BIBECHANA Vol. 20, No. 2, August 2023, 134–145 ISSN 2091-0762 (Print), 2382-5340 (Online) Journal homepage: http://nepjol.info/index.php/BIBECHANA Publisher:Dept. of Phys., Mahendra Morang A. M. Campus (Tribhuvan University)Biratnagar Surface modification of nylon 6 by 50 Hz dielectric barrier discharge produced in air and argon at atmospheric pressure Bikash Shrestha1, Rajesh Prakash Guragain1,∗, Binita Sedhai1 Hom Bahadur Baniya2, Ujjwal Man Joshi1, Deepak Prasad Subedi1 1Department of Physics, School of Science, Kathmandu University, Dhulikhel, Kavre 2Department of Physics, Amrit Campus, Tribhuvan University, Kathmandu, Nepal ∗Corresponding author. Email: rayessprakash@gmail.com Abstract This paper reports the use of dielectric barrier discharge (15.65 kV, 50 Hz) produced in an air and argon environment at atmospheric pressure to modify the surface of Nylon 6. Power dissipation in air and argon DBD was determined to be 14.60 W and 12.00 W, respectively. Similarly, the average density and temperature of an electron in air DBD were found to be 1.74 ×1011 cm−3 and 1.31 eV, respectively, while the values were 2.50 ×1011 cm−3 and 0.68 eV in argon DBD. The water contact angle (WCA) was measured to confirm the enhancement in wettability. On treating the sample with air DBD for 15 minutes, the contact angle reduced from 134.070 ± 3.200 to 89.110 ± 3.060 while it was reduced to 82.740 ± 4.200 within 1 minute using argon. The study found that treating a hydrophobic sample of Nylon 6 with DBD for a certain period of time transformed it into a hydrophilic one, and extending the treatment time further enhanced its wettability. The use of argon DBD was found to be more effective than air DBD in altering the surface properties of the sample, as the sample became hydrophilic after only one minute of treatment with argon DBD and completely wettable after three minutes. The findings suggest that air and argon DBD have potential applications in modifying the surface properties of Nylon 6, which could have practical implications in the production of textiles, membranes, and other materials. Keywords Dielectric Barrier Discharge (DBD), Electron density, Lissajous figure, Nylon 6, Polymer, Surface modification, Water contact angle (WCA). Article information Manuscript received: May 18, 2022; Accepted: April 26, 2023 DOI https://doi.org/10.3126/bibechana.v20i2.45159 This work is licensed under the Creative Commons CC BY-NC License. https://creativecommons. org/licenses/by-nc/4.0/ 1 Introduction Polymers have aided in the growth of technology, applied engineering, and materials science due to their remarkable material characteristics [1]. How- ever, polymers are frequently inappropriate for use in their pristine state as they are resistant to bio- logical and chemical agents [2, 3]. They have low surface energy, poor wettability, printability, and other technologically significant aspects [4, 5]. As 134 http://nepjol.info/index.php/BIBECHANA rayessprakash@gmail.com https://doi.org/10.3126/bibechana.v20i2.45159 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ Bikash Shrestha et al./ BIBECHANA 20 (2023) 134-145 135 a result, surface treatment is needed to transform them into more sophisticated materials for use in many commercial applications [6]. To modify poly- mer surfaces, a variety of surface treatments are available, ranging from large-scale treatments to precision ones [7]. Plasma treatment is one of the commonly used precise treatments as it has the ability to selectively alter the chemical and physi- cal features of the polymer surfaces without chang- ing their fundamental bulk properties. Further, plasma treatment is resource-efficient, environmen- tally friendly, and treatment time is comparatively shorter [8–12]. McCord used atmospheric pressure plasmas to modify nylon fabrics and demonstrated that modification can be done without affecting the bulk properties [13]. Swar et al. showed that due to the presence of amine groups, the surface of treated Nylon 6 films was likely to be bio-compatible for future medical