Alternating magnetic field heat behaviors of PVDF fibrous mats filled with iron oxide nanoparticles Alternating magnetic field heat behaviors of PVDF fibrous mats filled with iron oxide nanoparticles[.]
Alternating magnetic field heat behaviors of PVDF fibrous mats filled with iron oxide nanoparticles , , , Jinu Kim , Jung-Su Choi , Heejae Yang, Frank K Ko, and Ki Hyeon Kim Citation: AIP Advances 6, 055907 (2016); doi: 10.1063/1.4943054 View online: http://dx.doi.org/10.1063/1.4943054 View Table of Contents: http://aip.scitation.org/toc/adv/6/5 Published by the American Institute of Physics AIP ADVANCES 6, 055907 (2016) Alternating magnetic field heat behaviors of PVDF fibrous mats filled with iron oxide nanoparticles Jinu Kim,1,a Jung-Su Choi,2,a Heejae Yang,2 Frank K Ko,2 and Ki Hyeon Kim1,b Department of Physics, Yeungnam University, Gyeongsan, 38541, Korea Department of Materials Engineering, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada (Presented 13 January 2016; received November 2015; accepted December 2015; published online 25 February 2016) To study the magnetic heat behaviors, iron oxide nanoparticles (IONPs) and the polyvinylidene fluoride (PVDF) fibrous mats filled with IONPs were prepared by using coprecipitaion method and the electrospinning technique The synthesized IONPs exhibited a magnetization of about 72 emu/g with average diameter of about 10 nm The magnetizations of PVDF fibrous mats filled with IONPs showed 2.6 emu/g, 5.5 emu/g and 9.9 emu/g for wt.%, 10 wt.% and 20 wt.% IONPs concentration, respectively The heat of the magnetic fibrous mats were measured under various alternating magnetic fields (90, 128, and 167 Oe), frequencies (190, 250 and 355 kHz) The maximum saturated temperature showed up to 62 ◦C for 20 wt.% IONPs filled in PVDF fibrous mat under 167 Oe and 355 kHz C 2016 Author(s) All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License [http://dx.doi.org/10.1063/1.4943054] I INTRODUCTION Iron oxide nanoparticles (IONPs) have a high potential for bio-applications such as magnetic resonance imaging contrast enhancement, tissue repair, drug delivery and localized magnetic hyperthermia applications.1–4 In general, IONPs and their colloids have been widely studied in local hyperthermia.1–8 To apply the hyperthermia treatment, the IONPs should be evenly dispersed throughout the fluid And it must be shorten treatment time with the controllable loss The magnetic local hyperthermia provides the heat at the site of the tumor invasively by applying an external alternating magnetic field (AMF) to the IONPs with the heat range about 42◦C to 46◦C.4,5 The magnetic field-induced heating of IONPs occurs through a combination of eddy currents, hysteresis losses, and relaxation losses The eddy current loss is deeply related with the skin depth of materials which is defined by the applied frequency, conductivity and permeability of materials However, the eddy current loss can be negligible in a nano-sized particles within a few hundred kHz region In agglomerated magnetic nanoparticles (MNPs), the loss is mainly governed by the hysteresis loss due to the dipole interaction2 although Neel relaxation is generated by magnetic spins in single-domain MNPs.7–9 In the Brownian relaxation, the interaction between a thermal force and viscous drag in the suspending medium will influence the particle movement significantly The total loss of the MNPs is governed by the strength of the AMF and their operating frequencies as well as the intrinsic magnetic properties.4 In recent, researchers have been tried to employ the IONPs in composite sheet as well as IONPs colloids to healing of skin infections including hyperthermia-aided immunotherapy.10–15 The IONPs dispersed in fibrous mats have an advantage of easily usage to healing and wound area with an immovable IONPs, thus allowing a repeated localized heating Therefore, the PVDF was employed as a polymeric fibrous matrix for electrospinning, a Jinu Kim and Jung-Su Choi contributed equally to this work b Author to whom correspondence should be addressed Electronic mail: kee1@ynu.ac.kr 2158-3226/2016/6(5)/055907/6 6, 055907-1 © Author(s) 2016 055907-2 Kim et al AIP Advances 6, 055907 (2016) which PVDF has excellent biocompatibility and minimal cell adsorption and tissue response, as well as good electrical insulation, chemical resistance, and good thermal properties.16–18 And then we synthesized the PVDF fibrous mats filled with IONPs and verified the heat behaviors II EXPERIMENTAL PROCEDURE The IONPs were synthesized by coprecipitation method FeCl2·4H2O and FeCl3·6H2O with a molar ratio 1:2 were dissolved in deionized water under nitrogen with vigorous stirring at 80 ◦C and then the black colored IONPs were obtained by adding NH4OH (FeCl2·4H2O + 2FeCl3·6H2O + 8NH4OH → Fe3O4 + 8NH4Cl + 20H2O) And then the IONPs filled in PVDF fibrous mats were fabricated by using the electrospinning technique The spinning dopes were prepared by sonication of the IONPs in Dimethylformamide (DMF, Sigma-Aldrich) for 24 hours 20 wt.