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BADCy composite
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Materials Chemistry and Physics 108 (2008) 306–311
Study of dielectric property on BaTiO3/BADCy composite Fen Chao a , Guozheng Liang a,∗ , Weifeng Kong b , Xuan Zhang a a
Department of Applied Chemical, School of Science, Northwestern Polytechnical University, Xi’an, Shaanxi 710072, People’s Republic of China b School of materials science and engineering, Nanjing University of Technology, Nanjing, Jiangsu 210009, People’s Republic of China Received 6 March 2007; received in revised form 19 August 2007; accepted 30 September 2007
Abstract The barium titanate (BaTiO3 )/bisphenol A dicyanate (2,2 -bis(4-cyanatophenyl) isopropylidene) (BADCy) 0–3 dielectric composite was successfully prepared by casting. At 1 MHz and 298 K, the dielectric property of the composite was investigated systematically. The results showed that with the increase of the BaTiO3 content, the dielectric constant (ε) of the composite increased, while the dielectric loss (tan δ) decreased. When the mass fraction of BaTiO3 was 60%, ε reached its highest value (15.823) and tan δ was at its lowest (0.004). After post-curing at 230 ◦ C for 4 h, tan δ dropped to 0.001. Meanwhile, with the increase of the conversion of BADCy, ε ascended at first and then descended slightly, but tan δ descended during the whole curing period. In addition, a silane coupling agent ␥-aminopropyl triethoxy silane (KH-550) was applied to treat the filling so as to improve the dispersion of BaTiO3 particles, which led to enhance the dielectric property of the material. © 2007 Elsevier B.V. All rights reserved. Keywords: Composite material; Polymer; Ceramic; Dielectric property
1. Introduction Generally, polymers are flexible and are able to be processed easily, but their dielectric constants are relative low. Contrarily, although the ceramic has high dielectric constant, it is fragile and needs to be sintered at high temperature. For these reasons, the application of an individual polymer or ceramic is greatly restricted in many aspects. By combining the advantages of the two phases, the composite of polymer/ceramic can offer improved properties [1–7]. In addition, its dielectric and other properties can be designed according to specific requirements by adjusting the relative fraction of the starting materials [8], treating the component with different chemical or physical methods and changing the processing techniques. Therefore, the study of the ceramic/polymer composite has received attention worldwide. Cyanate ester resin is a type of thermosetting resins with high performance, and the processing technique is similar to epoxy resin. Compared with other kinds of thermosetting resins, cyanate ester resin provides superior dielectric property. In general, it has very low dielectric loss (0.002–0.006) and low moisture absorption. In addition, the dielectric property of ∗
Corresponding author. Tel.: +86 29 88474080; fax: +86 29 88474080. E-mail address: [email protected] (G. Liang).
0254-0584/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2007.09.039
cyanate ester resin is stable at various temperature and frequency of electromagnetic wave. Therefore, it is widely used within a variety of electronic and microelectronic applications [9–11]. Barium titanate, a well-known ferroelectric material with perovskite lattice structure, has a high dielectric constant and is widely utilized to make capacitors, piezoelectric transducers and optopelectronic elements [12]. The study has showed that epoxy/BaTiO3 dielectric composites can be used for the embedded capacitor. Therefore, it is possible for cyanate ester resins to function as an excellent matrix material of dielectric composites for embedded capacitor. But there is no report about the study of cyanate ester resin/BaTiO3 dielectric composite. In this work, the composite with controllable dielectric property has been prepared by using bisphenol A dicyanate (BADCy) as polymer matrix and BaTiO3 as dispersed particle. The dielectric property of the composite has been investigated systematically. 2. Experimental 2.1. Materials Bisphenol A dicyanate (2,2 -bis(4-cyanatophenyl) isopropylidene) (BADCy) was purchased from Shanghai Huifeng Kemao Ltd. (Shanghai, China), with at least 99 wt%. The coupling agent ␥-aminopropyl triethoxy silane (KH-550) was supplied by Jingzhou Jianghan fine chemical Ltd. (Jingzhou, China). Barium titanate (BaTiO3 ) was provided from Xi’an global chemical instrument company (Xi’an, China). The average diameter of BaTiO3 is 3 m.
F. Chao et al. / Materials Chemistry and Physics 108 (2008) 306–311
Fig. 1. Chemical structures of BADCy and KH-550.
