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6PREPARATION AND CHARACTERIZATION OF HIGHLY ALIGNED FERROMAGNETIC PVDF/ Fe3O4 NANOCOMPOSITE FIBROUS COATING
DILARA HUSEYNOVA R.
PhD in Nanotechnology, Khazar University, Baku, Azerbaijan
Abstract Nanocoatings have revolutionized the field of surface protection, offering advanced solutions that provide enhanced durability, resistance, and performance. These coatings, based on nanotechnology, have gained significant attention in recent years due to their unique properties and wide-ranging applications. In this research we synthesized a novel nano-magnetically enabled PVDF/Fe3O4 fibrous coatings. The highly aligned ferromagnetic nanofibers are fabricated using electrospinning process. By means of directional magnetic field in electrospinning equipment we obtained highly aligned nanofiber material to investigate their morphology structure. we employed several characterization approaches including scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR) tests. The results indicate that the prepared orderly arranged nanofibrous magnetic coatings.
Keywords: magnetic nanomaterial; PVDF; Fe3O4; high electroactive phase; electrospinning; highly alignment; nanofiber; fi-phase crystal structure.
Introduction Magnetic nanomaterial has recently become one of the most active research fields in the areas of chemistry and engineering [1]. Magnetically responsive flexible fabrics are a growing need for shielding electromagnetic interference especially in microelectronic applications to reduce growing electromagnetic pollution, sheaths for portable electronics and stealth weapon systems in military applications [2,3]. Their application could also be extended to icephobics and power electronic devices at extremely low temperatures [4,5].
PVDF is a polycrystalline polymer that started drawing scientific interest in the 70s, because of its extraordinary piezoelectric properties. PVDF is a widely used piezoelectric semi-crystalline polymer with five different crystalline phases (a, P, 5, у and s) [6]. Among these, a, P, and y-phases are predominant and important in technological application point of view. The a-phase has a semi-helical alternate trans-gauche (TGTG') conformation, which although is the most abundant and thermodynamically favorable polymorph, is insignificant in electronic applications due to non-polar nature. Contrarily, p, y, and 5-phases are polar and thereby electroactive due to parallel alignment of the dipoles. Among all polar phases, the pseudohexagonal P-phase with all-trans (TTTT) conformation holding high spontaneous polarization and remarkable piezo-, pyro- and ferroelectric properties is given paramount importance in development of easily scalable polymer-based nanogenerators with high power-density. While handling multi-phase PVDF for such applications, the main challenge is to improve the proportion of P counterpart. This can be achieved by mainly three ways: (a) mechanical: by application of stress/tension via stretching, bending, twisting or pressing [7] ;(b) high electric field poling [8]; and (c) chemical: by adding suitable filler materials [9], that can enhance the electrical, mechanical, thermal or optical properties of PVDF via appropriate ion-dipole or dipole-dipole interactions. The third process is not only cost-effective, but also concerns development of advanced multifunctional nanomaterials, which is noteworthy in materials researchers' perspective [10]. Its piezoelectric properties are directly related to its crystal phases [11]. Nonpolar a and polar p phase are the most common crystalline structures of PVDF where the P phase is responsible for the piezoelectric properties. Thereby, increasing p phase with eliminating a phase content in PVDF was a major area of focus or the last decade. Cold-drawing (stretching) [12], high-pressure quenching [13], and poling (applying a high electric field) of PVDF [14] were such processes to increase P phase [16]. Electrospinning is another optional simple one-step method for fabricating PVDF nanofibers under a high electric field which converts the a phase into the P phase. The high voltage that is involved in this process, boosts up the P phase of the fibers [17]. Moreover, electrospun fibers mats are highly flexible and mechanically strong compare to the solvent cast films [18].
