Article pubs.acs.org/IECR
Facile Approach for Superparamagnetic CNT-Fe3O4/Polystyrene Tricomponent Nanocomposite via Synergetic Dispersion Wu Zhong,† Peng Liu,*,† Zhaobin Tang,‡ Xueli Wu,§ and Jianhui Qiu§ †
State Key Laboratory of Applied Organic Chemistry and Institute of Polymer Science and Engineering, College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, China ‡ Ningbo Institute of Material Technology & Engineering, Chinese Academy of Sciences, Ningbo 315201, China § Department of Machine Intelligence and Systems Engineering, Faculty of Systems Engineering, Akita Prefectural University, Akita 015-0055, Japan ABSTRACT: A facile one-pot in-situ radical bulk polymerization strategy was developed for preparation of the superparamagnetic multiwalled carbon nanotubes-Fe3O4/polystyrene (CNT-Fe3O4/PS) tricomponent nanocomposite by the synergetic dispersion strategy via the multiwalled carbon nanotubes (CNT) immobilized Fe3O4 nanoparticles (CNT-Fe3O4) with oleic acid (OA) as surface modifier. Compared with the tricomponent nanocomposite prepared with the multiwalled carbon nanotubes and Fe3O4 nanoparticles added separately, immobilization of Fe3O4 nanoparticles on multiwalled carbon nanotubes could avoid efficiently aggregation of the Fe3O4 nanoparticles in polymer matrices. OA molecules adsorb onto the surfaces of the Fe3O4 nanoparticles immobilized on the multiwalled carbon nanotubes, improving efficiently the dispersibility of the multiwalled carbon nanotubes in styrene, which resulted in the well-dispersed CNT-Fe3O4/PS tricomponent nanocomposite.
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INTRODUCTION Polymer-based nanocomposites have attracted particular interest in the past decades and been studied extensively due to their various potential applications by combining the attractive functional properties of nanomaterials (electrical, optical, magnetic properties, etc) with the advantages of polymers, such as low cost and good processability.1 Various nanomaterials such as the magnetic nanoparticles and carbon nanotubes (CNTs) had been widely used as functional nanofillers for polymer-based magnetic2,3 or conductive4,5 nanocomposites with excellent potential applications, such as electromagnetic interference shielding, magneto-optical storage, biomedical sensing, flexible electronics, etc. Control over the dispersion of the nanoparticle or nanotube phase embedded in a polymer matrix is critical and often challenging.6,7 Multicomponent nanocomposites that contain two or more nanometer-scale components have attracted much attention recently owing to the two or more functions introduced by different nanometer-scale objects.8 Recently, the tricomponent nanocomposites with two nanometer-scale components in polymeric matrices have attracted interest due to their unique performance. Tricomponent polymer-based nanocomposites containing magnetic nanoparticles and carbon nanotubes exhibit potential application in electromagnetic shielding,9,10 electrochemical biosensing,11 tissue engineering, biomedicine, and bone fixation.12 Choi et al. prepared tricomponent nanocomposites containing magnetic nanoparticles and carbon nanotubes via adsorption of polymer-coated Fe3O4 nanoparticles onto the carboxyl MWNTs13 or adsorption of the carboxyl MWNTs onto polymer-coated carbonyl iron (CI) particles,14 and their magnetorheology was investigated. There are also some reports on the tricomponent bulky polymerbased nanocomposites containing magnetic nanoparticles and © 2012 American Chemical Society
carbon nanotubes in various polymer matrices, prepared via the physical blending technique.15−18 The in-situ polymerization technique is another efficient approach to prepare polymer-based nanocomposites with various nanometer-scale objects, especially for the in-situ bulk polymerization technique. It has been widely used for preparation of the bulky polymer-based nanocomposites with a single nanometer-scale object.19−23 To date, there has been no work on tricomponent nanocomposites via the in-situ polymerization technique. In the in-situ polymerization procedure, nanometer-scale objects should be surface modified to improve their dispersibility in the hydrophobic monomers. Our group developed the facile one-pot