Directional Water Transport Research Articles

Asymmetric water affinity on antibacterial electrospun sub-micro cellulose acetate Janus membrane

Cellulose triacetate (CTA) was hydrolyzed to lower degree of substitution (DS) of cellulose diacetate (CDA) at various hydrolysis time. Water affinity of cellulose acetate (CA) changed from hydrophobic to hydrophilic when DS decreased to 1.96 at 16 h. Then, Janus antibacterial CA membrane was fabricated by 2 h-electrospinning with 0.5, 1.0 and 2.0 wt% of silver nitrate (AgNO3) on the front side, and pure CTA on the back side. The silver nitrate was reduced to silver nano particles (AgNPs) and distributed in fibres to gain prominent antibacterial property against S. aureus and E. coli. The Janus membrane showed directional water transportation for various biomedical applications such as wound dressings.

Bioinspired Janus Textile with Conical Micropores for Human Body Moisture and Thermal Management.

Excessive sweat secreted from the skin often causes undesired adhesion from wetted textiles and cold sensations. Traditional hydrophilic textiles such as cotton can absorb sweat but retain it. A hydrophobic/superhydrophilic Janus polyester/nitrocellulose textile embedded with a conical micropore array with a hydrophilic inner surface that can achieve directional liquid transport (with an ultrahigh directional water transport capability of 1246%) and maintain human body temperature (2-3 °C higher than with cotton textiles) is demonstrated. When the hydrophobic polyester layer with large opening of hydrophilic conical micropores contacts the liquid, the Janus polyester/nitrocellulose textile can pump it to the superhydrophilic nitrocellulose layer through the hydrophilic conical micropores driven by capillary force. The Janus polyester/nitrocellulose textile can weaken undesired wet adhesion and heat loss due to the removal of liquid. The water wicking and air permeability of the Janus polyester/nitrocellulose textile is comparable to those of traditional cloths. This study is valuable for designing of functional textiles with directional water transport properties for personal drying and warming applications.

Application of surface wettability modified polypropylene nonwoven in Janus composite fibrous mats for the function of directional water transport

Textiles with the function of directional water (sweat) transport play a pivotal role in regulating human thermal and wet comfort. Polypropylene nonwoven (PPNW) fabric has an excellent moisture (sweat) conduction due to its inert water absorption, which makes moisture be difficult to adhere on the PP fiber surface. Nevertheless, excessive hydrophobicity also affects the comfort of clothing materials, and thus it is significant to improve wettability of PP fiber used in the field of textile. In this study, it was reported a kind of composite fibrous mats with the function of directional water transport. The polymerization of acrylic acid (AAc) was grafted on the surface of plasma‐treated PPNW (TPPNW) as the inner layer (TPPNW‐AAc), which was able to improve the wettability of the PPNW surface. Polyacrylonitrile containing alumina nano‐particles (PAN‐Al2O3) layer was deposited on the surface of TPPNW‐AAc by electrospinning technology as the outer layer. The wettability difference between the inner and outer layers of the material was utilized to induce the push‐pull effect to transport water from the TPPNW‐AAc layer to the PAN‐Al2O3 layer. The surface wettability of the TPPNW‐AAc layer and the performance of the directional water transport of composite fibrous mats were characterized systematically. Experimental results demonstrated that the composite fibrous mats showed the excellent accumulative one‐way transport index (AOTI, 870%), remarkable overall moisture management capacity (OMMC, 0.8) when the contact angle of the TPPNW‐AAc surface can be reduced from 119° to 30°, and decent wearability performance.

Multifunctional Directional Water Transport Fabrics with Moisture Sensing Capability.

