Fabrication of stable superhydrophobic coating on fabric with mechanical durability, UV resistance and high oil-water separation efficiency

Highlights

• A novel superhydrophobic coating on cotton fabric was fabricated by in situ growth and dip-coating method.

• The prepared cotton fabric showed superior resistance to various liquids and good stability.

• The prepared superhydrophobic cotton fabric exhibited high oil/water separation efficiency and durable reusability

Abstract

A durable and stable polydimethylsiloxane (PDMS) - copper stearate (CuSA₂) superhydrophobic coating has been fabricated on cotton fabric by a simple in-situ growth and dip-coating method. The surface morphology, roughness and composition of the superhydrophobic coating were analyzed by SEM, 3D optical profiler and FT-IR, respectively. The prepared cotton fabric (C-fabric) showed good superhydrophobicity (WCA ~ 158°) and a satisfactory chemical stability against strong acidic/alkali solution and various solvents. The C-fabric retained superhydrophobicity with WCA above 150° after 24 h ultraviolet (UV) irradiation, 10 times of mechanical abrasion and 12 h ultra-sonication treatment. The obtained C-fabric also possessed anti-fouling property for various common household liquids (coke, juice, tea, ink, coffee and milk) with CA above 144°. Furthermore, the C-fabric can be applied to the separation of oil/water mixture with separation efficiency of more than 96%.

Introduction

Superhydrophobic interface phenomenon was reported from “lotus effect” by Barthlott and Neinhuis in 1997 [1]. Superhydrophobic surface with special wettability is attracting great attention due to practical application value [2]. Superhydrophobic surface can be applied in the fields, such as self-cleaning [3,4], anti-corrosion [5,6], anti-flogging [7], anti-icing [8], drag reduction [9], water collection [10,11], oil-water separation [[12], [13], [14]] and so on. Superhydrophobic phenomena from lotus leaves, water strider legs, butterfly wings, spider silk and other natural organisms can be commonly found in the natural environment and these phenomena can be studied for scientific purpose. It was noted that the micro-/nanoscale dual structures on the surface of materials with low-surface-free-energy were responsible for the superhydrophobic property [[15], [16], [17]]. Many methods were developed from the above findings to fabricate superhydrophobic surface, which include template method [18,19], sol–gel [20,21], chemical etching [22,23], spraying approach [24], phase separation [25], and electrospinning method [26]. However, these methods have their limitations, such as time-consuming for the fabrication process, intricate instruments, rigorous reaction conditions, usage of high-cost materials and the poor mechanical durability. Therefore, the practical applications of artificial superhydrophobic products are restricted.

Cotton fabric can be widely used in daily life and industries for its advantage such as softness, comfort, warmth, breathability and biodegradability, but the drawback of vulnerability to pollution limits its application. Endowed with superhydrophobic property, the application of cotton fabric can be extended. A lot of superhydrophobic fabrics have been fabricated by researchers. A common strategy to fabricate superhydrophobic coating on fabric is coated nano-scale particles on the surface of micro-scale fiber and subsequently the dual scale hierarchical structure was modified with the low-surface-free-energy [27]. Zhou's group [28] fabricated a durable superhydrophobic fabric coating via dip-coating fluoroalkyl silane modified SiO₂ NPs, PDMS and fluoroalkyl silane mixture, the coated fabric exhibited excellent durability against strong acid, strong alkali, and the coating still showed great superhydrophobicity with WCA above 160° after 500 washing cycles and severe abrasion cycles, respectively. Li et al. [29] provided a one-step method to prepare superhydrophobic fabric by coating polyfluorowax (PFW) - graphite fluoride (GF) complexes on fabric with durable, easily repairable properties. Cao et al. [30] reported a robust and fluorine-free superhydrophobic fabric coating, firstly optimized ormosil was coated on the surface of fabric by dipping method and subsequently coating with PDMS, the fabric possessed great self-cleaning properties and superhydrophobicity with WCA ~ 160°, which can be used for rapid and continuous oil/water emulsion separation. TiO₂, SiO₂, Al₂O₃ and ZnO NPs are often employed to modify fabric to prepare rough and durable superhydrophobic surface. Huang et al. [31] successfully prepared marigold flower-like dual-scale TiO₂ particles on a cotton fabric surface via a one-pot hydrothermal method, this fabric displayed better mechanical and environmental stability, good self-cleaning property and high selectivity for oil/water mixtures separation. Baran et al. [32] reported a superhydrophobic coating based on in situ synthesis of ZnO/SiO₂ hybrid nanocomposite on cotton fabric with antibacterial. Ren et al. [33] fabricated an ultra-robust superhydrophobic fabric by a simple dip coating with ZnO-PDMS, the obtained fabric processed mechanical stability, UV durability, and UV shielding property. Usama Zulfiqar et al. [34] developed Al₂O₃ nanoparticles and PDMS composite coating with durable superhydrophobic properties (WCA = 165°). Zhu et al. [35] proposed a simple process to prepare multilayered PDMS-ZnO-PDMS composite coating on fabric, the prepared fabric can be applied to UV shielding and oil-water separation. Gao et al. [36] created robust super-hydrophobic surfaces on different kinds of substrates using a simple phase-separation approach, the prepared fabric exhibited a superb superhydrophobicity with a WCA larger than 150° and high separation efficiency (~100%). Li's group [37] presented a facile and low-cost ultrasound irradiation method to prepare robust superhydrophobic fabric bag which can be used for continuous, ultrafast absorption and collection of oils from water surface with high efficiency. Guo et al. [38] successfully fabricated superhydrophobic fabric and sponge via in situ growth of transition-metal/metal oxide nanoparticles with thiol modification, the fabric or sponge possessed superior superhydrophobicity and good ability to separate and absorb oils from water selectively. Though the reported researches achieved outstanding progresses for superhydrophobic coating fabrication, the preparation of superhydrophobic fabric coating with good mechanical durability and high separation efficiency for oil/water mixture still has great challenges.

In this work, a durable superhydrophobic fabric was prepared via in situ growth copper stearate (CuSA₂) and subsequent rational coating with PDMS, in which CuSA₂ could construct micro/nano-structure, PDMS serve as adhesive layer and hydrophobic agent, and the long alkyl chains from stearic acid (SA) provide the low surface energy. The preparation process has no complex procedures and the materials mentioned above are cheap, green, non-toxic and commonly. The obtained C-fabric exhibits good stability and durability against some harsh conditions. Furthermore, the C-fabric can be applied to separate oil from water effectively. The fabrication method can be applied on other porous materials such as polyester fabric, cotton/polyester fabric and sponge.