polymers
Article Poly(arylene ether nitrile) Composites with Surface-Hydroxylated Calcium Copper Titanate Particles for High-Temperature-Resistant Dielectric Applications
Junyi Yang 1, Zili Tang 1, Hang Yin 1, Yan Liu 1, Ling Wang 1, Hailong Tang 1,2,* and Youbing Li 1,2
1 College of Materials Science and Engineering, Chongqing University of Technology, Chongqing 400054, China; [email protected] (J.Y.); [email protected] (Z.T.); [email protected] (H.Y.); [email protected] (Y.L.); [email protected] (L.W.); [email protected] (Y.L.) 2 Chongqing Key Laboratory of Mold Technology, Chongqing University of Technology, Chongqing 400054, China * Correspondence: [email protected]; Tel.: +86-023-6256-3178
Received: 20 March 2019; Accepted: 19 April 2019; Published: 1 May 2019
Abstract: In order to develop high-performance dielectric materials, poly(arylene ether nitrile)-based composites were fabricated by employing surface-hydroxylated calcium copper titanate (CCTO) particles. The results indicated that the surface hydroxylation of CCTO effectively improved the interfacial compatibility between inorganic fillers and the polymer matrix. The composites exhibit not only high glass transition temperatures and an excellent thermal stability, but also excellent flexibility and good mechanical properties, with a tensile strength over 60 MPa. Furthermore, the composites possess enhanced permittivity, relatively low loss tangent, good permittivity-frequency stability and dielectric-temperature stability under 160 ◦C. Therefore, it furnishes an effective path to acquire high-temperature-resistant dielectric materials for various engineering applications.
Keywords: poly(arylene ether nitrile); composites; calcium copper titanate; dielectric properties; high-temperature-resistant
1. Introduction In recent decades, polymer-based composites with high dielectric permittivity and low loss tangents have received extensive attention in aerospace, microelectronic devices and electronic components such as film capacitors, embedded capacitors [1–5]. Although polymers have good mechanical properties and processability, their dielectric properties are not ideal. As far as we know, most ceramic fillers have good dielectric properties, such as high dielectric permittivity and low loss tangent [6,7]. Therefore, polymer-based composites have been developed to combine the advantages of polymers and ceramic fillers, which possess high dielectric permittivity and low loss tangent as well as good processability. Generally, fillers for dielectric composites are classified into conductive fillers (e.g., graphene [8–13], carbon nanotubes [14–19]) and dielectric fillers (e.g., barium titanate [20–22], strontium titanate [23]). Although polymer-based composites with conductive fillers have a large increase in dielectric permittivity, their loss tangents are also greatly increased. Moreover, when the content of the conductive fillers increases to a certain value (i.e., the percolation threshold), the loss tangent will increase exponentially, which is a fatal disadvantage for their practical applications. As a typical dielectric filler, calcium copper titanate (CCTO) has a high dielectric constant, low loss tangent and low-temperature dependency of dielectric permittivity [24,25]. However, there are
Polymers 2019, 11, 766; doi:10.3390/polym11050766 www.mdpi.com/journal/polymers Polymers 2019, 11, 766 2 of 11 two problems to be solved in order to fabricate polymer-based CCTO composites with excellent performance. Firstly, the poor compatibility between the inorganic fillers and the polymer matrix [26,27] needs to be improved. Secondly, the spontaneous aggregation of the fillers is another problem that will affect the performance of the composite. Dang et al. [28] achieved high dielectric permittivity and good thermal stability in functional hybrid films by employing giant dielectric permittivity calcium copper titanate as a functional inorganic filler and thermosetting polyimide as a polymer matrix. Tang et al. [29] prepared poly(arylene ether nitrile) nanocomposites by employing core-shell structured BaTiO3@polymer nanoparticles as hybrid nanofillers, which exhibited enhanced dielectric properties, good permittivity-frequency stability, excellent thermal stability, high mechanical strength and good flexibility. As a high-performance engineering plastic, poly(arylene ether nitrile)s (PAENs) have excellent mechanical properties, thermal properties, chemical resistance and easier processability [30–35]. Therefore, PAENs can be attractive candidates as polymer matrices in advanced functional materials. In this work, we performed the surface hydroxylation of CCTO to obtain hydroxylated CCTO (h-CCTO) particles, and then developed PAEN-based composites by employing h-CCTO particles as fillers. Furthermore, the mechanical properties, thermal properties and microscopic morphology of the composites were characterized in detail, and their dielectric properties were intensively investigated.
2. Materials and Methods
2.1. Materials Poly(arylene ether nitrile) was synthesized by the nucleophilic aromatic substitution polymerization of 2, 6-dichlorobenzonitrile and bisphenol A in N-methyl-2-pyrrolidone (NMP) medium with anhydrous potassium carbonate as a catalyst, according to the method in our previous literature [36]. The corresponding schematic procedure is shown in Figure S1. Calcium copper titanate particles (the size distribution is about 150–300 nm) were supplied by Shanghai Dian Yang Industry Co., Ltd., Shanghai, China. N-methyl-2-pyrrolidone (NMP) was purchased from Shanghai Titan Scientific Co., Ltd., Shanghai, China. Hydrogen peroxide (H2O2) was provided by Chengdu Jinshan Chemical Reagent Co., Ltd., Chengdu, China.
