Patent Application
20200131693
Clothing provides a microclimate between the body and the external environment, and acts as a barrier for heat and vapor transfer in between. There are various functional requirements for textile or fibrous systems for different clothing applications. In particular, the huge demand of sportswear and sports equipment has raised up development of new technologies with better functional properties. Generally, the sportswear clothing system has specific features that can be modulated using the properties of the constituent materials (fiber, yarn and fabric), of which, thermal comfort including moisture and liquid transport properties is a critical requirement. For instance, in sweating conditions under active sports, the fibrous system next to the skin should not absorb sweat (water), instead, it has to transport sweat (water) through the fabric promptly to avoid the discomfort of the fabric sticking to the skin. On the other hand, it is desirable to have the side of the fabric exposed to the external environment to be omni-repellent so as to protect rain, stains and liquid pathogen. Therefore, there is a high demand to design fabric materials that have directional water transport (also referred as “one-way” water transport) property, i.e. directionally transport water from the skin to the environment, but minimize the transport in the reverse direction (from the environment to the skin).
Recently, two major strategies have been reported to endow the fibrous materials with directional liquid transport properties. One is to create lyophilicity (e.g. hydrophilicity or oleophilicity) gradient through the fabric thickness, another one is to assemble two layers of materials with different lyophilicity as an asymmetric construct. In both cases, liquid tends to transport from lyophobic (e.g. hydrophobic or oleophobic) side to lyophobilic (e.g. hydrophilic or oleophilic) side of the fibrous materials, but is blocked in the reverse direction. For instance, for the first case, Wang et al., Kong et al. and Zhou et al. separately applied photo-sensitive superhydrophobic coating on cotton or polyester fabrics followed by UV illumination on one-side to induce hydrophilicity gradient to enable directional water transport abilities through the fabric thickness. Zhang et al. prepared hydrophilic-to-hydrophobic gradient dynamers via phase separation and used them as asymmetric membranes for directional water transport. For the second case, Wu et al. and Wang et al. used electrospinning to form hydrophobic/hydrophilic and oleophobic/oleophilic dual-layer nanofibrous membrane with directional water and oil transport properties, respectively. Tian et al. used vapor diffusion method to deposit fluoroalkyl silane on one side of cotton fabric to form hydrophilic/hydrophobic Janus-type membrane with directional water droplet gating behavior. Sun et al. used three-step plasma polymerization to create asymmetric wettability on bifacial fabrics to develop directional water transport ability. Zeng et al., Liu et al. and Wang et al. similarly electrosprayed a thin layer of hydrophobic coating on a hydrophilic fabric to endow the directional water transport ability. Yang et al. and Si et al. similarly treated hydrophobic membranes by floating one side on the hydrophilic solution to form Janus membranes with directional water penetration ability.
Although, in these current designs, liquid (e.g. water) is able to directionally transport from the hydrophobic side to the hydrophilic side of the fabrics or membranes, but not vice versa, liquid tends to spread and be absorbed on the hydrophilic side. Consequently, the directional water transport will stop when the hydrophilic side is fully saturated and the saturation of water on the hydrophilic side may also increase discomfort due to increased weight. In addition, the hydrophilic external side of the fabric make it non-preventive to external water, stain or liquid pathogen. A desirable situation for a smart sportswear is to mimic the behavior of human skin. Human skin is a desirable directional liquid transport material as it excretes liquid sweat and protect the body from external liquid contaminants. In a desirable “skin-like” directional liquid transport fabric, water (e.g., sweat) can not only transport from the water-source, e.g., skin side, to the environment side and keep the skin side dry, it can also transport through to the external side for evaporation, which results in cooling, and any extra sweat will be rolled off from the external side of the fabric; meanwhile, water (e.g., rain, liquid stain, or pathogen) will not transport from the external side to the skin side, neither will it be absorbed on the outer layer facing the environment.
Based on the foregoing, there exists an ongoing and unmet need for fabrics having desirable directional liquid transport and/or water repellent properties.
The present disclosure provides fabrics. The present disclosure also provides methods of making fabrics and uses thereof.
