ISSN 2277 – 8322 Surface Modifications Of High Density .

International Journal of Recent Research and Review, Vol. III, September 2012ISSN 2277 – 8322Surface Modifications of High Density Polycarbonate by ArgonPlasmaKhalaf Ibrahim Khaleel1, Awatif Sabir Jasim1, Mohamad Abdul Kareem Ahmed 1,Y. K. Vijay2, Subodh Srivastava2Department of Physics, College of Education, Tikrit University, IraqThin Film and Membrane Science Laboratory, University of Rajasthan, Jaipur, IndiaEmail: muhamed68@ymail.comAbstract The polycarbonate (PC) membranes wereimplanted to 16 W argon ions plasma. The samples weretreated for different exposure time 10 min, 30 min and60 min. The effect of argon ions implantation on opticaland chemical properties of PC membrane has beeninvestigated. The observed changes have beencorrelated with the induced structural changes in theimplanted layer using UV-Visible spectroscopy. TheAtomic Force Microscopy (AFM) and ScanningElectron Microscopy (SEM) were employed to study thesurface characteristics of the membrane. The AFMresults indicate significant changes in the surfacemorphology of the polymer membranes before and afterplasma treatment.valuable finished products have become an importantpart of the plastics industry [1,2].Surface modifications, such as plasma treatment,corona discharge and flame treatment, are frequentlyemployed to enhance the surface properties of thinfilms. Actually, a simple way to modify the chemicaland physical states of the polymer surface, withoutaltering the bulk properties, is by plasma treatment.The plasma treatment of polymers leads to thecreation of new chemical groups, cross-linking,degradation, branching of the macromolecules andformation of low-molecular weight oxidizedstructures like free radicals [3-8]. The rates of theseprocesses being a function of the plasma reactivitywhich depends strongly upon the structure ofpolymers and deposited energy by the ion irradiation.Therefore, appropriate plasma treatment can beapplied to improve the modifications occur in surfacelayer only and polymer bulk saves the sameunchanged mechanical properties. Furthermore, themodified surface layer can be affected by compositionof ambient atmosphere, and the modified surface layerwill able to have a good homogeneity.Argon plasma treatment can enhance sputteringof the PC surface layer, which increased surfaceroughness, and the sputtering depth is up to tens ofnanometers [9]. Furthermore, argon plasma causing across-linking of polymer matrices which can improvethe chemical resistance, optical density, hardness,cohesive strength of the surface and other surfaceproperties[10,11]. The argon plasma treatment canKeywords Polycarbonate (PC), Plasma treatment,AFM, SEM, UV-Visible spectroscopy.I. INTRODUCTIONFor several past decades, polymers have beenused in different fields such as adhesion, biomaterials,protective coatings, friction and wear, composites,microelectronic devices, and thin-film technology. Ingeneral, special surface properties with regard tochemical composition, hydrophilicity, roughness,crystallinity, conductivity, lubricity, and cross-linkingdensity are required for successful applications invarious fields. Most Polymers do not have the surfaceproperties required for these applications. They haveexcellent bulk physical and chemical properties, andare inexpensive and easy to process. For thesereasons, surface modification techniques which cantransform these advantageous materials into highly1

application, and can very well optimized by selectingtype of gas or the ions current [16]. In the presentwork the effect of Ar-ion plasma treatment on surfaceproperties for PC membranes under differenttreatment time was studied at discharge power of16W.also induce the direct energy transfer of the surface,due to vacuumed- ultra violet radiation (VUV)emitted by plasma glow [12]. The kinetic energy ofargon ions, fast neutrals, and UV-radiation from DCdischarge also causing a significant rearrangement ofthe surface structure. Surface roughness can bedepending on ion implementation, gas compositionand treatment conditions such as using an ions,electrons, fast neutrals and radicals. These species cancontribute to the polymer treatment, resulting inetching, activation and /or cross-linking [13,14]. Asynthetic polymer like Polycarbonate (PC) isconsidered an important polymer due to its variousdesirable properties. It is transparent about 90% in thevisible range of the electromagnetic spectrum, whichmake it an excellent substitute of glass substrate indifferent optical applications like solar cells,antireflective coatings, optical lenses, etc. Themonomer structure of PC is shown in Figure 1.The surface properties like etching, roughness,transmission and absorption so as mechanicalproperties can be modified depending on type of gasused [15]. Consequently, ions flow current i.e. thenumber of ions passing through plasma dischargechannel per unit time, or the energy deposited inmolecules matrix, depend basically on the acceleratedmolecular charges of specific gas used in plasmatreatment. Furthermore, surface treatment propertiescan be chosen according to type of requiredII. MATERIALS AND METHODA. Sample preparationThe 30µm thick PC membranes were preparedby solution cast method. The PC granular hasdissolved in dichloromethane (CH2C12) solutionusing magnetic stirrer for 10 hours. The solutionwas then pursed into flat-bottomed petrie-dishfloated on mercury to ensure the uniformity in thethickness. The solvent was allowed to evaporateslowly over a period of 12-14 hours in the dryatmosphere. The films so obtained were peeled offand dried in vacuum at 50 C, for 2 hours in order toensure the removal of the solvent [17].B. Plasma TreatmentThe schematic diagram of set up for plasmatreatment is shown in Figure 2.Typical configurationof a complete plasma processing system is constitutedby a stainless-steel cylinder with 40 cm length and 30cm diameter, electromagnetic energy (DC generator).The vacuum chamber connected to vacuum pumpsconsist of rotary and diffusion pumps, needle valve tocontrol gas pressure, and process gas sources with gasregulators. The 1x1 mm metal mesh shown in Figure(2) were used to repel the electrons and accelerates thepositive ions to impact PC membrane. The plasmachamber was evacuated to 10-4 mbar pressure.Samples of PC were treated by Ar-plasma at variousexposure times and 16 W discharge power. The PCsamples were located at the midpoint of the chamberusing a glass support.Fig. 1 Monomer structure of polycarbonate (PC)2

