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1.
This paper reports on the structural, thermal, and dielectric properties of polypyrrole/fullerene C60 nanocomposites synthesized by a interfacial polymerization method. Fourier transform infrared (FT-IR) and ultraviolet-visible (UV-vis) analyses clearly indicated the existence of interactions between polypyrrole (PPy) and the fullerene C60 nanoparticles. Thermal analyses indicated that the extrapolated onset degradation temperature (Tdeg) of PPy increased with increasing doping level. Scanning electron microscopy (SEM) images showed that the fullerene C60 changed the morphology of PPy. Dielectric analyses showed a temperature dependent dielectric relaxation behavior. The relaxation time of the nanocomposites with high doping levels tended to increase with increasing temperature. This behavior of the polypyrrole/fullerene C60 nanocomposites indicated that they could be used as a high temperature ultrasonic transducer.  相似文献   

2.
《Current Applied Physics》2015,15(2):135-143
Solid polymer electrolytes consisted of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) blend (50:50 wt/wt%) with lithium triflate (LiCF3SO3) as a dopant ionic salt at stoichiometric ratio [EO + (CO)]:Li+ = 9:1, poly(ethylene glycol) (PEG) as plasticizer (10 wt%) and montmorillonite (MMT) clay as nanofiller (3 wt%) have been prepared by solution cast followed by melt–pressing method. The X–ray diffraction study infers that the (PEO–PMMA)–LiCF3SO3 electrolyte is predominantly amorphous, but (PEO–PMMA)–LiCF3SO3–10 wt% PEG electrolyte has some PEO crystalline cluster, whereas (PEO–PMMA)–LiCF3SO3–10 wt% PEG–3 wt% MMT electrolyte is an amorphous with intercalated and exfoliated MMT structures. The complex dielectric function, ac electrical conductivity, electric modulus and impedance spectra of these electrolytes have been investigated over the frequency range 20 Hz to 1 MHz. These spectra have been analysed in terms of the contribution of electrode polarization phenomenon in the low frequency region and the dynamics of cations coordinated polymer chain segments in the high frequency region, and also their variation on the addition of PEG and MMT in the electrolytes. The temperature dependent dc ionic conductivity, dielectric relaxation time and dielectric strength of the plasticized nanocomposite electrolyte obey the Arrhenius behaviour. The mechanism of ions transportation and the dependence of ionic conductivity on the segmental motion of polymer chain, dielectric strength, and amorphicity of these electrolytes have been explored. The room temperature ionic conductivity values of the electrolytes are found ∼10−5 S cm−1, confirming their use in preparation of all-solid-state ion conducting devices.  相似文献   

3.
慕春红  刘鹏  贺颖  张丹  孟玲  边小兵 《物理学报》2008,57(4):2432-2437
采用固相反应法制备了CaCu3Ti4-xFexO12(0≤x≤0.2)陶瓷,通过X射线衍射、扫描电子显微镜、介电频谱和阻抗谱等手段研究了Fe对CaCu3Ti4O12陶瓷的结构和介电性能的影响.研究发现:CaCu3Ti4-xFex关键词: 巨介电常数 双阻挡层电容模型 界面极化  相似文献   

4.
Solid polymer nanocomposite electrolytes (SPNEs) consisted of poly(methyl methacrylate) (PMMA) and lithium perchlorate (LiClO4) of molar ratio C=O:Li+=4:1 with varying concentration of montmorillonite (MMT) clay as nanofiller have been prepared by classical solution casting and high intensity ultrasonic assisted solution casting methods. The dielectric/electrical dispersion behaviour of these electrolytes was studied by dielectric relaxation spectroscopy at ambient temperature. The dielectric loss tangent and electric modulus spectra have been analyzed for relaxation processes corresponding to the side groups rotation and the segmental motion of PMMA chain, which confirm their fluctuating behaviour with the sample preparation methods and also with change of MMT concentration. The feasibility of these relaxation fluctuations has been explained using a transient complex structural model based on Lewis acid–base interactions. The low permittivity and moderate dc ionic conductivity at ambient temperature suggest the suitability of these electrolytes in fabrication of ion conducting electrochromic devices and lithium ion batteries. The amorphous behaviour and the exfoliated/intercalated MMT structures of these nanocomposite electrolytes were confirmed by X-ray diffraction measurements.  相似文献   