Acetone was obtained from Xi’an chemical reagent corporation (Xi’an, China). The chemical structures of BADCy and KH-550 are shown in Fig. 1.
2.2. Preparation of BaTiO3 /BADCy composite After the mixture of BADCy monomer and BaTiO3 particles was dissolved at 100 ◦ C, the liquid mixture was precured at 150 ◦ C with continuous stirring until a homogeneous mixture was obtained. Afterwards the prepreg was immediately cast into the glass mould that was heated beforehand at 150 ◦ C and the air bladder in the mould was removed under vacuum at 100 ◦ C for 30 min. After that, the prepreg was cured at a programmed heating rate: 160 ◦ C/2 h + 180 ◦ C/2 h + 200 ◦ C/2 h, and then post treated at 230 ◦ C for 4 h. After the oven temperature was decreased naturally from 230 ◦ C to room temperature, the BaTiO3 /BADCy composite was obtained.
2.3. Characterization Fourier-transform infrared (FTIR) spectra of the BaTiO3 /BADCy composite sample were taken on a WQF-300 FTIR spectrometer that was purchased from Beijing Optical Instrument Factory in China. The specimen was prepared by grinding the BaTiO3 /BADCycomposite with potassium bromide (KBr). The phase morphology of the composite was imaged by HITACHI S-570 scanning electron microscopy (SEM). The fracture surface of the composite was sputtered with a thin layer (about 10 nm) of gold by vapor deposition on a stainless steel stub using a Polaron SC502 vacuum sputter coater.
Fig. 2. Dielectric properties of BaTiO3 /BADCy composites.
307
Fig. 3. FTIR spectra of BaTiO3 /BADCy composites with different curing technique: (a) original sample, (b) 160 ◦ C/2 h, (c) 160 ◦ C/2 h + 180 ◦ C/2 h, (d) 160 ◦ C/2 h + 180 ◦ C/2 h + 200 ◦ C/2 h, (e) 160 ◦ C/2 h + 180 ◦ C/2 h + 200 ◦ C/2 h + 220 ◦ C/1 h, (f) 160 ◦ C/2 h + 180 ◦ C/2 h + 200 ◦ C/2 h + 220 ◦ C/1 h + 230 ◦ C/4 h.
At 1 MHz and 298 K, dielectric constant and dielectric loss were measured on S914 dielectric loss instrument with QBG-3B high frequency apparatus manufactured by Shanghai Aishi Electronical Instrument Corporation according to GB1409-78 of China.
2.4. Determination of the conversion of —OCN group According to Ref. [13], quantitative estimation of characteristic group can be obtained by FTIR using internal standards. In this paper, the conversion of cyanate group of the composite was evaluated according to FTIR spectra by Eq. (1).
Wt,cyanate group =
St,cyanate group /St,Ph 1− S0,cyanate group /S0,Ph
× 100%
(1)
Where Wt,cyanate group is the conversion of —OCN group of the composite. St,cyanate group and St,Ph are the integral areas of characteristic peaks of cyanate group at about 2270 cm−1 and phenyl ring at about 1500 cm−1 of composite samples, respectively. S0 ,cyanate group and S0 ,Ph are the integral areas of characteristic peaks of cyanate group at about 2270 cm−1 and phenyl ring at about 1500 cm−1 of pure BADCy resin uncured.
Fig. 4. Influence of the conversion of BADCy on the dielectric properties of BaTiO3 /BADCy composites.
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Fig. 6. FTIR spectra of (a) BaTiO3 , (b) the mixture of BaTiO3 and KH550, (c) BaTiO3 treated with KH-550, (d) BADCy/BaTiO3 composite, (e) BADCy/BaTiO3 treated with KH-550 composite.
increases the proportion of the interface between padding and polymer, which leads to enhance the dipole of the interface [14]. The result of the dielectric loss of the composites showed that the dielectric loss decreased with the increase of BaTiO3 content, and the curve indicated almost linear tendency, it fitted the following linear. tan δ = 0.007 − 5.53571 × 10−5 x
Fig. 5. Influence of curing technique on the dielectric properties of BaTiO3 /BADCy composites.