applications [14]. Thomson et al. found a reduction in the concentration of oxygen in the treated surface was the main cause of the decrease in the wettability of the sample with an increase in treatment time [15]. In recent years, Nylon 6 polymers have been in high demand, such as in biomedical and industrial applications. In this study, non-thermal plasma at atmospheric pressure is generated through dielectric barrier discharge at 50 Hz frequency in air and argon environment. Two methods: electrical and optical are used for plasma diagnostics. The water contact angle and surface free energy of samples before and after treatment were measured to study the considerable changes in the surface properties of the treated sample. 2 Experimental Methods 2.1 Nylon 6 sample Nylon 6, also known as polycaprolactam or polyamide 6, is a synthetic polymer made up of a monomer, caprolactam [16, 17]. The Nylon 6 sam- ple used in this study is shown in Figure 1. The thickness of the sample is 0.32 mm and is yellow in color. The dimension of the sample used through- out the study was 2.5 cm × 2.5 cm. 2.2 Experimental set-up Figure 2 shows the experimental set-up of circular parallel plate electrode DBD system. The system comprises of a transparent, cylinder-shaped poly- carbonate reactor that is 10 cm in diameter, 10 cm in height, and 0.5 cm thick. Two circular brass elec- trodes of identical shape and size, each measuring 5.1 cm in diameter and 1.0 cm in thickness, are placed one on top of the other in the reactor, with a suitable gap between them. The upper electrode can be moved up and down on the vertical scale to adjust the electrode gap, whereas the lower elec- trode is fixed. A circular polycarbonate plate hav- ing a diameter of 9.7 cm and a thickness of 0.2 cm covering the lower electrode acts as a dielectric bar- rier. This inhibits the formation of arc discharges. The upper electrode is connected in series to the high ac power supply through a ballast resistor (20 MΩ, 2 W). The high tension to low tension ratio (HT/LT) of the step-up transformer used is 78.26. The lower electrode is grounded through the shunt resistance (10 KΩ, 10 W). The spacing between the electrodes had been maintained at 0.35 cm through- out the research study. 2.3 Electrical and optical diagnostics One should also be familiar with the properties of the plasma being used. A well-defined insight into some quantities that describe plasma state is needed to understand plasma properties. The most elemental quantities are electron density and elec- tron temperature. These quantities are known as plasma parameters. The most tempting feature of a plasma diagnostic approach is that it is non- invasive [18]. For electrical and optical diagnostics, an oscillo- scope probe (Kenwood PC-54 oscilloscope probe) is used to measure discharge current across shunt re- sistor. The voltage across the electrode is measured through a high-voltage probe (PINTEK HVP–28 HF). Both the high-voltage probe and the oscillo- scope probe are connected to the input channel of the digital oscilloscope (Tektronix TDS 2002) which records and displays voltage and current waveforms as a function of time. A small hole is drilled into the top circular base of the polycarbonate cylinder to allow the inlet of argon gas. The gas flow rate of argon was maintained at 2 L/min. A small hole is also drilled in the middle of the lateral surface of the polycarbonate cylinder, just opposite the elec- trode gap, for the insertion of fiber optical cable. The Ocean Optics USB2000+ Fiber Optic Spec- trometer is used to take optical spectra for optical characterization. Figure 3 shows the photograph of the DBD system used in this research work. Bikash Shrestha et al./ BIBECHANA 20 (2023) 134-145 136 Figure 1: Nylon 6 sample of dimension 2.5 cm × 2.5 cm. Figure 2: Schematic diagram of the experimental set-up. 3 Results and Discussion 3.1 Electrical Characterization Figure 4 shows the variation of applied voltage and discharge current of air and argon DBD as a func- tion of time. The applied voltage is sinusoidal in nature while the current signal consists of signif- icant number of individual non-uniform filaments referred to as micro-discharges. DBD generally has several non-uniform filaments at atmospheric pres- sure [19]. 