5.
In this study, mechanical properties of the linear low‐density polyethylene (LLDPE)/org‐clay nanocomposites prepared by melt processing were investigated. Aspect ratio (A f ) of the clay layers were estimated by using the Halpin‐Tsai (H‐T) micromechanical model based on the enhancement of the Young's modulus (E) with the clay loading (φ). Strength of interfacial interactions (τ and B parameters) between the clay layers and polymer chains were also quantified by two indirect modeling approaches based on the improvement in tensile strength (or yield stress) of the nanocomposite samples. Interfacial strength parameters, τ and B, were found as about 5 MPa and 17.3, respectively. The average value of A f was calculated as ~35 by the H‐T model. In the TEM study, it was observed that the nanocomposite samples showed mixed morphology that could be defined as some exfoliated layers, intercalated clay stacks, and two to three layered tactoids present together within the samples. An estimated A f value was also confirmed by the TEM study. On the other hand, it was also shown that the A f value is consistent with previously reported values calculated by the modeling of melt rheological data of samples obtained from dynamic oscillatory shear measurements.  相似文献   

6.
周学懋  陈晓萌  吴学邦  水嘉鹏  朱震刚 《物理学报》2011,60(3):36102-036102
通过原位自由基聚合方法制备了聚甲基丙烯酸甲酯(PMMA)以及含镓(Ga)质量分数为11.3%和13.5%的PMMA/Ga纳米复合材料.在玻璃化转变温度及以上温区,利用能量耗散技术研究PMMA/Ga纳米复合物的动力学弛豫行为,发现随着Ga含量的增加,复合物的α弛豫峰移向高温但峰高降低.此外,还定量研究了Ga含量对PMMA/Ga复合物的α' 弛豫的影响,并作出了相应的解释. 关键词: 相对能量耗散 玻璃化转变 力学弛豫  相似文献   

7.
采用固相烧结法合成了单相巨介电常数氧化物CaCu3Ti4O12(CCTO).用阻抗分析仪分析了10—420 K温度范围内的介电频谱和阻抗谱特性,并结合ZVIEW软件进行了模拟.结果表明:温度高于室温时,频谱出现两个明显的弛豫台阶,低频弛豫介电常数随温度升高而显著增大,表现出热离子极化特点;温度低于室温时,频谱表现出类德拜弛豫,且高、低平台介电常数值基本不随温度变化,表现出界面极化特点和较好的温度稳定性.频谱中依次出现的介电弛豫对应于阻抗谱中 关键词: 3Ti4O12')" href="#">CaCu3Ti4O12 介电频谱 阻抗谱 Cole-Cole半圆弧  相似文献   

8.
《Current Applied Physics》2020,20(5):611-618
Pure BST and doped BSTF (with BSTF2: Fe2O3 2 wt % and BSTF4: Fe2O3 4 wt %) ceramics were prepared by solid state reaction. XRD pattern showed the different phases were formed depend on the weight percent of Fe2O3. The crystal size and lattice parameters increased while the lattice strain decreased. The topography of the sintered samples shows increase of the grain size with increasing Fe2O3 ratio and hence enhances the compaction of ceramics. Broadband dielectric spectroscopy was employed to investigate the effect of magnetite nanoparticle on the dielectric properties of the pure BST ceramic. The interfacial polarization and the conductivity contribution reflect the high values of permittivity and its gradual increase as frequency decreases. The two BSTF samples show relaxation peak dynamic originated from presence of immobile species/electrons at low temperatures and defects/vacancies results from the formation of oxygen vacancies originates from the spontaneous change in oxidation states of Fe ions (Fe 3+/Fe2+) at high temperatures. The relaxation rate obeys Arrhenius law at high temperatures in case of BST sample with activation energy 225 kJ/mol. This high value of activation energy at higher temperatures reflects and confirms the slowed down of the dynamics at the interphase and the decoupling nature of the OH-dynamic and the interfacial polarization.  相似文献   