(2)
Where x is the mass fraction of BaTiO3 . This tendency is different from recent reports about ceramic/polymer composite [8,15]. The reason may be attributed to the inorganic filling with OH groups on the surface. BADCy can react with OH group at high temperature, so BaTiO3 particles prevent the movement of the polymer. With the increase of the mass fraction of BaTiO3 , it is more difficult for polymer to move leading to the decrease of the dielectric loss of the composite. Therefore, dielectric per-
3. Results and discussion 3.1. Influence of the BaTiO3 mass fraction on the dielectric property Experiments showed that it was difficult to prepare the composite by casting when the mass fraction of BaTiO3 was more than 60% because of the high viscosity of the mixture of BaTiO3 and BADCy. Therefore, the study only showed the dielectric property of the composites when the mass fraction of BaTiO3 was from 0% to 60%. The results were indicated in Fig. 2. The study found the dielectric constant increased with the increase of BaTiO3 content. When the mass fraction of BaTiO3 was 60%, the dielectric constant of the composite was 15.823, which was relatively higher in dielectric constant compared with individual BADCy (ε = 2.647). There are two reasons to explain the results. One is that BaTiO3 itself has high dielectric constant. The other is that the increase of the content of BaTiO3 particles
Fig. 7. The structures of KH-550 and BaTiO3 treated with KH-550. (a) The structure of KH-550. (b) The interface structure between BaTiO3 and KH-550.
F. Chao et al. / Materials Chemistry and Physics 108 (2008) 306–311
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Fig. 8. Reaction mechanism of silane coupling agent and BADCy.
formance of the BaTiO3 /BADCy composite has been enhanced by relative high dielectric constant and very low dielectric loss. In addition, the study also showed that the dielectric loss of the BaTiO3 /BADCy composite was 0.001 after the composite was post-cured at 230 ◦ C for 4 h. 3.2. Influence of curing technique on the dielectric property Different curing techniques lead to different degrees of resin curing, which also lead the structure of the polymer in composite distinctively. Therefore, the curing technique influences the dielectric property of the composite. In this work, with different curing techniques, the conversion of BADCy was calculated by FTIR spectra, and then the dielectric constant and dielectric loss were investigated.
Fig. 3 was the FTIR spectrum curve of BaTiO3 /BADCy composite and the conversion calculated according to Eq. (1). The data showed that the reaction velocity was fast at first, and then gradually became slow. The conversion was almost completed when the technique (e) and (f) were adopted. The influence of the curing technique on the dielectric property of BaTiO3 /BADCy composite can be seen from Fig. 4. It was indicated that the dielectric constant was improved with the increase of the conversion of BADCy at first, and then reduced slightly after —OCN group converted almost completely. For dielectric loss, it became lower and lower by heightening the conversion of BADCy, which was because that the movement of the matrix becomes more and more difficult with the improvement of its conversion.
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Fig. 5 indicated the difference of the dielectric properties between the composites post-cured and unpost-cured. Compared with the materials unposted, the result showed that the dielectric loss of post-cured materials dropped evidently, and the dielectric constant decreased slightly. The reason is also the distinction of the conversion that cannot be shown clearly from the FTIR spectrum but the difference exists. It is clear that the post cure at 230 ◦ C for 4 h is necessary to obtain BaTiO3 /BADCy composite with enhanced properties. 3.3. Influence of treated BaTiO3 with KH-550 on the dielectric property For inorganic/organic composite, the dispersion of inorganic particles is extremely important for achieving composite with good dielectric property. It has been proved that the adoption of coupling agent is efficient to improve the compatibility between polymer and filler by chemical process [16,17]. In this work, KH-550, a kind of silane coupling agent, was used to mix with BaTiO3 directly in a high-speed mixer for 10 min, and then the mixture reacted in an oven at 110 ◦ C for 2 h. Afterwards the composite was prepared. Fig. 6 was the FTIR spectra of BaTiO3 , the mixture of BaTiO3 and KH-550, BaTiO3 treated with