Superhydrophobic Lignocellulosic Wood Fiber/Mineral Networks Mehr Negar Mirvakili, Savvas G. Hatzikiriakos, and Peter Englezos* Department of Chemical and Biological Engineering and Pulp and Paper Centre, The University of British Columbia, 2360 East Mall, Vancouver, BC V6T 1Z3, Canada * S Supporting Information ABSTRACT: Lignocellulosic wood fibers and mineral fillers (calcium carbonate, talc, or clay) were used to prepare paper samples (handsheets), which were then subjected to a fluorocarbon plasma treatment. The plasma treatment was performed in two steps: first using oxygen plasma to create nanoscale roughness on the surface of the handsheet, and second fluorocarbon deposition plasma to add a layer of low surface energy material. The wetting behavior of the resulting fiber/mineral network (handsheet) was determined. It was found the samples that were subjected to oxygen plasma etching prior to fluorocarbon deposition exhibit superhydrophobicity with low contact angle hysteresis. On the other hand, those that were only treated by fluorocarbon plasma resulted in “sticky” hydrophobicity behavior. Moreover, as the mineral content in the handsheet increases, the hydrophobicity after plasma treatment decreases. Finally, it was found that although the plasma- treated handsheets show excellent water repellency they are not good water vapor barriers. KEYWORDS: superhydrophobic, paper, plasma, PECVD, filler, cellulose 1. INTRODUCTION Changing the wetting behavior of a surface to render it superhydrophobic may facilitate the development of novel materials in a wide range of potential applications. 1,2 The wettability of a surface is typically quantified in terms of the static and the dynamic contact angles (advancing and receding) with a water droplet. Superhydrophobic surfaces, which refer to surfaces with a water contact angle above 150° and contact angle hysteresis of less than 10°, have recently received tremendous attention in the literature due to their proven significance in industrial applications. 2 It is well established and understood that a combination of low surface energy and roughness are the main ingredients for the fabrication of hydrophobic surfaces. In most cases both surface chemistry and surface roughness should be modified to create a super- hydrophobic substrate, also known as lotus effect, which makes the process challenging. 3,4 Interestingly, most of the fabricated superhydrophobic surfaces are not from renewable and biodegradable materials. 5 On the other hand, the cellulosic surface made with wood and/or nonwood plant fibers provides a suitable platform. By rendering the cellulosic surface hydrophobic, a number of value-added applications can be pursued based on this biodegradable, renewable, and thus sustainable biopolymer which is abundant in nature. Paper has a hydrophilic surface because the cellulosic fibers contain hydrophilic groups such as hydroxyl and carboxyl groups. This inherent hydrophilicity poses some limitations in the applications, where hydrophobicity is highly required. For example, in packaging applications water and moisture resistance is a required property. 6 It is customary to improve the water resistance by employing internal sizing, surface sizing, and conventional barrier coating layers. 7 There is a limitation, however, due to the high cost of thick coating layers and the poor recyclability of the sized paper. Fluorocarbon thin-film coatings by plasma-enhanced chem- ical vapor deposition (PECVD) present several advantages over the conventional coating methods. The amount of fluoro- chemicals that is deposited on the surface of paper can be controlled depending on the degree of water repellency that is required. The fluorocarbon films that are deposited by PECVD are thin and breathable, and thus the paper is not as difficult to recycle as the coated papers with thick layers of coating by conventional methods. 8 Also a single thin film of deposited fluorocarbon on the surface of paper eliminates the need for multiple layer coatings to achieve barrier properties. The first application of plasma treatment on a cellulosic surface was performed in the 1970s by using microwave plasma for the modification of the bonding properties of cellulose. 9-12 A variety of precursor gases such as N 2 , Ar, O 2 ,H 2 , NH 3 , SO 2 , hydrocarbons, fluorocarbons, halogens, and organosilanes have been used depending on the desired properties of the cellulosic surface. 11 Pure cellulose is hydrophilic with a water contact angle of around 20°. However, depending on the pulping technique, the wood fiber may contain different amounts of cellulose, lignin, hemicelluloses, and extractives, and this will affect the final wettability of the handsheet. Hydrocarbon, organosilicon, and fluorocarbon plasma treat- ment have been employed to make hydrophobic paper Received: June 12, 2013 Accepted: August 19, 2013 Published: August 19, 2013 Research Article www.acsami.org © 2013 American Chemical Society 9057 dx.doi.org/10.1021/am402286x | ACS Appl. Mater. Interfaces 2013, 5, 9057-9066