2.2. Surface Hydroxylation of CCTO Particles Calcium copper titanate was chosen as the filler due to its giant dielectric permittivity and low dielectric loss. To prepare the surface hydroxylated CCTO particles, the pristine CCTO were ultrasonically dispersed in an aqueous solution of H2O2 (30%, 150 mL) for 0.5 h and refluxed at 105 ◦C for 4 h while being stirred vigorously, and then it was ultrasonically dispersed for 15 min. After centrifugation, the upper layer of the clarified liquid is sucked out with a dropper, and the lower mixture was washed with deionized water for five times. Finally, h-CCTO particles were obtained after drying in a vacuum oven at 60 ◦C for 24 h.
2.3. Preparation of PAEN/h-CCTO Composite Films PAEN/h-CCTO composite films were fabricated by the continuous ultrasonic dispersion technique and solution casting method. Firstly, a certain amount of h-CCTO particles were dispersed in NMP under violent ultrasonic treatment accompanying with vigorous stirring. Meanwhile, the PAEN was dissolved in NMP by heating and stirring. Afterward, the h-CCTO particles suspension was added slowly into the PAEN solution in an ultrasonic water bath at 60 ◦C with mechanical stirring for 1 h to ensure that the h-CCTO particles were uniformly dispersed in the PAEN solution. Simultaneously, a clean glass plate was put into the oven and kept horizontal. Finally, the homogeneous suspension was cast slowly on the glass plate and then dried in an oven at 60 ◦C, 80 ◦C, 120 ◦C and 160 ◦C (each for 2 h) to thoroughly evaporate the solvent. After naturally cooling to room temperature, PAEN/h-CCTO Polymers 2019, 11, 766 3 of 11 composite films with different mass fractions of h-CCTO (0 wt%, 15 wt%, 30 wt%, 45 wt% and 60 wt%) were obtained.
2.4. Characterizations Fourier transform infrared (FTIR) spectrum was recorded on a Nicolet iS10 FTIR spectrometer (Thermo Scientific, Waltham, MA, USA) by using the KBr pellet method. Scanning electron microscope (SEM) was performed on a Zeiss SIGMA HDTM field emission gun scanning electron microscope at 20 kV. SEM samples were fractured in liquid nitrogen and then sputtered with gold on the fracture surface. Thermogravimetric analysis (TGA) was operated on a TGA-Q50 (TA Instruments, New Castle, DE, USA) at a heating rate of 20 ◦C/min from room temperature to 800 ◦C. Differential scanning calorimetry (DSC) measurements were measured using a DSC-Q20 (TA Instruments) system at a heating rate of 10 ◦C /min from 30 ◦C to 200 ◦C under flowing nitrogen. A mechanical test was carried out on a SANS CMT6104 Series Desktop Electromechanical Universal Testing Machine. Dielectric properties of PAEN/h-CCTO composites were measured by the Partulab HDMS-1000 high-temperature dielectric measurement system (Wuhan Partulab Technology, Wuhan, China) combined with an Agilent 4294A Precision Impedance Analyzer (Agilent Technologies, Santa Clara, CA, USA). For dielectric measurements, the composite films (thickness: 0.03–0.05 mm) were cut into small square samples (12 mm 12 mm) × and then coated with colloidal silver electrodes on both sides.
3. Results and Discussion
3.1. Surface Hydroxylation of CCTO Particles
As reported in the literature [37], H2O2 treatment is a simple and efficient method to derive massive hydroxy groups on the surface of inorganic particles. The effect of H2O2 treatment on the 1 surface chemistry of CCTO particles was studied by FTIR. As shown in Figure1, the band at 604 cm − 1 corresponds to the Ti–O vibration of CCTO, and the weak peak at 1630 cm− may be attributed to the bending mode of H–O–H, resulting from the physically adsorbed water. In addition, a broad 1 and strong band at 3430 cm− was observed in the FTIR spectrum of h-CCTO particles, which was 1 assigned to the stretching mode of O–H. As a comparison, a relatively weak band at 3430 cm− was obtained in the FTIR spectrum of CCTO particles, which might be due to a small amount of physically adsorbed water. These results indicate that the CCTO particles after surface hydroxylation contain a large number of hydroxyl groups on the particles’ surface. This can enhance the compatibility between the organic-inorganic interface, due to the fact that it can produce strong dipole-dipole interactions between the polar hydroxyl groups and nitrile groups, as schemed in Figure2. Furthermore, it is also beneficial to improve the dispersibility of the particles in the polymer matrix, which can be verified by the SEM images and dispersion photograph of CCTO and h-CCTO particles, as shown in Figures S2 and S3, respectively. It was found that less and smaller particle aggregates were formed after surface hydroxylation of CCTO particles. Polymers 2019, 11, x FOR PEER REVIEW 3 of 10
2.4. Characterizations Fourier transform infrared (FTIR) spectrum was recorded on a Nicolet iS10 FTIR spectrometer (Thermo Scientific, Waltham, MA, USA) by using the KBr pellet method. Scanning electron microscope (SEM) was performed on a Zeiss SIGMA HDTM field emission gun scanning electron microscope at 20 kV. SEM samples were fractured in liquid nitrogen and then sputtered with gold on the fracture surface. Thermogravimetric analysis (TGA) was operated on a TGA-Q50 (TA Instruments, New Castle, DE, USA) at a heating rate of 20 °C/min from room temperature to 800 °C. Differential scanning calorimetry (DSC) measurements were measured using a DSC-Q20 (TA Instruments) system at a heating rate of 10 °C /min from 30 °C to 200 °C under flowing nitrogen. A mechanical test was carried out on a SANS CMT6104 Series Desktop Electromechanical Universal Testing Machine. Dielectric properties of PAEN/h-CCTO composites were measured by the Partulab HDMS-1000 high-temperature dielectric measurement system (Wuhan Partulab Technology, Wuhan, China) combined with an Agilent 4294A Precision Impedance Analyzer (Agilent Technologies, Santa Clara, CA, USA). For dielectric measurements, the composite films (thickness: 0.03–0.05 mm) were cut into small square samples (12 mm × 12 mm) and then coated with colloidal silver electrodes on both sides.