approach to graft polymers onto the surfaces of the inorganic nanoparticles, in which surface modification of the inorganic nanoparticles and the polymerization reaction (containing copolymerization of the surface modifier and monomer and homopolymerization of the monomer) take place simultaneously.24 In the present work, we prepared the superparamagnetic multiwalled carbon nanotubes-Fe3O4/polystyrene (CNTFe3O4/PS) tricomponent nanocomposite via facile one-pot in-situ radical bulk polymerization of styrene via the synergetic dispersion strategy of the multiwalled carbon nanotubes (CNT) immobilized Fe3O4 nanoparticles (CNT-Fe3O4) with oleic acid (OA) as surface modifier (Scheme 1). CNT-Fe3O4/ PS tricomponent nanocomposite was compared with the CNT/Fe3O4/PS tricomponent nanocomposite prepared with Received: Revised: Accepted: Published: 12017
April 4, 2012 August 15, 2012 August 21, 2012 August 21, 2012 dx.doi.org/10.1021/ie300891h | Ind. Eng. Chem. Res. 2012, 51, 12017−12024
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Scheme 1. Schematic Representation of the Synergetic Dispersion Mechanism
Table 1. Conditions of the Preparation of the CNTs-Fe3O4 Investigated CNTFe3O4 samples
CNTCOOH (g)
FeCl3·6H2O (g)
FeCl2·4H2O (g)
theoretical mass ratio of CNT-COOH and Fe3O4
S-1 S-2 S-3 S-4 S-5
0.1034 0.1000 0.1009 0.1002 0.0517
0.0162 0.0390 0.0782 0.1560 0.2060
0.0067 0.0143 0.0286 0.0572 0.0875
5:1 2:1 1:1 1:2 1:5
room temperature, the polymerization pipe was broken and the resulting nanocomposite (CNTs-Fe3O4/PS) was collected. For comparison, the CNT/Fe3O4/PS tricomponent nanocomposite was prepared with the CNT-COOH and Fe3O4 nanoparticles added separately in the radical bulk polymerization: 20.0 mL of styrene, 0.10 g of AIBN, 0.30 g of OA, 0.05 g of CNT-COOH, and 0.05 g of Fe3O4 nanoparticles were irradiated ultrasonically for 30 min and subsequently heated to 90 °C for 8 h in a glass polymerization pipe. In order to investigate their interfacial properties, the nanofillers in the two tricomponent nanocomposites were separated from the nongrafted free polystyrene via extraction with toluene.22 Analysis and Testing. A Bruker IFS 66 v/s infrared spectrometer (Bruker, Karlsruhe, Germany) was used for Fourier transform infrared (FTIR) spectroscopy analysis of the nanocomposites in the range of 400−4000 cm−1 with a resolution of 4 cm−1. The KBr pellet technique was adopted to prepare the sample for recording IR spectra. Raman measurements were carried out on powder samples using a FT-Raman spectrometer (SPEX1403, Spex Co., USA) with a Nd:YAG excitation laser (wavelength 633 nm). Thermogravimetric analysis (TGA) was performed with a Perkin-Elmer TGA-7 system at a scan rate of 10 °C min−1 to 800 °C in N2. The crystal structure of CNTs-Fe3O4 was measured with Xray diffraction (XRD, MAC, MXP21VAHF). XRD patterns were taken from 10° to 90° with a continuous scan mode to collect 2θ data using Cu Kα radiation. The average relative molecular weights of polystyrene in the composites were determined by gel permeation chromatography (GPC) with a HP1100 instrument using a binary liquid chromatography pump and an ultraviolet detector. Tetrahydrofuran (THF) was used as the eluent at a flow rate of 1 mL min−1. Polystyrene was separated from the tricomponent nanocomposites by being immersed in toluene. The morphologies of the carbon nanotubes immobilized Fe3O4 nanoparticles (CNT-Fe3O4) were characterized with a JEM-1200 EX/S transmission electron microscope (TEM). Powders were dispersed in water in an ultrasonic bath for 5 min and then deposited on a copper grid covered with a perforated carbon film. The interfacial property of the tricomponent nanocomposites was examined with a scanning electron microscope (SEM, S4300, Hitachi Co., Ltd., Tokyo, Japan). The fracture surface was sputter coated with gold to provide enhanced conductivity. The magnetic properties of the samples were detected by vibrating sample magnetometer (VSM) (Lakeshore 7304) at room temperature. The electrical conductivities of CNT-COOH and CNTFe3O4 were measured using a SDY-4 Four-Point ProbeMeter (Guangzhou Semiconductor Material Academe) at ambient
the multiwalled carbon nanotubes and Fe3O4 nanoparticles added separately in the radical bulk polymerization.