Previous fabrics with directional fluid transport capability typically have a single function to transport liquid. Multifunctional directional fluid fabrics are highly desirable for making "smart" textiles but remain a challenge to develop. In this study, we have for the first time prepared a multifunctional, directional water transport fabric. By using a two-step coating process, we applied polypyrrole (PPy), a conducting polymer, on one side of a hydrophilic fabric (cotton). We showed that the single-side PPy-coated fabrics had reasonable conductivity (surface resistance in the range of 43-54 kΩ/□) and a one-way water transport function. We further showed that by integrating metal-plated nylon wires on the two sides, the fabric can be used as a capacitive sensor to sense water content in the fabric. The conducting layer enables the sensor device to have a sufficient capacitance response. Reasonable integration of the metal electrodes allows the device to have a minimal effect on the directional water transport and breathability of the fabric. Such a novel multifunctional fabric may find applications in making "smart" clothing.

Effect of asymmetric wettability on directional transport of water through Janus fabrics prepared by an electrospinning technique

Janus fabric with directional water transport has attracted much attention in scientific and industrial communities. However, limited knowledge is available regarding combining a commercial woven fabric and an electrospun nonwoven fabric to prepare Janus fabric and the effect of asymmetric wettability on its directional water transport properties. Herein, we prepared two types of Janus fabric by depositing different thicknesses of polystyrene (PS) layers on the hydrophilic polyester fabrics (100 μm) and by depositing the same thickness of PS layer (6.0 μm) on different hydrophilic polyester fabrics. The Janus fabrics showed directional water transport features when the PS layer thickness was between 3.0 and 12.0 μm. On hydrophilic polyester, the fabric exhibited directional water transport and the penetration time of water decreased with increasing hydrophobicity. These novel results may be useful for designing and developing “smart” textiles with directional water transport properties for various applications.

Novel Water Harvesting Fibrous Membranes with Directional Water Transport Capability

AbstractPrevious studies about water harvesting from airborne moisture, which is driven by a directional water transport principle, are based on either a 2D surface or a 1D filament. Porous membranes with a directional water transport capability are seldom used for water harvesting. Herein, a novel hydrophobic/hydrophilic directional‐wicking nanofibrous membrane is reported showing enhanced water harvesting ability. In comparison to the hydrophobic or hydrophilic membranes of the same structure and dimension, the directional wicking fibrous membranes have much higher water harvesting capacity. This fantastic water harvesting capability is originated from strong force to draw water from the hydrophobic to the superhydrophilic layer and ever permeable channels formed by the hydrophobic fibrous structure. Larger pores in the hydrophobic layer and smaller pores in the superhydrophilic layer facilitate water harvesting because of the enhanced directional wicking ability. The variation in pore dimension between the hydrophobic and the hydrophilic layers can result in 1.7 times difference in water harvesting capacity. These novel understandings may be useful for the development of advanced water harvesters for various applications.

Preparation and characterization of multilayered superfine fibrous mat with the function of directional water transport.

Directional water transport in garment materials plays a pivotal role in maintaining human thermal and wet comfort. In the present work, a new type of multilayer fibrous mat with the specific function of directional water transport was prepared via the combination of melt-electrospinning and solution-electrospinning. The polypropylene (PP) fibrous layer prepared by melt-electrospinning technology was located in the inner layer (next to the skin), while the polyacrylonitrile-containing hydrophilic nano-silica particles (PAN-SiO2) layer with remarkable hydrophilicity was located in the outer layer, which could effectively transport water to the outer surface of the composites. Treatment of the as-prepared PAN-SiO2/PP with an alkaline aqueous solution of dopamine not only increased the wettability of the PP layer, but also further improved the hydrophilicity of PAN-SiO2. A layer of cotton woven mesh was added between the TPP layer and TPAN-SiO2 to form a sandwich structure in order to accelerate water transport in the bilayered fibrous mats. The directional water transport, mechanical flexibility, and permeability of the prepared multilayered superfine fibrous mat were characterized systematically. The experimental results exhibited that TPAN-SiO2/cotton mesh/TPP exhibited an excellent accumulative one-way transport index (AOTI, 1071%), remarkable overall moisture management capacity (OMMC, 0.88), and reasonably high water vapor transport rate (WVT, 11.6 kg d−1 m−2), indicating it is a promising candidate for the development of novel textile materials for use in the field of sportswear for fast sweat release applications.