3. Results and Discussion
3.1. Surface Hydroxylation of CCTO Particles
As reported in the literature [37], H2O2 treatment is a simple and efficient method to derive massive hydroxy groups on the surface of inorganic particles. The effect of H2O2 treatment on the surface chemistry of CCTO particles was studied by FTIR. As shown in Figure 1, the band at 604 cm−1 corresponds to the Ti–O vibration of CCTO, and the weak peak at 1630 cm−1 may be attributed to the bending mode of H–O–H, resulting from the physically adsorbed water. In addition, a broad and strong band at 3430 cm−1 was observed in the FTIR spectrum of h-CCTO particles, which was assigned to the stretching mode of O–H. As a comparison, a relatively weak band at 3430 cm−1 was obtained in the FTIR spectrum of CCTO particles, which might be due to a small amount of physically adsorbed water. These results indicate that the CCTO particles after surface hydroxylation contain a large number of hydroxyl groups on the particles’ surface. This can enhance the compatibility between the organic-inorganic interface, due to the fact that it can produce strong dipole-dipole interactions between the polar hydroxyl groups and nitrile groups, as schemed in Figure 2. Furthermore, it is also beneficial to improve the dispersibility of the particles in the polymer matrix, which can be verified by the SEM images and dispersion photograph of CCTO and h-CCTO particles, asPolymers shown2019 in, 11 Figures, 766 S2 and S3, respectively. It was found that less and smaller particle aggregates4 of 11 were formed after surface hydroxylation of CCTO particles.
Figure 1. TheThe Fourier Fourier transform transform infrared infrared (FTIR) (FTIR) spec spectratra of of calcium calcium copper copper titanate (CCTO) and Polymershydroxylated 2019, 11, x FOR CCTO PEER (h-CCTO) REVIEW particles. 4 of 10
Figure 2. TheThe schematic schematic diagram diagram of of the the hydroxylation hydroxylation of of CCTO CCTO particles particles and and interactions interactions between between h- h-CCTOCCTO particles particles and and poly(arylene poly(arylene ether ether nitrile)s nitrile)s (PAEN) (PAEN) matrix. matrix.
3.2. Morphologies of of PAEN PAEN/h-CCTO/h-CCTO Composites Composites The cross-sectional morphologies of the PAENPAEN/h-CCTO/h-CCTO composite filmsfilms were investigated by SEM. As shown in Figure3 3,, itit isis obvious obvious that that the the dispersion dispersion densitydensity ofof particlesparticles increasesincreases withwith thethe increasingincreasing mass fraction of h-CCTO. The particlesparticles are relativelyrelatively uniformly dispersed in the PAEN matrix for the composite composite with with 15 15 wt% wt% h-CCTO h-CCTO content. content. However, However, some some partial partial agglomerations agglomerations of ofparticles particles were were found found for forthe the composites composites with with high high h-CCTO h-CCTO loadings loadings (i.e., (i.e., 30 30wt%, wt%, 45 45wt% wt% and and 60 60wt%). wt%). Furthermore, Furthermore, the the phase phase interfaces interfaces between between the the particles particles and and the the PAEN PAEN matrix matrix are almostalmost indistinguishable,indistinguishable, whichwhich indicates indicates good good compatibility compatibility between between h-CCTO h-CCTO particles particles and the and PAEN the matrix.PAEN Thismatrix. may This be may attributed be attributed to the enhancedto the enhanced intermolecular intermolecular interactions interactions between between h-CCTO h-CCTO particles particles and PAENand PAEN matrix matrix through through the strong the strong dipole-dipole dipole-dipole interactions interactions of hydroxyl of hydroxyl groups groups and nitrile and groups. nitrile Asgroups. a contrast, As a the contrast, cross-sectional the cross-sectional SEM image of SE PAENM image composite of PAEN with 15composite wt% non-hydroxylated with 15 wt% CCTO non- particleshydroxylated is shown CCTO in Figureparticles S4 is (Supplementary shown in Figure Information). S4 (Supplementary It was foundInformation). that a lot It ofwas holes found arising that froma lot of particle holes extractionsarising from are particle distinctly extractions visible, and are thedistinctly phase interfacevisible, and between the phase CCTO interface particles between and the PAENCCTO matrixparticles is veryand the clear, PAEN which matrix indicates is very that clear, the compatibility which indicates between that the non-hydroxylated compatibility between CCTO particlesnon-hydroxylated and the PAEN CCTO matrix particles is very and poor. the ThesePAEN results matrix further is very verify poor. that These the surfaceresults hydroxylationfurther verify canthat etheffectively surface improve hydroxylation the interfacial can effectively compatibility improve between the interfacial CCTO particles compatibility and the between PAEN matrix. CCTO particles and the PAEN matrix.
