Chung Hee Park

Nanostructured self-cleaning lyocell fabrics with asymmetric wettability and moisture absorbency (part I)

A single-faced superhydrophobic lyocell fabric maintaining its inherent high moisture absorbing bulk property was produced by oxygen plasma-based nanostructuring and a subsequent coating with a low-surface-energy material. After 5 minutes of oxygen plasma etching, followed by 30 seconds of a plasma polymerized hexamethyldisiloxane coating, the treated surface of lyocell turned into a superhydrophobic surface with a static contact angle greater than 160° and a sliding angle less than 2°; however, the backside was hydrophilic, untreated lyocell fabric. As a result of oxygen plasma etching, dual hierarchical roughness was formed on the lyocell fabric as nano scale pillars or hairs were added onto the lyocell fabric surface with micro scale roughness. Extremely opposite wetting behavior was observed, when a water droplet was deposited on the face and backside of the plasma-treated lyocell fabric. A water droplet was immediately absorbed and spread out on the untreated backside, while it rolled off the treated surface, demonstrating a bouncing effect.

Waterproof and breathable properties of nanoweb applied clothing

This study compared the waterproof and breathable properties of clothing made from an electrospun nanoweb with those made from a conventional waterproof-breathable fabric, in order to determine the...This study compared the waterproof and breathable properties of clothing made from an electrospun nanoweb with those made from a conventional waterproof-breathable fabric, in order to determine the optimal environment for using electrospun nanoweb laminate with the most favorable performance for outdoor clothing. The water resistance and water vapor transmittance of the fabrics were evaluated under a range of conditions that simulate the clothing microclimate. In addition, the clothing microclimate and subjective sensations were examined under normal and rainy atmospheric conditions. The results showed that the nanoweb laminate had a higher water vapor transmission rate but lower water resistance than the polytetrafluoroethylene laminate. Results from the water penetration tests however suggest that water resistance may be sufficient to prevent wetting by rain. The wearing test revealed that nanoweb laminated clothing provided a more comfortable clothing-microclimate than polytetrafluoroethylene laminated clothing in a normal, warm environment similar to that when the wearer is exercising or sweating. In the rainy test conditions, no difference was observed between the polytetrafluoroethylene and the nanoweb laminated clothing in any of the measured variables.

Shape memory and breathable waterproof properties of polyurethane nanowebs

An intelligent textile with optimal environmental responses was developed from electrospun nanowebs with controllable pore structures via the spinning conditions. The use of shape memory polyurethane allowed the material’s shape to be retained and recovered through heating. The thickness of the electrospun nanoweb was varied so as to manufacture the membrane with various pore diameters. The samples were evaluated for shape memory performance, air and water vapor permeability. All samples showed shape recoveries of at least 99% and shape retentions of at least 94%. Increasing the thickness, increased the shape retention but slightly reduced the shape recovery. Pore size decreased with increasing thickness, thus decreasing air and water vapor permeability. Stretched nanowebs showed the greatest differences in water vapor permeability at 10°C with 90% RH and at 15°C with 90% RH compared with original nanowebs.

Effect of Ceramics on the Physical and Thermo-Physiological Performance of Warm-up Suit

The purpose of this study was to develop a warm-up suit that is comfortable as well as having a good thermal performance. Heat-insulating water vapor-permeable fabrics for warm-up suit were developed by applying ceramic powders to hydrophilic polyurethane films, which were then incorporated into textiles. Two types of ceramic compounds were used in this study: MU-4N and RT-3. The infrared emissivity was 92.6 for MU-4N and 94.8 for RT-3. In order to evaluate the effectiveness of using ceramics in a warm-up suit, we examined the effects of ceramics on selected variables: thermo-physiological properties of the clothing systems (using thermal manikin), and thermo-physiological responses and subjective sensations of human subjects. The infrared emissivity of textiles increased when ceramics were added to the film laminate. Ceramics slightly increased the thermal insulation value and decreased the water vapor transmission rate. The thermal manikin test also showed that ceramics enhanced the thermal insulation of the clothing system without increasing the evaporative resistance. The microclimate temperature was kept higher when subjects wore the warm-up suit with ceramics.The purpose of this study was to develop a warm-up suit that is comfortable as well as having a good thermal performance. Heat-insulating water vapor-permeable fabrics for warm-up suit were developed by applying ceramic powders to hydrophilic polyurethane films, which were then incorporated into textiles. Two types of ceramic compounds were used in this study: MU-4N and RT-3. The infrared emissivity was 92.6 for MU-4N and 94.8 for RT-3. In order to evaluate the effectiveness of using ceramics in a warm-up suit, we examined the effects of ceramics on selected variables: thermo-physiological properties of the clothing systems (using thermal manikin), and thermo-physiological responses and subjective sensations of human subjects. The infrared emissivity of textiles increased when ceramics were added to the film laminate. Ceramics slightly increased the thermal insulation value and decreased the water vapor transmission rate. The thermal manikin test also showed that ceramics enhanced the thermal insulation o...