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EXPERIMENTAL SECTION Materials. Multiwalled carbon nanotubes (CNTs, L. MWNTs-2040, purity of 95%, average diameter of 20−40 nm, and length range 5−15 μm) were obtained from Shenzhen Nanotech Port Co., Ltd. (Shenzhen, China). Styrene (St, analytical reagent, Tianjin Chemicals Co. Ltd., China) was dried over CaH2 and distilled under reduced pressure. The initiator, 2,2′-azobis (isobutylonitrile) (AIBN) (Tianjin Chemicals Ltd. Co. Tianjin, China), was recrystallization in ethanol. Ferric chloride hexahydrate (FeCl3·6H2O), ferrous chloride tetrahydrate (FeCl2·4H2O), ammonium hydroxide (NH4OH, 25% of ammonia), oleic acid (OA), and other reagents were analytical-grade reagents received from Tianjin Chemical Co., Ltd. (Tianjin, China) and used as received. Distilled water was used throughout. Multiwalled Carbon Nanotubes (CNT) Immobilized Fe3O4 Nanoparticles (CNT-Fe3O4). Multiwalled carbon nanotubes were functionalized by being refluxed in H2SO4:HNO3 (3:1, v/v) at 80 °C for 6 h to obtain the carboxylic acid functionalized carbon nanotubes (CNTCOOH), then washed with distilled water until neutral, and finally dried in vacuum for 24 h at 50 °C.25 CNT-Fe3O4 were prepared by coprecipitation of Fe3O4 nanoparticles in the presence of the carboxylic acid functionalized carbon nanotubes (CNT-COOH): CNT-COOH, FeCl3·6H2O, and FeCl2·4H2O were added into 100 mL of water with stirring and bubbling with N2 and soaking for 24 h. Then ammonium hydroxide (NH4OH, 25% of ammonia) was added dropwise into the mixture after it was heated to 80 °C. The reacting mixture was stirred for another 1 h after addition. Finally, products were collected by centrifuging at 8000 rpm for 6 min. Conditions of the preparation are given in Table 1. One-Pot in-Situ Radical Bulk Polymerization. Then the CNT-Fe3O4/PS tricomponent nanocomposite was prepared via the one-pot in-situ radical bulk polymerization of styrene in the presence of CNT-Fe3O4, with OA as surface modifier: 20.0 mL of styrene, 0.10 g of AIBN, 0.30 g of OA, and 0.10 g of CNTsFe3O4 (S-3) were added into a glass polymerization pipe; then the mixtures were irradiated ultrasonically for 30 min and subsequently heated to 90 °C for 8 h. After being cooled to 12018
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(422), (511), and (440) crystal planes of cubic Fe3O4, respectively. TEM images of the multiwalled carbon nanotubes immobilized Fe3O4 nanoparticles (CNT-Fe3O4) prepared via the coprecipitation technique with a theoretical mass ratio of CNT-COOH and Fe3O4 from 5:1 to 1:5 are presented in Figure 3. From the TEM images one can find that there some shorter carbon nanotubes appeared, indicating that the multiwalled carbon nanotubes had been cut into pieces in the oxidation procedure. It is interesting to note that almost all Fe3O4 nanoparticles with diameters near 10 nm were preferentially adhered to the surfaces of the multiwalled carbon nanotubes. It could be concluded that the Fe3O4 nanoparticles are stably attached to the surface of CNT-COOH following electrostatic adsorption by the carboxyl groups introduced (as shown in Scheme 1), making them strongly resistant to extensive washing. With the increasing feeding ratio of the precursors of Fe3O4 nanoparticles, more black dots (Fe3O4 nanoparticles) were found on the surfaces of the CNT, except that bigger Fe3O4 nanoparticles with a diameter of hundreds nanometers appeared with a theoretical mass ratio of CNT-COOH and Fe3O4 higher than 1:2 (Figure 3d of 1:2 and Figure 3e of 1:5). Therefore, the CNT-Fe3O4 sample S-3 with a theoretical mass ratio of CNT-COOH and Fe3O4 of 1:1 was used for preparation of the tricomponent nanocomposite. The