In this disclosure, a directional water transportable hydrophobic fabric by, for example, a selective plasma treatment via patterned mask to create gradient wettability channels through the fabric thickness. The gradient wettability was confirmed by chemical analysis, where hydrophobic chains were found etched away by plasma selective treatment. The directional water transport property was confirmed via various measurements, such as, for example, contact angle test, water dripping test, shower test as well as water flux test, where water was found to be directionally transported from a hydrophobic surface to a less hydrophobic surface or a hydrophilic surface through the spot channels across the fabric thickness, while non-treated surfaces on both sides remained hydrophobic. The technology can be readily extended for other membranes as well as directional flow of other types of liquid, such as oils.
In an aspect, the present disclosure provides fabrics. The fabrics comprise a plurality of domains (e.g., channels, pores, and the like), connecting (e.g., in fluid communication with) a first side of the fabric (e.g., superhydrophobic fabric, oleophobic fabric, and the like) and a second side of the fabric (e.g., superhydrophobic fabric, oleophobic fabric, and the like) opposite the first side.
In an aspect, the present disclosure provides methods of making fabrics. The fabrics may be fabrics of the present disclosure. In various examples, a fabric (e.g., a fabric of the present disclosure) is made by a method of the present disclosure. In various examples, the methods use selective formation (e.g., using masking and selective treatment) of a fabric to form domains exhibiting directional liquid (e.g., water and/or oil) transport. Non-limiting examples of methods of making fabrics are described herein.
In an aspect, the present disclosure provides uses of fabrics. Non-limiting examples of uses of fabrics of the present disclosure are described herein.
For a fuller understanding of the nature and objects of the disclosure, reference should be made to the following detailed description taken in conjunction with the accompanying figures.
Although claimed subject matter will be described in terms of certain embodiments and examples, other embodiments and examples, including embodiments and examples that do not provide all of the benefits and features set forth herein, are also within the scope of this disclosure. Various structural, logical, and process step changes may be made without departing from the scope of the disclosure.
Ranges of values are disclosed herein. The ranges set out a lower limit value and an upper limit value. Unless otherwise stated, the ranges include the lower limit value, the upper limit value, and all values between the lower limit value and the upper limit value, including, but not limited to, all values to the magnitude of the smallest value (either the lower limit value or the upper limit value).
The present disclosure provides fabrics. The present disclosure also provides methods of making fabrics and uses thereof.
In this disclosure, a directional water transportable hydrophobic fabric by, for example, a selective plasma treatment via patterned mask to create gradient wettability channels through the fabric thickness. The gradient wettability was confirmed by chemical analysis, where hydrophobic chains were found etched away by plasma selective treatment. The directional water transport property was confirmed via various measurements, such as, for example, contact angle test, water dripping test, shower test as well as water flux test, where water was found to be directionally transported from a hydrophobic surface to a less hydrophobic surface or a hydrophilic surface through the spot channels across the fabric thickness, while non-treated surfaces on both sides remained hydrophobic. The technology can be readily extended for other membranes as well as directional flow of other types of liquid, such as oils.
In an aspect, the present disclosure provides fabrics. The fabrics comprise a plurality of domains (e.g., channels, pores, and the like), connecting (e.g., in fluid communication with) a first side of the fabric (e.g., superhydrophobic fabric, oleophobic fabric, and the like) and a second side of the fabric (e.g., superhydrophobic fabric, oleophobic fabric, and the like) opposite the first side.
In various examples, the fabric (e.g., superhydrophobic fabric, oleophobic fabric, and the like) comprises a plurality of hydrophilic and/or oleophilic domains, which may be non-randomly distributed (e.g., distributed in a non-random pattern). The fabrics may exhibit directional liquid transport. In various examples, a fabric disclosed herein exhibits a gradient property, such as, for example, the directional liquid (such as, for example, water, sweat, oil, such as, for example, oily compounds or mixtures of such compounds, and the like, and combinations thereof) transport for the inner layer and water repellent properties for the outer layer. Non-limiting examples of fabrics are described herein.
In an example, a fabric of the present disclosure provides 1) a continuous hydrophobic nature, which may result from gradient wettability domains (which may be referred to as channels), and/or 2) an overall superhydrophobic surface.
In various examples, the hydrophilic domains account for 0.1-75 mol % or wt % (e.g., 0.5-50 mol % or wt %) of the surface area of the fabric, including all 0.1% values and ranges therebetween.
The plurality of domains may have a variety of shapes. The shapes may be cross-sectional shapes. Examples of shapes include, but are not limited to, round shape, rectangular, oval, kidney shaped, triangular, star shaped, and the like, and combinations thereof.
