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Controllable preparation of magnetic polymer nanospheres with high saturation magnetization by miniemulsion polymerization
Materials Letters 64 (2010) 119–121
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Controllable preparation of magnetic polymer nanospheres with high saturation magnetization by miniemulsion polymerization Xiaojuan Zhang a,b,⁎, Wei Jiang a, Fengsheng Li a, Zhendong Sun a, Zhi Ou'yang a a b
Nanjing University of Science & Technology, Nanjing 210094, China Jinling Institute of Technology, Materials Engineering Department, Nanjing 211169, China
a r t i c l e
i n f o
Article history: Received 5 June 2009 Accepted 6 October 2009 Available online 9 October 2009 Keywords: Polymers Nanocomposites Magnetic nanospheres Miniemulsion polymerization Superparamagnetic
a b s t r a c t Magnetic Fe3O4/poly(styrene-co-acrylamide) core/shell nanospheres were prepared by one-step miniemulsion polymerization in the presence of Fe3O4 ferrofluids. The functional monomer of acrylamide was used not only to modify the surface of the nanospheres with functional groups, but also to form modified bilayer with SDBS to control the encapsulation and particle size of nanospheres. The properties of magnetic nanospheres were characterized by IR, TEM, TG and VSM. The results indicated that the superparamagnetic nanopsheres had small particle size of 60 nm, high saturation magnetization of 27.1 emu/g, high magnetic content and abundant functional groups. The possible formation mechanism of magnetic nanospheres was discussed in detail. © 2009 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
Superparamagnetic polymer particles have been widely applied in magnetic resonance imaging (MRI), separation and purifying of biomolecules, hyperthermia and targeted radiotherapy [1–3]. For these biomedical applications, they should fulfill such requirements as nanosized distribution, high saturation magnetization, high and uniform magnetic content, and rich surface functional groups. So far, many processes have been developed for preparing magnetic polymer nanospheres, including soapless polymerization, seeded polymerization, and miniemulsion polymerization [4–6]. Among these methods, miniemulsion polymerization is very suitable for making such magnetic nanospheres, due to its monomer droplet nucleation mechanism [7]. Recently, Yi et al. [8] successfully prepare Fe3O4/poly(styrene-coacrylamide) [Fe3O4/poly(St-Am)] nanospheres by microwave-assisted emulsion polymerization. Wang et al. [9] achieve magnetic polyacrylamide nanospheres via inverse miniemulsion polymerization. However, these magnetic nanospheres have very low saturation magnetization. In this paper, we develop a modified one-step miniemulsion polymerization to controllable prepare magnetic Fe3O4/poly(St-Am) nanospheres with high saturation magnetization.
2.1. Preparation of Fe3O4/poly(St-Am) nanospheres Styrene (St) and divinyl benzene (DVB) were distilled under reduced pressure and potassium peroxodisulfate (KPS) was purified by recrystallization. And all the other reagents were obtained from commercial source and used without further purification. Firstly, hydrophobic Fe3O4 ferrofluids were prepared using the modified chemical coprecipitation [10]. Secondly, 7.2 g St, 0.87 g hexadecane (HD), 0.1 g DVB and 6 g ferrofluids constituted the oil phase and it was added to 72 g H2O containing 0.21 g sodium dodecyl benzene sulfonate (SDBS). The mixture was stirred for pre-emulsification, and then the emulsion was subjected to sonication in an icecooled bath with JY92-II sonifier at 250 W to form miniemulsion. The miniemulsion was purged with N2 before polymerization. To start the polymerization, 0.065 g potassium peroxodisulfate (KPS) was added, and the temperature was increased to 70 °C. Then 1.7 g Am was added and the polymerization was carried out for 18 h with stirring at
Table 1 Samples with different amounts of SDBS and Am added and their characteristics.