3.2 Electrical Diagnostics A standard approach for electrical diagnostics of DBD discharges is the Lissajous figure. The charge- voltage (Q-V) loop is commonly known as the Lis- sajous figure. The power dissipated, average elec- tron density, etc., parameters can be found from Lissajous figures as a function of several parame- ters [20,21]. Figure 3: Photograph of DBD system. Bikash Shrestha et al./ BIBECHANA 20 (2023) 134-145 137 (a) (b) Figure 4: I(t)–V(t) signal of (a) air and (b) argon DBD. (a) (b) Figure 5: Lissajous figure of discharge in (a) air and (b) argon DBD . Figures 5 show the Lissajous figure of DBD gen- erated in the air and argon environment at the ap- plied voltage of 15.65 kV with an air gap of 0.15 cm. The energy consumed per cycle is given by [22]: E = 4CdVmin  1 1 + Cg Cd  (Vmax − Vmin) (1) And, the power dissipated is given by [23,24]: P = 4fCdVmin  1 1 + Cg Cd  (Vmax − Vmin) (2) where, Cg = capacitance of air space, Cd = capac- itance of the dielectric, Vmax = maximum value of applied voltage required to initiate discharge, Vmin = minimum value of applied voltage, and f = fre- quency of input voltage. In this study, the values of Vmax, Vmin, C, Cd, and Cg obtained from the Lissajous figure [Figure 5(a) and 5(b)] were found to be 12.89 kV, 3.42 kV, 940.12 pF, 3195.40 pF, and 1332.01 pF, respectively in the case of air environment, while they were found to be 12.25 kV, 3.08 kV, 1230.05 pF, 3357.15 pF, and 1941.36 pF, respectively, in the case of ar- gon environment. With these values, the energy consumed per cycle was found to be 0.29 J and 0.24 J while the power dissipated was found to be 14.60 W and 12.00 W in the air and argon environments, respectively. The average electron density (ne) is calculated by [25]: ne = Jav eEµe (3) where, Jav = average current density, E = electric Bikash Shrestha et al./ BIBECHANA 20 (2023) 134-145 138 field in the discharge region, and µe= electron mo- bility which is calculated with the help of BOLSIG+ software. In the air environment, we found Jav = 150.05 mA/cm2, E = 16.07 kV/cm, and µe= 335.12 cm2/Vs. By substituting these values in equation (3), the average electron density (ne) was estimated to be 1.74 × 1011 cm−3. Similarly, in the argon en- vironment, we found Jav = 180.34 mA/cm2, E = 13.00 kV/cm, and Jav= 346.12 cm2/Vs. By sub- stituting these values in equation (3), the average electron density (ne) was estimated to be 2.50 × 1011 cm−3. 3.3 Variation of power dissipated Figure 6 shows the variation of power dissipated in the discharge in air and argon DBD at different applied voltages. It was found that as the applied voltage was increased, the power dissipated in air and argon DBD increased. This is because initially, available charged species are gaining energy from supplied voltages to cause further ionization of air and argon atoms [26]. At a particular applied volt- age, the power dissipated in air DBD was found to be higher in comparison to argon DBD. Air plasma consists of about 78% nitrogen. Nitrogen being a diatomic molecule, its breakdown voltage is com- paratively higher than argon in argon plasma [27]. 3.4 Variation of average electron density Figure 7 shows the variation of average electron density in air and argon DBD at different applied voltages. It was observed that when the applied voltage was increased, the average electron density was also found to be increased. This is because by increasing the voltage, the energy received by charge species also increases. As a result, kinetic energy rises, and the collisional mode shifts from elastic to inelastic. The emission of secondary elec- trons begins and will continue to increase as the applied voltage is increased [28]. Similarly, the average electron density in argon plasma was found to be higher in comparison to air plasma at the particular applied voltage, as the high number of argon atoms gets readily ionized, result- ing in a stream of secondary electrons due to the rel- atively lower breakdown voltage of argon plasma in comparison to air plasma. Also in air plasma, a dis- sociative recombination process between electrons and ionized nitrogen molecules takes place [27,29]. 