room-temperature magnetization hysteresis loops of the CNT-Fe3O4 sample S-3 and pure Fe3O4 nanoparticles prepared under the same reaction conditions were characterized using vibrating sample magnetometer (VSM). Magnetic measurements revealed that the nanocomposite films are superparamagnetic and showed no remanence or coercivity at room temperature.27 From Figure 4 it can be seen that the saturation magnetization of CNT-Fe3O4 decreases to 6.66 emu/g compared to the pure Fe3O4 nanoparticles (70.49 emu/ g), owing to the existence of CNT. The mass ratio of the Fe3O4 nanoparticles content in CNT-Fe3O4 was found to be about 9.5 wt %, calculated from the saturation magnetization of CNTFe3O4. It is much lower than that of the theoretical content of 50% due to isolation of the free Fe3O4 nanoparticles during centrifugation at 8000 rpm for 6 min. Furthermore, the absorbance peak at 710 cm−1 in the FT-IR spectrum of CNTFe3O4, which is not found in the FT-IR spectra of CNTCOOH or Fe3O4 nanoparticles, appeared. The stretching vibration due to interaction of Fe−O−Fe in γ-Fe 2 O 3 (maghemite) may be caused by oxidation of magnetite nanoparticles by oxygen-containing groups attached on the CNT-COOH,28,29 owing to their small size and high surface energy. It resulted in the low saturation magnetization of the CNT-Fe3O4, although so many nanoparticles could be seen on CNT-COOH (Figure 1). The electrical conductivity of the oxidized product CNTCOOH decreased from >100 to 1.60 S/cm through electrical conductivity measurements due to oxidation, cutting, and surface structure disruption of the multiwalled carbon nanotubes resulting from excessive treatment.30 The electrical conductivity of the CNT-Fe3O4 decreased further to 1.27 S/ cm after immobilization of the Fe3O4 nanoparticles. Tricomponent Nanocomposites. Since the nanofillers could not be dispersed in the monomer styrene due to their strong surface polarity, oleic acid (OA) was used as the surface modifier in the in-situ radical bulk polymerization. Until the amount of OA was increased to 0.30 g, the CNT-Fe3O4 could
temperature. Pellets were obtained by subjecting the powder sample to a pressure of 30 MPa. Surface resistivity and volume resistivity of the tricomponent nanocomposites were measured at 20 °C and a humidity of 15% using the surface resistance measuring device (Hiresta-Up MCP-HT450, Mitsubishi Chemical Corp., Japan). The reproducibility of the result was checked by measuring the electrical conductivity six times for each pellet. Pellets with a thickness of about 0.5 mm were obtained by subjecting the samples to a pressure of 10 MPa 170 °C. The sample speciemens (Figure 1) were prepared via injection molding with a Injection molding machine
Figure 1. Shape and measurement of specimens (mm).
(FANUC Ltd., ROBOSHOT S2000i 100A). Injection molding conditions: Extrusion temperature: 180 °C; Extrusion rate: 17.6 mm/s; Mold temperature: 40 °C; Cooling time: 30s. The tensile strength and modulus were measured by a single fiber tensile test according to JIS K7113 using a universal testing machine (Series 3360, Instron Co., Ltd., Canton, America) with a tensile speed of 5 mm/min at temperature of 23 °C ± 2 °C.
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RESULTS AND DISCUSSION CNT-Fe3O4. In the present work, the defect sites on the surfaces of the carbon nanotubes, which upon treatment under oxidative conditions are transferred to carboxylic acid moieties,26 allow immobilization of Fe3O4 nanoparticles. The XRD pattern of the CNT-Fe3O4 sample S-3 with a theoretical mass ratio of CNT-COOH and Fe3O4 of 1:1 is shown in Figure 2. Analysis indicates that the product is composed of two
Figure 2. XRD pattern of the CNT-Fe3O4.
