Preparation Of Superhydrophobic Surfaces For Textiles Based On Hybrid Nano-silica Hydrosols

Since lotus leaves'self-cleaning effect was discovered, superhydrophobic surfaces have attracted much focus from many scholars, and have made rapid progress both in theory research and preparation technology. Numerous studies have confirmed that, superhydrophobic surfaces could be achieved by the combination of low surface free energy and rough structure. In general, surfaces with a certain extent roughness can be obtained by introducing inorganic nano-materials. Nano-silica, as one of the most attractive nano-materials, which has the largest industrial production in the world at present, has been widely used to fabricate superhydrophobic surfaces. Unfortunately, the traditional sol-gel technique used to prepare silica nanoparticles usually involves a large amount of organic solvent as the reaction medium, which is expensive, inflammable, and unfavorable to production safety and application. Therefore, it is very important to investigate the simple and low cost technologies to prepare safe and environmental superhydrophobic surfaces.In this paper, based on the hybrid nano-silica hydrosols, according to the principle of "Lotus effect", superhydrophobic surfaces for textiles were prepared by combining sol-gel method with inorganic-organic emulsion polymerization. The major studies included:Preparation and characterization of monodisperse vinyl hybrid nano-silica hydrosols. In the water-based sol-gel system, monodisperse vinyl hybrid nano-silica (Ⅴ-SiO2) hydrosols were prepared using vinyltrimethoxysilane (VTMS) as the precursor and NH3·H2O as the catalyst in the presence of surfactant. The reaction mechanism was discussed. Main influence factors on particle sizes of V-SiO2 were analyzed. The results indicated that, theⅤ-SiO2 nanoparticles had good spherical shape and narrow size distribution. The surfactant was used as the emulsifier to disperse and stabilize the silica hydrosol. High NH3H2O concentration promoted the formation of a large number of smaller particles and the average particle size decreased. However, when the concentration of NH3·H2O was too high, the condensation reaction may become too fast to form monodisperse particles.Preparation of nano-silica/polymer containing short fluoroalkyl chains composite emulsion and its water repellency on polyester fabrics. Nano-silica/polymer containing short fluoroalkylchains (PFA/SiO2) composite emulsion was synthesized by semi-continuous seeded emulsion polymerization using vinyl hybrid nano-silica (V-SiO2) as the seed. The formation mechanism of PFA/SiO2 composite particles was discussed. Main influence factors on properties of PFA/SiO2 composite emulsion were analyzed. The optimum conditions for PFA/SiO2 preparation were found. The PFA/SiO2 composite emulsion was applied to the polyester fabrics by pad-dry-cure process. The results indicated that, the PFA/SiO2 composite emulsion had excellent film-forming property, high transformation rate and high stability. The PFA/SiO2 composite particles had core-shell structure and narrow size distribution, and the average particle size was 120.3nm. Inorganic phase and organic phase had a good compatibility. The treated polyester fabric had a water contact angle of 151.5°, a water roll-off angle of 12°, and water repellency rating of 95. When a water droplet is in contact with the treated fabric, the solid/liquid/gas three-phase contact interface was formed. Superhydrophobicity was achieved by the synergistic effect of organic phase with the low surface energy and inorganic phase providing surface topography.Superhydrophobic cotton surfaces prepared by two-step process based on methyl hybrid nano-silica hydrosols. The methyl hybrid nano-silica (M-SiO2) hydrosols were synthesized via sol-gel reaction with methyl trimethoxy silane (MTMS) as the precursor in the presence of the base catalyst and surfactant. Main influence factors on particle sizes of M-SiO2 were analyzed. The M-SiO2 nanoparticles had good spherical shape and narrow size distribution. Superhydrophobic cotton fabrics were prepared via two-step non-fluoro process by the incorporation of M-SiO2 nanoparticles and subsequent hydrophobization with hexadecyltrimethoxysilane (HDTMS). The treated cotton had a water contact angle of 151.9°, and a water roll-off angle of 13°. But its water repellency rating was only 70, and its durability was bad. It was found that M-SiO2 nanoparticles with narrow size distribution were beneficial for improving the hydrophobicity of treated fabrics. SEM, SPM, XPS, TG analysis showed that HDTMS with low surface free energy was self-assembled on particle-based cotton surface. When a water droplet sits on the rough surface of the superhydrophobic cotton fabric, there is more air trapped between silica nanoparticles. So the water droplet only contacts the top of the asperities, and rolls off easily, achieving superhydrophobicity.Superhydrophobic cotton surfaces prepared by one-step process based on a modified silica hydrosol. The modified silica hydrosols were prepared via water-based sol-gel reaction with MTMS and HDTMS as the precursors under alkaline condition in the presence of surfactant. The modified silica hydrosols were applied to the cotton fabrics by one-step process. The treated cotton fabric showed superhydrophobicity, with a water contact angle of 152.1°, a water roll-off angle of 8°, and water repellency rating of 100. It was found that modified SiO2 nanoparticles with narrow size distribution were beneficial for improving the hydrophobicity of treated fabrics. SEM, SPM, XPS, TG analysis showed that the surface roughness due to the SiO2 particles and the material with low surface free energy on the top of the rough surface were simultaneously incorporated onto the cotton fabric. The large fraction of air was trapped between silica nanoparticles underneath the water droplet. So the water droplet only contacts the top of the asperities, repelling the water penetration.Compared with the two-step process to prepare superhydrophobic surfaces, one-step process is simple and inexpensive. The treated fabric had better dynamic hydrophobicity and durability. But the durability needed further improvement. So, in order to enhance washing durability of superhydrophobic cotton, the composite modified silica hydrosols prepared by adding silane coupling agents during the preparation of modified silica hydrosols, were applied to the cotton fabrics. The effects of the types of silane coupling agents and the adding dosages on the washing durability of hydrophobic cotton were investigated. The results showed that, when 2wt% tetraethyl orthosilicate (TEOS) was added to the modified silica hydrosol, the adhesion between cotton fiber and hydrophobic film were strengthened. The corresponding treated fabrics had a much better durability with a water contact angle of 141.5°, a water roll-off angle of 25°and water repellency rating of 75 after 20 washing cycles.