KH-550, BADCy/BaTiO3 composite, and BADCy/BaTiO3 treated with KH-550 composite. Compared with Fig. 6(a), Fig. 6(b) showed the new absorption band at 1085 cm−1 , which was the characteristic peak of Si—O—C group from KH-550 itself (showed in Fig. 7(a)), and Fig. 6(c) indicated the absorption bands at 1130 and 1030 cm−1 , which were attributed to Si—O—Si group and Si—O—Ba group (showed in Fig. 7(b)), respectively. It was proved that there was physisorbed KH-550 on BaTiO3 particles after KH-550 and BaTiO3 just blended and that chemisorbed KH-550 on BaTiO3 was appeared after treated at 110 ◦ C for 2 h [18]. Therefore, BaTiO3 particles can be treated efficiently with silane coupling agent KH550 after the mixture is heated in an oven at 110 ◦ C for 2 h. Compared Fig. 6(d) with Fig. 6(e), there was no difference between FTIR spectra of BADCy/BaTiO3 composite and BADCy/BaTiO3 treated with KH-550 composite. It was showed that silane coupling agent KH-550 did not affect the conversion of BADCy. The reason can be explained from the reaction mechanism between OCN group and NH2 group as shown in Fig. 8. During the process of the interaction between OCN group and NH2 group, Fig. 8(a) showed the existence of two kinds of products (A1 and A2) were determined by the ratio between OCN groups and NH2 groups at low temperature. However, when there were a few of NH2 groups in the reaction system, the reaction mechanism was just like Fig. 8(b). At that time, A1 and A2 were obtained at first, and then polymerization took place at high temperature. During the whole reaction process, NH2 group was as catalyst [19–21]. In this study, the percentage of KH-550 was 1.3% of the amount of BADCy. Although KH-550 combined with BADCy by chemical bond, the influence to the polymerization of BADCy could be neglected.
Fig. 9. Influence of modifier on dielectric constant and loss tangent ((a)160 ◦ C/2 h, (b) 160 ◦ C/2 h + 180 ◦ C/2 h, (c) 160 ◦ C/2 h + 180 ◦ C/2 h + 200 ◦ C/2 h, (d) 160 ◦ C/2 h + 180 ◦ C/2 h + 200 ◦ C/2 h + 220 ◦ C/1 h, (e) 160 ◦ C/2 h + 180 ◦ C/2 h + 200 ◦ C/2 h + 220 ◦ C/1 h + 230 ◦ C/4 h).
Fig. 9 inspected the influence of coupling agent KH-550 on the dielectric constant and the dielectric loss of the composite. It was indicated that the dielectric constant was increased and the dielectric loss was almost unchanged. Therefore, it is useful to enhance the dielectric property of BaTiO3 /BADCy composite with silane coupling agent KH-550. 3.4. The morphology of the composites Fig. 10 showed the morphology of the composites measured by SEM. Fig. 10(a) was the SEM picture of BaTiO3 /BADCy composite with untreated BaTiO3 particles. Fig. 10(b) was the SEM picture of BaTiO3 /BADCy composite with BaTiO3 particles treated with KH-550. By comparison, it was indicated that BaTiO3 particles with KH-550 were more uniformly distributed throughout the BADCy matrix, and there was no obvious aggregation of BaTiO3 particles in the composites. Consequently, silane coupling agent KH-550 is beneficial to improve the compatibility between BaTiO3 particles and the BADCy matrix.
F. Chao et al. / Materials Chemistry and Physics 108 (2008) 306–311
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References
Fig. 10. Fracture scanning electron microscope photographs of BaTiO3 /BADCy composites: (a) BaTiO3 /BADCy composite with untreated BaTiO3 particles, (b) BaTiO3 /BADCy composite with modified BaTiO3 particles.
4. Conclusions A series of BaTiO3 /BADCy dielectric composites were successfully prepared by casting. Compared with the dielectric property of BADCy, BaTiO3 /BADCy composite had relatively high dielectric constant and very low dielectric loss. The dielectric property of BaTiO3 /BADCy composite could be controllable by adjusting the fraction of BaTiO3 , treating the surface of BaTiO3 with different chemical or physical methods and changing the curing techniques. The dielectric constant of the composite increased but the dielectric loss of the composite decreased with the increase of the BaTiO3 content, which was different from previously reported ceramic/polymer composites. Meanwhile, with the increase of the conversion of BADCy, the dielectric constant ascended at first and then descended slightly, while the dielectric loss descended obviously all the time. The postcure at 230 ◦ C for 4 h was necessary to obtain BaTiO3 /BADCy composite with enhanced properties. The silane coupling agent KH-550 was beneficial to improve the compatibility between BaTiO3 particles and the BADCy matrix and enhance the dielectric property of the composite.