ОФ "Международный научно-исследовательский центр "Endless Light in Science"
Magnetite Fe3O4 has recently gained increasing interest since bulk Fe3O4 has a high Curie temperature (Tc 850 K) and is almost fully spin-polarized at room temperature (RT). Both properties are of great interest for applications in giant magneto-electronic and spinvalve devices [19]. It has been reported previously that ferroferric oxide (Fe3O4) spherical shaped nanoparticles are excellent fillers for highdielectric-constant polymer composites [20-22]. Some researchers found that the ferroelectric properties of PVDF are improved by adding Fe3O4 nanoparticles [23-26]. This is generally explained by the interaction between the nanoparticles and the CH2 groups of the polymer chains, which promotes the nucleation of the polar p phase of PVDF [27,28]. Magnetite nanoparticles (Fe3O4) have attracted increasing interest also within the fields of applied nanoscience and technology attributed to their unique and new physicochemical properties that are achieved according to their particle size, shape morphology, and shape of geometric films. Various methods of preparation of magnetite nanoparticles were performed through several techniques, including co-precipitation showing that the addition of nanoparticles to the polymer and/or polymer blend may enhance compatibility between the polymers. Magnetite nanoparticles (Fe3O4) are one of most nanoparticles to improve and enhance the magnetic properties for polymer nanocomposites in the industry [29,30]. These nanoparticles can be found commercially with diameters between about 1 and 100 nanometers, with purity above 95% [31,32].
In this work by using electrospinning equipment is gained highly aligned nano-magnetically enable PVDF-Fe3O4 composite material and investigated morphology structure via scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR) tests.
2. Materials and Methods
2.1 Materials Polyvinylidene fluoride (PVDF) pellet has Mw = 1.8 x 104 with linear chemical structure (-CH2CF2-)n were pouched from Sigma-Aldrich, FeeO4 was obtained from Sigma-Aldrich with an average particle size of 20-30 nm. Acetone and N, N-dimethylformamide (DMF) were purchased from Sigma-Aldrich, Polysorbate Tween purchased from Sigma-Aldrich. Neodymium battery, Metal bar
2.2. Preparation of PVDF solution PVDF powders were dissolved in mixed organic solvents DMF/ Acetone = 1/1 at 10 wt% (w/w) by stirring at maximum 350C for 2 hours using magnetic stirrer in a 250 ml beaker at 35 rpm. After getting completely dissolving, ultrasonication was performed with Ultrasonic Cleaner Digital Pro for 2 hours until getting without bubbles homogenous PVDF solution.
2.3. Preparation of Fe3O4 solution. Fe3O4 nanoparticle powders were dissolved (1wt%) in 50 ml of DMF and added 10ml of Polysorbate Tween as a surfactant at 300C temperature by stirring at 35 rpm for 2 hours. Then followed sonication was carried out for 2 hours until getting non-homogenous solution. After ultrasonication, 2 phased solution was obtained, and upper phase was used for electrospinning process. After that, a non-homogeneous solution was obtained by sonication for the following two hours. After ultrasonication, a two-phased solution formed, with the upper phase being employed for the electrospinning procedure.
2.4. High electroactive phase inversion technique. Using a mechanical stretching force to stretch the nanofibers can provide elongation forces during electrospinning and organize the lamellae to form fibers aligned along the fiber axis. Electric and magnetic field stretching at the same time were used as mechanical stretching forces in this study. Only electric field stretching in electrospinning was also tested. For mentioned purposes, in this work metal bar and neodymium battery were inserted in PVDF/Fe3O4 nanofiber preparation via electrospinning. Neodymium battery combined with metal bar was joined grinding line of equipment. By this way P-phase content increases rapidly and gained high aligned PVDF/Fe3O4 nanofiber.
2.5. Preparation of highly aligned PVDF Fiber Mats by electrospinning. Pristine PVDF nanofiber (M1sample) prepared at Flow rate-0.5 ml/hr., Output Voltage 15.38 kV, rotating drum speed 80 rpm. Distance between rotating collector and metal bar was 4cm. Metal bar was fixed in electrospinning process for generating electric field stretching.