Each of the plurality of domains has a size. In various examples, each of the plurality of domains has a size (e.g., one or more dimension(s)) of, individually, 100 microns to 5 mm, including all integer micron values and ranges therebetween. In various examples, each of the plurality of domains has a size (e.g., one or more dimension) of, individually, 500 microns to 3 mm. Each domain may be the same size, each domain may have a different size, or at least one of the domains of the plurality of the domains has a size that is different from at least one other domain of the plurality of domains.
A fabric of the present disclosure may comprise or be a fabric, which may be a hydrophobic fabric, comprising or made of natural fibers (e.g., cotton, flax, jute, wool, silk, linen, and the like), or synthetic fibers (e.g., polyester, nylon, polyolefin, acrylic, acetate, polyurethane, and the like), or semi-synthetic fibers (e.g. rayon, viscose, and the like), or a combination thereof. These fabrics may have a structure, including, but not limited to, a knitted fabric, a woven fabric, a non-woven fabric, and the like.
A fabric of the present disclosure may be characterized by a gradient in hydrophilicity (e.g., from hydrophobic character to hydrophilic character) and/or oleophobicity (e.g., from oleophobic character to oleophilic character) of (e.g., within) the plurality of domains along a direction from the first side (e.g., an interior side) to the second side (e.g., an exterior side) of the fabric (e.g., a superhydrophobic fabric, oleophobic fabric, and the like).
The gradient in hydrophilicity (e.g., from hydrophobic character to hydrophilic character) and/or oleophilicity (e.g., from oleophobic character to oleophilic character) results from a gradient in concentration of hydrophobic and/or oleophobic groups (e.g., fluoroalkyl groups, such as, for example, perfluoroalkyl groups, and the like; alkyl groups, such as, for example, propyl groups, and the like; silsesquioxane groups, such as, for example, polyoctahedral silsesquioxanes (POSS), and the like; and siloxane groups, such as, for example, polydimethylsiloxane (PDMS), and the like)) and, optionally, a plurality of nanoparticles and/or disposed on one or more (e.g., both) fabric surface(s) (e.g., the first side and/or second side of a fabric) and/or through at least a portion or all of a thickness of the fabric (e.g., to one or more fiber of the fabric). In various examples, the hydrophobic and/or oleophobic groups account for 1-10, 1-25, 1-50, 1-75, or 1-100 (e.g., 10-50, 10-75, or 10-100) mol % or wt % (based on the total weight of the fabric), including all 0.1 mol % or wt % values and ranges therebetween, of the fabric and/or the nanoparticles account for 1-50 (e.g., 1-20) wt % (based on the total weight of the fabric), including all 0.1 wt % values and ranges therebetween, of the fabric. In various other examples, the hydrophobic and/or oleophobic groups account for 1-100 (e.g., 10-100) wt % (where the weight percentage is the relative weight of hydrophobic and/or oleophobic groups to the weight of the fabric, for example, the weight of hydrophobic and/or oleophobic groups divided by the weight of the fabric multiplied by 100), including all 0.1 wt % values and ranges therebetween, of the fabric and/or the nanoparticles account for 1-50 (e.g., 1-20) wt % (based on the total weight of the fabric), including all 0.1 wt % values and ranges therebetween, of the fabric.
A plurality of nanoparticles (or at least a portion of the nanoparticles) may have a plurality of superhydrophobic groups (e.g., fluoroalkyl groups, such as, for example, perfluoroalkyl groups, and the like) covalently bound to a surface of the nanoparticles. The nanoparticles may be superhydrophobically-modified nanoparticles. Non-limiting examples of superhydrophobically-modified nanoparticles include fluorosilane-modified nanoparticles (such as, for example, fluorosilane-modified titania nanoparticles).