Biomimetic Fibrous Murray Membranes with Ultrafast Water Transport and Evaporation for Smart Moisture-Wicking Fabrics.

Both antigravity directional water transport and ultrafast evaporation are critical to achieving a high-performance moisture-wicking fabric. The transpiration in vascular plants possess both of these features, which is due to their optimized hierarchical structure composed of multibranching porous networks following Murray's law. However, it remains a great challenge to simultaneously realize the ultrafast water transport and evaporation by mimicking nature's Murray networks in the synthetic materials. Here, we report a synergistic assembly strategy to create a biomimetic micro- and nanofibrous membrane with antigravity directional water transport and quick-dry performance by combining a multibranching porous structure and surface energy gradient, overcoming previous limitations. The resulting fiber-based porous Murray membranes exhibit an ultrahigh one-way transport capability ( R) of 1245%, a desired overall moisture management capability (OMMC) of 0.94, and an outstanding water evaporation rate of 0.67 g h-1 (5.8 and 2.1 times higher than the cotton fabric and Coolmax fabric, respectively). Overall, the successful synthesis of these biomimetic porous Murray membranes should serve as a source of inspiration for the development of moisture-wicking technologies, providing personal comfort in hot or humid environments.

Ultrafast water harvesting and transport in hierarchical microchannels.

Various natural materials have hierarchical microscale and nanoscale structures that allow for directional water transport. Here we report an ultrafast water transport process in the surface of a Sarracenia trichome, whose transport velocity is about three orders of magnitude faster than those measured in cactus spine and spider silk. The high velocity of water transport is attributed to the unique hierarchical microchannel organization of the trichome. Two types of ribs with different height regularly distribute around the trichome cone, where two neighbouring high ribs form a large channel that contains 1-5 low ribs that define smaller base channels. This results in two successive but distinct modes of water transport. Initially, a rapid thin film of water is formed inside the base channels (Mode I), which is followed by ultrafast water sliding on top of that thin film (Mode II). This two-step ultrafast water transport mechanism is modelled and experimentally tested in bio-inspired microchannels, which demonstrates the potential of this hierarchal design for microfluidic applications.

Fabrication of a Peristome Surface Structure of Nepenthes alata by Elliptical Vibration Cutting

The phenomenon of continuous directional water transport on the peristome surface of Nepenthes alata (N. alata) has been found to be of great significance to the applications of microfluids, anti-adhesion surface texture, lubrication and so on. Various methods are used to fabricate the bionic structure of the peristome surface. However, the size of processing area and the fabrication material are limited in the previous methods, which results in the limitation of the bionic structure applications. In order to solve the remained problems of small-scale and limited materials, the mechanical machining is creatively applied to the fabrication of bionic structure of peristome surface of N. alata in this paper. An elliptical vibration cutting system (EVC) driven by mechanical structure is designed and built to satisfy the size requirements of the bionic structure. The surface topographies corresponding to the tool trajectories of cutting and extrusion are obtained, respectively. The results demonstrate that both the two methods can realize the fabrication of bionic inclined microcavities while few defects can be seen on the extruded surface. According to the measured structure dimensions, it can be found the EVC system keeps a superior machining repeatability. As a consequence, the availability of the newly proposed method for the large-area fabrication of the bionic structure is verified.

Ultrafast Achievement of a Superhydrophilic/Hydrophobic Janus Foam by Femtosecond Laser Ablation for Directional Water Transport and Efficient Fog Harvesting.