phases: cubic Fe3O4 (JCPDS card No. 75-0033) and multiwalled carbon nanotubes. The diffraction peak at 2θ = 26.48 could be ascribed to the (002) reflection of the multiwalled carbon nanotubes. According to the JCPDS cards (No. 751609), the corresponding diffraction peaks at 30.0, 35.5, 43.0, 53.3, 57.2, and 62.7 can be assigned to (220), (311), (400), 12019
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Figure 3. TEM image of as-prepared CNTs-Fe3O4 samples.
in the presence of the CNT-Fe3O4, with OA as surface modifier, the uniformly dark brown CNT-Fe3O4/PS tricomponent nanocomposite was obtained. For comparison, the CNT/ Fe3O4/PS tricomponent nanocomposite was prepared with the CNT-COOH and the Fe3O4 nanoparticles added separately in the radical bulk polymerization. The CNT/Fe3O4/PS tricomponent nanocomposite is light brown with black dots being seen with the naked eyes, which might be the aggregated Fe3O4 nanoparticles. The two tricomponent nanocomposites CNT-Fe3O4/PS and CNT/Fe3O4/PS exhibited superparamagnetic characteristics with saturation magnetization of 0.05 and 0.12 emu/g, respectively. It indicated that the crystal structure of the cubic Fe3O4 remained during the in-situ radical bulk polymerization.23 The surface resistance (ρs) and volume resistance (ρv) of the two tricomponent nanocomposites are summarized in Table 2. Compared with those of pure PS of about 1016 Ω/γ and 1017 Ω·cm,31 the two tricomponent nanocomposites decreased by about 6 orders of magnitude with less than 0.50
Figure 4. Magnetization curves of the samples at room temperature.
be dispersed well in styrene. Thus, 0.30 g of OA was added as the surface modifier in the in-situ radical bulk polymerization. After the one-pot in-situ radical bulk polymerization of styrene 12020
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Table 2. Electrical and Mechanical Properties of the Tricomponent Nanocomposites electrical properties
mechanical properties
samples
ρs (Ω/γ)
ρv (Ω·cm)
E (GPa)
σt (MPa)
εt (%)
PSa CNTFe3O4/ PS CNT/ Fe3O4/ PS
>1017 5.23 × 1011
>1016 5.44 × 1010
3.8−4.8 1.58
37.9−48.3 26.9
1.0 1.78
3.94 × 1011
6.12 × 1010
1.14
11.7
1.11
a
According to ref 31.
wt % content of CNT-COOH. Both of them exhibited semiconductive characteristics. The thermal stability of the two tricomponent nanocomposites (CNT-Fe3O4/PS and CNT/Fe3O4/PS) is compared with pure polystyrene (PS) in Figure 5. The two
Figure 6. Stress−strain behavior of the two tricomponent nanocomposites.
stability is similar. However, the mechanical properties of the CNT-Fe3O4/PS tricomponent nanocomposite are not as high as expected, even lower than that of the pure PS (Table 1). It results from the relatively lower number-average molecular weight (3.53 × 104) and wider molecular weight distribution (6.15) of the polystyrene separated from the CNT-Fe3O4/PS tricomponent nanocomposite, resulting from the low polymerizing ability of oleic acid33 and the effect of the CNTs.19 Compared with the tricomponent nanocomposite prepared with the multiwalled carbon nanotubes and Fe3O4 nanoparticles added separately, immobilization of Fe3O4 nanoparticles on multiwalled carbon nanotubes could avoid magnetic aggregation of the Fe3O4 nanoparticles in styrene. Then oleic acid molecules adsorb onto the surfaces of the Fe3O4 nanoparticles immobilized on the multiwalled carbon nanotubes, improving efficiently the dispersibility of the multiwalled carbon nanotubes in the monomer (Scheme 1). After in-situ radical bulk polymerization, the CNT-Fe3O4/PS composite with excellent dispersion is obtained. As a result, it exhibited the higher mechanical properties (Figure 6). SEM images of the fracture surfaces of the two tricomponent nanocomposites are given in Figure 7. The rougher fracture surface of the CNT/Fe3O4/PS sample compared with that of the CNT-Fe3O4/PS might result from aggregation of the two nanomaterials. Furthermore, some clusters of particles could be seen only in the fracture surface of the CNT/Fe3O4/PS. It indicated that the nanomaterials had been dispersed excellently in the CNT-Fe3O4/PS composite via the synergetic dispersion strategy. Synergetic Dispersion Effect. During in-situ radical bulk polymerization, styrene might be grafting polymerized from the side walls of the carbon nanotubes via radical addition33 and copolymerized with oleic acid adsorbed on the surfaces of the Fe3O4 nanoparticles,32 although the polymerizing