Study on the Surface Characteristic of PTFE after Atmospheric Plasma Treatment

Transcription

1 2015 2nd International Conference on Biomedical Engineering (ICoBE), March 2015, Penang Study on the Surface Characteristic of PTFE after Atmospheric Plasma Treatment Noor Albatyiah Nordin a, *, SK Zaaba b, Balqissiah Baharuddin c, A. Zakaria d, Khairunizam Wan e, AB Shahriman f, a,b,d,e,f School of Mechatronic Engineering, Universiti Malaysia Perlis, Kampus Pauh Putra,02600 Arau, Perlis Malaysia. c Microbiology Laboratory, Pathology Department, Hospital Tuanku Fauziah. Perlis, Malaysia. a nooralbatyiah@gmail.com, b khadijah@unimap.edu.my, c balqis.baha@gmail.com, d ammarzakaria@unimap.edu.my, e khairunizam@unimap.edu.my, f shahriman@unimap.edu.my, Abstract This paper discuss the preliminary result for surface characteristic of polytetrafloroethylene (PTFE) after atmospheric plasma treatment. An atmospheric pressure plasma system has been assembled and the effect of helium plasma treatment on PTFE surfaces was studied by scanning electron microscope (SEM). The contact angle of PTFE surface after helium plasma treatment were measured and recorded. Results showed that the contact angle of sample decreased with the increase of helium plasma treatment time. Also, relative increment of surface hydrophilicity could be optimized by the plasma conditions. Based on the preliminary findings, atmospheric plasma with helium as a working gas treatment on the PTFE surfaces improved the surface hydrophilicity and increased the surface area of the sample. Keywords: Atmospheric plasma treatment, Helium, PTFE, SEM, contact angle, surface hydrophilicity. I. INTRODUCTION Polymer is one of the important materials for making devices in the medical industry, electronic component and equipment, and consumer product. In the medical field, polymers are also used in artificial tissue or organ. However, the nature of the polymer is low hydrophilic and this makes it difficult to stick perfectly with host tissue. The surface characteristic of polymer that has poor hydrophilic will affect the adhesion. Poor adhesion to other material is disadvantaged in any industrial application [1]. In order to improve the hydrophilicity, wettability and adhesion of the polymer, cold plasma process is used. Cold plasma treatment processing is used to modify the surface of polymer to increase the surface area for adhesion, wettability and hydrophilic of the surface. It is suitable for polymer because the temperature of the cold plasma is close to room temperature [1]. The term of plasma was found by Tonks and Langmuir at 1929 to describe the inner region containing balanced charges of ions and electrons that produced by electric discharge in a tube [2-5]. Plasma is also known as the fourth state of matter because it is complementing solid, liquids and gases [3-5]. The increasing temperature will affect the bonding of the molecule and increase the energy of molecule to transform matter from one state to another state. Continually increasing temperature makes the molecule of gas becomes more energetic and transform to plasma matter with increasing the temperature [3-5]. Plasma can be produced when high voltages are supplied to the flowing gas in the glass tube or the chamber. Gas flows between the electrode segment and produces the plasma. Plasma treatment is one of the method that fulfills the requirement for surface treatment. Surface treatments are commonly used on polymeric material. The most important in the treatment is to modify the surface, but at the same time the bulk properties of material need to retain [6,7]. Polytetrafloroethylene (PTFE) is commonly used as materials for artificial organ, implants and medical devices. PTFE is used in biomedical application because of its special properties such as high thermal stability, chemical inertness, low surface tension and low coefficient friction [1,8-13]. PTFE is also known for its hydrophobic characteristic and can be decreased by plasma treatment [14]. Hydrophobicity is based on the polarity of chemical compound which is closely related to the distribution between liquid of different polarities [15]. The ability of plasma treatment to modify the surface characteristic without affecting the bulk properties makes it widely used for treatments of polymer [16]. According to other studies, the effect of plasma treatment on a PTFE surface is the hydrophilic surface of PTFE was increased [17-23]. Plasma treatment can be creating reactive site on polymer surface to increase the hydrophilicity characteristic. Hydropilicity of the polymer can be determined by the value of the contact angle. Contact angles after treated with atmospheric plasma are decreasing with the increasing time of plasma exposure [23-28]. Contact angle was affected by the chemical structure and morphology of the polymer surface layer [23]. Helium gas, argon gas, nitrogen gas and oxygen gas are commonly used as working gas in generating the plasma. Another researcher used the different gas for generating the /15/$ IEEE

