Effect of needle diameters on the diameter of electrospun PVDF nanofibers
1,2 Bilal Zaarour*, Nizar Mayhoub2
1 Textile Industries Mechanical Engineering and Techniques Department, Faculty of Mechanical and Electrical Engineering, Damascus University, Damascus, Syria
2 Syrian International Academy, Damascus, Syria
Emails: bz@sia-sy.net
Abstract
Electrospinning is a technique that generates nanofibers via an electrically charged jet of polymer melt or polymer solution. The significance of this method lies in the tiniest diameter of fibers that can be produced because nanofibers provide more performance advantages in various fields and area as their diameters decrease. Different parameters of electrospinning (solution parameters, process parameters, and ambient parameters) play a vital role in determining the diameter of electrospun nanofibers. In this work, the relationship between the needle diameter and diameter of electrospun poly (vinylidene fluoride) (PVDF) nanofibers is investigated. The results show that there is a positive relationship between the needle diameter and the diameter of electrospun PVDF nanofibers.
Keywords
Electrospinning- PVDF – nanofibers- needle diameter- fiber diameter
1. Introduction
Electrospinning is a method for producing fibers by pumping and lengthening polymer jets by electrostatic forces. The diameter of electrospun fibers can be ranged from nanometers scale to micrometers scale 1.
Since electrospun nanofibers have outstanding properties (e.g. small diameters 2, ease of functionality 3, low density 4, high porosity 3, good pore structures 1, good mechanical properties 5, a variety of morphology and structure 6, and flexibility 1), they can be used in many applications such as self-cleaning surfaces 7, filtration 8, 9, catalyst 10, 11, energy harvesting 12, 13, biomedical applications 14, 15, sensors 16, 17, and so on.
Studies have proved that the diameter of electrospun fibers is affected by the working parameters of electrospinning: (I) solution parameters (viscosity, polymer concentration, molecular weight, conductivity, and surface tension) 18, 19, (II) processing parameters (applied voltage, distance between the tip of the needle and the collector (DTC), flow rate, collectors type, and needle diameter) 20, 21, and (III) ambient parameters (temperature and relative humidity) 22, 23.
Polyvinylidene fluoride (PVDF) is a semi-crystalline polymer which can be found in different polymorphs (α, β, γ, δ, and ε) 24, 25. It has been widely studied because of its exceptional piezoelectric and ferroelectric properties, low cost, good mechanical properties, low density, and high flexibility 26. Therefore, it can be used in different applications such as energy harvesting 27, oil cleanup 28, 29, filtration 30, 31, and so on.
Previously, Kizildag et al. demonstrated the effect of needle diameter on the diameter of electrospun silk fibroin nanofibers. They found that there is a positive relationship between the needle diameter and diameter of silk fibers 32.
Abunahel et al. studied the effect of needle diameter on the diameter of electrospun n-Bi2O3/Epoxy-PVA nanofibers. They concluded that there is a positive relationship between the needle diameter and diameter of n-Bi2O3/Epoxy-PVA nanofibers 33.
In this study, we demonstrate the effect of the needle diameter on the diameter of PVDF fibers fabricated via electrospinning. Herein, PVDF was selected as the model as a result of its outstanding properties.
To the best of our knowledge, up to now, no studies have been systematically investigated the effect of needle diameter on the diameter of electrospun PVDF fibers. We concluded that the needle diameter plays a significant role in determining the diameter of PVDF fibers. This work can be used as a good reference for controlling the diameter of electrospun PVDF fibers by maneuvering the needle diameter.
2. Experimental
2.1. Materials
PVDF pellets at a molecular weight of 275000 were purchased from Sigma-Aldrich, USA. Acetone (ACE) and N, N-dimethylformamide (DMF) were purchased from Shanghai Chemical Reagents Co., Ltd, China.
2.2. Methods
Electrospinning: 15% (w/v) PVDF solution with ACE/DMF at the solvent ratio of 2:1 was prepared and loaded in the plastic syringe. The polymer concentrations and the solvents used were selected to obtain nanofibers smoothly 18. Herein, the solvent ratio was the volume ratio, and the solution concentration was the weight/volume (w/v) (g/ml). A syringe needle was used as the spinneret, which was fixed on a syringe pump (KDS 100, KD Scientific Inc., USA) connected to a high-voltage supplier (Tianjin Dongwen Co., Ltd., China). A grounded collector was used to obtain nonwoven nanofibers. All the experiments were carried out with an applied voltage of 18 kV; flow rate of 1.5 ml/h, the distance between the tip of the needle and the collector (DTC) of 18 cm, needle diameter of 0.1-0.83 mm (Figure 1). All of the samples were prepared at the relative humidity of 65% and temperature of 20 °C.
2.3. Characterization
The surface morphology of the electrospun PVDF fibers was checked under field emission scanning electron microscopy (FE-SEM, S-4800 Hitachi, Japan). Fiber diameter was determined using image processing software (ImageJ 1.45s).
Figure 1. Schematic diagram of the electrospinning apparatus used in this work.
