Elsevier

Applied Surface Science

Volume 254, Issue 9, 28 February 2008, Pages 2882-2888
Applied Surface Science

Studies on surface modification of poly(tetrafluoroethylene) film by remote and direct Ar plasma

https://doi.org/10.1016/j.apsusc.2007.10.029Get rights and content

Abstract

Poly(tetrafluoroethylene) (PTFE) surfaces are modified with remote and direct Ar plasma, and the effects of the modification on the hydrophilicity of PTFE are investigated. The surface microstructures and compositions of the PTFE film were characterized with the goniometer, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Results show that the remote and direct plasma treatments modify the PTFE surface in morphology and composition, and both modifications cause surface oxidation of PTFE films, in the forming of some polar functional groups enhancing polymer wettability. When the remote and direct Ar plasma treats PTFE film, the contact angles decrease from the untreated 108–58° and 65.2°, respectively. The effect of the remote Ar plasma is more noticeable. The role of all kinds of active species, e.g. electrons, ions and free radicals involved in plasma surface modification is further evaluated. This shows that remote Ar plasma can restrain the ion and electron etching reaction and enhance radical reaction.

Introduction

Surface modification of polymers by plasma treatment is industrially attractive, as the technique is simple, easy to implement, reliable, no pollution, and cost effective [1], [2], [3], [4], [5]. Many studies [6], [7] have been reported using various plasma-based approaches and process gases, which about investigations of plasma surface modification technologies, the effects of plasma treatment, the nature of the plasma environment, and the mechanisms that drive the plasma–surface interaction. Plasma treatment affects the polymer surface to an extent of several hundred to several thousand angstroms. The bulk properties of polymers, therefore, remain unchanged. Apart from being a surface-sensitive modification technique, plasma treatment does not give rise to toxic waste problems as in the case of chemical treatment. Plasma containing electrons, ions, and radicals can interact with polymer surfaces and modify their chemical and physical properties. The plasma is capable of exerting four major effects [1], [8], [9], [10], that is, surface cleaning, surface ablation or etching, surface cross-linking, and modification of the surface chemical structure, both in situ and on subsequent exposure to the atmosphere. These effects depend on the presence of active species in plasma. However, so far researches on plasma surface modification have merely been limited to a mixed atmosphere constituted solely by active species [11], [12], [13], [14], [15]. How great is the contribution of the different active species to surface modification?

Plasma is a mixture of electrons, ions, and radicals. These species disappear in processes of the electron–positive ion recombination, the positive ion–negative ion recombination, and the radical–radical recombination. The rate constant of these reactions is in the order of 10−7 and 10−33 cm3/s, respectively [16]. Therefore, radicals can possess extremely longer lifetime than electrons and ions. Taking advantage of the different lifetime of various active particles such as electrons, ions and free radicals, these active particles are separated in a special plasma field and the super pure and high free radical concentration is attained at the position away from the plasma discharge region. This is the concept of a remote plasma treatment [9], [10], [17], [18], that is, the concentration of the ion and electron is relatively low and the concentration of free radicals is relatively high in remote Ar plasma. The article studies the effects of remote and direct Ar plasma surface treatment on poly(tetrafluoroethylene) (PTFE) films in terms of changes in surface wettability and surface chemistry. The surface properties are characterized by the water contact angle measurement, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Finally the mechanism is analyzed, and the role of all kinds of active species, e.g. electrons, ions and free radicals involved in plasma surface modification is further evaluated.

Section snippets

Materials

The PTFE films used in this study are supplied by Fuxing Fluorin Chemical Works Ltd. (China). Films of 25 mm × 50 mm are Soxhlet-extracted with acetone for 24 h to remove any surface impurities. Clean films are dried under vacuum at ambient temperature (22 °C) and stored in a desiccator before use. Diiodomethane used is of analytical grade. Deionized water is used in all experiments.

Remote plasma treatment

A self-designed reactor is used for the remote and direct Ar plasma treatments of the PTFE samples, as shown in Fig. 1.

Contact angle of water on PTFE film surfaces treated with the remote and direct Ar plasma

Fig. 2, Fig. 3, Fig. 4 show results for the contact angle of water on PTFE surfaces modified by remote and direct Ar plasma as function of the plasma treatment time, the plasma treatment power, and the Ar flow. Regardless of the treatment conditions, the PTFE films treated with the Ar plasma have smaller contact angles than the original PTFE film, their surfaces becoming, and remote Ar plasma treatment leading to a higher hydrophilicity than the direct Ar plasma treatment (Fig. 2, Fig. 3, Fig. 4

Conclusions

PTFE surfaces are modified with remote and direct Ar plasma, and the effects of the modification on the hydrophilicity of PTFE are investigated. The remote and direct Ar plasma treatment produces a noticeable decrease in the contact angle, which is mainly due to the introduction of some polar functional groups (oxygen-containing functional groups) into the PTFE surface. The remote Ar plasma gives rise to higher hydrophilicity than the direct Ar plasma. The hydrophilicity depends on the plasma

Acknowledgements

The authors thank the financial support of the National Natural and Science Foundation Council of China 30571636 and 20174030, the specialized research Fund for the Doctoral Program of Higher Education 20060698002, the key Scientific Technique item of Shaanxi province 2003K10-G61, and the key Scientific Technique item of Xi’an city GG06049.

References (20)

  • E. David et al.

    J. Mater. Process. Technol.

    (2004)
  • K.M. Baumgartner et al.

    Surf. Coatings Technol.

    (2001)
  • H. Xu et al.

    Mater. Chem. Phys.

    (2003)
  • H.S. Choi et al.

    Surf. Coatings Technol.

    (2004)
  • C. Wang et al.

    Appl. Surf. Sci.

    (2007)
  • E.T. Kang et al.

    Adv. Mater.

    (2000)
  • C. Wang et al.

    Basic Sci. J. Textile Univ.

    (2004)
  • N. Inagaki et al.

    J. Appl. Polym. Sci.

    (2002)
  • K.S. Siow et al.

    Plasma Process. Polym.

    (2006)
  • J.M. Grace et al.

    J. Dispers. Sci. Technol.

    (2003)
There are more references available in the full text version of this article.

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