Figure 3. The cross-sectional scanning electron microscope (SEM) images of PAEN/h-CCTO composite films: (a) 15 wt%, (b) 30 wt%, (c) 45 wt%, (d) 60 wt%.
Polymers 2019, 11, x FOR PEER REVIEW 4 of 10
Figure 2. The schematic diagram of the hydroxylation of CCTO particles and interactions between h- CCTO particles and poly(arylene ether nitrile)s (PAEN) matrix.
3.2. Morphologies of PAEN/h-CCTO Composites The cross-sectional morphologies of the PAEN/h-CCTO composite films were investigated by SEM. As shown in Figure 3, it is obvious that the dispersion density of particles increases with the increasing mass fraction of h-CCTO. The particles are relatively uniformly dispersed in the PAEN matrix for the composite with 15 wt% h-CCTO content. However, some partial agglomerations of particles were found for the composites with high h-CCTO loadings (i.e., 30 wt%, 45 wt% and 60 wt%). Furthermore, the phase interfaces between the particles and the PAEN matrix are almost indistinguishable, which indicates good compatibility between h-CCTO particles and the PAEN matrix. This may be attributed to the enhanced intermolecular interactions between h-CCTO particles and PAEN matrix through the strong dipole-dipole interactions of hydroxyl groups and nitrile groups. As a contrast, the cross-sectional SEM image of PAEN composite with 15 wt% non- hydroxylated CCTO particles is shown in Figure S4 (Supplementary Information). It was found that a lot of holes arising from particle extractions are distinctly visible, and the phase interface between CCTO particles and the PAEN matrix is very clear, which indicates that the compatibility between non-hydroxylated CCTO particles and the PAEN matrix is very poor. These results further verify Polymersthat the2019 surface, 11, 766 hydroxylation can effectively improve the interfacial compatibility between CCTO5 of 11 particles and the PAEN matrix.
Figure 3.3.The The cross-sectional cross-sectional scanning scanning electron electron microscope microscope (SEM) images(SEM) ofimages PAEN /h-CCTOof PAEN/h-CCTO composite films:composite (a) 15 films: wt%, ( (ab) )15 30 wt%, wt%, (b (c)) 30 45 wt%, wt%, ( (cd) )45 60 wt%, wt%. (d) 60 wt%.
3.3. Thermal Properties of PAEN/h-CCTO Composites As a high-performance engineering plastic, PAEN possesses excellent thermal properties. As shown in Figure4, the thermally induced phase transition and thermal decomposition behaviors of PAEN/h-CCTO composites were examined by DSC and TGA under a nitrogen atmosphere, respectively. Their glass transition temperatures (Tgs), decomposition temperatures at 5% weight loss (T5%s), temperatures of the maximum decomposition rate (Tmaxs) and char yields (CYs) are summarized in Table1. As shown in Figure4a, all the composites have a pretty high Tg, and their Tgs were found to gradually increase from 172 ◦C to 178 ◦C when the h-CCTO loadings increased from 0 to 60 wt%. This may be due to the fact that the rigid particles hinder the movement of the molecular segments. As can be seen in Figure4b and Table1, It is obvious that all the PAEN /h-CCTO composites have a high T5% (over 500 ◦C), with a slight variation around 510 ◦C, and their Tmaxs are around 530 ◦C. Furthermore, the CYs at 800 ◦C were found to gradually increase with the progressive increase of h-CCTO contents, from 56.4% for pure PAEN to 78.7% for the composite with 60 wt% h-CCTO content. This is consistent with the amount of h-CCTO loadings in the composites. The above results indicate that the PAEN/h-CCTO composites have high Tg and excellent thermal stability, which is mainly attributed to the excellent thermal properties of the PAEN matrix, and thus the composites might be a good application prospect in high-temperature-resistant electronic components. Polymers 2019, 11, x FOR PEER REVIEW 5 of 10
3.3. Thermal Properties of PAEN/h-CCTO Composites As a high-performance engineering plastic, PAEN possesses excellent thermal properties. As shown in Figure 4, the thermally induced phase transition and thermal decomposition behaviors of PAEN/h-CCTO composites were examined by DSC and TGA under a nitrogen atmosphere, respectively. Their glass transition temperatures (Tgs), decomposition temperatures at 5% weight loss (T5%s), temperatures of the maximum decomposition rate (Tmaxs) and char yields (CYs) are summarized in Table 1. As shown in Figure 4a, all the composites have a pretty high Tg, and their Tgs were found to gradually increase from 172 °C to 178 °C when the h-CCTO loadings increased from 0 to 60 wt%. This may be due to the fact that the rigid particles hinder the movement of the molecular segments. As can be seen in Figure 4b and Table 1, It is obvious that all the PAEN/h-CCTO composites have a high T5% (over 500 °C), with a slight variation around 510 °C, and their Tmaxs are around 530 °C. Furthermore, the CYs at 800 °C were found to gradually increase with the progressive increase of h-CCTO contents, from 56.4% for pure PAEN to 78.7% for the composite with 60 wt% h-CCTO content. This is consistent with the amount of h-CCTO loadings in the composites. The above results indicate that the PAEN/h-CCTO composites have high Tg and excellent thermal stability, which is
Polymersmainly2019 attributed, 11, 766 to the excellent thermal properties of the PAEN matrix, and thus the composites6 of 11 might be a good application prospect in high-temperature-resistant electronic components.