9.
In this article, ZnS nanoparticles were prepared by wet chemical precipitation method using zinc sulphate (ZnSO4), sodium sulphide (Na2S) and thio-glycerol. These nanoparticles were characterized through X-ray diffraction (XRD) and transmission electron microscope (TEM) measurements. The solution-based processing was used to prepare Poly methyl methacrylate (PMMA) nanocomposites with different weight percents (0, 2, 4, 6 and 8) of ZnS nanoparticles. The obtained ZnS/PMMA nanocomposites were characterized through XRD, scanning electron microscope and TEM measurements. The dynamic mechanical analyzer was used to obtain the storage modulus and glass transition temperature (T g) of the nanocomposites. The apparent activation energy of the glass transition region was also determined using the Vogel–Fulcher–Tammann equation. The results indicated that the thermal stability of ZnS/PMMA nanocomposites was higher than PMMA and 6 wt. % of ZnS nanoparticles in PMMA matrix showed the maximum activation energy, which indicated that this nanocomposite had higher thermal stability than other composites.  相似文献   

10.
Differential scanning calorimetry (DSC), broadband dielectric relaxation spectroscopy (DRS), and thermally stimulated depolarization current (TSDC) techniques were employed to investigate glass transition and polymer dynamics in nanocomposites of polyurethane (PU) and organically modified montmorillonite (MMT) (weight fraction 0%–15%) prepared by solution casting. The PU matrix was obtained from oligo(oxytetramethylene glycol) of molar mass 1000 g/mol, 4,4′-diphenylmethane diisocyanate and 1,1-dimethylhydrazine as chain extender. Wide-angle X-ray scattering confirmed the formation of partly exfoliated structures at low MMT content. DSC, DRS, and TSDC show, in agreement with each other, that a fraction of polymer makes no contribution to the glass transition and to the corresponding α relaxation, whereas the rest exhibits similar glass transition dynamics as the pure matrix. This fraction of immobilized polymer reaches a maximum at about 5 wt% MMT. Effects of MMT on the microphase-separated structure of PU are negligible, as indicated by the study of glass transition and interfacial dielectric polarization/relaxation. No effects of MMT on the local, secondary γ and β relaxations were observed. Mechanical properties show a maximum improvement at about 5 wt% MMT, in good correlation with morphology and dynamics.  相似文献   

11.
Polymer nanocomposite electrolytes (PNCEs) of poly(ethylene oxide) and sodium perchlorate monohydrate complexes with montmorillonite (MMT) clay up to 20 wt.% MMT concentration of poly(ethylene oxide) (PEO) are synthesized by melt compounding technique at melting temperature of PEO (∼70 °C) and NaClO4 monohydrate (∼140 °C). Complex dielectric function, electric modulus, alternating current (ac) electrical conductivity, and impedance properties of these PNCEs films are investigated in the frequency range 20 Hz to 1 MHz at ambient temperature. The direct current conductivity of these materials was determined by fitting the frequency-dependent ac conductivity spectra to the Jonscher power law. The PNCEs films synthesized at melting temperature of NaClO4 monohydrate have conductivity values lower than that of synthesized at PEO melting temperature. The complex impedance plane plots of these PNCEs films have a semicircular arc in upper frequency region corresponding to the bulk material properties and are followed by a spike in the lower frequency range owing to the electrode polarization phenomena. Relaxation times of electrode polarization and ionic conduction relaxation processes are determined from the frequency values corresponding to peaks in loss tangent and electric modulus loss spectra, respectively. A correlation is observed between the ionic conductivity and dielectric relaxation processes in the investigated PNCEs materials of varying MMT clay concentration. The scaled ac conductivity spectra of these PNCEs materials also obey the ac universality law.  相似文献   