In various examples, hydrophobic and/or oleophobic groups (e.g., fluoroalkyl groups such as, for example, perfluoroalkyl groups) are connected to the fabric surface (e.g., to one or more fiber of the fabric) via one or more covalent bonds (e.g., —O—Si(—R)—O— moieties, where R is a hydrophobic group or an oleophobic group). The hydrophobic and/or oleophobic groups may be formed from (e.g., result from reaction of) one or more compound(s) and/or polymer(s), which may be inorganic polymers or organic polymers, comprising hydrophobic and/or oleophobic groups. In various examples, hydrophobic and/or oleophobic groups are formed from/using polyolefins, such as, for example, polypropylene, and the like, waxes, such as, for example, paraffin wax, and the like. In various examples, fluoroalkyl groups are formed from (e.g., result from reaction of) precursor compounds, such as, for example, 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PFOTES), 1H,1H,2H,2H-perfluorodecyltrichlorosilane (PFTDS), 1H,1H-perfluorooctylamine (PFOTA), perfluorooctylated quaternary ammonium silane coupling agent (PFSC), 1H,1H,2H,2H-perfluorooctyltrichlorosilane (PFOTS), poly(tetrafluoroethylene) (PTFE), 1H,1H,2H,2H-perfluorodecyltrichlorosilane (PFODS), 1H,1H,2H-perfluoro-1-dodecene (PFDDE), (heptadecafluoro-1,1,2,2-tetrahydrodecyl)trichlorosilane (FDTS), perfluoroalkyl methacrylic copolymer (PMC), and the like, and combinations thereof. The fluoroalkyl groups (e.g., perfluorinated alkyl groups) may be connected to the surface via one or more covalent bonds.
In various examples, the plurality of nanoparticles are chosen from titania nanoparticles, silica nanoparticles, zinc oxide nanoparticles, carbon nanoparticles (which may be carbon nanotubes), and the like, and combinations thereof. The nanoparticles may have a size (e.g., longest dimension) of 1 nm to 1 micron (e.g., 5 nm to 1 micron), including all integer nm values and ranges therebetween.
In an aspect, the present disclosure provides methods of making fabrics. The fabrics may be fabrics of the present disclosure. In various examples, a fabric (e.g., a fabric of the present disclosure) is made by a method of the present disclosure. In various examples, the methods use selective formation (e.g., using masking and selective treatment) of a fabric to form domains exhibiting directional liquid (e.g., water, sweat, oil, such as, for example, oily compounds or mixtures of such compounds, and the like, and combinations thereof) transport. Non-limiting examples of methods of making fabrics are described herein.
The fabrics, which may be hydrophobic fabrics, may be made of natural fibers (e.g., cotton, flax, jute, wool, silk, linen, and the like), synthetic fibers (e.g., polyester, nylon, viscose, polyolefin, acrylic, acetate, polyurethane, and the like), semi-synthetic fibers (e.g., rayon, viscose, and the like), or the like, or a combination thereof. In various examples, a fabric is chosen from cotton fabrics, polyester fabrics, nylon fabrics, viscose fabrics, polyurethane fabrics, and combinations thereof.
In various examples, a method of forming a fabric (e.g., superhydrophobic and/or oleophobic fabric, and the like) exhibiting directional liquid (e.g., water, sweat, oil, such as, for example, oily compounds or mixtures of such compounds, and the like, and combinations thereof) transport (e.g., a superhydrophobic and/or oleophobic fabric), the method comprising: exposing selected areas (e.g., selected areas of one side) of a superhydrophobic and/or oleophobic fabric to an oxygen or air plasma (e.g., using a mask), chemical etching (e.g. sodium hydroxide), or chemical deposition (e.g., fluorochemicals), such that one or more domains exhibiting a water (e.g., wettability), sweat, oil, such as, for example, oily compounds or mixtures of such compounds, and the like, and combinations thereof transport gradient from a first side of the fabric to the second side of the fabric opposite the first side of the fabric are formed, where the superhydrophobic and/or oleophobic fabric exhibiting directional liquid (e.g., water and/or oil) transport is formed. For example, the method is carried out at room temperature and ambient/unaltered atmospheric conditions.
In various examples, the exposing selected areas of the superhydrophobic and/or oleophobic fabric to a plasma (e.g. oxygen plasma, air plasma, and the like) or UV luminance, chemical etching (e.g. sodium hydroxide), chemical deposition (e.g., fluorochemicals) is carried out using a masking material (e.g., a paper tape mask, hot melt film mask, impermeable lining film, water-based adhesive or resist (e.g. glue) to form a mask film, and the like) having a plurality of apertures, the apertures corresponding to the selected areas (e.g., plurality of domains). For example, the plasma conditions are 50-500 W, including all integer W values and ranges therebetween, and/or treatment time of 30 s (s=second(s)) to 30 min (min=minute(s)) (e.g., 30 s to 10 min), including all integer second values and ranges therebetween (e.g., the plasma power is 100-300 W and treatment time is 1-15 min (e.g., 1-5 min) (shorter time may be desirable if the power is higher)).