The effects of surface energy and roughness on the hydrophobicity of woven fabrics

The wetting behavior of a hydrophobic rough surface is investigated on a surface fabricated by applying low surface tension materials such as silicone or fluoropolymer to polyester woven fabric consisting of multifilament yarns. The roughness factor of various woven fabrics can be calculated by Wenzel’s and Cassie–Baxter’s equations. For the fabrics treated with silicone or fluoropolymer, the Cassie–Baxter model was applied, showing a level of agreement for the fabric specimens non-textured filament fibers between the predicted contact angles and the measured values. More precisely, the fabrics treated with silicone or fluoropolymer represent the transitional state between the Wenzel type and the Cassie–Baxter type; that is, the fractional contact area between the water and air f2 is greater than zero, and the sum of the fractional contact areas for solid–water f1 and air–water f2 is greater than 1. A surface with lower energy and higher roughness gave f1 + f2 close to 1 with smaller f1 and larger f2, which resulted in a high contact angle.

A quantitative analysis on the surface roughness and the level of hydrophobicity for superhydrophobic ZnO nanorods grown textiles

This study has identified the quantitative relationship between the level of hydrophobicity and the surface roughness, represented f1, of superhydrophobic nylon fabrics treated with ZnO nanorods and n-dodecyltrimethoxysilane. With this objective, ZnO nanorods were uniformly grown to give varied particle dimensions on nylon fabrics by a hydrothermal process at a range of solution concentrations. ZnO nanorods, having a unique rod-like hexagonal section structure, were assessed in terms of their dimensions and density to estimate the solid area fraction, f1, in the Cassie–Baxter model. While the static contact angle did not discriminate between the hydrophobicity of superhydrophobic surfaces, the sliding angle and shedding angle were able to achieve this. The estimated value of f1 was quantitatively associated with hydrophobicity. The assumption that there was no penetration of into the gaps between nanorods (zero h′) appeared to be valid for superhydrophobic surfaces, and this was confirmed by the strong correlation between the increased sliding and shedding angles and the increase in f1.

Preparation of breathable and superhydrophobic polyurethane electrospun webs with silica nanoparticles

Polyurethane (PU) is a unique polymeric material with excellent chemical and physical properties and is widely used in textile materials. There has been a need for superhydrophobic PU for wider applications, such as coating materials. In this research, SiO2 nanoparticle (SNP) incorporated PU webs with superhydrophobic and breathable properties were prepared by one-step sol-gel electrospinning and post-treated with a non-fluorinated water repellent chemical, n-dodecyltrimethoxysilane (DTMS). SNPs were observed to be distributed evenly all over the fiber surfaces when 1–6 wt% SNP and tetraethoxysilane (TEOS)/acetic acid solution were added. TEOS was hydrolyzed to form larger nanoparticles while developing cross-linking with aromatic groups of the PU matrix. Interestingly, the addition of 20 nm SNPs was thought to act as nucleating seeds for enhanced hydrolysis of TEOS within the PU matrix. The hierarchical surface roughness consists of different sized SNPs and polymer beads, which resulted in superhydrophobicity with water contact angles as high as 157° and shedding angles as low as 5°. Laminating PU/SNP/DTMS webs onto polyester fabrics maintained the air permeability and water vapor transmission rate, which proves the potential of the developed PU/SNP/DTMS webs for practical applications as textile laminate materials with simple processing.