FigureFigure 4.4. ((aa)) TheThe didifferentialfferential scanningscanning calorimetrycalorimetry (DSC)(DSC) andand ((bb)) thermogravimetricthermogravimetric analysisanalysis (TGA)(TGA) andand derivativederivative thermogravimetrythermogravimetry (DTG)(DTG) curvescurves ofof PAENPAEN/h-CCTO/h-CCTO composites. composites.
Table 1. The data of thermal properties of poly(arylene ether nitrile)s (PAEN)/hydroxylated calcium Table 1. The data of thermal properties of poly(arylene ether nitrile)s (PAEN)/hydroxylated calcium copper titanate (h-CCTO) composites. copper titanate (h-CCTO) composites.
Mass FractionMass of h-CCTO Fraction of h-CCTO 0 wt% 0 wt% 15 wt%15 wt% 30 30 wt% wt% 45 wt% 45 wt%60 wt% 60 wt%
Tg (◦C)Tg (°C) 172 172 175175 177 177 178 178178 178 T5% (◦C)T5% (°C) 516 516 511511 501 501 510 510505 505 Tmax (◦C)Tmax (°C) 539539 531531 529 529 529 529522 522 CY (%)CY (%) 56.4 56.4 60.260.2 66.0 66.0 73.7 73.778.7 78.7
3.4.3.4. Dielectric Properties Properties of PAENof PAEN/h-CCTO/h-CCTO Composites Composites AsAs shownshown inin FigureFigure5 5,, the the dielectric dielectric permittivitypermittivity andand lossloss tangenttangent ofof PAENPAEN/h-CCTO/h-CCTO compositescomposites werewere measuredmeasured at 1 1 kHz kHz to to discern discern the the effect effect of of th thee h-CCTO h-CCTO content content on ontheir their dielectric dielectric properties. properties. As Aswe wecan can see, see, the the dielectric dielectric permittivity permittivity gradually gradually increases increases with with the the increase increase of of the the h-CCTO h-CCTO content. WhenWhen thethe mass mass fraction fraction of h-CCTOof h-CCTO increases increases from from 0 wt% 0 towt% 60 wt%, to 60 the wt%, dielectric the dielectric permittivity permittivity increases fromincreases 2.86 from to 6.31. 2.86 Comparedto 6.31. Compared with pure with PAEN, pure PA theEN, dielectric the dielectric permittivity permittivity of the of composite the composite with 60with wt% 60 wt% h-CCTO h-CCTO loading loading increased increased by aboutby about 121%. 121%. To To further further illustrate illustrate the the e ffeffectect of of fillers fillers onon thethe dielectricdielectric propertiesproperties ofof composites,composites, theoreticaltheoretical calculationscalculations werewere conductedconducted basedbased onon Lichtenecker’sLichtenecker’s logarithmiclogarithmic mixturemixture modelmodel [[38],38], asas summarizedsummarized inin thethe SupplementarySupplementary InformationInformation (Section(Section S2S2 andand TableTable S1).S1). TheThe comparisoncomparison ofof experimentalexperimental andand theoreticaltheoretical dielectricdielectric permittivitypermittivity is alsoalso shownshown inin Figure 5. As we can see, when the mass fraction of h-CCTO particles increased from 0 to 45 wt%, the experimental dielectric permittivities are in good agreement with the theoretical values calculated by Lichtenecker’s logarithmic mixture model. However, for the composite with 60 wt% h-CCTO content, the experimental dielectric permittivity is lower than the theoretical value. This may be caused by a decrease in interfacial polarizations due to the more serious agglomeration in the composite with high particle content. Loss tangent is also an important parameter for dielectric materials. Generally, composites with a higher loss tangent tend to dissipate more energy in the form of heat, which is detrimental to the application in electronic components. Although the loss tangent of the composites increases with the increase of the h-CCTO content, from 0.018 for pure PAEN to 0.028 for the composite with 60 wt% h-CCTO loading, it is still in a relatively low range for practical applications. The low loss tangent is mainly attributed to the good compatibility between the particles and the polymer matrix, which leads to a reduction of the loss tangent derived from interfacial polarization. Polymers 2019, 11, x FOR PEER REVIEW 6 of 10 Polymers 2019, 11, x FOR PEER REVIEW 6 of 10