% of Polyvinylidene Fluoride (PVDF, Kynar) to DMF were then added to the prepared IONPs/DMF mixture The solutions mixtures were stirred for 24 hours before the electrospinning at 90 ◦C IONPs of 5, 10 and 20 wt.% in PVDF solutions were prepared, which solutions were electrospun using NEU (Kato Tech) electrospinning device The distance between spinneret to target was set as 15 cm and gauge 18 blunt ended syringe needle was used as spinneret The voltage applied to the spinning nozzle was varied between 10∼15 kV to obtain stable and continuous fiber fabrication while solution was pumped at a rate of 0.1 ml/min The fabricated mats dried at 100 ◦C for 12 hrs and had a heat treatment at 150 ◦C during 12 hrs under Ar gas atmosphere The morphologies and structures of PVDF fibrous mats filled with IONPs were determined by using Field Emission Scanning Electron Microscopy (FE-SEM, Philips s-4800), X-ray diffractometer (XRD, Cu Kα, λ = 1.54059 Å) and Raman spectroscopy (XploRA Plus, Horbia Ltd.) The magnetic properties were measured by using Vibrating Sample Magnetometer (VSM, Lakeshore 7410) The induction heat temperature were measured by AC heating system which is composed of RF power supply (AMERITHERM INC., HOTSHOT 2.4 kW) and 5.5 turns-helical shaped Cu coil with the 80 mm-height and 70 mm-inner diameter as an AC magnetic field applicator which the strength of AMF was measured by a magnetic field transducer (SENIS AG.) The temperature was measured by using channel thermometer (FISO, TMI4) and fiber optic probes (FISO, FOT-L-BA) with the resolution and accuracy of 0.1◦C and ±1◦C, respectively III RESULTS AND DISCUSSION Figure 1(a)–1(d) shows the FESEM images of the PVDF fibrous mats filled with IONPs concentration from wt.%, wt.%, 10 wt.% and 20 wt.%, respectively The average thickness of mats and their fiber diameter are about 70 µm and about 500 - 700 nm The synthesized IONPs and FIG FESEM images (a)-(d) of the PVDF fibrous mats filled with IONPs concentrations and TEM images (e) of the as-synthesized IONPs and (f)-(h) PVDF fiber filled with IONPs concentrations, respectively 055907-3 Kim et al AIP Advances 6, 055907 (2016) FIG (a) XRD patterns and (b) Raman spectra of PVDF fibrous mats filled with IONPs concentration in comparison with those of IONPs after heat treatment and as-synthesized IONPs, respectively fibers filled in IONPs were observed by TEM as shown in Fig 1(e)–1(h) TEM images of IONPs revealed the average diameter of about 10 nm with chain-like structure in Fig 1(e) IONPs in fibers exhibited not evenly distributed but locally agglomerated, which would be caused by the chain-like structure of IONPs The XRD peaks of the PVDF fibrous mats filled with IONPs concentration, the oxidized and as-synthesized iron oxide powder were compared with those of the magnetite (Fe3O4, JCPDS 19-0629), maghemite (γ-Fe2O3, JCPDS 39-1346) and hematite (α-Fe2O3, JCPDS 33-0664),19 respectively, as shown in Fig 2(a) The diffraction peaks of the as-synthesized IONPs are correspond to (220), (311), (400), (511) and (440) reflections of magnetite and the PVDF fibrous mats filled with IONPs are closely match with those of maghemite, respectively It indicates that the synthesized Fe3O4 particles could be partially transformed to γ-Fe2O3 in the process of electrospinning due to the presence of oxygen and heat treatment To confirm the transformation of magnetic phase from Fe3O4 to γ-Fe2O3, the as-synthesized IONPs were annealed at 150 ◦C for 12 hrs, which is the same temperature of final heat treatment for electrospinning process The diffraction peaks of the IONPs after heat treatment were a little bit shifted from Fe3O4 to γ-Fe2O3, which is not sufficient for evidence of the phase transformation Thus, the phase transformation was verified by Raman spectroscopy which is powerful tool to distinguish the different structural phases of iron oxide Figure 2(b) depicts the Raman spectra of the PVDF