2 plasma. In this study, helium gas was chosen as a working gas. The helium gas was selected as working gas because it can stabilize homogeneous glow discharge much easier than other gases at the lower voltage for generating plasma at atmosphere pressure. Also, helium gas was chosen due to its principal effect to excite the plasma where it possesses low breakdown voltage. Helium is also very suitable for use in the treatment of the polymer surface, low degradation and reaction enthalpy at the rate of heat transfer to the surface, and also the properties of the high crosslinking and functionalization of the surface [29-32]. II. METHODS AND MATERIALS The principle operation of the atmospheric plasma is high voltage supplied to the flowing gas in a glass tube. In this work, the development of plasma system consists of plasma generating devices, including electronic instrument, power supply, helium gas, and PTFE. Figure 1 shows the diagram of the plasma setup in this experiment. Power supply is an important component in this setup which will affect the production of the plasma. The power supply is a device that supplies the electric power to the electric load. It converts the AC or DC power into the required voltage according to the user setting such 16.5V [33]. In this experiment, pulse inverter was used to convert 24VDC to 10KV AC. This experiment used helium gas with purity 99.9 %, as working gas and it flows at constant flow rate 1 liter per min. The helium (99.9%) gas flows in the quartz glass tube through gas regulator, gas tube, flow meter and then to the quartz glass tube, where the excitation of gas occurs. In this experiment the outer diameter (d o ) for the quartz glass tube is 1.5 millimeters and the inner diameter (d i ) is 1.5 millimeter. While the gas flowing through the gas tube to the quartz glass, power supply was assembled from an AC / DC converter, and current regulator. The gas flow, electrode distance, and voltage were adjusted to stabilize the plasma discharge. In this experiment, 16.6V of voltage and 0.8A of current from power supply was used to generate the plasma. Helium gas flows through the tubing to the flow meter. The flow was set to 1 L/min. The copper electrodes were attached to the outer of the quartz glass tube with the distance between two electrodes approximately 25mm. This created a dielectric barrier discharge to produce atmospheric plasma. The gap between the end of the quartz glass tube and the sample (d e ) is approximately 5mm. The detailed description of the gap between two electrodes is shown in fig. 2. The surface sample is exposed to the plasma for 30 and 60 seconds for surface area measurements and 15,30,45 and 60 seconds for contact angle measurements. Then, the sample was coated with platinum using the Auto fine coater (JEOL, JFC 1600). The surface was of the sample was observed using Scanning Electron Microscopy (SEM) (Hitachi TM3000) to analyze the surface after the plasma treatment. The surface of the sample was analyzed by using the ImageJ software to measure the surface area and contact angle [34,35]. A. PTFE preparation and plasma treatment PTFE that was used in this project is an industrial grade at 6mm thickness. The polymer was cut into 1cm x 1cm and each sample was exposed to atmospheric plasma at the center of the sample. The PTFE samples were cleaned using an alcohol swab to remove dust or any contamination on the surface before the treatment. The sample was placed on a cover plate to avoid any contamination on the surface before exposing. For surface area measurements, samples were exposed to plasma for 30 and 60 seconds and for contact angle measurements, the samples were exposed for 15,30,45, and 60 seconds. Gas tube d e =25mm d i =1.5mm d o =2.5mm Helium tank Fig. 1. Plasma setup Flow meter Glass tube Electrode Fig. 2. Spacing between electrode Sample Power supply