FigureFigure 5. 5. As As we we can can see, see, when when the the mass mass fractionfraction ofof h-CCTOh-CCTO particlesparticles increasedincreased fromfrom 0 to 45 wt%, the experimentalexperimental dielectric dielectric permittiviti permittivitieses are are in in goodgood agreementagreement withwith thethe theoreticaltheoretical values calculated by Lichtenecker’sLichtenecker’s logarithmic logarithmic mixture mixture model. model. However, However, forfor thethe compositecomposite withwith 6060 wt%wt% h-CCTO content, thethe experimental experimental dielectric dielectric permittivity permittivity isis lowerlower ththanan thethe theoreticaltheoretical value.value. This may be caused by a decreasedecrease in in interfacial interfacial polarizationspolarizations duedue toto thethe momorere seriousserious agglomerationagglomeration in the composite with highhigh particle particle content. content. Loss Loss tangent tangent is is also also anan impoimportantrtant parameterparameter forfor dielectricdielectric materials. Generally, compositescomposites with with aa higherhigher lossloss tangenttangent tendtend toto dissipatedissipate moremore energyenergy inin the form of heat, which is detrimentaldetrimental to to the the application application in in electronic electronic componcomponents.ents. AlthoughAlthough thethe lossloss tangent of the composites increasesincreases withwith thethe increaseincrease ofof thethe h-CCTOh-CCTO content,content, fromfrom 0.0180.018 forfor purepure PAENPAEN to 0.028 for the compositecomposite with with 60 60 wt% wt% h-CCTO h-CCTO loading, loading, itit isis stillstill inin aa relativelyrelatively lowlow rangerange for practical applications. ThePolymersThe low low2019 loss loss, 11 tangent ,tangent 766 isis mainlymainly attributedattributed toto thethe goodgood compatibilitycompatibility between the particles and7 ofthe 11 polymerpolymer matrix, matrix, which which leads leads to to a a reduction reduction ofof thethe lossloss tangenttangent derivedderived from interfacial polarization.
FigureFigureFigure 5. 5.5. The The experimental experimental dielectric dielectric dielectric properties properties properties ofof of PAPA PAENEN/h-CCTOEN/h-CCTO/h-CCTO compositescomposites composites as asa function a function of the of theh- CCTOh-CCTOCCTO content content content at at at 11 1kHzkHz kHz andand and theoreticaltheoretical theoretical dielectricdielectric dielectric pepe permittivityrmittivityrmittivity basedbased onon Lich Lichtenecker’sLichtenecker’stenecker’s logarithmic mixturemixturemixture model. model.model.
Moreover,Moreover,Moreover, thethe dielectricdielectric dielectric properties propertiesproperties were werewere measured measmeasuredured as asas functions functionsfunctions of of frequency frequency and and temperature temperature to todiscernto discerndiscern their theirtheir frequency-dependence frequency-dependencefrequency-dependence and temperature-dependence,andand tempertemperature-dependence,ature-dependence, respectively. respectively. As shown As inshown Figure in6, FiguretheFigure dielectric 6,6, thethe permittivity dielectricdielectric permittivitypermittivity of the composites ofof thethe has compcomp a slightositesosites decrease hashas aa slightslight with the decrease increasing with frequency, the increasing with a fluctuationfrequency, with range a withinfluctuation6% range over within the frequency ± 6% over from the 100frequency Hz to 100from kHz. 100 Hz The to loss 100 tangentkHz. The of loss the frequency, with a fluctuation± range within ± 6% over the frequency from 100 Hz to 100 kHz. The loss tangentcompositestangent of of the the demonstrates composites composites ademonstrates demonstrates decrease with aa decreasethedecrease increase wiwithth of thethe frequency increaseincrease from ofof frequencyfrequency 100 Hz to from 20 kHz, 100 andHz to then 20 kHz,presentskHz, and and athen then slight presents presents increase a a slight slight at frequencies increase increase at at exceeding freq frequenciesuencies 20 exceedingexceeding kHz. Overall, 2020 kHz.kHz. the Overall, PAEN/h-CCTO the PAEN/h-CCTO composites compositespossesscomposites a good possess possess permittivity-frequency a a good good permittivity-frequency permittivity-frequency stability and stabilitystability a relatively andand lowaa relativelyrelatively loss tangent. low loss tangent.
FigureFigureFigure 6.6. ( (aa()a) The) TheThe dielectric dielectricdielectric permittivity permittivitypermittivity and andand (b) loss((bb)) loss tangentloss tangenttangent of PAEN ofof PAEN/h-CCTO/PAEN/h-CCTOh-CCTO composites composites as a function as a functionoffunction frequency of of frequency frequency from 100 from Hzfrom to 100 100 100 Hz Hz kHz. to to 100 100 kHz.kHz.