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Materials Chemistry and Physics 108 (2008) 306–311
Study of dielectric property on BaTiO3/BADCy composite Fen Chao a , Guozheng Liang a,∗ , Weifeng Kong b , Xuan Zhang a a
Department of Applied Chemical, School of Science, Northwestern Polytechnical University, Xi’an, Shaanxi 710072, People’s Republic of China b School of materials science and engineering, Nanjing University of Technology, Nanjing, Jiangsu 210009, People’s Republic of China Received 6 March 2007; received in revised form 19 August 2007; accepted 30 September 2007
Abstract The barium titanate (BaTiO3 )/bisphenol A dicyanate (2,2 -bis(4-cyanatophenyl) isopropylidene) (BADCy) 0–3 dielectric composite was successfully prepared by casting. At 1 MHz and 298 K, the dielectric property of the composite was investigated systematically. The results showed that with the increase of the BaTiO3 content, the dielectric constant (ε) of the composite increased, while the dielectric loss (tan δ) decreased. When the mass fraction of BaTiO3 was 60%, ε reached its highest value (15.823) and tan δ was at its lowest (0.004). After post-curing at 230 ◦ C for 4 h, tan δ dropped to 0.001. Meanwhile, with the increase of the conversion of BADCy, ε ascended at first and then descended slightly, but tan δ descended during the whole curing period. In addition, a silane coupling agent ␥-aminopropyl triethoxy silane (KH-550) was applied to treat the filling so as to improve the dispersion of BaTiO3 particles, which led to enhance the dielectric property of the material. © 2007 Elsevier B.V. All rights reserved. Keywords: Composite material; Polymer; Ceramic; Dielectric property
1. Introduction Generally, polymers are flexible and are able to be processed easily, but their dielectric constants are relative low. Contrarily, although the ceramic has high dielectric constant, it is fragile and needs to be sintered at high temperature. For these reasons, the application of an individual polymer or ceramic is greatly restricted in many aspects. By combining the advantages of the two phases, the composite of polymer/ceramic can offer improved properties [1–7]. In addition, its dielectric and other properties can be designed according to specific requirements by adjusting the relative fraction of the starting materials [8], treating the component with different chemical or physical methods and changing the processing techniques. Therefore, the study of the ceramic/polymer composite has received attention worldwide. Cyanate ester resin is a type of thermosetting resins with high performance, and the processing technique is similar to epoxy resin. Compared with other kinds of thermosetting resins, cyanate ester resin provides superior dielectric property. In general, it has very low dielectric loss (0.002–0.006) and low moisture absorption. In addition, the dielectric property of ∗
Corresponding author. Tel.: +86 29 88474080; fax: +86 29 88474080. E-mail address: [email protected] (G. Liang).
0254-0584/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2007.09.039
cyanate ester resin is stable at various temperature and frequency of electromagnetic wave. Therefore, it is widely used within a variety of electronic and microelectronic applications [9–11]. Barium titanate, a well-known ferroelectric material with perovskite lattice structure, has a high dielectric constant and is widely utilized to make capacitors, piezoelectric transducers and optopelectronic elements [12]. The study has showed that epoxy/BaTiO3 dielectric composites can be used for the embedded capacitor. Therefore, it is possible for cyanate ester resins to function as an excellent matrix material of dielectric composites for embedded capacitor. But there is no report about the study of cyanate ester resin/BaTiO3 dielectric composite. In this work, the composite with controllable dielectric property has been prepared by using bisphenol A dicyanate (BADCy) as polymer matrix and BaTiO3 as dispersed particle. The dielectric property of the composite has been investigated systematically. 2. Experimental 2.1. Materials Bisphenol A dicyanate (2,2 -bis(4-cyanatophenyl) isopropylidene) (BADCy) was purchased from Shanghai Huifeng Kemao Ltd. (Shanghai, China), with at least 99 wt%. The coupling agent ␥-aminopropyl triethoxy silane (KH-550) was supplied by Jingzhou Jianghan fine chemical Ltd. (Jingzhou, China). Barium titanate (BaTiO3 ) was provided from Xi’an global chemical instrument company (Xi’an, China). The average diameter of BaTiO3 is 3 m.
