Facile preparation of poly(ethyl a-cyanoacrylate) superhydrophobic and gradient wetting surfaces Xiaofeng Li a,b , Hongjun Dai a,b , Shuaixia Tan a,b , Xiaoyan Zhang a,b , Haiyun Liu a , Yongxin Wang a,b , Ning Zhao a , Jian Xu a, * a Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Polymer Physics and Chemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, PR China b Graduate University of Chinese Academy of Sciences, Beijing 100190, PR China article info Article history: Received 16 July 2009 Accepted 12 August 2009 Available online 15 August 2009 Keywords: Poly(ethyl a-cyanoacrylate) Vapor phase polymerization Gradient wetting Superhydrophobic abstract Hollow microspheres of poly(ethyl a-cyanoacrylate) were prepared via vapor phase polymerization using micro-waterdroplets as template and initiator. Depending on the ratio of the shell thickness to the radius, the hollow microspheres would crimple to form either microballoons or microcups during drying. These two types of microparticles were used as building blocks to construct surfaces with diverse wettability. The microballoons linked up to form a porous-netlike surface which was rough enough to render the surface superhydrophobic, while the microcups-built surface showed less hydro- phobicity. In addition, surfaces consisting of both microparticles with gradual decrease of roughness along the length direction were obtained, which presented gradient wetting property varied from superhydrophobic to hydrophobic. The as-formed superhydrophobic or gradient wetting surfaces may find potential applications in biomedical field because of the biocompatibility of poly(ethyl a-cyanoacrylate). Ó 2009 Elsevier Inc. All rights reserved. 1. Introduction Surfaces with special wettability have attracted much interest in both fundamental study and industrial fields recently. Superhydro- phobic surfaces, which exhibit apparent water contact angle above 150°, especially draw the most attention due to their fascinating self-cleaning property. It is well known that the wetting behavior of a solid surface is governed by both surface roughness and chemi- cal composition [1–6]. Increasing surface roughness can effectively enhance the surface wettability. Generally a superhydrophobic sur- face fabrication process involves amplifying a hydrophobic surface’s roughness or modifying a coarse surface with low energy materials. Up to now, numerous methods and technologies have been devel- oped to create ultra water-repellent surfaces [7–21]. But most of them require either expensive materials or harsh conditions, which impedes their practical applications. Also, biocompatible materials have seldom been involved, which restricts the application of super- hydrophobic surfaces in bioengineering fields [22]. Herein, a facile one-step method was developed to create a biocompatible superhy- drophobic poly(ethyl a-cyanoacrylate) (PECA) surface. The whole process was carried out under mild conditions, and the as-formed surface did not need any further modification. Because of the bio- compatibility and biodegradability of PECA, the obtained surfaces might be used in the biomedical field [23,24]. PECA can be synthesized by anionic polymerization from ethyl a- cyanoacrylate (ECA) based on a nucleophilic attack mechanism [25]. ECA is one of the most reactive monomers in anionic polymerization [26]. Its polymerization is very fast at room temperature when cata- lyzed by weak basic materials or even trace amount of water [27– 29]. ECA has relatively high vapor pressure and the polymerization can occur directly at the interface between the monomer vapor and water or nucleophilic substituents [30,31]. These properties have been employed to ‘‘develop” fingerprints [32], grow nanofibers [25] and coat on silica nanoparticles [33,34]. ECA is also used as super glue and finds applications in medicine such as liquid bandages and suture-less surgery. Usually, hollow micro or nanoparticles of PECA are prepared in microemulsion for drug deliver system [35,36]. To the best of our knowledge, fabrication of hollow micro PECA spheres by vapor phase polymerization has rarely been reported. In our report, PECA hollow microparticles were fabricated via vapor phase polymerization at the surface of micro-waterdroplets in air. The as- prepared microparticles constructed the rough surfaces and endowed them with diverse wettability. In addition, being prepared with gradient roughness, PECA surface could display gradient wet- ting behavior, which leads to potential applications in bimolecular interaction investigations, cell-motility studies, diagnostics and so on [5,37–41]. 0021-9797/$ - see front matter Ó 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2009.08.017 * Corresponding author. Fax: +86 10 82619667. E-mail address: jxu@iccas.ac.cn (J. Xu). Journal of Colloid and Interface Science 340 (2009) 93–97 Contents lists available at ScienceDirect Journal of Colloid and Interface Science www.elsevier.com/locate/jcis