In this study, the relationship between the functionality and comfort of conductive fabrics for smart clothing is investigated by examining changes in the mechanical, electrical, and comfort properties of knitted fabrics based on the blending ratio of conductive yarns. Hence, flat knitted fabrics of the same structure are manufactured using polyester and silver-coated polyamide yarns. Subsequently, their weight, thickness, tensile strength, tensile strain, bending rigidity, breathability, surface properties are measured, and their cool touch feeling, surface resistance, and electrical heating performance are evaluated. Because the strength and specific gravity of a silver-coated conductive yarn are high, with an increase in its blending ratio, its weight, tensile strength, and bending rigidity increase, whereas its strain decreases. In terms of the comfort properties, the air permeability increases as the blending ratio of the conductive yarn increases, because the pores on the surface of the knitted fabric are increased structurally owing to the conductive yarns. However, the water vapor transmission rate remains unchanged. Meanwhile, the surface roughness does not change significantly in the wale direction; however, it increases in the course direction as the blending ratio of the conductive yarn increases. The recoverability from compression decreases, and the work of compression increases as the blending ratio of the conductive yarn increases. This implies that the conductive fabric can be compressed easily but is less likely to recover from compression. Changes in the surface roughness and compression property show that the hand value of the knitted fabric is altered by the insertion of the conductive yarn. The electrical properties improved by increasing the blending ratio of the conductive yarns. In particular, even with only 33% insertion of conductive yarns, extremely good electrical properties are obtained, that is, low resistance, sensitive resistance change due to stretching, and heating of 48°C. Therefore, blending conventional and conductive yarns instead of using only conductive yarns improve comfort and wearability when applying conductive knitted fabrics to smart clothing.

In this study, the behaviors of water droplets on superhydrophobic polyester (PET) films as well as on woven and knitted fabrics with different surface microstructures were analyzed. The water droplet volume, height of release ( h), and surface inclination were modified to study the dynamic behavior of water droplets using a pressure balance and the Weber number ( We). The droplet volume did not affect the static contact angle. However, the shedding and sliding angles decreased with an increase in droplet volume. The water droplets rebounded on the surface of the superhydrophobic PET films with nano-roughness regardless of the surface inclination angle or h. However, the water droplets with h = 10 cm were pinned on the horizontal surfaces of the woven and knitted fabrics with micro-sized pores, where the dynamic pressure ( Pd) exceeded the capillary pressure. On an inclined surface, the water droplets rebounded on the surface of the woven fabric, owing to a decrease in Pd and an increase in the surface inclination angle. However, on the surface of the knitted fabric, pinning was observed even when the surface was tilted, regardless of the inclination angle. The sliding velocity of the droplets after rebound decreased in the following order: film, knitted fabric, woven fabric. With an increase in the inclination angle of the surface and the droplet volume, the sliding velocity increased, which was accompanied by a decrease in vertical impact velocity ( V) and an increase in the gravitational force. In terms of We, the droplets with a low We rebounded on all superhydrophobic surfaces, whereas the droplets with a high We were pinned on the surface of the woven and knitted fabrics.

This study seeks to analyze the effect of geometric structures of weft-knitted fabrics on superhydrophobicity and the dynamic behavior of water droplets. A flat knitting machine with different stitch patterns was used to prepare 100% polyester knitted fabrics. For the superhydrophobic surface, nano-roughness through alkaline treatment and a hydrophobic coating were introduced on prepared knitted fabrics. To analyze micro-roughness, pore size, cover factor, surface roughness, and air permeability were measured. Surface wettability was evaluated by contact and shedding angle measurements, and the dynamic behavior of droplets. Micro-roughness was greater in the order of tuck, purl, and plain jersey stitch patterns with a small cover factor and large pore size. In addition, tuck and purl stitches showed differences in surface roughness according to the wale and course directions. Nano-roughness was discernible as the alkaline treatment time increased. Following an evaluation of the wettability, the purl stitches exhibited a contact angle of 150° or more with only the hydrophobic coating. After imparting nano-roughness by alkaline treatment, the contact angle was more than 150° in all the samples. In the case of shedding angle, the tuck and purl stitches showed differences according to the course and wale directions. The shedding angle was lower when the roughness was high and the ridge and the droplet sliding directions were parallel. This difference decreased as the nano-roughness increased according to the alkaline treatment time. An evaluation of the dynamic behavior of water droplets on the superhydrophobic knitted fabric showed that rebound behavior appeared in all the samples on the horizontal surface, when the water droplet was small. However, with large droplets, the rebound behavior appeared only in purl stitches. Meanwhile, on the surface inclined at 15°, rebound behavior was observed in the tuck and purl stitches, with the tuck stitches rebounding faster in the wale direction and the purl stitches in the course direction regardless of the droplet volume. The plain jersey stitches showed pinning behavior after water droplets fell on the surface. Therefore, it is important not only to introduce nano-roughness but also properly to form geometrical micro-roughness of knitted fabric with pores and loops to induce rebound behavior of water droplets.

A superhydrophobic conductive fabric is developed to solve the problem of functional deterioration due to oxidation by air and water through alkaline hydrolysis and hydrophobic coating.