F. Chao et al. / Materials Chemistry and Physics 108 (2008) 306–311
Fig. 1. Chemical structures of BADCy and KH-550.
Acetone was obtained from Xi’an chemical reagent corporation (Xi’an, China). The chemical structures of BADCy and KH-550 are shown in Fig. 1.
2.2. Preparation of BaTiO3 /BADCy composite After the mixture of BADCy monomer and BaTiO3 particles was dissolved at 100 ◦ C, the liquid mixture was precured at 150 ◦ C with continuous stirring until a homogeneous mixture was obtained. Afterwards the prepreg was immediately cast into the glass mould that was heated beforehand at 150 ◦ C and the air bladder in the mould was removed under vacuum at 100 ◦ C for 30 min. After that, the prepreg was cured at a programmed heating rate: 160 ◦ C/2 h + 180 ◦ C/2 h + 200 ◦ C/2 h, and then post treated at 230 ◦ C for 4 h. After the oven temperature was decreased naturally from 230 ◦ C to room temperature, the BaTiO3 /BADCy composite was obtained.
2.3. Characterization Fourier-transform infrared (FTIR) spectra of the BaTiO3 /BADCy composite sample were taken on a WQF-300 FTIR spectrometer that was purchased from Beijing Optical Instrument Factory in China. The specimen was prepared by grinding the BaTiO3 /BADCycomposite with potassium bromide (KBr). The phase morphology of the composite was imaged by HITACHI S-570 scanning electron microscopy (SEM). The fracture surface of the composite was sputtered with a thin layer (about 10 nm) of gold by vapor deposition on a stainless steel stub using a Polaron SC502 vacuum sputter coater.
Fig. 2. Dielectric properties of BaTiO3 /BADCy composites.
307
Fig. 3. FTIR spectra of BaTiO3 /BADCy composites with different curing technique: (a) original sample, (b) 160 ◦ C/2 h, (c) 160 ◦ C/2 h + 180 ◦ C/2 h, (d) 160 ◦ C/2 h + 180 ◦ C/2 h + 200 ◦ C/2 h, (e) 160 ◦ C/2 h + 180 ◦ C/2 h + 200 ◦ C/2 h + 220 ◦ C/1 h, (f) 160 ◦ C/2 h + 180 ◦ C/2 h + 200 ◦ C/2 h + 220 ◦ C/1 h + 230 ◦ C/4 h.
At 1 MHz and 298 K, dielectric constant and dielectric loss were measured on S914 dielectric loss instrument with QBG-3B high frequency apparatus manufactured by Shanghai Aishi Electronical Instrument Corporation according to GB1409-78 of China.
2.4. Determination of the conversion of —OCN group According to Ref. [13], quantitative estimation of characteristic group can be obtained by FTIR using internal standards. In this paper, the conversion of cyanate group of the composite was evaluated according to FTIR spectra by Eq. (1).
Wt,cyanate group =
St,cyanate group /St,Ph 1− S0,cyanate group /S0,Ph
× 100%
(1)
Where Wt,cyanate group is the conversion of —OCN group of the composite. St,cyanate group and St,Ph are the integral areas of characteristic peaks of cyanate group at about 2270 cm−1 and phenyl ring at about 1500 cm−1 of composite samples, respectively. S0 ,cyanate group and S0 ,Ph are the integral areas of characteristic peaks of cyanate group at about 2270 cm−1 and phenyl ring at about 1500 cm−1 of pure BADCy resin uncured.
Fig. 4. Influence of the conversion of BADCy on the dielectric properties of BaTiO3 /BADCy composites.
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Fig. 6. FTIR spectra of (a) BaTiO3 , (b) the mixture of BaTiO3 and KH550, (c) BaTiO3 treated with KH-550, (d) BADCy/BaTiO3 composite, (e) BADCy/BaTiO3 treated with KH-550 composite.
increases the proportion of the interface between padding and polymer, which leads to enhance the dipole of the interface [14]. The result of the dielectric loss of the composites showed that the dielectric loss decreased with the increase of BaTiO3 content, and the curve indicated almost linear tendency, it fitted the following linear. tan δ = 0.007 − 5.53571 × 10−5 x
Fig. 5. Influence of curing technique on the dielectric properties of BaTiO3 /BADCy composites.