⁎ Corresponding author. Jinling Institute of Technology, Materials Engineering Department, Nanjing 211169, China. Tel./fax: +86 25 84318649. E-mail address: [email protected] (X. Zhang). 0167-577X/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2009.10.002
Samples
SDBS (g)
Am (g)
Average size (nm)
Magnetic content (determined by TG, wt.%)
1 2 3 4
0.23 0.22 0.21 0.19
1.5 1.6 1.7 1.9
85 80 60 85
27.1 36.1 36.5 51.2
120
X. Zhang et al. / Materials Letters 64 (2010) 119–121
Fig. 1. FT-IR spectra of (a) Fe3O4 nanoparticles and (b) Fe3O4/poly(St-Am) nanospheres.
250 rpm. The obtained magnetic nanospheres were collected using a magnet and washed with ethanol and distilled water for removing the unreacted monomers. For comparison, four samples prepared with different amounts of SDBS and Am added were shown in Table 1. 2.2. Characterization IR spectra of KBr powder pressed pellets were recorded on a Bruker VECTOR 22 spectrometer. Transmission electron microscopy
Fig. 3. Magnetic hysteresis loops of magnetic nanospheres: (a) sample 1 (b) sample 3 and (c) sample 4.
(TEM) images were recorded on a Tecnai 12 transmission electron microscope. The America TA corp. SDT Q600 thermal analyzer was used at a heating rate of 20 °C⋅min− 1 in N2 over the range 50–800 °C with Al2O3 as reference. And the magnetic properties of the samples were detected at room temperature by vibrating sample magnetometer (VSM, Lake Shore 7410).
Fig. 2. TEM images of magnetic nanospheres: (a) sample 1, (b) sample 2, (c) sample 3 and (d) sample 4.
X. Zhang et al. / Materials Letters 64 (2010) 119–121
121
Fig. 4. Scheme of the formation processes of magnetic nanospheres by miniemulsion polymerization.
3. Results and discussion Fig. 1 shows the IR spectra of Fe3O4 nanoparticles and Fe3O4/poly (St-Am) nanospheres. In Fig. 1a, the characteristic absorption band of Fe3O4 appears at 572 cm− 1, and it also appears in the spectrum of Fe3O4/poly(St-Am) nanospheres (Fig. 1b). In Fig. 1b, the peaks at 692, 756 and 1597 cm− 1 are the absorption bands of St and the peaks at 3398 and 3194 cm− 1 are assigned to the peaks of the –NH2 group. Furthermore, the peaks at 1653 cm− 1 are the absorption bands of C=O bonds. These results indicate that the functional groups (–CONH2) are located on the surfaces of the magnetic nanospheres. Fig. 2 shows the TEM images of Fe3O4/poly(St-Am) nanospheres prepared under different amounts of SDBS and Am. Interestingly, the dosage of SDBS and Am affects not only the particle size but also the encapsulation of nanospheres. Fig. 2a shows that the magnetic content of the nanospheres is lower when prepared by adding 1.5 g Am and 0.23 g SDBS. It can be concluded that when Am is not enough, it could not effectively prevent the overflow of Fe3O4 and realize full encapsulation. Fig. 2c shows that magnetic nanopsheres with the smallest and uniform particle size, good dispersibility and high magnetic content can be obtained by adding 0.21 g SDBS and 1.7 g Am. On the other hand when 0.19 g SDBS and 1.9 g Am are added (Fig. 2d), the particle size of the nanospheres increases and becomes nonuniform. It can be attributed that Am is over the limit value, and excessive Am would make partial SDBS crush into the reaction solution, leading to the instability and growth of monomer droplets. The possible formation process of fine magnetic nanospheres is to be discussed in detail later. The magnetic properties of magnetic nanospheres are most important for further biomedical application and the magnetization curves of nanospheres are shown in Fig. 3. All the samples show a typical superparamagnetic behavior without any hysteresis loop [11] and the superparamagnetic behavior is also reflected in the low residual magnetization (Mr) and coercivity (Hc) values. Fig. 3a and c stands for samples 1 and 4, and their saturation magnetization (Ms) values are 19.64 and 44.42 emu/g, respectively. From