Figure7 depicts the dielectric permittivity and loss tangent of PAEN /h-CCTO composites as a function of temperature from 40 ◦C to 180 ◦C at 1 kHz. It was found that the dielectric permittivity and loss tangent were relatively stable when the temperature is below the turning point temperature (Tt). When the temperature reaches and exceeds the turning point temperature, both the dielectric permittivity and loss tangent display a rapid increase. It is important to note that the turning point temperatures (160~170 ◦C) are close to their glass transition temperatures (around 175 ◦C), which suggests that the Tg of polymer matrix plays a dominant role in determining the dielectric-temperature stability of polymer-based composites. This phenomenon might be attributed to polymer molecular motions. When the temperature is below Tg, there are mainly local motions of the side groups on the macromolecular chains, and these motions are relatively weak. However, when the temperature Polymers 2019, 11, x FOR PEER REVIEW 7 of 10
Figure 7 depicts the dielectric permittivity and loss tangent of PAEN/h-CCTO composites as a function of temperature from 40 °C to 180 °C at 1 kHz. It was found that the dielectric permittivity and loss tangent were relatively stable when the temperature is below the turning point temperature (Tt). When the temperature reaches and exceeds the turning point temperature, both the dielectric permittivity and loss tangent display a rapid increase. It is important to note that the turning point temperatures (160~170 °C) are close to their glass transition temperatures (around 175 °C), which suggests that the Tg of polymer matrix plays a dominant role in determining the dielectric- temperature stability of polymer-based composites. This phenomenon might be attributed to polymer molecular motions. When the temperature is below Tg, there are mainly local motions of the Polymers 2019, 11, 766 8 of 11 side groups on the macromolecular chains, and these motions are relatively weak. However, when the temperature reaches and exceeds the Tg, the motion intensity of the side groups is greatly reachesincreased, and accompanied exceeds the T byg, the more motion intense intensity segmental of the movements side groups of is macromolecular greatly increased, chains. accompanied This will bylead more to the intense rapid segmental increase movementsof molecular of macromolecularpolarizations (contribution chains. This to will dielectric lead to thepermittivity) rapid increase and ofconduction molecular loss polarizations (contribution (contribution to a loss tangent), to dielectric whic permittivity)h can be further and verified conduction by the loss relationship (contribution of toelectrical a loss tangent), conductivity which of can the be furthercomposite verified vers byus the temperature relationship (Figure of electrical S5 conductivityin Supplementary of the compositeInformation). versus The temperatureabove results (Figure indicate S5 that in Supplementary the PAEN/h-CCTO Information). composites The possess above good results dielectric- indicate thattemperature the PAEN stability/h-CCTO under composites 160 °C, possess which good is greatly dielectric-temperature significant for their stability potential under 160applications◦C, which as is greatlyhigh-temperature-resistant significant for their potential electronic applications components. as high-temperature-resistant electronic components.
FigureFigure 7.7.( a()a) The The dielectric dielectric permittivity permittivity and and (b) loss(b) tangentloss tangent of PAEN of /PAEN/h-CCTOh-CCTO composites composites as a function as a offunction temperature of temperature from 40 ◦ Cfrom to 180 40 °C◦C. to 180 °C.
3.5. Mechanical Properties and Flexibility of PAEN/h-CCTO Composites 3.5. Mechanical Properties and Flexibility of PAEN/h-CCTO Composites As shown in Figure8, the tensile strength and breaking elongation of the composites were As shown in Figure 8, the tensile strength and breaking elongation of the composites were tested tested to study the effect of h-CCTO particle loadings on the mechanical properties of the composites. to study the effect of h-CCTO particle loadings on the mechanical properties of the composites. It was Itfound was that found the that tensile the strength tensile strength gradually gradually decreased decreased with the withincrease the of increase h-CCTO of loading, h-CCTO from loading, 102 fromMPa 102for the MPa pure for PAEN the pure to PAEN60 MPa to for 60 the MPa composite for the composite with 60 wt% with h-CCTO 60 wt% loading. h-CCTO This loading. is due This to the is duepartial to theself-aggregation partial self-aggregation phenomenon phenomenon arising from arising the fromincrease the increaseof the particle of the particleloading loadingfor the forcomposites the composites with a large with number a large of number inorganic of inorganicparticles, which particles, is consistent which is with consistent the SEM with observations the SEM observations(Figure 3b–d). (Figure Nonetheless,3b–d). Nonetheless, the tensile thestrength tensile of strength the PAEN/h-CCTO of the PAEN / h-CCTOcomposites composites can still can be stillcomparable be comparable to other to otherordinary ordinary engineering engineering plasti plastics,cs, such such as as polyamides, polyamides, polyformaldehyde. polyformaldehyde. AsAs shownshown inin FigureFigure8 8b,b, the the breaking breaking elongation elongation also also gradually gradually decreased decreased with with the the increase increase of of h-CCTO h-CCTO loading,loading, rangingranging fromfrom 4.1%4.1% toto 5.3%.5.3%. ItIt isis worthworth notingnoting thatthat thethe compositecomposite filmsfilms cancan bebe easilyeasily bentbent andand curledcurled intointo multi-layermulti-layer cylinders, cylinders, even even for for the the composite composite film film with with 60 60 wt% wt% h-CCTO h-CCTO content content (Figure (Figure9), which9), which is beneficial is beneficial for theirfor their potential potential application applicatio inn film in film capacitors. capacitors. The The above above results results demonstrate demonstrate that thethat PAEN the PAEN/h-CCTO/h-CCTO composites composites possess possess a relatively a relatively high high tensile tensile strength strength and excellentand excellent flexibility, flexibility, and canand fullycan fully satisfy satisfy the requirements the requirements for the for practical the prac applicationstical applications in electronic in electronic components. components.
Polymers 2019, 11, 766 9 of 11 Polymers 2019, 11, x FOR PEER REVIEW 8 of 10
FigureFigure 8. ((aa)) The The tensile tensile strength strength and and ( (bb)) breaking breaking elongation elongation of of PAEN/h-CCTO PAEN/h-CCTO composites.