(2)
Where x is the mass fraction of BaTiO3 . This tendency is different from recent reports about ceramic/polymer composite [8,15]. The reason may be attributed to the inorganic filling with OH groups on the surface. BADCy can react with OH group at high temperature, so BaTiO3 particles prevent the movement of the polymer. With the increase of the mass fraction of BaTiO3 , it is more difficult for polymer to move leading to the decrease of the dielectric loss of the composite. Therefore, dielectric per-
3. Results and discussion 3.1. Influence of the BaTiO3 mass fraction on the dielectric property Experiments showed that it was difficult to prepare the composite by casting when the mass fraction of BaTiO3 was more than 60% because of the high viscosity of the mixture of BaTiO3 and BADCy. Therefore, the study only showed the dielectric property of the composites when the mass fraction of BaTiO3 was from 0% to 60%. The results were indicated in Fig. 2. The study found the dielectric constant increased with the increase of BaTiO3 content. When the mass fraction of BaTiO3 was 60%, the dielectric constant of the composite was 15.823, which was relatively higher in dielectric constant compared with individual BADCy (ε = 2.647). There are two reasons to explain the results. One is that BaTiO3 itself has high dielectric constant. The other is that the increase of the content of BaTiO3 particles
Fig. 7. The structures of KH-550 and BaTiO3 treated with KH-550. (a) The structure of KH-550. (b) The interface structure between BaTiO3 and KH-550.
F. Chao et al. / Materials Chemistry and Physics 108 (2008) 306–311
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Fig. 8. Reaction mechanism of silane coupling agent and BADCy.
formance of the BaTiO3 /BADCy composite has been enhanced by relative high dielectric constant and very low dielectric loss. In addition, the study also showed that the dielectric loss of the BaTiO3 /BADCy composite was 0.001 after the composite was post-cured at 230 ◦ C for 4 h. 3.2. Influence of curing technique on the dielectric property Different curing techniques lead to different degrees of resin curing, which also lead the structure of the polymer in composite distinctively. Therefore, the curing technique influences the dielectric property of the composite. In this work, with different curing techniques, the conversion of BADCy was calculated by FTIR spectra, and then the dielectric constant and dielectric loss were investigated.
Fig. 3 was the FTIR spectrum curve of BaTiO3 /BADCy composite and the conversion calculated according to Eq. (1). The data showed that the reaction velocity was fast at first, and then gradually became slow. The conversion was almost completed when the technique (e) and (f) were adopted. The influence of the curing technique on the dielectric property of BaTiO3 /BADCy composite can be seen from Fig. 4. It was indicated that the dielectric constant was improved with the increase of the conversion of BADCy at first, and then reduced slightly after —OCN group converted almost completely. For dielectric loss, it became lower and lower by heightening the conversion of BADCy, which was because that the movement of the matrix becomes more and more difficult with the improvement of its conversion.
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Fig. 5 indicated the difference of the dielectric properties between the composites post-cured and unpost-cured. Compared with the materials unposted, the result showed that the dielectric loss of post-cured materials dropped evidently, and the dielectric constant decreased slightly. The reason is also the distinction of the conversion that cannot be shown clearly from the FTIR spectrum but the difference exists. It is clear that the post cure at 230 ◦ C for 4 h is necessary to obtain BaTiO3 /BADCy composite with enhanced properties. 3.3. Influence of treated BaTiO3 with KH-550 on the dielectric property For inorganic/organic composite, the dispersion of inorganic particles is extremely important for achieving composite with good dielectric property. It has been proved that the adoption of coupling agent is efficient to improve the compatibility between polymer and filler by chemical process [16,17]. In this work, KH-550, a kind of silane coupling agent, was used to mix with BaTiO3 directly in a high-speed mixer for 10 min, and then the mixture reacted in an oven at 110 ◦ C for 2 h. Afterwards the composite was prepared. Fig. 6 was the FTIR spectra of BaTiO3 , the mixture of BaTiO3 and KH-550, BaTiO3 treated