. Here, we demonstrate an engineered asymmetric heterogeneous membrane by combining a porous block copolymer (BCP) membrane, polystyrene-b-poly(4-vinylpyridine) (PS48400-b-P4VP21300), with a track-etched asymmetric porous polyethylene terephthalate membrane. The introduction of chemical, geometrical, and electrostatic heterostructures provides our heterogeneous membrane with excellent anion selectivity and ultrahigh ionic rectification with a ratio of ca. 1075, which is considerably higher than that of existing ionic rectifying systems. This anion-selective heterogeneous membrane was further developed into an energy conversion device to harvest the energy stored in an electrochemical concentration gradient. The concentration polarization phenomenon that commonly exists in traditional reverse electrodialysis can be eliminated with an asymmetric bipolar structure, which considerably increases the output power density. This work presents an important paradigm for the use of versatile BCPs in nanofluidic systems and opens new and promising routes to various breakthroughs in the fields of chemistry, materials science, bioscience, and nanotechnology.

Engineered Asymmetric Heterogeneous Membrane: A Concentration-Gradient-Driven Energy Harvesting Device

The osmotic energy existing in fluids is recognized as a promising “blue” energy source that can help solve the global issues of energy shortage and environmental pollution. Recently, nanofluidic channels have shown great potential for capturing this worldwide energy because of their novel transport properties contributed by nanoconfinement. However, with respect to membrane-scale porous systems, high resistance and undesirable ion selectivity remain bottlenecks, impeding their applications. The development of thinner, low-resistance membranes, meanwhile promoting their ion selectivity, is a necessity. Here, we engineered ultrathin and ion-selective Janus membranes prepared via the phase separation of two block copolymers, which enable osmotic energy conversion with power densities of approximately 2.04 W/m2 by mixing natural seawater and river water. Both experiments and continuum simulation help us to understand the mechanism for how membrane thickness and channel structure dominate the ion transport pr...

Ultrathin and Ion-Selective Janus Membranes for High-Performance Osmotic Energy Conversion.

Ion transport in nanofluidic devices for energy harvesting

In living systems, ion conduction plays a major role in numerous cellular processes and can be controlled by biological ion channels in response to specific environmental stimuli. This article describes biomimetic ionic gates for ion conduction based on sodium and potassium activated nanochannels. The Na+ activated ionic gate and K+ activated ionic gate were developed by immobilizing the alkali metal cation-responsive functional molecules, 4′-aminobenzo-15-crown-5 and 4′-aminobenzo-18-crown-6, respectively, onto the conical polyimide nanochannels. When the ionic gate was in the presence of the specific alkali metal cation, positively charged complexes formed between the crown ether and the alkali metal cation. On the basis of the resulting changes in surface charge, wettability and effective pore size, the nanochannel can achieve reversible switching. The switching behaviors of the two complexes differed due to the differences in binding strength between the two complexes. The Na+ activated ionic gate is ...

Kai Xiao

Papers

Bioinspired Conical Copper Wire with Gradient Wettability for Continuous and Efficient Fog Collection

Engineered Asymmetric Heterogeneous Membrane: A Concentration-Gradient-Driven Energy Harvesting Device

Ultrathin and Ion-Selective Janus Membranes for High-Performance Osmotic Energy Conversion.

Ion transport in nanofluidic devices for energy harvesting

Engineered Ionic Gates for Ion Conduction Based on Sodium and Potassium Activated Nanochannels