3.5 Optical Characterization The line intensity ratio method has been used to estimate electron temperature [30,31]: R1 R2 = I1 I2 I3 I4 = ( Apq Ars )( gp gr )( λrs λpq )( Auv Axy ) × ( gu gx )( λxy λuv ) exp [ −−Ep − Er − Ex + Ev kBTe ] (4) where, λ is the wavelength of spectral lines, I is the intensity of spectral lines, A is the transition probability, g is the statistical weight and E is the energy of spectral lines. a. Calculation of electron temperature in air DBD Figure 8 shows the optical spectra of discharge in air plasma and corresponding values of intensity ranging from 300 to 460 nm at an applied voltage of 15.65 kV. From the spectral lines of the discharge in air DBD, four suitable nitrogen lines - nitrogen first line NI (413.76 nm, 439.24 nm) and nitrogen second line NII (411.10 nm, 437.95 nm) were taken for elec- tron temperature estimation. The NIST database is used to obtain the values of Aji, gi, and Ei for these four lines [32]. Table 1 shows the possible values of electron temperature and their corresponding intensity ra- tio values in the case of air DBD. Figure 9 shows the variation of intensities ratio R1 R2 for different possible values of electron tem- perature. The four nitrogen lines taken have an intensities ratio equal to 1.03 which corresponds to an electron temperature of 1.31 eV. b. Calculation of electron temperature in argon plasma Figure 10 shows the optical spectra of discharge in argon plasma and corresponding values of inten- sity ranging from 300 to 900 nm at the applied volt- age of 15.65 kV. From the spectral lines of the dis- charge in argon plasma, four suitable argon lines - argon first-line AI (696.02 nm, 750.38 nm) and argon second-line AII(336.65 nm, 356.32 nm) were taken for electron temperature estimation. The val- ues of Aji, gi, , and Ei for these four lines are ob- tained from the NIST database [32,33]. Table 2 shows the possible values of electron temperature and their corresponding intensity ra- tios values of the spectral lines in the case of argon plasma. Bikash Shrestha et al./ BIBECHANA 20 (2023) 134-145 139 Figure 11 shows the variation of intensities ratio R1 R2 for different possible values of electron tempera- ture. The four argon lines taken have an intensities ratio equal to 0.49 which corresponds to an electron temperature of 0.68 eV. Table 1: Electron temperature (Te) and intensity ratio. Electron tempera- ture (Te) Intensity Ratio ( R1 R2 ) 0.80 13.44 0.90 7.06 1.00 4.21 1.20 1.94 1.40 1.12 1.60 0.74 1.80 0.54 Table 2: Electron temperature (Te) and their cor- responding intensity ratios. Electron tempera- ture (Te) Intensity Ratio ( R1 R2 ) 0.60 1.88 0.65 0.78 0.70 0.37 0.80 0.11 0.90 0.04 1.00 0.02 Figure 6: Variation of power dissipated at different voltages. Figure 7: Variation of average electron density at different applied voltages. Figure 8: Optical emission spectra of discharge in air DBD. Figure 9: Variation of intensities ratio with electron temperature. Bikash Shrestha et al./ BIBECHANA 20 (2023) 134-145 140 Figure 10: Optical emission spectra of discharge in argon DBD. Figure 11: Variation of intensities ratio with elec- tron temperature. 