In various examples, a superhydrophobic and/or oleophobic fabric is formed by: contacting a fabric (e.g., a hydrophilic and/or oleophilic fabric) with: i) one or more hydrophobic group precursor (e.g., fluoroalkyltrialkoxysilane(s)) and/or one or more oleophobic group precursor (e.g., fluoroalkyltrialkoxysilane(s)), ii) optionally, nanoparticles, ii) optionally, a solvent (e.g., ethanol, propanol, acetone, dimethyl formamide (DMF), and the like, and combinations thereof) to form a superhydrophobic and/or oleophobic fabric.
Fabrics prepared by a method of the present disclosure may have a hydrophobic and/or oleophobic coating (e.g., the fabric is subjected to a hydrophobic and/or oleophobic finishing process). A finishing process may comprise contacting the fabric with a plurality of nanoparticles and the like. For example, in the case of a hydrophilic and/or oleophilic fabric, subjecting the hydrophilic and/or oleophilic fabric to a process (e.g., a pre-finishing process) may provide a hydrophobic and/or oleophobic fabric. Examples of suitable processes for rendering a hydrophilic fabric hydrophobic are known in the art.
In various examples, the one or more hydrophobic group precursors and/or one or more oleophobic group precursors, optionally the plurality of nanoparticles, and optionally the solvent are present as a preformed mixture. For example, the one or more hydrophobic and/or oleophobic precursors comprise 1-100 (e.g., 10-100) mol % or wt % based on the total weight of the fabric, including all 0.1% values and ranges therebetween, and/or the plurality of nanoparticles comprise 1-50 (e.g., 1-20) wt % based on the total weight of the fabric, including all 0.1% values and ranges therebetween.
Various hydrophobic group precursors may be used in a method of the present disclosure. For example, fluoroalkyltrialkoxysilane groups are used. Non-limiting examples of fluoroalkyltrialkoxysilane groups include 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PFOTES), 1H,1H,2H,2H-perfluorodecyltrichlorosilane (PFTDS), 1H,1H-perfluorooctylamine (PFOTA), perfluorooctylated quaternary ammonium silane coupling agent (PFSC), 1H,1H,2H,2H-perfluorooctyltrichlorosilane (PFOTS), poly(tetrafluoroethylene) (PTFE), 1H,1H,2H,2H-perfluorodecyltrichlorosilane (PFODS), 1H,1H,2H-perfluoro-1-dodecene (PFDDE), (heptadecafluoro-1,1,2,2-tetrahydrodecyl)trichlorosilane (FDTS), perfluoroalkyl methacrylic copolymer (PMC), and the like, and combinations thereof.
Various nanoparticles may be used in a method of the present disclosure. Examples of nanoparticles include, but are not limited to, titania nanoparticles, silica nanoparticles, zinc oxide nanoparticles, carbon nanoparticles (which may be carbon nanotubes), and the like, and combinations thereof. The nanoparticles may have a size (e.g., longest dimension) of 1 nm to 1 micron (e.g., 5 nm to 1 micron), including all integer nm values and ranges therebetween.
In an aspect, the present disclosure provides uses of the fabrics. Non-limiting examples of uses of the fabrics of the present disclosure are described herein.
An article of manufacture may be an article of clothing. The article of clothing may be a breathable article of clothing. For example, the article of clothing is rainwear, outdoor clothing, sportswear, skiwear, hiking wear, underwear, or the like. The article of clothing may be a jacket, pants, or the like.
In various examples, articles of manufacture may comprise fabrics of the present disclosure. An article of manufacture may be a wearable article, such as, for example, an article of clothing (e.g., a waterproof or oil-proof article of clothing). In various examples, wearable articles include, but are not limited to, rainwear, outerwear, outdoor clothing, sportswear, skiwear, hiking wear, under garments (e.g., underwear, undershirt, and the like), socks, t-shirts, hats, gloves, mittens, jackets, coats, ponchos, or the like. The articles of manufacture may be an article of outdoor equipment article. In various examples, outdoor equipment article is a tent, an awning, a tarp, a sleeping bag, or the like.