ability of oleic acid is not so high.34 Thus, the nanofillers in the two tricomponent nanocomposites were analyzed after being separated from the nongrafted free polystyrene via extraction with toluene in order to investigate their interfacial properties and grafting results. After removal of the free nongrafted polystyrene, the characteristic absorbance bands of polystyrene, polystyrene aromatic C−H stretching vibrations at 3003, 3026, 3059, 3081, 3105, 755, and 697 cm−1, the aliphatic C−H stretch at 2924 and 2851 cm−1, and styrene C−C vibrations at 1450 and 1493 cm−1,35 were all found in the FTIR spectra of the separated nanofillers from the two tricomponent nanocomposites. It
Figure 5. TGA curves of the two tricomponent nanocomposites (CNT-Fe3O4/PS and CNT/Fe3O4/PS) and their polystyrene-grafted nanofillers (CNT-Fe3O4-PS and CNT/Fe3O4-PS) separated.
tricomponent nanocomposites exhibited the similar thermal decomposition, although the nanomaterials were added in different forms. The two tricomponent nanocomposites (CNTFe3O4/PS and CNT/Fe3O4/PS) exhibited a weight loss of 4.3% and 3.2% at 350 °C, respectively. The weight losses were higher than that of the pure PS of 2.6% at the same temperature range due to decomposition of OA.32 The larger weight loss of the CNT-Fe3O4/PS than the pure PS is consistent with the OA content in the two tricomponent nanocomposites (1.6%), indicating that the OA-modified CNT-Fe3O4 was dispersed excellent in the tricomponent nanocomposite CNT-Fe3O4/PS, in proportion to the CNT/Fe3O4/PS. Decomposition of PS in the two tricomponent nanocomposites occurred in the temperature range of 410−440 °C, while the pure PS decomposed in the temperature range of 390−420 °C. It indicated that the thermal stability of PS had been improved significantly by addition of nanomaterials.19,22 Mechanical properties were evaluated by stretching strips of the sample speciemens of the two tricomponent nanocomposites (CNT-Fe3O4/PS and CNT/Fe3O4/PS) to failure and plotting the true stress−strain curves (Figure 6). Tensile properties such as Young’s modulus (E), strength at break (σt), and strain at break (εt) evaluated from the experimental stress− strain curves are summarized in Table 2. The tricomponent nanocomposite CNT-Fe3O4/PS showed much higher mechanical properties than the CNT/Fe3O4/PS, although their thermal 12021
dx.doi.org/10.1021/ie300891h | Ind. Eng. Chem. Res. 2012, 51, 12017−12024
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Figure 7. SEM images of the fracture surfaces of the two tricomponent nanocomposites.
modified carbon nanotubes (CNT-Fe3O4, CNT-Fe3O4−PS, and CNT/Fe3O4−PS) as shown in Figure 8.37 The D/G-band
indicated that polystyrene had been grafted from the nanofillers by copolymerization with oleic acid adsorbed or radical addition onto CNTs. The saturation magnetization of the polystyrene grafted nanofillers (CNT-Fe3O4-PS and CNT/Fe3O4-PS) separated from the two tricomponent nanocomposites CNT-Fe3O4/PS and CNT/Fe3O4/PS was found to be 2.66 and 5.50 emu/g (Figure 4), respectively. The decrease in the saturation magnetization indicated that polystyrene had been grafted from the nanomaterials. The grafting percentages (mass ratio of polymer grafted and nanomaterials) of the CNT-Fe3O4/PS and CNT/Fe3O4/PS could be calculated to be 20.6% and 33.7% from the weight loss at 500 °C in the TGA analysis (Figure 5), respectively.36 In fact, the values also contained the contribution of the surface modifier (oleic acid). Furthermore, CNT-Fe3O4/PS and CNT/ Fe3O4/PS also showed the weight decreasing at above 500 °C, resulting from decomposition of the defects in the carbon nanotubes. The defects in the carbon nanotubes of the tricomponent nanocomposites contained the two sections formed by oxidization with mixed acid in the purification procedure and radical addition in the radical bulk polymerization. Raman spectroscopy has played an important role in the structural characterization of graphitic materials in the past and also become a powerful tool for understanding the behavior of electrons and phonons in polymer,36 aimed at gaining a better understanding of the structural information on CNTs. There are two bands in the Raman spectrum: a D band (defects/ disorder-induced modes) at 1320 cm−1 and G band (in-plane stretching tangential modes) at 1570 cm−1 for all three
Figure 8. Raman spectra of the modified carbon nanotubes.