12.
The effect of organomodified nanoclay on the morphology and properties of a (70/30 w/w) nylon 6/poly(methyl methacrylate) (PMMA) blend prepared by a melt processing method was investigated. The number average domain diameter (Dn ) of the dispersed PMMA phase was found to decrease with the addition of a small amount [0.5 per hundred resin (phr)] of clay in the blend. A much finer dispersion of the minor phase in the presence of a higher amount (5 phr) of clay indicated better mixing efficiency and improved morphology in the blend. X-ray diffraction indicated the exfoliation of the clays in the nylon 6 matrix, whereas PMMA chains only intercalated into the clay layers. However, the same effect of the clay was not observed in a (30/70 w/w) nylon 6/PMMA blend when nylon 6 became the dispersed domains. In the (30/70 w/w) nylon 6/PMMA blend, the addition of organomodified nanoclay (up to 2 phr) increased the Dn of the nylon 6 domains by preferential location of the clays inside the nylon 6 domains. Addition of styrene-maleic anhydride (SMA) copolymer effectively reduced the Dn of disperse phases in both compositions of the nylon 6/PMMA blends. Thus, in nylon 6/PMMA blends, clay platelets could prevent the coalescence of dispersed domains during melt mixing as long as it was dispersed in the matrix phase of the blend. Mechanical properties and thermal stability of the blends were also improved in the presence of clay.  相似文献   

13.
Nanoparticles of pure and Eu-doped BaF2 have been prepared through sol-gel colloidal synthesis. In addition, BaF2-filled PMMA polymer nanocomposites were fabricated and dielectric properties were measured. The as-synthesized pure and Eu-doped BaF2 nanoparticles were analyzed by both X-ray diffraction and transmission electron microscopy and consisted of crystalline BaF2 particles with an average diameter of 13.6 nm with a standard deviation of about ±2.4 nm. The photoluminescence properties of the pure and Eu-doped (2%, 4% and 8%) nanoparticles showed characteristic emission of Eu3+ (5D07F J (J=1–4) transitions). We also measured significantly enhanced dielectric breakdown strength of up to 30% for BaF2 nanocomposites over the unfilled PMMA polymer. This study thus offers some promise of sol-gel synthesis of nanocomposite dielectrics with great potential for use as electrical insulation materials in cryogenic high-voltage applications.  相似文献   

14.
We report the ac conductivity and relaxation behavior analysis for a heterogeneous polymer–clay nanocomposite (PNC) having composition (polyacrylonitrile)8LiCF3SO3 + x wt.% dodecylamine modified montmorillonite. Charge transport behavior in an ionically conducting PNC has been analyzed systematically and correlated with the macroscopic parameters like polymer glass transition temperature and available free mobile charge carriers. Intercalation of cation coordinated polymer into the nanometric clay channels has been confirmed by high-resolution transmission electron microscopy. The electrical properties of the intercalated PNC films have been studied using complex impedance/admittance spectroscopy. Excellent correlation of relaxation behavior with polymer glass transition temperature (T g) confirmed the objectives of the work. An analysis of dielectric relaxation indicates that PNC films are lossy when compared with polymer–salt film. This result is a direct outcome of faster ion dynamics leading to strong electrode polarization effect due to the accumulation of charge carriers at the interface.  相似文献   

15.
The nanocrystalline material of 15 mol% Gd-doped ceria (Ce0.85Gd0.15O2−δ ) was prepared by citrate auto ignition method. The electrical study and dielectric relaxation technique were applied to investigate the ionic transport process in this nanocrystalline material with an average grain size of 13 nm and the dynamic relaxation parameters are deduced in the temperature range of 300–600°C. The ionic transference number in the material is found to be 0.85 at 500°C at ambient conditions. The oxygen ionic conduction in the nanocrystalline Ce0.85Gd0.15O2−δ material follows the hopping mechanism. The grain boundary relaxation is found to be associated with migration of charge carriers. The frequency spectra of modulus M″ exhibited a dielectric relaxation peak corresponding to defect associates (Gd-Vo\blacksquare \blacksquare)\blacksquare(\mathrm{Gd}\mbox{-}\mathrm{V}_{\mathrm{o}}^{_{_{{\blacksquare\,\blacksquare}}}})^{_{_{{\blacksquare}}}}. The material exhibits very low values of migration energy and association energy of the oxygen vacancies in the long-range motion, i.e., 0.84 and 0.07 eV, respectively.  相似文献   