Fig. 3b, the Ms of sample 3 is 27.1 emu/g, which is also higher than the reported values of the functional magnetic nanospheres [9,12]. It can be seen that magnetic nanospheres with high saturation magnetization is obtained by controlling the reaction conditions. The possible formation processes of fine magnetic nanopsheres by miniemulsion polymerization are presented in Fig. 4. The hydrophobic Fe3O4 ferrofluids by modified coprecipitation have good dissolubility in oil phase. In the ultrasonic miniemulsification, SDBS form an outer modified layer round the monomer droplet by physical absorption. In the polymerization process, hydrophilic Am and hydrophobic St shape into short-chain free radicals by monomer copolymerization. The free radicals act as surfactant-like and form inner modified layer round the
monomer droplet by chemical bonding. Not only the compact modified bilayer can enhance the stability of droplets to prevent the growth, but also to prevent the outflow of Fe3O4 nanoparticles to realize the complete encapsulation. 4. Conclusion In summary, Fe3O4/poly(St-Am) nanospheres with high saturation magnetization have been prepared by one-step miniemulsion polymerization. The procedure is facile and well-controlled for the synthesis of Fe3O4/poly(St-Am) nanospheres and could be potentially applied to the preparation of other functional magnetic polymer nanospheres. The SDBS–Am modification bilayer is the key factor controlling the particle size and encapsulation of magnetic nanospheres. Further works on their biomedical application are now in progress in our laboratory. Acknowledgments We gratefully acknowledge the National Natural Science Foundation of China (No: 50602024) and the scientific research fund from Jiangsu province of China (No. BK2007214). References [1] Kim DK, Zhang Y, Voit W, Rao KV, Kehr J, Bjelke B, et al. Supermagnetic iron oxide nanoparticles for bio-medical applications. Scr Mater 2001;44:1713–7. [2] Lübbe AS, Alexiou C, Bergemann C. Clinical applications of magnetic drug targeting. J Surg Res 2001;95:200–6. [3] Zhang CF, Sun HW, Xia JY, Yu JF, Yao SD, Yin DZ, et al. Synthesis of polyacrylamide modified magnetic nanoparticles and radiolabeling with 188Re for magnetically targeted radiotherapy. J Magn Magn Mater 2005;293:193–8. [4] Wang PC, Chiu WY, Lee CF, Young TH. Synthesis of iron oxide/poly(methyl methacrylate) composite latex particles: nucleation mechanism and morphology. J Polym Sci Part A Polym Chem 2004;42:5695–705. [5] Lu S, et al. Preparation of magnetic polymeric composite nanoparticles by seeded emulsion polymerization. Mater Lett 2009, doi:10.1016/j.matlet.2008.12.045. [6] Vaihinger D, Landfester K, Kräuter I, Brunner H, Tovar GEM. Molecularly imprinted polymer nanospheres as synthetic affinity receptors obtained by miniemulsion polymerisation. Macromol Chem Phys 2002;203:1965–73. [7] Lu SL, Ramos J, Forcada J. Self-stabilized magnetic polymeric composite nanoparticles by emulsifier-free miniemulsion polymerization. Langmuir 2007;23:12893–900. [8] Huang JJ, Pen H, Xu ZS, Yi CF. Magnetic Fe3O4/poly(styrene-co-acrylamide) composite nanoparticles prepared by microwave-assisted emulsion polymerization. React Funct Polym 2008;68:332–9. [9] Xu ZZ, Wang CC, Yang WL, Deng YH, Fu SK. Encapsulation of nanosized magnetic iron oxide by polyacrylamide via inverse miniemulsion polymerization. J Magn Magn Mater 2004;277:136–43. [10] Zheng WM, Gao F, Gu HC. Magnetic polymer nanospheres with high and uniform magnetite content. J Magn Magn Mater 2005;288:403–10. [11] Sun Y, Wang B, Wang HP, Jiang JM. Controllable preparation of magnetic polymer microspheres with different morphologies by miniemulsion polymerization. J Colloid Interface Sci 2007;308:332–6. [12] Xu H, Tong NH, Cui LL, Lu Y, Gu HC. Preparation of hydrophilic magnetic nanospheres with high saturation magnetization. J Magn Magn Mater 2007;311:125–30.