FigureFigure 9. TheThe digital digital photo photo of of PAEN/h-CCTO PAEN/h-CCTO composite filmsfilms curled into multilayer cylinders.
4. Conclusions Conclusions In summary,summary, a seriesa series of PAENof PAEN/h-CCTO/h-CCTO composites composites were fabricated were fabricated through continuousthrough continuous ultrasonic ultrasonicdispersion techniquedispersion and technique solution and casting solution method casting by employing method surface-hydroxylatedby employing surface-hydroxylated CCTO particles, CCTOand the particles, surface hydroxylation and the surface of CCTO hydroxylation effectively of improved CCTO theeffectively interfacial improved compatibility the interfacial between compatibilityinorganic fillers between and the inorganic polymer matrix.fillers and The the results polymer indicated matrix. that The the results composites indicated have highthat Tthegs (overcomposites 170 ◦C) have and high excellent Tgs (over thermal 170 stability, °C) and with excellentT5%s exceedingthermal stability, 500 ◦C. Furthermore,with T5%s exceeding the composites 500 °C. Furthermore,exhibited improved the composites dielectric properties, exhibited such improv as enhanceded dielectric permittivity, properties, relatively such low as loss enhanced tangent permittivity,and good permittivity-frequency relatively low loss stability,tangent and as well good as goodpermittivity-frequency dielectric-temperature stability, stability as well under as 160 good◦C. dielectric-temperatureIn addition, the composites stability also exhibitedunder 160 good °C. mechanicalIn addition, properties the composites and excellent also flexibility,exhibited withgood a mechanicaltensile strength properties over 60 and MPa. excellent In view flexibility, of their excellent with a overalltensile performances,strength over 60 the MPa. composites In view will of their have potentialexcellent overall applications performances, in the field the of composites high-temperature-resistant will have potential electronic applications components, in the field such of as high- film temperature-resistantcapacitors, embedded electronic capacitors, components, etc. such as film capacitors, embedded capacitors, etc.
Supplementary Materials: Supplementary Materials: The following are available online at at www.mdpi.com/xxx/s1,http://www.mdpi.com/2073-4360 Figure S1./11 Schematic/5/766/s1, Figure S1. Schematic synthesis procedure of poly(arylene ether nitrile). Figure S2. Field emission scanning electron synthesismicrograph procedure (FE-SEM) of images poly(arylene of (a) CCTO ether and nitrile). (b) h-CCTO Figure particles.S2. Field Figureemission S3. scanning Digital photo electron of dispersions micrograph of pure(FE- SEM)CCTO images and h-CCTO of (a) particlesCCTO and in ethanol (b) h-CCTO after standingparticles. for Figu fourre hours. S3. Digital Figure photo S4. Cross-sectional of dispersionsSEM of pure image CCTO of PAEN and h-CCTOcomposites particles with 15 in wt% ethanol non-hydroxylated after standing CCTO for four particles. hours. Figure Figure S5. S4. Electrical Cross-sectional conductivity SEM of image PAEN of/h-CCTO PAEN composite with 30 wt% h-CCTO content as a function of temperature. Figure S6. TGA and DTG curves of h-CCTO composites with 15 wt% non-hydroxylated CCTO particles. Figure S5. Electrical conductivity of PAEN/h-CCTO particles.composites Table with S1. 15 Experimentalwt% non-hydroxylat and theoreticaled CCTO dielectric particles. permittivity Figure S5. Electrical of PAEN /conductivityh-CCTO composites. of PAEN/h-CCTO composite with 30 wt% h-CCTO content as a function of temperature. Figure S6. TGA and DTG curves of h- Author Contributions: Conceptualization, J.Y. and H.T.; validation, Y.L. (Yan Liu) and L.W.; investigation, J.Y. CCTO particles. Table S1. Experimental and theoretical dielectric permittivity of PAEN/h-CCTO composites. and Z.T.; data curation, Z.T. and H.Y.; writing-original draft preparation, J.Y.; writing—review and editing, H.Y. and H.T.; supervision, H.T.; project administration, Y.L. (Youbing Li); funding acquisition, H.T. Author Contributions: Conceptualization, J.Y. and H.T.; validation, Y.Liu and L.W.; investigation, J.Y. and Z.T.; Funding: This research was funded by National Natural Science Foundation of China (No. 51603027), dataNatural curation, Science Z.T. Foundation and H.Y.; writing-or of Chongqingiginal draft (No. preparation, cstc2016jcyjA0519 J.Y.; writing and— cstc2018jcyjAX0565),review and editing, H.Y. Scientific and H.T.; and Technologicalsupervision, H.T.; Research project Program administrati of Chongqingon, Y.Li; funding Municipal acquisition, Education H.T. Commission (Grant No. KJ1600920).
Funding:Conflicts ofThis Interest: researchThe was authors funded declare by National no conflict Natural of interest. Science Foundation of China (No. 51603027), Natural Science Foundation of Chongqing (No. cstc2016jcyjA0519 and cstc2018jcyjAX0565), Scientific and Technological Research Program of Chongqing Municipal Education Commission (Grant No. KJ1600920).
Conflicts of Interest: The authors declare no conflict of interest.
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