2.6. Preparation of highly aligned PVDF/Fe3O4 Fiber Mats by electrospinning. A dual channel programmable syringe pump was used to feed the polymer and Fe3O4 solution. The 2 channels were independently controlled. The PVDF solution was placed in a plastic syringe fitted with a 20G needle and electrospun at 13 kV voltage. The flow speed of PVDF solution was 0.5 ml/h. The distance between the needle and collector was 5 cm. The experimental set up was described in figure 1. Electrospinning of PVDF solution was carried out via the rotating drum, with 3000 rpm (figure 2). Neodymium battery was fixed to the electrospinning equipment by using metal bar for obtaining of magnetic field. Fe3O4 solution was injected with tubeless plastic syringe, which was directly connected to the needle, saving expensive nanoparticle material. The syringe fitted with an another 20G needle was used the injection of Fe3O4 solution via the same syringe pump for generating magnetic field. The flow speed of magnetite solution was 5 ml/h. Obtained magnetic field is observed as a thin thread and gave rise to generating of alignment structure in during PVDF solution spinning process. At 3000 rpm, a spinning roller with nonstick aluminum foil was capturing the fiber. M2 sample was created using via mentioned parameters. Different samples were prepared at different conditions and parameters. M3 sample was prepared using an electrospinning technique with a metal bar set at 556 rpm, 16.48 kV output voltage, and the presence of an aqueous solution of Fe3O4. The same electrospinning conditions were used to prepare the PVDF/Fe3O4 Fiber Mats. sample, but a static collector was used instead. The M4 sample was created using a neodymium battery, a metal bar, and a solution of Fe3O4 at a voltage of 13 kV and a spinning drum speed of 2500-2900 rpm. 3.1 Morphological structure analysis. Alignment structure was observed from AFM image of pristine PVDF nanofiber (M1 sample) prepared. AFM and Optic images of M3 sample indicated alignment structure also in the PVDF/Fe3O4 Fiber Mats. Network structure from organized lamellae was observed in the M3sample, which was collected on the static metal surface. SEM images of sample showing the size and morphology of the PVDF nanofibers are presented in figure 3 and 4. The acceleration voltage used in SEM imaging was 10 kV. The nanofibers obtained from 10 wt,% PVDF have uniform morphology without twisting and beaded structures. SEM image with only at 10^m scale bar shows highly aligned structure of PVDF/Fe3O4 nanofiber material. These figures represent the formation of ultrafine fibers having diameter in the range of 134-411 nm (figure 5). The average diameter of fiber is 224 nm. Electrospun nanofiber were morphologically uniform with columnar shape and independent with each other. SEM images of M3 sample with rotating collector was also confirmed with AFM and Optic microscope images results (figure 6,7,8). FTIR analysis The FTIR measurement results of M4 sample present valuable information about a material structure and also allow us to differentiate between the several crystalline forms of PVDF [33,34]. The complexation of nanocomposite was studied using Fourier transform infrared (FTIR) spectroscopy at wavenumber range of 4000 cm-1 - 500 cm-1. The IR spectroscopy study of the PVDF samples indicated the existence of two crystalline forms of the polymer: a and p. As can be seen in figure 9 the Vibration bands at 834,32 cm-1 (CH2 rocking) correspond to p phase of PVDF [35]. aphase absorption bands are clearly identified at 763, 875.55, and 1069.82 cm-1 wavenumbers. The absorption bands at 1404 and 1069.82 cm-1 are assigned to CH2 wagging mode. The absorption band at 1171.81 cm-1 is assigned to CF2 asymmetric stretching mode since CF2 group is absorbed strongly in the region of 1120 - 1350 cm-1 [36]. PVDF membrane shows peaks at 1398.54 cm-1 and 1171.81 cm-1, attributing to C-H and C-F stretching and deformation.
