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Novel conducting PVA/Carbon quantum dots (CQDs) nanocomposite for high anti-electromagnetic wave performance
摘要： Novel conductive PVA/CQDs nanocomposite films were synthesized through the casting technique for the electromagnetic (EM) wave protection at microwave band. The surface morphology, thermal and mechanical properties were briefly studied. The SEM micrograph showed an excellent distribution, dispersion and a high adhesion property of the CQDs in the PVA chains. Also, DSC analysis showed an increase in the glass temperature (Tglass) from 83.2 °C for fresh PVA to 95.4 °C for 8 wt% of CQD and the increase in melting temperature from 215 °C for fresh PVA to 227.7 °C for the same CQDs concentration. It was found that Young's modulus is directly proportional to CQD nano-particles concentration in the nano-composites from 0.14 GPa for fresh PVA to 4.48 GPa for 8 wt% of CQDs. It was found that the strength at break increases, but the elongation declines with the increase of CQDs nano-particles. The EM shielding effectiveness (SE) of (PVA/CQDs) nanocomposite is measured in the microwave frequency range, and it is found around 36.8 dB with the CQDs concentration (8 wt%). Finally, the PVA/CQDs nano-composite is of promising potential applications in electronics and microwave devices at an affordable cost.
关键词： PVA,Mechanical properties,Electromagnetic shielding,Thermal properties,CQDs nano-particles
更新于2025-09-19 17:13:59
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Graphenea??based polymer composites with ultraa??high ina??plane thermal conductivity: A comparison study between optothermal Raman spectroscopy and laser flash method
摘要： We developed a simple solution mixing and molding process for the incorporation of graphene nano-flakes (GNFs) in polymer films. Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and poly(ethylene-co-methacrylic acid) (PEMAA) were used for preparation of the samples. The orientation and stacking of GNFs were confirmed using a scanning electron microscope. The thermal conductivity values for these composites were obtained using (1) laser flash method (commercially available) and (2) an optothermal Raman (OTR) technique (homemade device). The former measures the thermal diffusivity (α) and one needs to measure the density (ρ) and the heat capacity (Cp) of the composites in order to measure the in-plane thermal conductivity (κ = α.ρ.Cp), while the latter measures the in-plane thermal conductivity directly from the relation between the excitation power and the position of the Raman resonance. The data obtained from Raman spectroscopy were analyzed, assuming heat propagation in three and two dimensions. The Raman results obtained based on the two-dimensional model were very close to the results obtained using the laser flash method with less than 10% difference. The OTR spectroscopy was found to be a promising technique for measuring the in-plane thermal conductivity of carbon-based polymer composites. PVDF-HFP and PEMAA composite films with very high in-plane thermal conductivity (25 W m?1 K?1) were obtained through the incorporation of GNFs (20 wt % concentration). Considering a very low thermal conductivity of these polymers (<0.2 W m?1 K?1), this corresponds to a large enhancement of roughly 12 400%. ? 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48927.
关键词： nanotubes,conducting polymers,fullerenes,graphene,thermal properties,composites
更新于2025-09-19 17:13:59
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Synthesis, structural characterization, and thermal properties of Caa?? and Laa??doped sodaa??lime glasses by laser melting
摘要： Laser melting techniques have been used in the preparation of unconventional glass compositions with high melting temperatures. Thus, we wanted to test the feasibility of using a CO2 laser in the preparation of nitrogen rich oxynitride glasses and nitride silicate glasses. Melting from oxides and metallic raw materials, we wanted to study first glass formation and possible evaporation losses of the glass components. Two glass series were prepared and studied for their structure and thermal properties, one with Ca2+- and a higher melting La3+-doped soda lime silicate series. In less than three minutes of laser melting, spheres of up to six mm diameter were successfully fabricated. The obtained glass samples were homogeneous and transparent in the visible region. X-ray diffraction and Raman spectroscopic analysis confirmed the amorphous nature of the synthesized samples. Sodium losses increase as calcium is added to the soda lime silicate glass. As expected, increasing Ca2+ or La3+ addition leady to increased depolymerization of the silicate network. Moreover, the increases in Tg with the addition of Ca2+ or La3+ ions indicating strengthening of the soda lime silicate glass by increasing strength of the M-O bonds of divalent and trivalent ions over monovalent sodium ions, weak Na-O bonds also resulting in significant evaporation loss during the short laser melting times. The thermal stability decreases upon addition of Ca2+ or La3+ ions to the soda lime silicate glasses.