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Controllable preparation of magnetic polymer nanospheres with high saturation magnetization by miniemulsion polymerization Xiaojuan Zhang a,b,⁎, Wei Jiang a, Fengsheng Li a, Zhendong Sun a, Zhi Ou'yang a a b
Nanjing University of Science & Technology, Nanjing 210094, China Jinling Institute of Technology, Materials Engineering Department, Nanjing 211169, China
a r t i c l e
i n f o
Article history: Received 5 June 2009 Accepted 6 October 2009 Available online 9 October 2009 Keywords: Polymers Nanocomposites Magnetic nanospheres Miniemulsion polymerization Superparamagnetic
a b s t r a c t Magnetic Fe3O4/poly(styrene-co-acrylamide) core/shell nanospheres were prepared by one-step miniemulsion polymerization in the presence of Fe3O4 ferrofluids. The functional monomer of acrylamide was used not only to modify the surface of the nanospheres with functional groups, but also to form modified bilayer with SDBS to control the encapsulation and particle size of nanospheres. The properties of magnetic nanospheres were characterized by IR, TEM, TG and VSM. The results indicated that the superparamagnetic nanopsheres had small particle size of 60 nm, high saturation magnetization of 27.1 emu/g, high magnetic content and abundant functional groups. The possible formation mechanism of magnetic nanospheres was discussed in detail. © 2009 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
Superparamagnetic polymer particles have been widely applied in magnetic resonance imaging (MRI), separation and purifying of biomolecules, hyperthermia and targeted radiotherapy [1–3]. For these biomedical applications, they should fulfill such requirements as nanosized distribution, high saturation magnetization, high and uniform magnetic content, and rich surface functional groups. So far, many processes have been developed for preparing magnetic polymer nanospheres, including soapless polymerization, seeded polymerization, and miniemulsion polymerization [4–6]. Among these methods, miniemulsion polymerization is very suitable for making such magnetic nanospheres, due to its monomer droplet nucleation mechanism [7]. Recently, Yi et al. [8] successfully prepare Fe3O4/poly(styrene-coacrylamide) [Fe3O4/poly(St-Am)] nanospheres by microwave-assisted emulsion polymerization. Wang et al. [9] achieve magnetic polyacrylamide nanospheres via inverse miniemulsion polymerization. However, these magnetic nanospheres have very low saturation magnetization. In this paper, we develop a modified one-step miniemulsion polymerization to controllable prepare magnetic Fe3O4/poly(St-Am) nanospheres with high saturation magnetization.
2.1. Preparation of Fe3O4/poly(St-Am) nanospheres Styrene (St) and divinyl benzene (DVB) were distilled under reduced pressure and potassium peroxodisulfate (KPS) was purified by recrystallization. And all the other reagents were obtained from commercial source and used without further purification. Firstly, hydrophobic Fe3O4 ferrofluids were prepared using the modified chemical coprecipitation [10]. Secondly, 7.2 g St, 0.87 g hexadecane (HD), 0.1 g DVB and 6 g ferrofluids constituted the oil phase and it was added to 72 g H2O containing 0.21 g sodium dodecyl benzene sulfonate (SDBS). The mixture was stirred for pre-emulsification, and then the emulsion was subjected to sonication in an icecooled bath with JY92-II sonifier at 250 W to form miniemulsion. The miniemulsion was purged with N2 before polymerization. To start the polymerization, 0.065 g potassium peroxodisulfate (KPS) was added, and the temperature was increased to 70 °C. Then 1.7 g Am was added and the polymerization was carried out for 18 h with stirring at
Table 1 Samples with different amounts of SDBS and Am added and their characteristics.
