Elsevier

Vacuum

Volume 85, Issue 3, 24 September 2010, Pages 406-410
Vacuum

Improvement in the hydrophilic property of inner surface of polyvinyl chloride tube by DC glow discharge plasma

https://doi.org/10.1016/j.vacuum.2010.08.002Get rights and content

Abstract

A DC glow discharge plasma was generated inside polymer tube at low pressure. The polyvinyl chloride (PVC) tube with 4 mm inner diameter and 50 mm length was treated by Ar plasma generated inside the tube. The hydrophilic property of the inner surface of the PVC tube was remarkably improved after the plasma treatment. The water contact angle of the inner surface decreased to 37° from 75° for the untreated sample as the treatment time increase to 30 min. The water contact angle of plasma-treated PVC tube decreases with increasing applied voltage, but increase with increase in working pressure. When the Ar plasma-treated PVC tubes are stored in air at room temperature, the contact-angles of the inner surface quickly increases and finally reaches a plateau value which is still considerably lower than the 75° for the untreated sample.

Introduction

Polymer tubes have been widely used in the medical and biological field, for applications such as catheters, conduits, heart valves, vascular graft, or, dialysis systems. However, when the internal diameter of the polymer tube is very small (e.g., <5 mm), the hydrophobic inner surface of the polymer tubes leads to unwanted protein adsorption and cell adhesion [1], [2], [3]. It is of increasing interest to modify the inner surface of the polymer tubes to transform them into products with high bio-compatibility.

A wide range of surface treatment techniques have been developed to modify the properties of polymer surfaces without changing polymer bulk properties, such as low temperature plasmas, UV-light, electron beams, ion beams, X-rays and lasers [4], [5], [6]. Among these techniques, the low temperature plasma treatment is probably the most versatile one. The active species generated in the plasma interact with polymeric chains on the polymer surface, inducing etching, grafting, polymerization, cross-linking on the surface [7], [8], [9], [10]. Thus the treatment can modify the surface properties of polymer to satisfy various applications. Most studies of plasma-modified polymer material usually employed a plasma reactor to modify the plane surface of a small disk or film substrate [11], [12]. Such reactors are not suitable for inner surface modification of narrow polymer tubes, because the plasma itself cannot penetrate into the tube to achieve a homogeneous modification of the inner surface [13], [14].

Techniques capable of creating plasma inside the polymer tubes are desired for homogeneous modification of the inner surface. In the recent decade, a variety of techniques generating atmospheric [15], [16], [17] or low pressure [18], [19], [20], [21], [22], [23], [24] discharge plasma inside the polymer tube have been proposed. For example, Prat [18] and his coworkers developed a special electrode comprising two copper plates helically wound around a cylindrical glass, to produce an atmospheric glow discharge inside a PVC tube with 6.5 mm inner diameter by applying a high voltage alternating current with a frequency of 20 kHz across the electrode. Kitazaki and Hayashi [16] suggested an approach to produce low pressure discharge plasma inside a silicon rubber tube by ac high voltage.

We have developed an approach to generate a DC glow discharge plasma inside the polymer tubes. In the present work, the inner surface of polyvinyl chloride (PVC) tube with 4 mm inner diameter and 50 mm length were treated by Ar plasma generated inside the tube. Improvement in the hydrophilic property of inner surface of PVC tubes was studied by measuring the water contact-angle. The effect of treatment time, applied voltage and working pressure on hydrophilic property of inner surface of the PVC tube was investigated.

Section snippets

Apparatus

The scheme of experimental setup is shown in Fig. 1. A copper rod anode of 5 mm in diameter was placed in a stainless steel vacuum chamber of length 340 mm and 280 mm diameter and acts as a cathode. The vacuum chamber was evacuated to 10−1 Pa by a rotary pump and then pure argon (99.99%) was introduced into the chamber through a mass flow controller to sustain the working pressure. PVC tubes of 4 mm in inner diameter and 50 mm in length were treated. One end of the PVC tube was directly

Result and discussion

The effect of treatment time, applied voltage and working pressure on hydrophilic property of inner surface of the PVC tube was investigated.

Fig. 4a shows the evolution of the water contact-angle of the inner surface of the plasma-treated PVC tubes measured 20 mm away from the anode as a function of treatment time. The applied voltage and the working pressure were fixed at 700 V and 40 Pa, respectively. The water contact-angle of the untreated inner surface of the tube is 75° and rapidly

Conclusion

A method to generate DC glow discharge plasma inside the polymer tubes has been developed. The inner surface of PVC tubes with 4 mm inner diameter and 50 mm length were treated by Ar plasma generated inside the tube. Significant and homogeneous improvement on the hydrophilic property of the inner surface of the PVC tube was achieved by the Ar plasma treatment. The water contact-angle of the inner surface decreased to 37° from 75° for the untreated sample as the treatment time increased to

Acknowledgement

This work was supported by the Natural Science Foundation of China under Grant No. 50307002. The authors would like to thank Professor Ren Chunsheng for his technical support in contact-angle measurement.

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