4 Surface Characterization 4.1 Mass loss (%) To ensure the etching and deposition of the plasma ion process, mass loss (%) calculation was done given by [34]: Mass loss(%) = ( Mi −Mf Mi ) × 100 (5) where, Mi = initial mass of the sample before treat- ment and Mf= final mass of the sample after treat- ment. A nylon 6 sample of dimension 2.5 cm × 2.5 cm was taken and its mass was measured in analytical balance (MG124Ai). Then, the sample was treated in air and argon DBD for a specified time and the mass of the treated sample was measured immedi- ately after treatment. Figures 12(a) and 12(b) show the mass loss (%) in the Nylon 6 sample after being treated in air and argon DBD for specified times. Initially, mass loss (%) was found to be increased on increasing the treatment time (from 5 to 15 minutes) in air DBD. Then, no significant difference in mass loss (%) was found between 15 and 20 minutes of treat- ment time. Initially, there was a 1.52% mass loss when the sample was treated for 1 minute in ar- gon DBD. Then on further increase in treatment time, there was no significant difference in mass loss (%). This might be because once all the etchable materials have been removed from the surface, the remaining material is difficult to remove, resulting in a decrease in etching rates. The re-deposition of sputtered fragments could also contribute to the decline in etching rate [34,35]. (a) (b) Figure 12: Mass loss (%) at different treatment times in (a) air and (b) argon DBD. Bikash Shrestha et al./ BIBECHANA 20 (2023) 134-145 141 4.2 Water contact angle A liquid’s ability to wet a solid’s surface is measured by the contact angle. It is the most important tech- nique for studying the properties of a surface. The contact angle is the angle formed by a liquid at the three-phase boundary, where a liquid, gas, and solid meet [36,37]. The water contact angle is calculated using Young’s equation for a perfect, uniform, and ho- mogeneous surface at equilibrium [Figure 13] and is given by [38]: cos θ = γsv − γsl γlv (6) where, θ = contact angle, γsv = solid surface free energy, γlv = liquid surface free energy, and γsl = solid/liquid interfacial free energy. In this study, the water contact angle of 2 µl distilled water kept on the sample surface was mea- sured using a goniometer (Rame Hart contact angle goniometer, model 200). Figures 14 (a) and 14 (b) shows the water contact angle of the controlled and treated Nylon 6 sample in air and argon DBD, re- spectively. Figure 13: Schematic representation of Young’s equation (a) (b) Figure 14: Water contact angle of the controlled and treated sample in (a) air and (b) argon DBD. Bikash Shrestha et al./ BIBECHANA 20 (2023) 134-145 142 It was found that there was a decrease in wa- ter contact angle when the treatment time was in- creased in both air and argon plasma. The result shows that the sample became hydrophilic after be- ing treated for 15 minutes in air DBD. Whereas, the sample became hydrophilic when treated for 1 minute in argon DBD. Moreover, the sample was completely wettable when treated for 3 minutes in argon DBD. The increase in the hydrophilicity of the sample after being treated in air and ar- gon DBD could be because of the inclusion of hy- drophilic groups such as CO, COOH, C-OH, -OH, etc [13–15,39]. 4.3 Surface free energy The surface tension of a solid can be taken as a mea- sure of surface-free energy. The behavior of any liq- uid on the surface may be predicted by knowing the solid’s surface free energy. The surface free energy of solids from a single contact angle measurement of a liquid with a known surface tension is calcu- lated by using the Kwok and Neumann equation and given by [40,41]: γl(1 + cos θ) = 2 √ γsγl [ 1− βl(γs − γl) 2 ] (7) where, βl = 0.0001057 (m2/mJ)2. Figure 15 shows the variation of surface free en- ergy with treatment time in air and argon DBD respectively. The surface free energy of the controlled sample was (5.26 ± 1.11) mJ/m2. The surface free energy of the sample when treated in air DBD for 5 min- utes, 10 minutes, 15 minutes, and 20 minutes were found to be (19.23 ± 4.31) mJ/m2, (27.52 ± 2.51) mJ/m2, (29.78 ± 1.91) mJ/m2 and (35.10 ± 1.85) mJ/m2 respectively. Similarly, the surface free en- ergy of the sample when treated in argon plasma for 1 minute and 2 minutes were found to be (33.77 ± 2.63) mJ/m2 and (34.26 ± 2.63) mJ/m2 respec- tively. The result showed that the surface free en- ergy of the sample increases as the treatment time is increased. (a) (b) Figure 15: Variation of surface free energy with treatment time in (a) air and (b) argon DBD. 5 Conclusions A custom-designed dielectric