Substrate-Independent, Transparent OilRepellent Coatings with Self-Healing and Persistent Easy-Sliding Oil Repellency Li Yu,† George Y. Chen,‡ Haolan Xu,† and Xiaokong Liu*,† †
Future Industries Institute, University of South Australia, Mawson Lakes, South Australia 5095, Australia Laser Physics and Photonic Devices Laboratories, University of South Australia, Mawson Lakes, South Australia 5095, Australia
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S Supporting Information *
ABSTRACT: Herein we report a simple and substrate-independent approach to fabricate transparent oil-repellent coatings, which involves alternate deposition of poly(diallyldimethylammonium) (PDDA) and poly(styrenesulfonate) (PSS) onto substrates, followed by incubation of the coated objects into perfluorooctanoate (PFO) aqueous solutions for 2 min. Various low-surface-tension liquids can easily slide down the coating surfaces on flat substrates at a sliding angle lower than 12° for 10 μL droplets. The coatings are applicable to different substrates including Si, glass, plastic, steel, and wood, and those with complex shapes and large surface areas. They are also applicable to rough substrates with roughness at both micro/nanoscale and macroscopic scales to realize the easysliding oil repellency. Incubation of the PDDA/PSS polyelectrolyte multilayers (PEMs) into PFO solutions induces an effective but nondestructive substitution of PFO anions for PSS in the PEMs, which results in a composite coating with PFO anions homogeneously interspersed in both the coating surface and the bulk. Thanks to the as-described “repeating-layer” composition/structure of the coatings, their easy-sliding oil repellency can be self-healed after surface decomposition or well maintained after physical damages, due to the replenishing surface. Therefore, the advantageous characteristics of the as-developed oil-repellent coatings and the simplicity of the preparation protocol make the coatings highly practical for real-world applications. It is believed that the coatings can perform as antismudge coatings that shield against oil-borne contaminants, chemical-shield coatings that protect coated plastics from dissolution by organic solvents, and nonstick coatings (of oil tankers or pipelines) that enable loss-free oil transportation. KEYWORDS: oil-repellent coatings, layer-by-layer assembly, polyelectrolyte multilayers, self-healing, self-cleaning
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such coatings, which involves alternate deposition (i.e., layer-bylayer (LbL) assembly29−36) of poly(diallyldimethylammonium) (PDDA) and poly(styrenesulfonate) (PSS) onto solid substrates, followed by incubation of the coated objects into perfluorooctanoate (PFO, sodium salt) aqueous solutions. The as-fabricated coatings are highly transparent, and low-surfacetension (e.g., lower than 20 mN/m) liquids can slide down the coated surfaces when slightly inclined. The LbL assembly technique that is made advantageous by its compatibility to different substrates29−36 enables the fabrication of our coatings onto substrates of Si, glass, plastic, steel, and wood. It is intriguing that the incubation of the LbL-assembled PDDA/ PSS polyelectrolyte multilayers (PEMs) into PFO solutions induces the displacement of the majority of PSS in the PEMs
uring the past decade, water-repellent (i.e., superhydrophobic) coatings that shield against dust and water-borne contaminants have been extensively studied.1−8 However, compared to dust and water-borne contaminants that can be cleaned up by water, oily contaminants on solid surfaces are notoriously difficult to remove. This is because oil can aggressively wet common solid surfaces due to its low surface tension,9−11 including those that are superhydrophobic (e.g., lotus leaves),9 and oil is immiscible to water. Thus, the research focus in this field has recently shifted to oil-repellent coatings that can considerably ease the motion of low-surface-tension liquids.12−28 Real-world applications require the coatings to be compatible to different substrates, transparent, and persistent to surface decomposition (e.g., sunlight irradiation) and physical damages (e.g., scratch by wind-blown sands). However, few protocols are currently available to fabricate oil-repellent coatings possessing all these characteristics. Herein, we report a simple protocol to fabricate © 2016 American Chemical Society
Received: October 12, 2015 Accepted: January 4, 2016 Published: January 5, 2016 1076
DOI: 10.1021/acsnano.5b06404 ACS Nano 2016, 10, 1076−1085
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ACS Nano by PFO anions throughout the films. Meanwhile, the film’s integrity is maintained, which is irrespective of the outmost layer of the PEMs. Therefore, the as-obtained films/coatings exhibit a “repeating-layer” composition/structure (Scheme 1),
to the previous knowledge that PFO anions could only be electrostatically adsorbed onto the surface of PDDA/PSS PEMs with PDDA as the outmost layer through the counterion exchange with Cl− ions (i.e., counterions of PDDA).37−39 Thanks to the “repeating-layer” composition/structure of the coatings, their easy-sliding oil repellency can be self-healed after surface decomposition or well maintained after even severe physical damages. To date, there have been mainly three approaches to realize oil-repellent coatings. The dominant concept is to apply fluorinated micro- and/or nanoarchitectures, which can suspend oil droplets with static contact angles (CA) above 150° and facilitate an easy roll-off at low sliding angles (SA,
