Applied Surface Science 362 (2016) 63–69 Contents lists available at ScienceDirect Applied Surface Science jou rn al h om ep age: www.elsevier.com/locate/apsusc Surface modification of polypropylene (PP) using single and dual high radio frequency capacitive coupled argon plasma discharge D. Akbar Hacettepe University, Advanced Technology Research Center, Beytepe Campus, 06800 Beytepe, Ankara, Turkey a r t i c l e i n f o Article history: Received 15 July 2015 Received in revised form 7 November 2015 Accepted 21 November 2015 Available online 2 December 2015 Keywords: Single and dual RF plasma Polypropylene Crystallite size Scherrer equation XRD a b s t r a c t Single (40.68 MHz) and dual (40.68/2.1 MHz) high radio frequency (RF) argon plasma discharge was employed as a source of a low-temperature treatment mechanism that was used to modify the surface of polypropylene (PP). The effects of argon plasma on the surface chemistry and the surface morphology of PP were studied using X-ray diffraction analyses. In this study, samples were treated under different plasma operation conditions for parameters such as RF power, gas pressure and treatment time. Furthermore, the crystallite size was calculated (using Scherrer equation) from the diffraction pattern of the ˇ fraction (Full Width at Half maximum) for PP samples. The results reveal that the crystallite size strongly increases with RF power and treatment time, but decreases with gas pressure. From the analysis, it was found that the treated samples have higher crystallite sizes in compared to those of the single RF plasma discharge. This happens because the increase of plasma temperature leads to increases in the crystallization of PP sample, so that the crystallite size also increases. Furthermore, because of the advantageous features of the dual-RF plasma mode, the surface modification of PP sample can occur more quickly than is possible via the single-RF plasma discharge. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Polypropylene (PP) is a biomaterial that is extensively used in syringes, surgical sutures, catheters, blood transfusion bags and hemodialysis membranes [1,2]. Moreover, the mechanical prop- erties and lower thermal conductivity of PP lead to its use in food-packing industry. Conversely, its biomedical applications are restricted due to low surface polarity and hydrophobic nature, in spite of its good mechanical properties and lightweight [3]. For these reasons, it is very important to modify the surface proper- ties of PP without changing its bulk properties [4,5]. Therefore, plasma discharge treatment is one of the best treatment methods, as plasma interacts with the polymer surface and not with its bulk. The interaction typically occurs via physical activation followed by chemical reactions: Electrons, ions, photons, and free radicals inter- act with a polymer surface via processes that leads to heating and then breaking of chemical bonds to prepare the surface for the reac- tion. The combinations among the chemical groups then occur in the plasma environment [6]. Consequently, researches have used several surface modification techniques to change the properties of PP, such as flame treatment, corona discharge and UV irradiation [7–9]. However, the interest in low-temperature high frequency E-mail address: dak-bar@hacettepe.edu.tr capacitively coupled plasma discharge was increased because of the possibility of modifying a wide list of natural and synthetic poly- mers without significant changes in their molecular structures [10]. The main advantage of this versatile technique is that it is confined to the surface layer of a material and dose not affect its bulk prop- erties. Moreover, it is a clean, fast, dry and time-efficient process with a large variety of controllable process parameters (e.g. dis- charge gas, power input, pressure, treatment time). In this process, the gaseous molecules are excited to energetic states while their kinetic temperature remains close to room temperature [11,12]. Different studies have explored the use of different gaseous plasma discharge techniques for the surface modification of poly- mers. One of these studies used reactive gas plasma to add new chemical functionalities to the exposed layers that where accom- panied by small morphological changes, in contrast to the most intense surface deterioration mechanisms that exist with inert gas plasmas [13]. Furthermore, surface functionalization of PP surfaces under different plasma operation conditions (e.g. low-pressure and high-pressure plasma, RF power, and exposure time) was investi- gated, with the resulting surface characteristics (surface polarity, permeability, adhesion, etc.) were indexed [14–16]. During low-pressure plasma treatment, many free radicals can be created on the surfaces of materials if an inert gas (such as argon) is employed as a process gas. Therefore, the argon gas plasma discharge treatment (as observed previously) creates new http://dx.doi.org/10.1016/j.apsusc.2015.11.191 0169-4332/© 2015 Elsevier B.V. All rights reserved.