Water scarcity is a serious global challenge, especially in arid and desert regions. Functional devices for directional water transport and fog collection have received increasing attention. Existing methods and technologies suffer from low fog-collecting efficiencies, complicated fabrication processes, and high fabrication costs. Herein, we report a simple and low-cost method to rapidly fabricate nanoparticle-covered microstructures on one side of a copper foam surface, using one-step femtosecond laser direct writing technology, which enormously improved processing efficiency. The resulting foam exhibits superhydrophilic/hydrophobic Janus properties. The foam allows water droplets to pass from the hydrophobic side to the superhydrophilic side, but not in the opposite direction. The Janus foam can therefore be used for harvesting water in fog environments, and the maximum water-collecting efficiency is 3.7 g cm-2 h-1, which is much better than existing data. The Janus foam exhibits excellent stability during abrasion and hydraulic wash tests. This water-collecting design may provide an efficient route for overcoming future water shortages.

Highly Permeable, Directional Water Transport Cotton Fabrics

AbstractA novel concept of preparing directional water transport cotton fabrics with high air permeability even if at a fully wetted state is demonstrated here. A two‐step electrospraying technique is employed to form a superhydrophobic pattern array on cotton fabric at the first step followed by single‐side electrospray treatment. The superhydrophobic pattern plays key roles not only in maintaining the cotton fabric at a high air permeability in wet state but also in enhancing one‐way transport capacity. In comparison to the single side electrosprayed fabric, which shows directional water transport property without superhydrophobic pattern, the one with a superhydrophobic pattern has 1.89 times higher one‐way transport index, whereas its air permeability is just reduced by 1.8% when it is wetted with water. This novel concept may be useful for design of high performance moisture management fabrics for various applications.

Breakdown in the directional transport of droplets on the peristome of pitcher plants

Over the centuries, scientists and engineers have been fascinated by the directional transport of water on the peristome of pitcher plant. Through experimental investigation and theoretical analysis, here we reveal the more complex picture of droplet transport on this peculiar natural surface. First, we demonstrate that in addition to the presence of the asymmetric arch-shaped microcavity with gradient wedge corners and sharp edges, the structural gradient in the first-tier microgroove of the pitcher’s peristome also plays an important role in the regulation of the directional droplet transport. Moreover, the directional liquid transport only occurs in a limited condition. Without the intricate control of the interplay between its multiscale structures and multiscale sources of water, as well as the dynamic conditions of water, the preferential directional droplet transport will collapse. The new transport phenomenon and the mechanisms we reveal will provide important insights for the design of asymmetric morphologies for droplet manipulation.

Continuous, Spontaneous, and Directional Water Transport in the Trilayered Fibrous Membranes for Functional Moisture Wicking Textiles.

Directional water transport is a predominant part of functional textiles used for continuous sweat release in daily life. However, it has remained a great challenge to design such textiles which ensure continuous directional water transport and superior prevention of water penetration in the reverse direction. Here, a scalable strategy is reported to create trilayered fibrous membranes with progressive wettability by introducing a transfer layer, which can guide the directional water transport continuously and spontaneously, thus preventing the skin from being rewetted. The resulting trilayered fibrous membranes exhibit a high one-way transport index R (1021%) and a desired breakthrough pressure (16.1 cm H2 O) in the reverse direction, indicating an ultrahigh directional water transport capacity. Moreover, on the basis of water transport behavior, a plausible mechanism is proposed to provide insight into the integrative and cooperative driving forces at the interfaces of trilayered hydrophobic/transfer/superhydrophilic fibrous membranes. The successful synthesis of such fascinating materials would be valuable for the design of functional textiles with directional water transport properties for personal drying applications.

Continuous and controlled directional water transportation on a hydrophobic/superhydrophobic patterned surface

Directional transportation of water flow, which is frequently seen in nature, is of not only great importance to organisms but also crucial demand for advanced science and technologies. Numerous contributions have been dedicated to the motion manipulation of single drops on chemically heterogeneous surfaces, which have hydrophilic/superhydrophobic patterns in general. Drop retention is therefore difficult to avoid due to the hydrophilic regions, and continuous transportation of water flow still remains a challenge. Here, a hydrophobic/superhydrophobic patterned surface, featured with chemical homogeneity, is developed via a simple coating on a morphologically heterogeneous surface. Such surface can guide the continuous water motions, and relationship between the surface patterns and the motion controllability is clarified. Additionally, the potential application of the patterned films is explored as a micro-mixing device for different drops. The finding and results are essential for advancing more applications of microfluidics and microchips.