The organic solvent of PVDF-DMF is also the source of the occurrence of the stretching vibration of C=O amide groups at 1646 cm-1 [37]. Table 1 summarizes the typical bands of each crystalline phase. _
Phase of a P
PVDF
763 834.32
Wavenumber, 875.55 1171.81
cm-1
1069.82 1398.54
1646
Table 1. Phase of PVDF The incorporation of Fe3O4 nanoparticles on the polymer resulted in the peak around 500-700 cm-1 that could be attributed to the existence of Fe-O vibration [38]. FTIR measurements show that there is no chemical bonding between the filler (Fe3O4) nanoparticles and the polymer matrix (PVDF). The construction of an ideal single phase of PVDF is usually complicated because of its semi-crystalline nature. The FTIR spectrum is dependent on molecular mass distribution, crystalline nature, orientation, head-to-head and tail-to-tail defects, and also the thickness of samples. There still may be some problems to analyze the FTIR spectrum, for this reason, the obtained results about the crystalline forms of PVDF may be also supported by the XRD technique [39].
Figure 1. Experimental set-up of electrospinning equipment by adding directional magnetic field
Figure 3. M4 sample (Rotating Drum speed=2500-2900; Voltage-13) at 100 |im and 10 |im images.
Figure 4. M3 sample PVDF/Fe3O4 nanofiber (Rotating Drum speed=556; Voltage-16.48) at 100 |im
and 50 [im images.
|Label |Area | Mean |Min | Мах |Angle | Length
1 0.005 154.259 65.167 190.984 -4.399 0.192
2 0.01 О 1 79.690 B1.ООО 203.424 -53.746 0.41 1
3 0.003 196.690 1 10.000 219.333 -99.462 0.134
4 0 .004 166.778 1 1 9. ООО 1 96.250 -172.875 0.178
5 0 .005 183.076 1 47. ООО 203.333 -49.399 0.204
6 0. .004 187.556 171. ООО 203.000 -ЭО.ООО 0.1 77
7 0 007 1B6 102 1 25 ООО 206.4-08 -39.289 0.31 4
В 0 ooe 168.282 36 ООО 200.250 -1 31 634 0.266
9 0 .005 219.182 1 55.ООО 246 ООО -90 ООО 0.221
1 О 0 .005 189.785 1 1 4 ООО 223 ООО -36.870 0.221
1 1 0 .005 189.219 1 24 ООО 208.667 -1 39.399 0.204
1 2 0 ОГМ 179 804 1 23 ООО 201 ООО -1 05.945 0.161
1 3 Mean 0 005 183.953 1 1 4.1 81 208.471 -84.418 0.224
1 4 SD 0 .002 16.216 38 042 1 4.778 49.264 0.076
15 Mi n 0.003 154.259 36. ООО 190.984 -172.875 0.134
16 Max 0.010 219.182 171.000 246.000 -4.399 0.41 1
Figure 5. Calculation average length size (diameter) of PVDF/Fe304 nanofiber.
Figure 6. AFM image of pristine PVDF nanofiber (Ml sample)
V. ' V
- • гщ|
a)-----'-:--b)l
Figure 7. AFM image (a) and Optic image (b) of M3 sample PVDF/Fe3O4 nanofiber (Rotating Drum speed=556; Voltage-16.48) in the presence of metal bar.
яёНМрМИ
a) — b)
Figure 8. AFM image (a) and Optic image (b) of M3 sample PVDF/Fe3O4 nanofiber (with static collector, Voltage-16.48) in the presence of metal bar.
3500 3000 2500 2000 1500 1000 500
Волновое число (см-1)
Figure 9. FTIR spectrum of PVDF/ Fe3O4 nanofiber Conclusions
In this research we synthesized a novel nano-magnetically enabled PVDF/Fe3O4 fibrous film material. The highly aligned ferromagnetic nanofibers were produced utilizing the electrospinning technique, it can be clearly inferred from the SEM pictures results. By means of directional magnetic field in electrospinning equipment we obtained highly aligned nanofiber material to investigate their morphology structure. we employed several characterization approaches including scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR) tests. These findings from FTIR analysis showed that the majority of the PVDF crystal structure in electrospun nanofiber membranes is in the P-phase.
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