barrier discharge sys- tem operating at line frequency and at atmospheric pressure, utilizing air and argon as working gases, was used for surface modification of Nylon 6. The average electron density in both air and argon DBD was found to be in the order of 1011 cm−3. The power dissipated and average electron density in the discharge were found to be increased on in- creasing the applied voltage in both air and argon DBD. At a particular applied voltage, the average density of electrons in argon DBD was found to be relatively higher in comparison to air DBD. In contrast, the temperature of electrons in air DBD was found to be comparatively higher than in ar- gon plasma. The generated air and argon DBD significantly enhanced the hydrophilicity of Nylon 6, which was previously hydrophobic. In addition, the hydrophilicity and surface free energy of the sample was found to be increased by increasing the treatment time in both air and argon DBD. After 15 minutes of treatment with air DBD and 1 minute of treatment with argon DBD, the hydrophobic sam- ple became hydrophilic. This shows that argon DBD is more effective than air DBD in the sur- face modification of Nylon 6. These findings have implications for the surface modification of other polymers and may have practical applications in in- dustries such as medical devices and packaging. Acknowledgments The corresponding author was supported by the Nepal Academy of Science and Technology (NAST), Nepal through a Ph.D. fellowship. The authors Bikash Shrestha et al./ BIBECHANA 20 (2023) 134-145 143 would also like to acknowledge all the researchers of the Plasma Physics Laboratory, Kathmandu Uni- versity who provided valuable suggestions and help for the completion of this work. References [1] Md Rabiul Rahman et al. Importance of sustainable polymers for modern soci- ety and development. Advances in Sustain- able Polymer Composites, pages 1–35, 2021. doi.org/10.1016/B978-0-12-820338-5.00001-1 [2] Xiaofang Jia, Margarita Herrera-Alonso, and Thomas J McCarthy. Nylon surface modi- fication. part 1. targeting the amide groups for selective introduction of reactive func- tionalities. Polymer, 47(14):4916–4924, 2006. doi.org/10.1016/j.polymer.2006.05.038 [3] M. S. B. Reddy, Deepalekshmi Ponnamma, Ruchi Choudhary, and Kishor Kumar Sada- sivuni. A comparative review of nat- ural and synthetic biopolymer composite scaffolds. Polymers, 13(7):1105, 2021. doi.org/10.3390/polym13071105 [4] H. B. Baniya, R. P Guragain, and D. P. Subedi. Cold atmospheric pressure plasma technology for modifying polymers to enhance adhesion: A critical review. In Progress in Adhesion and Adhesives, pages 841–879. 2021. doi.org/10.1002/9781119846703.ch19 [5] Wei Zhang, L Johnson, SRP Silva, and MK Lei. The effect of plasma mod- ification on the sheet resistance of ny- lon fabrics coated with carbon nanotubes. Applied Surface Science, 258(20):8209–8213, 2012.doi.org/10.1016/j.apsusc.2012.05.023 [6] Fabienne Poncin-Epaillard et al. Surface treatment of polymeric materials controlling the adhesion of biomolecules. Journal of Functional Biomaterials, 3(3):528–543, 2012. doi.org/10.3390/jfb3030528 [7] S. K. Nemani et al. Surface modification of polymers: Methods and applications. Ad- vanced Materials Interfaces, 5(24):1801247, 2018. doi.org/10.1002/admi.201801247 [8] R. P. Guragain et al. Improvement of hy- drophilicity of polypropylene film by dielec- tric barrier discharge generated in air at at- mospheric pressure. Reviews of Adhesion and Adhesives, 9(1):153–166, 2021. [9] G. Borcia, C. A. Anderson, and N. M. D. Brown. The surface oxidation of selected polymers using an atmospheric pressure air dielectric barrier discharge. part i. Ap- plied Surface Science, 225(1-4):186–197, 2004. doi.org/10.1016/j.apsusc.2003.10.002 [10] Y. Akishev, M. Grushin, V. Karalnik, D. Medvedev, N. Trushkin, A. Vasiliev, J. Schmitt, and K. D. Weltmann. Studies on cold plasma–polymer surface interaction by ex- ample of pp-and pet-films. Journal of Physics D: Applied Physics, 41(23):235203, 2008. [11] C. Feng, Y. Liu, W. Zheng, X. Yan, Z. Huang, and