Pore size effect on one-way water-transport cotton fabrics

Fabrics with spontaneous one-way water transport property have received much attention in scientific and industrial communities in the recentyears. However, limited knowledge is available about how to control and adjust directional water transport capacity on fabrics. In this study, we have prepared one-way water transport fabrics using three plain-woven cotton fabrics, which have different pore sizes, as substrates. An electrospray technique was employed to deposit hydrophobic coating on one side of the fabrics. One-way water transport property was attained when the coating thickness was in the range of 9.0–23.9 μm. The fabric pore size was found to be a critical factor deciding the maximum one-way water transport capacity that can be achieved on the fabric. With the same coating thickness, the fabric with smaller pores showed larger one-way transport capacity. These novel results may be useful for designing high performance one-way water transport fabrics for various applications.

A facile approach to achieve bioinspired PDMS@Fe3O4 fabric with switchable wettability for liquid transport and water collection

The robust PDMS@Fe3O4 fabric can be switched between the superhydrophobic state and slippery state via an external magnetic field and shows excellent directional water transport, self-cleaning and water collection properties.

Long‐lasting oil wettability patterns fabrication on superoleophobic surfaces by atmospheric pressure DBD plasma jet

Water wettability patterns on superhydrophobic surfaces have been widely designed to meet requirements of many fields, such as lab-on-a-chip devices and bioengineering. However, these systems are easily invalidated by oily liquids. Therefore, oil wettability patterns, which have rarely been focused on, are urgently needed. In this work, the authors successfully control oil wettability of superoleophobic surface by an atmospheric pressure dielectric barrier discharge (DBD) plasma jet. The results indicate that oil wettability is strongly influenced by treatment time, applied voltage and distance between plasma jet outlet and samples. They find that superoleophobic surfaces can be modified to be superoleophilic within 15 s, and that small holes can be etched on the surfaces under high applied voltages. Then, superoleophobic-superoleophilic patterns are prepared via selective plasma jet irradiation on superoleophobic surfaces, and both directional and antigravity transport of water and oily liquids are thus realised without external electrical or magnetic field. Additionally, ageing experiments show that the plasma-treated areas can maintain the induced wettability for >30 days storing under normal ambients, demonstrating superior time stability. The results presented here show the potential of atmospheric pressure DBD plasma jet for rapid oil wettability control and fabrication of long-time-effective oil wettability patterns.

Large-scale water collection of bioinspired cavity-microfibers

Large-scale and high-efficient water collection of microfibers with long-term durability still remains challenging. Here we present well-controlled, bioinspired spindle-knot microfibers with cavity knots (named cavity-microfiber), precisely fabricated via a simple gas-in-water microfluidic method, to address this challenge. The cavity-microfiber is endowed with unique surface roughness, mechanical strength, and long-term durability due to the design of cavity as well as polymer composition, thus enabling an outstanding performance of water collection. The maximum water volume collected on a single knot is almost 495 times than that of the knot on the cavity-microfiber. Moreover, the spider-web-like networks assembled controllably by cavity-microfibers demonstrate excellent large-scale and high-efficient water collection. To maximize the water-collecting capacity, nodes/intersections should be designed on the topology of the network as many as possible. Our light-weighted yet tough, low-cost microfibers with high efficiency in directional water transportation offers promising opportunities for large-scale water collection in water-deficient areas.

Stable Janus superhydrophilic/hydrophobic nickel foam for directional water transport

Janus superhydrophilic/hydrophobic macroporous nickel foam for directional water transport has been demonstrated via a simple floating strategy. Water can transport from hydrophobic to superhydrophilic layer through Janus nickel foam, but cannot transfer from superhydrophilic to hydrophobic layer. This “3D water diode” Janus nickel foam shows extremely high transport rate and outstanding stability. After damaged by abrasion, its directional water transport property retains well.