16.
Mechanical relaxation behavior in ultrathin polystyrene (PS) films supported on silicon oxide (SiOx) and gold (Au) substrates has been studied by dynamic viscoelastic measurement. Based on the method, effects of free surface and substrate interface on the segmental dynamics were discussed. In the case of thin PS films with a thickness of approximately 200 nm, αa-relaxation process corresponding to the segmental motion did not show any deviation from the bulk behavior. In contrast, for the films thinner than about 50 nm, the relaxation time distribution for the αa-process became broader, probably due to a mobility gradient in the surface and interfacial regions. When we sandwiched an ultrathin PS film between SiOx layers, another relaxation process, in addition to the original αa-process, appeared at a higher temperature side that we assigned to the interfacial αa-relaxation process. However, this was never seen for an ultrathin PS film between Au layers, implying that restriction from the substrate interface might be weak in this case.  相似文献   

17.
The relative complex dielectric function, electric modulus and alternating current electrical conductivity spectra and complex impedance plane plots of aqueous solution cast poly(ethylene oxide)–montmorillonite clay (PEO–MMT) nanocomposite films were investigated over the frequency range 20 Hz to 1 MHz at ambient temperature. The intercalated and exfoliated structures of nanoclay dispersed in PEO matrix were recognized by the significant change in real part of dielectric function with clay concentration in the range 0%–20 wt%. The relaxation times corresponding to PEO chain segmental motion and ionic conduction relaxation processes were used to explore the interactions compatibility between PEO molecules and the dispersed MMT clay nanoplatelets and their effect on PEO chain dynamics. Real part of conductivity spectra of these nanocomposites over five decades of frequency has nonlinear behavior, which is influenced by the MMT clay concentration. The complex impedance plane plots confirm the bulk properties of these nanocomposites over the experimental frequency range.  相似文献   

18.
Polycyanurate‐modified montmorrilonite (PCN‐MMT) nanocomposites were synthesized by polymerization of dicyanate ester of bisphenol A in the presence of MMT dispersed by ultrasound. Techniques of IR spectroscopy, WAXD, and TEM were applied to study polymerization kinetics and structure of the nanocomposites prepared, whereas their dynamics and thermal/mechanical properties over the ?30 to 420°C range were studied by using DSC, laser‐interferometric creep rate spectroscopy (CRS), and dielectric relaxation spectroscopy (DRS) techniques. It was shown that a small amount of MMT additive acts as a catalyst of polymerization and results in the formation of complicated intercalated/exfoliated structures, as well as strongly modifies the dynamics in the PCN network. Pronounced dynamic heterogeneity was observed for PCN/MMT nanocomposites. Along with the main PCN glass transition, two new glass transitions, at much higher and much lower temperatures, were revealed as a consequence of constrained dynamics in matrix interfacial nanolayers and due to incomplete local cross‐linking in the PCN matrix, respectively. In addition, increased sub‐T g mobility was observed in these nanocomposites. A two‐fold rise of modulus of elasticity as well as increasing thermal stability and arising microplasticity at low temperatures, promoting, obviously, improved crack resistance in a brittle PCN network, were found for the PCN‐MMT nanocomposites.  相似文献   

19.
Dielectric properties are reported on polycrystalline cubic ordered-perovskite cuprate Sr2Cu(Re0.69Ca0.31)O6 in the frequency range 10 Hz-100 kHz at temperature from 300 to 500 K. Both the dielectric permittivity and dielectric loss factor are found to be frequency and temperature dependent. The enhanced value of the low frequency dielectric permittivity is associated to ionic polarization and interfacial phenomena. The material is found to possess significantly high dielectric permittivity. The calculated ac conductivity suggests semiconducting behaviour for the Sr2Cu(Re0.69Ca0.31)O6.  相似文献   

20.
ZnO压敏陶瓷中缺陷的介电谱研究   总被引:3,自引:0,他引:3       下载免费PDF全文
从理论上证明了介电松弛过程在介电谱上等效于电子松弛过程,认为室温下105Hz处特征损耗峰起源于耗尽层处本征缺陷所形成的电子陷阱.在-130—20℃范围内测量了三种配方ZnO陶瓷的介电频谱,发现ZnO压敏陶瓷室温下105Hz处的特征损耗峰在低温下分裂为两个特征峰,认为它们起源于耗尽层中的本征缺陷(锌填隙或/和氧空位)的电子松弛过程.发现ZnO-Bi2O3二元系陶瓷特征峰仅仅由锌填隙引起,而ZnO-Bi2关键词: ZnO压敏陶瓷 本征缺陷 介电谱 热处理  相似文献   

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