Facile and Universal Superhydrophobic Modification to Fabricate Waterborne, Multifunctional Nacre-Mimetic Films with Excellent Stability Qiong Wu, Dan Guo, Youwei Zhang, Hewei Zhao, Dezhi Chen, Jianwei Nai, Junfei Liang, Xianwu Li, Na Sun, and Lin Guo* School of Chemistry and Environment, Beihang University, Beijing 100191, China * S Supporting Information ABSTRACT: Although numerous kinds of waterborne, nacre- mimetic films with excellent properties have been fabricated via different assembly methods, it remains difficult to put those kinds of lightweight materials into practical applications because they are sensitive to water in the environment. Herein, a simple superhydrophobic modification method was used to enhance the repellency of film to water and/or corrosive liquids in the environment. Furthermore, it lowered the gas transmission rate of the films dramatically and improved the heat and flame shield capabilities. This approach could also be applied to other kinds of nacre-mimetic films, proving to be a versatile, low-cost, fast, and facile method to produce large-area and thick, waterborne, multifunctional films with excellent repellency to water and some corrosive liquids in the environment, which will pave the road for the practical applications of nacre-mimetic films. KEYWORDS: nacre-mimetic, superhydrophobic, repellency, gas barrier, heat and flame shield ■ INTRODUCTION Quite often, nature could produce lightweight materials with robust stability and excellent properties in simple components at low cost, 1-4 for example, nacre, bone, spider silk, and tooth. Thus, scientists and engineers have long been taking lessons from nature to manufacture lightweight materials with superior properties, which undoubtedly are needed in a wide area of fields. 5-8 Among all the biological materials, nacre has gained tremendous interest because it has exceptional stability and excellent properties owing to its unique brick-and-mortar structure, constituted of highly aligned inorganic platelets surrounded by a protein matrix that serves as a glue between the platelets. 9-11 A great amount of bioinspired research has been extensively investigated to produce nacre-mimetic materials, 12-16 such as inorganic platelet-reinforced composites (Al 2 O 3, 17-20 clay, 21-26 LDH (layered double hydroxide), etc. 27-30 ) and carbon-reinforced composites (graphene, 31 graphene oxide (GO), 32-34 carbon nanotubes (CNTs), 35,36 etc.). Probably the most studied are the clay/waterborne polymer composites, such as montmorillonite (MTM)/poly(vinyl alcohol) (PVA) and montmorillonite (MTM)/poly- (diallyldimethylammonium) chloride (PDDA), because MTM is naturally abundant, is cheap, and possesses many exceptional properties, for example, distinguished thermal shield capabil- ities. Also, the waterborne polymer is compatible to the nanoclay and moreover very attractive for environmental reasons. Up to now, MTM nacre-mimetic composites with excellent properties have been successfully fabricated in different compositions 5,22,26 and component content 21,25,37 at different scales via various assembly methods. 21,25,38-40 However, industrial applications such as coatings for buildings and spaceships, not to mention biomedical implants, typically require robust repellency to water and/or some corrosive liquids in the environment and simplified low-cost fabrication procedures, besides superior properties. However, the waterborne components are very susceptible to water, leading to hydration-induced decay of various properties of the composite. 21,41 Thus, deposited water and/or corrosive liquid (such as rain and unintended sprayed liquid), which are common in the environment, will be inevitably detrimental to the performance of the composite. Although this phenomenon was discovered a long time ago and the problem is vital to advance the composites into practical applications, it has been ignored until recently. There are several methods that try to preserve the properties of the film after exposure to water. 42,43 However, those solutions are not satisfactory because it will take a long time for post-treatment (at least 24 h) or it is not suitable when the film is exposed to deposited water. Thus, we explored a faster and more efficient method to solve the Received: January 16, 2014 Accepted: November 6, 2014 Published: November 6, 2014 Research Article www.acsami.org © 2014 American Chemical Society 20597 dx.doi.org/10.1021/am505265x | ACS Appl. Mater. Interfaces 2014, 6, 20597-20602