3. Results and Discussion
SEM images of PVDF nanofibers generated from three different types of needle diameters are shown in Figure. 1 (A-C). Figure. 1 (A) shows the nanofibers generated from the needle with a diameter of 0.21 mm, while figure (2 A) presents nanofibers generated from the needle with a diameter of 0.41 mm, whereas figure (2 A) shows nanofibers generated from the needle with a diameter of 0.83 mm. As shown in Figure. 1 (A-C) there is a significant difference in the morphology of electrospun PVDF nanofibers between the different types of needle diameters.
Figure 2. SEM images of electrospun PVDF nanofibers fabricated at needle diameter of A) 0.21 mm, B) 0.41 mm, C) 0.83 mm.
The results showed that beaded free nanofibers with different diameters were obtained from all samples fabricated at different diameters of needles.
Figure 2. The distribution of electrospun PVDF nanofibers diameters fabricated at needle diameter of A) 0.21 mm, B) 0.41 mm, C) 0.83 mm.
The diameter of nanofibers generated at a needle diameter of 0.21 mm is 155 ± 29 nm. While the diameter of nanofibers produced at needle diameter of 0.41 mm is 377 ± 38 nm, whereas, the diameter of nanofibers generated at needle diameter of 0.86 mm is 455 ± 77 nm as shown in Figure 2 and Table 1. So, when the diameter of the needle decreased, the diameter of fabricated nanofibers decreased. Furthermore, the fiber porosity increased by decreasing the diameter of the needle owing to decreasing the diameter of fibers 30.
These results could be explained as follow, at a small needle diameter, a tiny drop of polymer solution forms at the top of the needle with high surface tension compared with a large needle diameter. Polymer with high surface tension requires increasing the potential difference to overcome the high surface tension. When the high potential difference is used, the electrostatic force which is responsible for stretching the polymer jet and divides it into many smaller jets is also increased resulting in forming nanofibers with small diameters 32, 33.
Table 1. Summarizing the polymer solution, processing parameters, and fibers diameter of samples electrospun at different diameters of the needle
|
Polymer solution |
Applied voltage (kV) |
DTC (cm) |
Flow rate (ml/h) |
Needle diameter (mm) |
Fibers diameter (nm) |
|
15% (w/v) ACE/DMF |
18 |
18 |
1.5 |
0.21 |
155 ± 29 |
|
14% (w/v) ACE/DMF |
18 |
18 |
1.5 |
0.41 |
377 ± 38 |
|
14% (w/v) ACE/DMF |
18 |
18 |
1.5 |
0.86 |
455 ± 77 |
Conclusions
PVDF nanofibers were obtained using different needles with different diameters (0.21 nm, 0.41nm, and 0.86 nm). The diameter of fibers was detected from the SEM images of studied samples. The results proved that there is a correlation between the diameter of the needle used and the average diameter of nanofibers obtained. The average diameter of fibers increased from 155 ± 29 nm at needle diameter of 0.21 nm, into 377 ± 38 nm at needle diameter of 0.41 mm, into 455 ± 77 nm at needle diameter of 0.86 mm. We believe this work can be served as a good reference for generating electrospun nanofibers with adjustable diameters by maneuvering the needle diameter.
References
1. Ko FK and Wan Y. Introduction to nanofiber materials. Cambridge University Press, 2014.
2. Greiner A and Wendorff JH. Electrospinning: a fascinating method for the preparation of ultrathin fibers. Angewandte Chemie International Edition 2007; 46: 5670-5703.
3. Bhardwaj N and Kundu SC. Electrospinning: a fascinating fiber fabrication technique. Biotechnology advances 2010; 28: 325-347.
4. Jiang S, Helfricht N, Papastavrou G, et al. Low‐Density Self‐Assembled Poly (N‐Isopropyl Acrylamide) Sponges with Ultrahigh and Extremely Fast Water Uptake and Release. Macromolecular rapid communications 2018; 39: 1700838-1700845.
5. Jiang S, Chen Y, Duan G, et al. Electrospun nanofiber reinforced composites: a review. Polymer Chemistry 2018; 9: 2685-2720.
6. Zaarour B, Zhang W, Zhu L, et al. Maneuvering surface structures of polyvinylidene fluoride nanofibers by controlling solvent systems and polymer concentration. Textile Research Journal 2019; 89: 2406-2422.
7. Daoud WA. Self-cleaning materials and surfaces: a nanotechnology approach. 2013.
8. Podgórski A, Bałazy A and Gradoń L. Application of nanofibers to improve the filtration efficiency of the most penetrating aerosol particles in fibrous filters. Chemical Engineering Science 2006; 61: 6804-6815.
9. Zhu M, Han J, Wang F, et al. Electrospun nanofibers membranes for effective air filtration. Macromolecular Materials and Engineering 2017; 302: 1600353-1600379.
10. Mu H, Li C, Bai J, et al. In situ synthesis of Cu/CNFs composite catalyst by electrospun nanofibers wrapped copper chloride and applied for Ullmann coupling reaction. Journal of Molecular Structure 2018; 1165: 90-100.