W. Cao. The effect of apgd plasma treatment on silk fabric. Surface Engineering, 36(5):485–491, 2020. doi.org/10.1080/02670844.2019.1609716 [12] M. Laroussi, X. Lu, M. Keidar, and K. Os- trikov. Low temperature plasma-based steril- ization: Overview and state-of-the-art. Plasma Processes and Polymers, 2(5):391–400, 2005. doi.org/10.1002/ppap.200400078 [13] M. G. McCord et al. Modifying ny- lon and polypropylene fabrics with at- mospheric pressure plasmas. Textile Research Journal, 72(6):491–498, 2002. doi.org/10.1177/004051750207200605 [14] R.P. Guragain et al. Characterization of di- electric barrier discharge (dbd) produced in air at atmospheric pressure and its applica- tion in surface modification of high-density polyethylene (hdpe). The Journal of Techno- logical and Space Plasmas, 1(1):27–35, 2020. doi.org/10.31281/jtsp.v1i1.11 [15] R. Thompson, K. R. J. Lovelock, K. Potts, S. Thornthwaite, and K. K. Koziol. Low- frequency plasma activation of nylon 6. Applied Surface Science, 544:148929, 2021. doi.org/10.1016/j.apsusc.2021.148929 [16] J. Lian, X. Jin, J. Jiang, S. Ye, X. Zhou, J. Zheng, and Z. Wang. Organocatalytic copolymerization of cyclic lysine derivative and -caprolactam toward antibacterial nylon- 6 polymers. ACS Macro Letters, 11(1):46–52, 2021. [17] S. Kim, N. Lee, and J. Lee. Pyrol- ysis for nylon 6 monomer recovery from teabag waste. Polymers, 12(11):2695, 2020. doi.org/10.3390/polym12112695 [18] F. F. Chen. Introduction to plasma physics. Springer Science & Business Media, 2012. [19] R. P. Guragain, H. B. Baniya, B. Shrestha, D. P. Guragain, and D. P. Subedi. Germi- nation enhancement of mustard (brassica ni- gra) seeds using dielectric barrier discharge https://doi.org/10.1016/B978-0-12-820338-5.00001-1 https://doi.org/10.1016/j.polymer.2006.05.038 https://doi.org/10.3390/polym13071105 https://doi.org/10.1002/9781119846703.ch19 https://doi.org/10.1016/j.apsusc.2012.05.023 https://doi.org/10.3390/jfb3030528 https://doi.org/10.1002/admi.201801247 https://doi.org/10.1016/j.apsusc.2003.10.002 https://doi.org/10.1080/02670844.2019.1609716 https://doi.org/10.1002/ppap.200400078 https://doi.org/10.1177/004051750207200605 https://doi.org/10.31281/jtsp.v1i1.11 https://doi.org/10.1016/j.apsusc.2021.148929 https://doi.org/10.3390/polym12112695 Bikash Shrestha et al./ BIBECHANA 20 (2023) 134-145 144 (dbd). AIP Advances, 13(3):035338, 2023. doi.org/10.1063/5.0146955 [20] H Jiang, T Wang, Y Liu, T Shao, and J Fang. Experimental study of qv lissajous figures in nanosecond-pulse surface discharges. IEEE Transactions on Dielectrics and Electrical In- sulation, 20(4):1101–1111, 2013. [21] R. P. Guragain, H. B. Baniya, B. Shrestha, D. P. Guragain, and D. P. Subedi. Non- thermal plasma: A promising technol- ogy for the germination enhancement of radish (raphanus sativus) and carrot (dau- cus carota sativus l.). Journal of Food Quality, 2023:Article ID 4131657, 2023. doi.org/10.1155/2023/4131657 [22] X. Tao, R. Lu, and H. Li. Electrical character- istics of dielectric-barrier discharges in atmo- spheric pressure air using a power-frequency voltage source. Plasma Science and Technol- ogy, 14(8):723, 2012. [23] T. C. Manley. The electric characteristics of the ozonator discharge. Transactions of the Electrochemical Society, 84(1):83, 1943. [24] R. P. Guragain et al. Growth enhancement of radish seed induced by low-temperature argon plasma. Plasma Chemistry and Plasma Pro- cessing, 43(1):111–137, 2023. [25] R. P. Guragain et al. Impact of non-thermal plasma treatment on the seed germination and seedling development of carrot (daucus carota sativus l.). Journal of Physics Communica- tions, 5(12):125011, 2021. [26] G. D. Deepak, N. K. Joshi, U. Pal, and R. Prakash. Electrical characteriza- tion of atmospheric pressure dielectric bar- rier discharge-based cold plasma jet us- ing ring electrode configuration. Laser and Particle Beams, 34(4):615–620, 2016. doi.org/10.1017/S0263034616000501 [27] Phongsakorn Jitsomboonmit, Manop Nisoa, and Somsak Dangtip. Experimental study of current-voltage