The steps of the method described in the various embodiments and examples disclosed herein are sufficient to produce a fabric of the present disclosure. Thus, in an embodiment, a method consists essentially of a combination of the steps of the methods disclosed herein. In another embodiment, a method consists of such steps.
The following examples are presented to illustrate the present disclosure. The examples are not intended to be limiting in any matter.
This example provides examples of fabrics of the present disclosure, characterization of same, methods of making same, and uses of same.
Asymmetric wettability channels were created on a hydrophobic fabric to enable directional water transport properties. A combination of superhydrophobic finishing via fluorosilane-coated titanium dioxide (TiO2) nanoparticles and selective plasma treatment via patterned mask were used to create gradient wettability channels through the cotton fabric thickness (
The water transport ability was confirmed via various measurements, such as contact angle test, water dripping test, shower test as well as water flux test. For instance,
While the phenomena of directional water transport looks similarly at the first glance as those reported in prior studies, our technology differs from them in two advantages, 1) the continuous hydrophobic nature on the top spot, and/or 2) an overall superhydrophobic surface on other non-spot areas. To be more specific, firstly, the as-showed top spot area (plasma treated under 300 W, for 3 min) has an average CA of 97° and did not change within 3 s and longer time (
These two advantages of our technology were further validated by another water transport test, where the fabrics were placed inclinedly with an angle of 45°, and water was dripped from either top or back spot areas of the fabric.
The design of selective hydrophilicity gradient across the fabric thickness enabled directional water transport occurs only in the spot channel areas, while the hydrophobic nature of the other larger areas will provide the water repellency for the fabric and thereafter thermal comfort for the clothing application. The technology is applicable for all kinds of fabrics. For hydrophilic fabrics, as in the example of cotton fabric, one needs to first make it hydrophobic, such as pre-finishing, and then make the hydrophilic gradient channels; for hydrophobic fabrics, this pretreatment is not necessary. A desirable percentage of the hydrophilic areas on the external side provides directional water transport, i.e. if the percentage is too small, it will not transport water effectively and reduce the water evaporation area for evaporative cooling, while too large, the water droplets will not fall off. Either the hydrophobic pre-finishing or plasma selective treatment is simple, cost-effective and efficient, therefore will be very feasible for the commercial applications.
This technology can be used to provide a directional water transportable hydrophobic fabric. It has a high significance to the apparel industry to provide the clothing systems, particularly sportswear, with both directional water property and water repellency, therefore would bring a huge value for the industry players and market end-users. The technology can also be leveraged into other fabric or membrane applications, such as water-treatment films, fuel cells in energy industries, and wound dress, hygiene clothes in health-care industries.
The following example provides examples of fabrics of the present disclosure, characterization of same, methods of making same, and uses of same.
Personal moisture management fabrics that facilitate sweat transport away from the skin is highly desirable for wearer's comfort and performance. Demonstrated herein, for the first time, is a “skin-like” directional liquid transport fabric which enables continuous one-way liquid flow through spatially distributed channels acting like “sweating glands,” yet repels external liquid contaminants. The water transmission rate was up to 15 times greater than that of best commercial breathable fabrics. This exceptional property is achieved by creating gradient wettability channels across a predominantly superhydrophobic substrate. The flow directionality is explained by the Gibbs pinning criterion. In additional to functional clothing, this concept can be extended to develop materials for oil-water separation, wound dressing, geotechnical engineering, flexible microfluidics and fuel cell membranes.
A fabric acts like a skin in directionally excreting water droplets and expelling external liquid contaminants, with the water transmission rate being 15 times greater than that of best commercial breathable fabrics.
Described in this example is a conceptually novel design strategy that biomimetically mimics the behavior human skin. Human skin is a desirable directional liquid flow material as it excretes liquid sweat and protect the body from external liquid contaminants (
Firstly, the wetting behavior of the fabrics was checked before and after superhydrophobic finishing and successive selective plasma treatment. As shown in
An initial guess for the reason of the water transport was that either differentiated wettability or wettability gradient occurred along the vertical direction of the spot areas through the fabric thickness. To verify the cause, the “real” CAs of the spot areas on the back side of the fabrics need to be “measured”. To do this, two layers of the superhydrophobic finished fabric were assembled, then covered the top and back sides of the assembly with the patterned tape mask (
XPS was then used to investigate the chemical elements of the fabrics before and after superhydrophobic finishing and plasma treatment (300 W, 3 min). As shown in the table of
In order to confirm that the dual directional flow property and water repellency, the fabrics were placed at an incline angle of 45°, and water was dripped from either top or back spot areas of the fabric by a needle connecting with a continuous water source at a flow rate of 10 μL/min.