fibrous mats filled with IONPs concentration in comparison with those of as-synthesized IONPs and the IONPs after heat treatment, respectively For PVDF fibrous mats filled with IONPs concentration, the typical maghemite bands (720 cm−1, 536 cm−1, and 306 cm−1) are dominant with the broadness of peaks due to the mixed magnetic phase of Fe3O4 and γ-Fe2O3,20 which results are comparable to the IONPs after heat treatment The PVDF fibrous mat without IONPs reveal the peaks at 795 cm−1 and 839 cm−1.21 The magnetite phase is easily discernible by its main band centered at around 665 cm−1 for as-synthesized IONPs.20 In general, when the magnetic phase of Fe3O4 transferred to γ-Fe2O3 by heat treatment over 150 ◦C, the values of magnetization should be reduced such as 92 emu/g to 73.5 emu/g for bulk22,23 and 78 emu/g to 59 emu/g for nanoparticles.24 The measured magnetization values of the as-synthesized and the oxidized IONPs by heat treatment exhibited about 72 emu/g and 60 emu/g at room temperature, which the external magnetic field was applied up to 1.5T as shown in Fig 3(a) The magnetizations of PVDF fibrous mats filled with IONPs of wt.%, 10 wt.% and 20 wt.% were obtained 2.6 emu/g, 5.5 emu/g and 9.9 emu/g, respectively, in Fig 3(b) Theses magnetization values showed lower values in comparison with those of the weight ratio of the as-synthesized IONPs As the magnetic phases are partially transferred from as-synthesized Fe3O4 to γ-Fe2O3 during the electrospinning process, the magnetizations for PVDF fibrous mats filled with IONPs of wt.%, 10 wt.% and 20 wt.% can be deduced by that of the oxidized IONPs (γ-Fe2O3) about emu/g, emu/g and 12 emu/g, respectively These approximations were nearly agreement with those of measured magnetization values The slight differences in comparison with the measured magnetizations would be result from the different oxidation conditions between the oxidized IONPs 055907-4 Kim et al AIP Advances 6, 055907 (2016) FIG The magnetization curves of (a) the as-synthesized IONPs and IONPs after heat treatment and (b) the PVDF fibrous mats with the change of IONPs concentrations, respectively and the PVDF fibrous filled with IONPs To verify the heat elevation of the PVDF fibrous mats filled with IONPs, the specimens were placed in an isolated air environment with ambient temperature of 36 ◦C which is similar with that of human body The intensity of AMF was generated with 90 Oe, 128 Oe and 167 Oe at the selective frequency of 190 kHz, 250 kHz and 355 kHz, respectively To confirm the reliability of the measuring temperature, the temperature change of reference specimen was simultaneously detected with that of IONPs filled in fibrous mats under same measuring conditions, which reference specimen was employed the PVDF fibrous mats without IONPs Figure 4(a)–4(c) shows the heat behaviors of PVDF fibrous mats filled with IONPs for the increment of AMF at 190 kHz The temperatures were linearly increased with the increment of IONPs concentration and intensity of AMF from 90 Oe to 167 Oe The saturated temperatures were exhibited up to about 44, 53 and 60 ◦C for the 20 wt.% of IONPs concentration with the increment of AMF of 90, 128 and 167 Oe at 190 kHz, respectively To evaluate the frequency dependence of heat, the elevated temperatures of PVDF fibrous composites with IONPs were measured at 190 kHz, 250 kHz and 355 kHz with the fixed AMF of 128 Oe, respectively, as shown in Fig 4(d)–4(f) The saturated temperatures were increased with the increment of frequency and IONPs concentration, respectively The saturated temperatures were elevated up to about 53, 57 and 62 ◦C for the 20 wt.% of IONPs concentration with the increment of frequency of 190, 250 and 355 kHz at 128 Oe, respectively The loss mechanism of magnetic nanoparticles (MNPs) under AC magnetic fields should FIG (a)-(c) The measured temperature of the PVDF fibrous mats filled with IONPs concentration with increment of AMF from 90 Oe to 167 Oe at 190 kHz and (d)-(f) with the increment of frequency from 190 kHz to 355 kHz at AMF of 128 Oe, respectively 055907-5 Kim et al AIP Advances 6, 055907 (2016) FIG (a)-(b) The elevated temperature of the PVDF fibrous mats filled with IONPs concentration, (c)-(d) the values of initial slope of the time-temperature heating curve, and (e)-(f) the power loss with increment of AMF from 90 Oe to 167 Oe at 190 kHz and with the increment of frequency from 190 kHz to 355 kHz at AMF of 128 Oe, respectively be considered whether