⁎ Corresponding author. Jinling Institute of Technology, Materials Engineering Department, Nanjing 211169, China. Tel./fax: +86 25 84318649. E-mail address: [email protected] (X. Zhang). 0167-577X/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2009.10.002
Samples
SDBS (g)
Am (g)
Average size (nm)
Magnetic content (determined by TG, wt.%)
1 2 3 4
0.23 0.22 0.21 0.19
1.5 1.6 1.7 1.9
85 80 60 85
27.1 36.1 36.5 51.2
120
X. Zhang et al. / Materials Letters 64 (2010) 119–121
Fig. 1. FT-IR spectra of (a) Fe3O4 nanoparticles and (b) Fe3O4/poly(St-Am) nanospheres.
250 rpm. The obtained magnetic nanospheres were collected using a magnet and washed with ethanol and distilled water for removing the unreacted monomers. For comparison, four samples prepared with different amounts of SDBS and Am added were shown in Table 1. 2.2. Characterization IR spectra of KBr powder pressed pellets were recorded on a Bruker VECTOR 22 spectrometer. Transmission electron microscopy
Fig. 3. Magnetic hysteresis loops of magnetic nanospheres: (a) sample 1 (b) sample 3 and (c) sample 4.
(TEM) images were recorded on a Tecnai 12 transmission electron microscope. The America TA corp. SDT Q600 thermal analyzer was used at a heating rate of 20 °C⋅min− 1 in N2 over the range 50–800 °C with Al2O3 as reference. And the magnetic properties of the samples were detected at room temperature by vibrating sample magnetometer (VSM, Lake Shore 7410).
Fig. 2. TEM images of magnetic nanospheres: (a) sample 1, (b) sample 2, (c) sample 3 and (d) sample 4.
X. Zhang et al. / Materials Letters 64 (2010) 119–121
121
Fig. 4. Scheme of the formation processes of magnetic nanospheres by miniemulsion polymerization.
3. Results and discussion Fig. 1 shows the IR spectra of Fe3O4 nanoparticles and Fe3O4/poly (St-Am) nanospheres. In Fig. 1a, the characteristic absorption band of Fe3O4 appears at 572 cm− 1, and it also appears in the spectrum of Fe3O4/poly(St-Am) nanospheres (Fig. 1b). In Fig. 1b, the peaks at 692, 756 and 1597 cm− 1 are the absorption bands of St and the peaks at 3398 and 3194 cm− 1 are assigned to the peaks of the –NH2 group. Furthermore, the peaks at 1653 cm− 1 are the absorption bands of C=O bonds. These results indicate that the functional groups (–CONH2) are located on the surfaces of the magnetic nanospheres. Fig. 2 shows the TEM images of Fe3O4/poly(St-Am) nanospheres prepared under different amounts of SDBS and Am. Interestingly, the dosage of SDBS and Am affects not only the particle size but also the encapsulation of nanospheres. Fig. 2a shows that the magnetic content of the nanospheres is lower when prepared by adding 1.5 g Am and 0.23 g SDBS. It can be concluded that when Am is not enough, it could not effectively prevent the overflow of Fe3O4 and realize full encapsulation. Fig. 2c shows that magnetic nanopsheres with the smallest and uniform particle size, good dispersibility and high magnetic content can be obtained by adding 0.21 g SDBS and 1.7 g Am. On the other hand when 0.19 g SDBS and 1.9 g Am are added (Fig. 2d), the particle size of the nanospheres increases and becomes nonuniform. It can be attributed that Am is over the limit value, and excessive Am would make partial SDBS crush into the reaction solution, leading to the instability and growth of monomer droplets. The possible formation process of fine magnetic nanospheres is to be discussed in detail later. The magnetic properties of magnetic nanospheres are most important for further biomedical application and the magnetization curves of nanospheres are shown in Fig. 3. All the samples show a typical superparamagnetic behavior without any hysteresis loop [11] and the superparamagnetic behavior is also reflected in the low residual magnetization (Mr) and coercivity (Hc) values. Fig. 3a and c stands for samples 1 and 4, and their saturation magnetization (Ms) values are 19.64 and 44.42 emu/g, respectively. From