The breakthrough pressures of the top and back sides of the designed fabric having one spot were also experimentally examined via a water flux test by placing a plastic hollow cylinder on either side to hold water (
The directional water transport ability was further proved via another test by showering either top or back side of the fabric capping over a glass vessel loaded with blue silica gel beads (
Theoretical basis has been proposed to explain the design approach and understand the mechanisms of the directional water transport and the release of water drops from the fabric surface. The dependence of the flow directionality and the breakthrough pressure on the microstructure and wettability of the fibrous systems has also been analyzed.
Water transport by liquid drops is much faster than that by vapor evaporation, while one water drops contains millions of vapor molecules. The underlying principle of the fluid directionality in the porous spot with gradient wettability is illustrated in
It can also be seen from
where
It has been shown in
In the opposite flow direction, the contact angles will be
with contact angle at 0° when ω=−π/2 to the bottom surface with contact angle at θ0 when ω=π/2. The maximum value of the contact angle on the face away from plasma exposure is obtained as θ0=109° for the sample with 3-min treatment (
The detachment of water drops is essential to the continual directional water transport process. In this work, patterned hydrophilic porous spots are distributed on the predominantly superhydrophobic surface for easy water removal. The size and wettability of the spots are related to the breakthrough pressure and detachment of water drops. It is noted that the capillary pressure varies at different positions of fluid fronts, and the maximum value of capillary pressure that blocks the water transport will be equal to the breakthrough pressure when the gravitation force is negligible. The capillary pressure within the channel between yarns is determined by the Young-Laplace equation,
where L=a+c−a cos ω is the half distance of the width of the fluid front and c is the half distance between yarns. It is clear that the capillary pressure is all negative in the OL flow direction in
With increasing water supply, the volume of water drops increases until they fall off from the porous spot with the gravitational force overcoming the surface tension. The contacting circle interface line among the air, the water drop and the fabric cannot enlarge due to the repellence of the surrounding hydrophobic regions (
r˜R3 (3)
which holds until the detachment of the water drops. Eq. (3) has been well verified by the experimental results of detachment of water drops at different sizes of porous spots (
When the fibrous layer is placed at an incline angle at λ=45°, the surface tension drag is generated by the hydrophilic and hydrophobic areas, Fa=πγRf(cos θr−cos θa), where θa and θr are the advancing and receding contact angle, respectively (
mgsin λ˜πγRf(cos θr−cos θa) (4)
where the mass of water drop scales with the cubic drop radius Rf, viz., m˜Rf3. Analogous to the phenomenon described in Eq. (3), the increase in m is much faster than that of Rf in Eq. (4), which explains the detachment of growing water eventually drops. The directional water transport will stop if the Laplace pressure of the supplied water drop is equal to the hydrostatic pressure of the water column or water drop generated in the other side of the fabric. However, this condition cannot be met in reality as the water drop will fall off when growing slightly big.
In summary, described herein is a novel “skin-like” fabric with both directional water transport and water repellency. Distributed porous spot channels with gradient wettability across the thickness of hydrophobic fabrics via a combination of superhydrophobic finishing and selective plasma treatment were created. While these channels serve for directional liquid transport, the predominantly untreated surface area remained superhydrophobic, therefore repels external liquid contaminants. The mechanism of directional flow is explained by the Gibbs pinning criterion. The technology might be applicable for all kinds of fabrics. Either the hydrophobic pre-finishing or selective plasma treatment is simple and efficient, therefore will be very feasible for the commercial applications. The proposed fibrous materials can have a direct application in developing smart and high performance clothing, especially for sportswear. It has a high significance to the apparel industry, for bringing both directional water transport property and water repellency, therefore would bring a huge value for the industry players and market end-users. The technology can also be leveraged into other fabric or membrane applications, such as liquid separation and purification, fuel cells, wound dressing, and flexible microfluidic devices.