intensity ratio (ID/IG) typically changes when covalent functionalization of the graphite sheet occurs.38 For the CNT-Fe3O4, the intensity ratio (ID/IG) was 1.05, which is much higher than that of the raw multiwalled carbon nanotubes of 0.74 due to the defects introduced during purification of the CNTs with mixed acids. After in-situ radical bulk polymerization, the ID/IG values of the CNT-Fe3O4−PS and CNT/ Fe3O4−PS separated from the tricomponent nanocomposites CNT-Fe3O4/PS and CNT/Fe3O4/PS increased to 1.08 and 1.13, respectively. It indicated that the polystyrene chain radicals had been grafted onto the CNTs via the radical addition reaction during in-situ radical bulk polymerization.33 12022
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However, radical addition onto the CNT-Fe3O4 was difficult because of the surface modification of oleic acid, while there is less containment shell of OA in the tricomponent nanocomposite CNT/Fe3O4/PS because the OA molecules were mainly adsorbed onto the Fe3O4 nanoparticles. Therefore, more polystyrene chain radicals had been grafted onto the CNT-COOH in the CNT/Fe3O4/PS than those in the CNTFe3O4/PS. Thus, the synergetic dispersion in the tricomponent nanocomposite CNT-Fe3O4/PS could be speculated as follows: magnetic aggregation of the Fe3O4 nanoparticles in polymer matrices was avoided by immobilization of Fe3O4 nanoparticles on multiwalled carbon nanotubes. Then the OA molecules adsorbed onto the surfaces of the Fe3O4 nanoparticles immobilized on the multiwalled carbon nanotubes to improve efficiently the dispersibility of the CNT-Fe3O4 in styrene monomer. In the in-situ radical bulk polymerization, the polystyrene chains grafted onto the CNT-Fe3O4 through copolymerization of styrene with the OA molecules adsorbed onto the surfaces of the CNT-Fe3O4 and the radical addition reaction of the polystyrene chain radicals onto the CNTs. As a result, the products, the CNT-Fe3O4−PS, exhibited excellent dispersibility in polystyrene matrices. Thus, the well-dispersed tricomponent nanocomposite CNT-Fe3O4/PS with better mechanical properties was obtained.
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CONCLUSIONS In summary, a facile synergetic dispersion strategy was developed to prepare the CNT-Fe3O4/polystyrene tricomponent nanocomposite via in-situ radical bulk polymerization. It exhibited superparamagnetic characteristics, although the magnetic properties of the magnetite have really been degraded by being immobilized onto the oxidized CNTs. Its mechanical, electrical, magnetic, and thermal properties were compared with the tricomponent nanocomposite CNT/Fe3O4/PS prepared with the multiwalled carbon nanotubes and Fe3O4 nanoparticles added separately. In addition, the synergetic dispersion effect was confirmed by investigating the interfacial properties of the nanofillers in the polystyrene matrices with SEM, TGA, and Raman analysis. Furthermore, the synergetic dispersion strategy developed could be popularized for various multicomponent nanocomposites.
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AUTHOR INFORMATION
Corresponding Author
*Tel.: 86-931-8912516. Fax: 86-931-8912582. E-mail: pliu@ lzu.edu.cn. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This project was granted financial support from the Fundamental Research Funds for the Central Universities and the Open Project of Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University (Grant No. LZUMMM2012005).
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dx.doi.org/10.1021/ie300891h | Ind. Eng. Chem. Res. 2012, 51, 12017−12024
Industrial & Engineering Chemistry Research
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