characteristics and op- tical emission of various gases in dielec- tric barrier discharge at atmospheric pres- sure. Physics Procedia, 32:723–731, 2012. doi.org/10.1016/j.phpro.2012.03.625 [28] A. A. Khan, Y. S. Ling, and Z. Z. Chowd- hury. Effect of varying voltage on elec- tron density in oxygen homogenous dielectric barrier discharge under atmospheric pressure. Malaysian Journal of Science, 30(Sp3):10–20, 2019. doi.org/10.22452/mjs.sp2019no3.2 [29] M. Moravej, V. M. Donnelly, A. R. Gibson, and R. Boswell. Physics of high-pressure helium and argon radio-frequency plasmas. Journal of Applied Physics, 96(12):7011–7017, 2004. doi.org/10.1063/1.1815047 [30] N. Balcon, A. Aanesland, and R. Boswell. Pulsed rf discharges, glow and filamen- tary mode at atmospheric pressure in ar- gon. Plasma Sources Science and Technology, 16(2):217, 2007. [31] H. B. Baniya et al. Generation and character- ization of an atmospheric-pressure plasma jet (appj) and its application in the surface modi- fication of polyethylene terephthalate. Interna- tional Journal of Polymer Science, 2020, 2020. [32] Alexander Kramida, Yuri Ralchenko, John Reader, and NIST ASD Team. Nist atomic spectra database (version 5.10). Online, 2022. doi.org/10.18434/T4W30F [33] R. P. Guragain et al. Effect of plasma treat- ment on the seed germination and seedling growth of radish (Raphanus sativus). Plasma Science and Technology, 24(1):015502, 2021. [34] B. Paosawatyanyong, K. Kamlangkla, and S. K. Hodak. Hydrophobic and hydrophilic surface nano-modification of PET fabric by plasma process. Journal of Nanoscience and Nanotechnology, 10(11):7050–7054, 2010. doi.org/10.1166/jnn.2010.2849 [35] R. R. Deshmukh and N. V. Bhat. The mechanism of adhesion and printability of plasma processed PET films. Materi- als Research Innovations, 7:283–290, 2003. doi.org/10.1007/s10019-003-0265-z [36] Z. Shi et al. Dynamic contact angle hys- teresis in liquid bridges. Colloids and Surfaces A: Physicochemical and En- gineering Aspects, 555:365–371, 2018. doi.org/10.1016/j.colsurfa.2018.07.004 [37] O. Ozkan and H. Y. Erbil. Interpreting contact angle results under air, water and oil for the same surfaces. Surface Topography: Metrology and Properties, 5(2):024002, 2017. [38] M. A. Q. Siddiqui et al. Current un- derstanding of shale wettability: A re- view on contact angle measurements. Earth-Science Reviews, 181:1–11, 2018. doi.org/10.1016/j.earscirev.2018.04.002 [39] A. Kuzminova et al. Study of the effect of atmospheric pressure air dielectric bar- rier discharge on nylon 6, 6 foils. Polymer Degradation and Stability, 110:378–388, 2014. https://doi.org/10.1063/5.0146955 https://doi.org/10.1155/2023/4131657 https://doi.org/10.1017/S0263034616000501 https://doi.org/10.1016/j.phpro.2012.03.625 https://doi.org/10.22452/mjs.sp2019no3.2 https://doi.org/10.1063/1.1815047 https://doi.org/10.18434/T4W30F https://doi.org/10.1166/jnn.2010.2849 https://doi.org/10.1007/s10019-003-0265-z https://doi.org/10.1016/j.colsurfa.2018.07.004 https://doi.org/10.1016/j.earscirev.2018.04.002 Bikash Shrestha et al./ BIBECHANA 20 (2023) 134-145 145 doi.org/10.1016/j.polymdegradstab.2014.10.001 [40] T. Zhang and T. Cui. Tunable wetting prop- erties of patterned silicon microchannels with varied surface free energy based on layer-by- layer nano self-assembly. Journal of Microme- chanics and Microengineering, 21(4):045015, 2011. [41] D. K. Owens and R. C. Wendt. Estimation of the surface free energy of polymers. Journal of Applied Polymer Science, 13(8):1741–1747, 1969. doi.org/10.1002/app.1969.070130815 https://doi.org/10.1016/j.polymdegradstab.2014.10.001 https://doi.org/10.1016/j.polymdegradstab.2014.10.001 https://doi.org/10.1002/app.1969.070130815 Introduction Experimental Methods Nylon 6 sample Experimental set-up Electrical and optical diagnostics Results and Discussion Electrical Characterization Electrical Diagnostics Variation of power dissipated Variation of average electron density Optical Characterization Surface Characterization Mass loss (%) Water contact angle Surface free energy Conclusions