Materials and Methods. Superhydrophobic finishing of cotton fabrics. The fabrics used for the experiment were woven cotton fabrics. They were treated via conventional desizing, scouring, and bleaching process prior to the use.
The superhydrophobic coating was prepared using the following protocol. 2.0 g 1H, 1H, 2H, 2H-Perfluorooctyltriethoxysilane (C14H19F13O3Si, 97%, Oakwood) (noted as PFOTES) was dissolved in 198 g ethanol via vigorous mixing for 2 hours. The solution was subsequently mixed with 10 g Degussa P25 titanium dioxide nanoparticles (TiO2, Rutile: Anatase/85:15, 99.9%, 20 nm; Degussa) to form a suspension. The cotton fabrics with designed sizes were immersed in the coating suspension for 5 min, and dried in air for 10 min before testing.
Selective plasma treatment of the finished fabrics. One side of the superhydrophobic finished cotton fabric (notated as top side) was tightly covered by a layer of paper tape mask with laser-cut hole patterns (diameter varies from 0.5 to 3 mm, with a typical one of 1 mm, the intervals between holes is 10 mm), another side (notated as back side) was covered by the same tape mask without the hole patterns (
Characterization
Contact Angle Measurement:
Contact angles (CA) of the fabrics were measured via the sessile drop method using a Movie Contact Angle (VCA) System (AST Products, Billerica, Mass.) equipped with the software (VCA Optima XE). The fabrics were cut into strips, and hung in the air by fixing two ends using a thick (˜8 mm) epoxy putty tape on a glass slide. A 10 μL water droplet was placed on the fabric surface to check either its contact angle or the transport properties. At least five parallel measurements from both spot and non-spot areas on both sides of the fabrics were conducted on each specimen, and the results of either contact angles or transport time were averaged for each fabric sample.
Morphology Analysis:
Scanning electron microscopy (SEM, Tescan Mira3 FESEM) was used to study the microstructure of the cotton fabric before and after superhydrophobic and plasma selective treatments. The samples were coated with a thin layer of gold palladium before observation.
Chemical Analysis:
The surface chemical information of the cotton fabrics before and after superhydrophobic finishing and plasma treatment were analyzed using X-ray photoelectron spectroscopy (XPS) (SSX-100, Surface Science Instruments) with operating pressure of ˜2×10−9 Torr. Monochromatic Al Kα x rays (1486.6 eV) with 1 mm diameter beam size was used. Photoelectrons were collected at a 55° emission angle. Electron kinetic energy was determined by a hemispherical analyzer using a pass energy of 150 V for wide/survey scans ranging from 0 to 1100 eV. A flood gun was used for charge neutralization of all the samples. The data analysis was performed on CasaXPS software.
Thermal Analysis:
A thermogravimetric analyzer (TGA 500, TA Instruments) was used to determine the amount of TiO2 nanoparticles deposited on the treated fabric. 5-10 mg of each sample was placed in an alumina ceramics crucible and thermally heated from 30 to 990° C. in a nitrogen gas medium with a heating rate of 10° C./min. The weight percentage of TiO2 nanoparticles was estimated by calculating the difference between the remaining weight of pristine cotton fabric and TiO2/PFOTES-coated fabric.
Water Dripping Test:
Water droplets of ˜20 μL per droplet were dripped onto either top or back sides of the horizontally laid superhydrophobic finished fabrics after selective plasma treatment. Continuous water droplet supplied from a syringe pump (SK-500 III, Shenzhen Shenke Medical, China) with a flow rate of 10 μL/min was dripped by a needle on either top or back sides of the 45° inclinedly laid fabrics.
Water Flux Test:
A home-made device was set-up to measure the breakthrough pressure of the fabrics (
Water shower test: The water transport properties were further measured by a water shower test. A testing fabric was capped over on a 20 mL glass vessel loaded with ˜1 g blue silica gel beads. The vessel was then showered by an eye shower for 10 s, and the color of inside silica gel beads was checked to find whether there was water transported through the fabric. Both top and back sides of the fabrics were tested to check the transport difference.
Although the present disclosure has been described with respect to one or more particular embodiments and/or examples, it will be understood that other embodiments and/or examples of the present disclosure may be made without departing from the scope of the present disclosure.
This application claims priority to U.S. Provisional Application No. 62/750,062, filed on Oct. 24, 2018, the disclosure of which is hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62750062 | Oct 2018 | US |