11. Pagliaro M, Ciriminna R, Yusuf M, et al. Application of nanocellulose composites in the environmental engineering as a catalyst, flocculants, and energy storages: A review. Journal of Composites and Compounds 2021; 3: 114-128.
12. Zaarour B, Zhu L, Huang C, et al. A review on piezoelectric fibers and nanowires for energy harvesting. Journal of Industrial Textiles 2019: 1528083719870197.
13. Guan X, Xu B, Wu M, et al. Breathable, washable and wearable woven-structured triboelectric nanogenerators utilizing electrospun nanofibers for biomechanical energy harvesting and self-powered sensing. Nano Energy 2021; 80: 105549.
14. Zaarour B, Zhu L, Huang C, et al. A mini review on the generation of crimped ultrathin fibers via electrospinning: Materials, strategies, and applications. Polymers for Advanced Technologies 2020; n/a. DOI: 10.1002/pat.4876.
15. Ma X, Wu G, Dai F, et al. Chitosan/polydopamine layer by layer self-assembled silk fibroin nanofibers for biomedical applications. Carbohydrate Polymers 2021; 251: 117058.
16. Yang B, Myung NV and Tran TT. 1D metal oxide semiconductor materials for chemiresistive gas sensors: a review. Advanced Electronic Materials 2021; 7: 2100271.
17. Halicka K and Cabaj J. Electrospun Nanofibers for Sensing and Biosensing Applications—A Review. International Journal of Molecular Sciences 2021; 22: 6357.
18. Zaarour B and et al. Maneuvering surface structures of polyvinylidene fluoride nanofibers by controlling solvent systems and polymer concentration. Text Res J 2019; 89: 2406.
19. Jacobs V, Anandjiwala RD and Maaza M. The influence of electrospinning parameters on the structural morphology and diameter of electrospun nanofibers. Journal of applied polymer science 2010; 115: 3130-3136.
20. Zaarour B, Zhu L and Jin X. Maneuvering the secondary surface morphology of electrospun poly (vinylidene fluoride) nanofibers by controlling the processing parameters. Materials Research Express 2019.
21. Mohammad Khanlou H, Chin Ang B, Talebian S, et al. Electrospinning of polymethyl methacrylate nanofibers: optimization of processing parameters using the Taguchi design of experiments. Textile Research Journal 2015; 85: 356-368.
22. Zaarour B, Zhu L, Huang C, et al. Controlling the Secondary Surface Morphology of Electrospun PVDF Nanofibers by Regulating the Solvent and Relative Humidity. Nanoscale Research Letters 2018; 13: 285-296.
23. Shahabadi SMS, Kheradmand A, Montazeri V, et al. Effects of process and ambient parameters on diameter and morphology of electrospun polyacrylonitrile nanofibers. Polymer Science Series A 2015; 57: 155-167.
24. Trevino JE, Mohan S, Salinas AE, et al. Piezoelectric properties of PVDF‐conjugated polymer nanofibers. Journal of Applied Polymer Science 2021; 138: 50665.
25. Yousry YM, Yao K, Chen S, et al. Mechanisms for enhancing polarization orientation and piezoelectric parameters of PVDF nanofibers. Advanced Electronic Materials 2018; 4: 1700562.
26. Cozza ES, Monticelli O, Marsano E, et al. On the electrospinning of PVDF: influence of the experimental conditions on the nanofiber properties. Polymer International 2013; 62: 41-48.
27. Zaarour B, Zhu L, Huang C, et al. Enhanced piezoelectric properties of randomly oriented and aligned electrospun PVDF fibers by regulating the surface morphology. Journal of Applied Polymer Science 2019; 136: 47049-47056.
28. Zhu L, Zaarour B and Jin X. Unexpectedly high oil cleanup capacity of electrospun poly (vinylidene fluoride) fiber webs induced by spindle porous bowl like beads. Soft Materials 2019: 1-8.
29. Wu J, Ding Y, Wang J, et al. Facile fabrication of nanofiber-and micro/nanosphere-coordinated PVDF membrane with ultrahigh permeability of viscous water-in-oil emulsions. Journal of Materials Chemistry A 2018; 6: 7014-7020.
30. Zaarour B, Tina H, Zhu L, et al. Branched nanofibers with tiny diameters for air filtration via one-step electrospinning. Journal of Industrial Textiles 2020; 0: 1528083720923773. DOI: 10.1177/1528083720923773.
31. Leung WW-F and Sun Q. Charged PVDF multilayer nanofiber filter in filtering simulated airborne novel coronavirus (COVID-19) using ambient nano-aerosols. Separation and purification technology 2020; 245: 116887.
32. Kizildag N, Beceren Y, Kazanci M, et al. Effect of needle diameter on diameter of electropsun silk fibroin nanofibers. In: RMUTP International Conference: Textiles and Fashion, Bangkok, Thailand 2012, Citeseer.
33. Abunahel BM, Azman NZN and Jamil M. Effect of Needle Diameter on the Morphological Structure of Electrospun n-Bi2O3/Epoxy-PVA Nanofiber Mats. Chem Mater Eng 2018; 12: 296-299.