Fig. 3b, the Ms of sample 3 is 27.1 emu/g, which is also higher than the reported values of the functional magnetic nanospheres [9,12]. It can be seen that magnetic nanospheres with high saturation magnetization is obtained by controlling the reaction conditions. The possible formation processes of fine magnetic nanopsheres by miniemulsion polymerization are presented in Fig. 4. The hydrophobic Fe3O4 ferrofluids by modified coprecipitation have good dissolubility in oil phase. In the ultrasonic miniemulsification, SDBS form an outer modified layer round the monomer droplet by physical absorption. In the polymerization process, hydrophilic Am and hydrophobic St shape into short-chain free radicals by monomer copolymerization. The free radicals act as surfactant-like and form inner modified layer round the
monomer droplet by chemical bonding. Not only the compact modified bilayer can enhance the stability of droplets to prevent the growth, but also to prevent the outflow of Fe3O4 nanoparticles to realize the complete encapsulation. 4. Conclusion In summary, Fe3O4/poly(St-Am) nanospheres with high saturation magnetization have been prepared by one-step miniemulsion polymerization. The procedure is facile and well-controlled for the synthesis of Fe3O4/poly(St-Am) nanospheres and could be potentially applied to the preparation of other functional magnetic polymer nanospheres. The SDBS–Am modification bilayer is the key factor controlling the particle size and encapsulation of magnetic nanospheres. Further works on their biomedical application are now in progress in our laboratory. Acknowledgments We gratefully acknowledge the National Natural Science Foundation of China (No: 50602024) and the scientific research fund from Jiangsu province of China (No. BK2007214). References [1] Kim DK, Zhang Y, Voit W, Rao KV, Kehr J, Bjelke B, et al. Supermagnetic iron oxide nanoparticles for bio-medical applications. Scr Mater 2001;44:1713–7. [2] Lübbe AS, Alexiou C, Bergemann C. Clinical applications of magnetic drug targeting. J Surg Res 2001;95:200–6. [3] Zhang CF, Sun HW, Xia JY, Yu JF, Yao SD, Yin DZ, et al. Synthesis of polyacrylamide modified magnetic nanoparticles and radiolabeling with 188Re for magnetically targeted radiotherapy. J Magn Magn Mater 2005;293:193–8. [4] Wang PC, Chiu WY, Lee CF, Young TH. Synthesis of iron oxide/poly(methyl methacrylate) composite latex particles: nucleation mechanism and morphology. J Polym Sci Part A Polym Chem 2004;42:5695–705. [5] Lu S, et al. Preparation of magnetic polymeric composite nanoparticles by seeded emulsion polymerization. Mater Lett 2009, doi:10.1016/j.matlet.2008.12.045. [6] Vaihinger D, Landfester K, Kräuter I, Brunner H, Tovar GEM. Molecularly imprinted polymer nanospheres as synthetic affinity receptors obtained by miniemulsion polymerisation. Macromol Chem Phys 2002;203:1965–73. [7] Lu SL, Ramos J, Forcada J. Self-stabilized magnetic polymeric composite nanoparticles by emulsifier-free miniemulsion polymerization. Langmuir 2007;23:12893–900. [8] Huang JJ, Pen H, Xu ZS, Yi CF. Magnetic Fe3O4/poly(styrene-co-acrylamide) composite nanoparticles prepared by microwave-assisted emulsion polymerization. React Funct Polym 2008;68:332–9. [9] Xu ZZ, Wang CC, Yang WL, Deng YH, Fu SK. Encapsulation of nanosized magnetic iron oxide by polyacrylamide via inverse miniemulsion polymerization. J Magn Magn Mater 2004;277:136–43. [10] Zheng WM, Gao F, Gu HC. Magnetic polymer nanospheres with high and uniform magnetite content. J Magn Magn Mater 2005;288:403–10. [11] Sun Y, Wang B, Wang HP, Jiang JM. Controllable preparation of magnetic polymer microspheres with different morphologies by miniemulsion polymerization. J Colloid Interface Sci 2007;308:332–6. [12] Xu H, Tong NH, Cui LL, Lu Y, Gu HC. Preparation of hydrophilic magnetic nanospheres with high saturation magnetization. J Magn Magn Mater 2007;311:125–30.