the MNPs is dispersed or agglomerated, respectively The heat generation by magnetic losses of the agglomerated MNPs is governed by hysteresis loss and interparticle interactions2 although the dispersed MNPs is given by the Brown and Neel relaxations.9 Especially, the effective magnetic loss of the polymeric fibrous mats filled with IONPs is not easy to predict due to the complicated magnetic interactions for the mixed magnetic phases and structures with the locally aggregated and partially dispersed IONPs in fiber Thus, the practical magnetic losses for the mixed structure with the dispersed and aggregated IONPs in fibrous mats could properly evaluate by the experimental heat behaviors The magnetic losses for heat generation can be expressed by the specific loss power (SLP), also called the specific absorption rate (SAR), which is defined as the thermal dissipation per unit of mass of the magnetic material in the presence of an AMF SLP is equal to c × ∆T/∆t × msample/mparticle, where c is the specific heat capacity of sample, msample is the mass of sample, mparticle is the mass of the magnetic material in specimen, and ∆T/∆t is the initial slope of the time-temperature heating curve.25 For polymer matrix filled with IONPs such as a composite, the heat capacity of the system corresponds to (mparticle·cparticle + mcomposite·ccomposite + mair·cair)/(mparticle + mcomposite), where mcomposite and ccomposite are the mass and specific heat capacity of composite, respectively.4,25 Figure shows the ∆T, ∆T/∆t and their SAR of the PVDF fibrous mats filled with IONPs concentration for the change of AMF and frequency, respectively The initial slope of the time-temperature heating curves were fitted by use of the phenomenological Box-Lucas equation given by T(t) = A(1 − e−Bt).26 The fitting parameters A and B are related to the initial slope of the time-temperature heating ratio The ∆T, ∆T/∆t and SAR values increased with the increment of AMF and frequency as well as IONPs concentration in fibrous mats The maximum ∆T and ∆T/∆t showed about 26 ◦C and 0.2 at AMF of 167 Oe and 190 kHz The SAR values were calculated on the measured time-temperature increasing ratio (∆T/∆t) with the change of AMF, frequency and the increment of IONPs filled in PVDF fibrous mats, as shown in Fig 4(e) and 4(f), respectively Although the SAR values were not dominant with the change of IONPs concentrations in fibers, these values increased from about 0.4 W/g to 1.7W/g with the increment of AMF at the fixed frequency of 190 kHz and from about 0.95 W/g to 1.6 W/g for the increment of frequency at the fixed AMF of 128 Oe, respectively IV CONCLUSIONS As-synthesized Fe3O4 particles are partially transferred to γ-Fe2O3 in fibrous mats by electrospinning process, the XRD and Raman results are the clear evidence along with the change of 055907-6 Kim et al AIP Advances 6, 055907 (2016) magnetizations The heating effects for the PVDF fibrous mats filled with IONPs concentration were studied in various strengths of AMF and frequencies All the PVDF fibrous mats filled with IONPs showed that the temperatures increased with the increment of AMF, frequency and IONPs concentration, respectively The maximum saturated temperature and ∆T showed about 62 ◦C and 26 ◦C for the 20 wt.% of IONPs concentration and their maximum SAR exhibited about 1.7 W/g at 167 Oe, 190 kHz, respectively SAR values may not dominant on IONPs concentration in fibers but the strength of AMF and their frequency As results, these flexible PVDF fibrous mats filled with IONPs could be helpful for hyperthermia treatment and skin wound healing applications ACKNOWLEDGMENTS This study was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (NRF-2013R1A1A2A 10058888) Calvin H Li, Paul Hodgins, and G.P Peterson, J Appl Phys 110, 054303 (2008) E Lima, Jr., E De Biasi, M Vasquez 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(2016) Alternating magnetic field heat behaviors of PVDF fibrous mats filled with iron oxide nanoparticles Jinu Kim,1,a Jung-Su Choi,2,a Heejae Yang,2 Frank K Ko,2 and Ki Hyeon Kim1,b Department of. .. spectra of the PVDF fibrous mats filled with IONPs concentration in comparison with those of as-synthesized IONPs and the IONPs after heat treatment, respectively For PVDF fibrous mats filled with. .. verify the heat elevation of the PVDF fibrous mats filled with IONPs, the specimens were placed in an isolated air environment with ambient temperature of 36 ◦C which is similar with that of human