Analysis of the wetting state of super-repellent fabrics with liquids of varying surface tension

In designing a super-repellent surface that is not wet to liquids with a lower surface tension than water, micro and nano-scale surface roughness have a great impact in addition to low surface energy. In this study, a super-repellent fabric was fabricated using oxygen plasma etching and plasma enhanced chemical vapor deposition (PECVD) with hexamethyldisiloxane (HMDSO). The influence of dual roughness on wettability in micro and nano-scale structures was analyzed using the contact angles of test reagents whose surface tension ranges from 33–72 dyn cm−1. The treated fabrics produced dual scale roughness, and exhibited contact angles greater than 160° against the test liquid whose surface tension was greater than 42 dyn cm−1. The Cassie–Cassie theoretical model, which is based on the non-wetting assumption of either micro-scale or nano-scale roughness, explained well the actual water contact angles on the treated fabrics. For the liquid with 42 dyn cm−1 surface tension, the wetting behavior followed behavior between the Cassie–Wenzel state and Cassie–Cassie state depending on the aspect ratio of the nano-scale roughness. With an increased etching time of 7 min or longer, the actual contact angles were measured to be larger than those predicted using the Cassie–Cassie model, which may be a result of the formation of partial re-entrant structures at the tips of the nano-pillars. Self-cleaning effects were demonstrated for solid particles adhered on the treated fabrics such as silicon carbide and Sudan Black B. Water was more effective in adhering to both particle types and rolling off the surface than isopropyl alcohol solution.

Fabrication of self-cleaning textiles by TiO2-carbon nanotube treatment:

The purpose of this study is to fabricate self-cleaning textiles with photocatalyst excited by sunlight irradiation. Self-cleaning textiles were realized by coating carbon nanotube (CNT)-TiO2-acrylate copolymer on cotton and nylon fabrics using the dip-pad-dry process. The effect of CNT addition to TiO2 was observed on the self-cleaning performance and tensile stress of the treated fabrics. The morphology, chemical structure and particle size of acrylate copolymer with CNT-TiO2 and treated fabrics were analyzed using transmission electron microscopy, field emission scanning electron microscopy, Fourier transform infrared spectroscopy and a dynamic particle-size analyzer. The self-cleaning efficiency of the treated samples was examined by decomposition rates of methylene blue in aqueous solution and that of a wine stain under sunlight irradiation. It was found that the decomposition rates both for methylene blue and the wine stain were improved by CNT addition to TiO2 treatment on fabrics. When tensile degradation by photocatalytic reaction was monitored for TiO2 and CNT-TiO2-treated fabrics, the tensile deterioration after 48 hours of irradiation appeared to be mitigated by CNT addition to TiO2 treatment.

Influence of micro and nano-scale roughness on hydrophobicity of a plasma-treated woven fabric

A superhydrophobic fabric surface was fabricated by forming a dual roughness structure in combination with lowered surface energy. The contribution of the innate micro-scale roughness resulting from the waviness of filaments and yarns in a woven fabric on hydrophobicity was investigated in comparison with a smooth film surface. Though the micro-scale roughness coming from the multi-filaments of fabric was conducive in enhancing the hydrophobicity of the surface, the micro-scale roughness itself was not enough to create superhydrophobicity. Thus a nano-scale roughness was introduced by an anisotropic etching employing oxygen plasma etching followed by plasma enhanced chemical vapor deposition. As for the nano-scale roughness, however, it was possible to achieve the superhydrophobicity only with nano-scale roughness, but with a very large aspect ratio of nano-pillar structure. In the presence of dual-scale roughness consisting of both micro- and nano-scale structures, the superhydrophobic characteristic was effectively achieved even at a small aspect ratio of nano-pillar. By adjusting the number of filaments in a yarn and by controlling the plasma process time, it was possible to control the dual-scale roughness of a woven fabric and its wettability. An excessive thinning and lengthening of nano-pillars may negatively affect the hydrophobicity by the collapse and aggregation of pillar tips, and an appropriate processing condition is critical to design a durable superhydrophobic surface.