Development, Characterization and Comparison of Facile SuperHydrophobic Textile Coatings based on Combination of Micro-Nanostructures and Functionalization Strategies

Abstract

In the highly competitive era of technological advances and continuous scientific development, the consumer market demands for value added multi-functional products have escalated tremendously. As the public and manufacturer interests have shifted from mere aesthetics towards functionality and comfort in apparel and footwear, the need of facile and upgraded synthesis of robust, waterproof and breathable materials for these practical applications has emerged as a stimulating opportunity for researchers. Designing functionalized textiles has gained significant interest in the recent research trends, especially the engineering and fabrication of water repellent textile finishes due to their vast commercial and industrial uses. This has generated an extensive variety of alternatives in terms of substrates, hydrophobizing agents and application techniques. The present work focuses on the facile design and fabrication of an assortment of nearly superhydrophobic coatings on cotton substrates with effective water repellency, longterm chemical durability and immunity to climatic conditions. The research aims to develop, characterize, compare and endorse the most efficient, eco-friendly, inexpensive, practical and unorthodox hydrophobizing formula without the use of harsh and non-biodegradable solvents and materials. For this purpose, dip-coating treatment method was selected due to its scalability, straightforwardness and mild reaction conditions and a selection of functionalizing chemicals were examined, namely polyvinylidene fluoride (PVDF), stearic acid (SA), Hexadecyltrimethoxysilane (HDTMS) and polydopamine (PDA) supported on the ZIF-8 nanostructured coating. The traditional choices for achieving dual scale hierarchical roughness include silica, titania and ZnO nanoparticles, therefore, the use of ZIF-8 as a water repellent nanocoating over cotton substrates is a relatively novel and advanced concept. The MOF nano-crystal (ZIF-8) coatings were combined with the low surface energy reagents oneby-one in tunable concentrations and multilayer assembly to successfully accomplish nearly superhydrophobic textile surfaces with water contact angle as high as 144o , water sliding angle as low as 2 o and the extraordinary AATCC water repellency grade of 6. The modified fabrics were scrutinized by scanning electron microscopy (SEM), water contact angle measurement (WCA), water sliding angle (WSA), fourier- transform infrared vi spectroscopy (FTIR), X-ray diffraction analysis (XRD), AATCC water repellency test method 193-2007, self-cleaning tests, water absorption and robustness assessments to identify the optimal conditions and methodology. The characterization results demonstrated excellent nearly superhydrophobic character with pure water and aqueous solutions with up to 25.4 dynes/cm surface tension, as well as superior chemical and physical durability under water and organic solvent sonication baths. The coatings also exhibited excellent endurance towards prolonged immersion in water, exposure to direct sunlight and water spotting without any deterioration or losses in hydrophobicity. Additionally, the functionalized textiles were self- cleaning and substantially stain resistant. Thus, near superhydrophobicity in cotton was achieved effectively via fluorine-free, durable, cost effective and environmentally safe approach by fine- tuning the active contents, synergy and multilayer application of micro-nanostructures, alkyl silane, long chain carboxylic acid and self polymerizing waterborne polydopamine.