with KH-550, BADCy/BaTiO3 composite, and BADCy/BaTiO3 treated with KH-550 composite. Compared with Fig. 6(a), Fig. 6(b) showed the new absorption band at 1085 cm−1 , which was the characteristic peak of Si—O—C group from KH-550 itself (showed in Fig. 7(a)), and Fig. 6(c) indicated the absorption bands at 1130 and 1030 cm−1 , which were attributed to Si—O—Si group and Si—O—Ba group (showed in Fig. 7(b)), respectively. It was proved that there was physisorbed KH-550 on BaTiO3 particles after KH-550 and BaTiO3 just blended and that chemisorbed KH-550 on BaTiO3 was appeared after treated at 110 ◦ C for 2 h [18]. Therefore, BaTiO3 particles can be treated efficiently with silane coupling agent KH550 after the mixture is heated in an oven at 110 ◦ C for 2 h. Compared Fig. 6(d) with Fig. 6(e), there was no difference between FTIR spectra of BADCy/BaTiO3 composite and BADCy/BaTiO3 treated with KH-550 composite. It was showed that silane coupling agent KH-550 did not affect the conversion of BADCy. The reason can be explained from the reaction mechanism between OCN group and NH2 group as shown in Fig. 8. During the process of the interaction between OCN group and NH2 group, Fig. 8(a) showed the existence of two kinds of products (A1 and A2) were determined by the ratio between OCN groups and NH2 groups at low temperature. However, when there were a few of NH2 groups in the reaction system, the reaction mechanism was just like Fig. 8(b). At that time, A1 and A2 were obtained at first, and then polymerization took place at high temperature. During the whole reaction process, NH2 group was as catalyst [19–21]. In this study, the percentage of KH-550 was 1.3% of the amount of BADCy. Although KH-550 combined with BADCy by chemical bond, the influence to the polymerization of BADCy could be neglected.
Fig. 9. Influence of modifier on dielectric constant and loss tangent ((a)160 ◦ C/2 h, (b) 160 ◦ C/2 h + 180 ◦ C/2 h, (c) 160 ◦ C/2 h + 180 ◦ C/2 h + 200 ◦ C/2 h, (d) 160 ◦ C/2 h + 180 ◦ C/2 h + 200 ◦ C/2 h + 220 ◦ C/1 h, (e) 160 ◦ C/2 h + 180 ◦ C/2 h + 200 ◦ C/2 h + 220 ◦ C/1 h + 230 ◦ C/4 h).
Fig. 9 inspected the influence of coupling agent KH-550 on the dielectric constant and the dielectric loss of the composite. It was indicated that the dielectric constant was increased and the dielectric loss was almost unchanged. Therefore, it is useful to enhance the dielectric property of BaTiO3 /BADCy composite with silane coupling agent KH-550. 3.4. The morphology of the composites Fig. 10 showed the morphology of the composites measured by SEM. Fig. 10(a) was the SEM picture of BaTiO3 /BADCy composite with untreated BaTiO3 particles. Fig. 10(b) was the SEM picture of BaTiO3 /BADCy composite with BaTiO3 particles treated with KH-550. By comparison, it was indicated that BaTiO3 particles with KH-550 were more uniformly distributed throughout the BADCy matrix, and there was no obvious aggregation of BaTiO3 particles in the composites. Consequently, silane coupling agent KH-550 is beneficial to improve the compatibility between BaTiO3 particles and the BADCy matrix.
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References
Fig. 10. Fracture scanning electron microscope photographs of BaTiO3 /BADCy composites: (a) BaTiO3 /BADCy composite with untreated BaTiO3 particles, (b) BaTiO3 /BADCy composite with modified BaTiO3 particles.
4. Conclusions A series of BaTiO3 /BADCy dielectric composites were successfully prepared by casting. Compared with the dielectric property of BADCy, BaTiO3 /BADCy composite had relatively high dielectric constant and very low dielectric loss. The dielectric property of BaTiO3 /BADCy composite could be controllable by adjusting the fraction of BaTiO3 , treating the surface of BaTiO3 with different chemical or physical methods and changing the curing techniques. The dielectric constant of the composite increased but the dielectric loss of the composite decreased with the increase of the BaTiO3 content, which was different from previously reported ceramic/polymer composites. Meanwhile, with the increase of the conversion of BADCy, the dielectric constant ascended at first and then descended slightly, while the dielectric loss descended obviously all the time. The postcure at 230 ◦ C for 4 h was necessary to obtain BaTiO3 /BADCy composite with enhanced properties. The silane coupling agent KH-550 was beneficial to improve the compatibility between BaTiO3 particles and the BADCy matrix and enhance the dielectric property of the composite.
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