3 B. Scanning Electron Microscope (SEM) The morphology of the PTFE treated and untreated sample was observed by SEM. After samples were treated by plasma, the samples were contained in a petri dish to make sure the surface of the sample is not contaminated from any dust or unwanted particle. Then the samples were coated with platinum and the surface morphology was observed using the SEM. Coating with platinum is conducted to provide an electrically conductive thin film representative of the specimen to be viewed by SEM. The image of the sample transferred to the Image J software to measure the surface area of the samples. The area of each hole in surface was measured and the results were compared between control and treated samples. C. Contact angle measurements The effects of plasma on the PTFE untreated and treated surfaces were analyzed by measuring contact angle. The contact angle is an angle between liquid with the solid surface when both materials are in contact. In this experiment distilled water was chosen to measure contact angle. Using a micro pipette, 10 microliter of distilled water was dropped on the treated area. Then, the image of the distilled water drop was taken and the contact angle was measured as shown in Figure. 3. compared to control sample (a). The area that was exposed to plasma was measured and each pore on the surface of the sample will be measure by Image J software. The measurement result showed that the surface areas of treated sample are larger than control samples. The results of surface area measurements are shown in Table 1. From the result in Table 1, it can be seen that the surface area of the treated area is larger than the control sample. All the samples show the increasing value of the surface area when increasing time exposure. Sample 1 show that the treated sample has μm² more area than the control sample area. The surface area is increased when the exposure time is increased. The area for 60 seconds is μm², μm² more than 30 seconds exposed sample. The treated sample produces the same result. The increasing areas exposed are similar to other sample. The long time exposures the area exposures are increasing. These results showed that the plasma treatment increased the surface area of the sample. III. RESULTS AND DISCUSSION A. Result of Scanning Electron Microscope (SEM) Figure 3 shows the image of the PTFE sample before treatment and after treatment. Control sample is the untreated sample. Two different samples were exposed to the plasma for 30 and 60 seconds. Then, all the samples, treated and untreated sample was coated with platinum on the surface. The PTFE samples, then were viewed using SEM to observe the changes of surface untreated and treated samples. The results in Figure 4 showed that, the control sample originally has un-smooth surface and small holes on its surface. The treated samples (b) have more cracks and pores on the surface (a) (b) Fig. 4. SEM image for the surface of treatment sample [a] control sample [b] treated sample Fig. 3. Contact angle measurement of distilled water drop on the PTFE surface

4 B. Contact angle after plasma treatment The purpose of contact angle measurement is to determine the hydrophilic properties of PTFE. Hydrophilic properties increase with smaller contact angle between surface and liquid. Figure 5 shows the result of contact angle measurements. The average contact angle of the control sample (0 minutes exposure) is For 15 seconds exposure the contact angle has decreased 13.04% where the contact angle became Then, after 60 seconds exposure, the contact angle decreased to It is clear that the contact angle decreased in comparison with the control sample even after short time treatment. The results indicate that contact angle values decrease with increasing treatment time. The decreasing of the contact angles showed the increasing the wettability. The wettability of PTFE increased according to the increasing the hydrophilic of PTFE surface. Based on previous studies, when the wettability increase, the hydrophilic also increases, contact angle decreases and the rough surface also increases [5, 19, 21, 22, 36, 37]. The values indicate that plasma treatment makes the surface more hydrophilic and the longer the plasma treatment time, the more hydrophilic the surface of specimen became [23]. Sample TABLE I. AVRAGE FOR SURFACE AREA MEASUREMENTS Time [Sec] Area [μm²] Fig. 5. The result of average measurement of contact angle versus treatment time. IV. CONCLUSION This work studies the effect of plasma treatment to PTFE polymers. PTFE is known as one of the highest hydrophobic polymers which make it difficult to stick with another molecule. The plasma treatment was used to improve the characteristic of PTFE surface to increase its hydrophilic properties. The PTFE sample was exposed to helium plasma. Experiments to analyze the surface of PTFE such as contact angle measurement and SEM image analysis were conducted to study the effect of exposing plasma to PTFE. The plasma treatments have shown changes of surface characteristics of PTFE. Results showed that the longer plasma treatment exposure, the lower contact angle will become. The surface area of the treated sample also showed increment. In conclusion, exposing plasma with helium as its working gas to PTFE, resulted in PTFE improving its hydrophilic properties and increasing its area. ACKNOWLEDGMENT This research was supported by Short Term Grant, University Malaysia Perlis ( ). REFERENCES [1] A. Sarani, N. De Geyter, A. Y. Nikiforov, R. Morent, C. Leys, J. Hubert, & F. Reniers. Surface modification of PTFE using an atmospheric pressure plasma jet in argon and argon+ CO 2. Surface and Coatings Technology, 206(8), , [2] K. Samanta, M. Jassal, & A. K. Agrawal. Atmospheric pressure glow discharge plasma and its applications in textile. In Indian Journal of Fibre and Textile Research, 31(1), 83, [3] A. Fridman, Introduction to Theoretical and applied Plasma Chemistry: Plasma as the Fourth state of matter, in Plasma Chemistry, New York: Cambridge University Press, 2008, pp

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