Fig. 2. Experimental set-up for plasma treatment systemmorphology as in Fig. 3(b), whereas the root meansquare value of roughness (Rrms) for treated filmwithin 10 min time is 9.58 nm. The Higher values ofroughness were observed only for over-expositions(30 min. or more) as in Fig. 3(c) and 3(d), whereas theRrms increased up to 15.33 nm and 29.79 nm fortreatment time of 30 min and 60 min, et.at reportedthe direct dependence between the degree ofcrystallinity of polymer and surface roughness afterthe plasma treatment [19-20]. Plasma predominantlyetches the amorphous regions than the crystalline oneswhich are bonded with higher energy. Hence, afterplasma treatment, these crystalline regions will remainpresent, while amorphous are etched away which isleading to rougher surface, because our samples wereamorphous. These results have been corroborated bySEM measurements as described in next section.C. CharacterizationsThe Atomic Force Microscope (AFM) type(Veeco,diCp-II) was used for surface morphology.The Scanning Electron Microscope (SEM)manufactured by ZEISS, EVD 18 to study the surfaceproperties. We use the UV-visible spectroscopy foroptical properties manufactured by HITACHI modelU-2900 spectrophotometer in the wavelength range of200 to 500 nm. The Fourier Transform ZU) was used to study the chemicalstructures of the polymeric membrane surface.III. RESULTS AND DISCISSIONA. Atomic Force MicroscopeFig. 3(a) shows the corresponding AFMtopographical images of the untreated membrane, andFig. 3(b), (c) and (d) for treated membranes by argonplasma at 10 min., 30 min. and 60 min. respectively. Itis well known, that the plasma treatment is slightlychange the morphology of the polymer surface andcan depend on the gas composition and pressure.Argon Plasma treatment leads to the ablation of thepolymer surface layers, the ablation rate beingdifferent for different polymers. As expected, thethickness of the ablated layer is an increasing functionof the plasma exposure time [18]. The AFMmeasurements show clearly, that the short time argonplasma treatment does not influence the surfaceB. Scanning Electron Microscope (SEM)The results discussed in the preceding paragraph werefurther confirmed by SEM analysis. The SEM images,Fig.4 shows that the image of the pristine PC film hassmooth surface structure without any changes onsurface morphology. It can be observed from Fig.4 (b)that after a treatment time of 10 min, some unevengranular like defect spots began to appear on thesurface. It seems that the PC film begins rough due tothe nucleation process during the plasma treatment. Itwas observed that defective spots increased in density3

as well as became larger with longer treatment time asshown in Fig.4(c) and (d).Fig.3. AFM images of Polycarbonate film with different plasma treatment time (a) untreated, (b) 10 min, (c) 30 min, and (d) 60min.Fig. 4. SEM micrographs of polycarbonate film (a) untreated, (b) 10 min, (c) 30 min and (d) 60 min.average roughness will result in a decrease intransmittance due to light scattering effects, but theaction of some species present in the plasma promoteschain scission (as described in introduction), and thiscould lead to etching and material removal, thuspromoting changes in surface roughness which inmost cases positively contributes to a transparencydecrease. The increased roughness may be envisionedas the increase in the concentration and sizes of theC. UV-Visible SpectroscopyThe optical transparency for treated PC films wasevaluated by recording the UV-visible transmissionspectra for various argon plasma glowing duration asshown in Fig.5, the reference used for transmissionmeasurements is untreated PC film. It is well knownthat the transparency of a bulk film strongly dependson the surface roughness and an increase in the4

degradations on surface, which leads to higher lightscattering [20]. This effect shown clearly in PCmembrane treated with argon gas for higher treatmenttime such as 30 min. and 60 min. as in Fig.5 and alsocorroborated by Atomic Force Microscopy imagesshown in Fig.3.Fig. 5. UV-Visible spectrum for polycarbonate treated membrane for different irradiation time (a) 10 min (b) 30 min (c) 60 min.Fig. 6. FTIR spectrum for polycarbonate film (a) untreated, (b) 10 min, (c) 30 min and (d) 60 min.5