关键词： Laser melting,soda lime silicate glass,thermal properties,Ca2+,glass structure,La3+
更新于2025-09-19 17:13:59
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Anharmonic Effects in Single-Walled Carbon Nanotubes Analyzed through Low-Temperature Raman Imaging
摘要： The high thermal conductivity of single-walled carbon nanotubes (SWCNT) has gained much attention for their applications in potential thermal devices. Here, we investigate anharmonic effects, originated from phonon interactions, of SWCNT bundles by temperature dependent Raman imaging using our home-built mini cryostat system. The cryostat system is small enough to be mounted on a piezo scanner that suppresses thermal drift, enabling Raman imaging at different temperatures. We obtained Raman spectral images of several SWCNT bundles with a spatial resolution of a few hundred nanometers at different temperatures. We found that different bundles show different temperature dependences of Raman peak intensity, shift, and width. The temperature dependence was further elucidated by considering the sample topography observed by atomic force microscopy, where bundle effects seem to play an important role to influence the anharmonicity. The temperature-dependent Raman analysis based on spatially resolved imaging will be a powerful tool to investigate anharmonic effects of advanced carbon nanomaterials as well as to realize in-situ visualization of thermal properties for future thermal devices.
关键词： single-walled carbon nanotubes,anharmonic effects,low-temperature,Raman imaging,thermal properties
更新于2025-09-19 17:13:59
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Structure and thermal investigation of the effect of laser radiation in Chitosan-MgO nanocomposite film
摘要： In this study, Chitosan-MgO nanocomposite was prepared using a simple chemical precipitation method and characterized using scanning electron microscopy (SEM). Chitosan-MgO nanocomposite samples were exposed to laser pulses with fluencies ranging from 2 to 25 J/cm2. The structural modifications in the exposed nanocomposite samples were studied as a function of laser fluencies using various characterization techniques such as X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results indicate that the laser exposure up to 25 J/cm2 results in the production of broken molecular chains, reducing the thermal stability of the Chitosan-MgO nanocomposite. In addition, the melting temperature is found to be sensing the crystalline domains. Higher laser fluences cause the generation of defects that can lead to lowering the melting temperature.
关键词： laser,XRD,Nanocomposites,FTIR,thermal properties
更新于2025-09-19 17:13:59
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Concentration dependent thermo-optic properties of yellow emissive ZnO quantum dots
摘要： This paper study the thermal properties of ZnO quantum dots (QDs) synthesized by sol-gel method. The structural and morphological properties were investigated using x-ray diffraction technique (XRD) and transmission electron microscopy (TEM). Thermal properties of ZnO QDs were measured using dual beam mode matched thermal lens technique. The results reveal that the thermal diffusivity of the nano?uid depends on the concentration of ZnO QDs. There is an optimum concentration of ZnO QDs, above which thermal diffusivity increases more than that of the base ?uid whereas thermal diffusivity decreases below the optimum concentration. This variation in thermal diffusivity of ZnO QDs nano?uid is explained using absorption and emission spectra.
关键词： optical properties,ZnO QDs,thermal properties,nano?uids
更新于2025-09-11 14:15:04
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Investigation of thermal and electrical properties of As–Se glasses modified with Cu using DSC and AC impedance spectroscopy
摘要： Investigations of thermal properties of CuxAs50Se50 ? x chalcogenides were carried out using a differential scanning calorimeter. It was established that copper introduction significantly affects the complexity of structural network. This was indicated by double-stage crystallization process in the compound Cu15As50Se35. Besides α relaxation, all the glasses during heating show β relaxation. The complexity of the network influences the conductivity values and transport properties in a way of higher DC and AC conductivity for the compound with the highest Cu share. Impedance spectra show two semicircles, indicating the existence of two polarization processes in different frequency ranges. The presence of kinetic and as well as diffusion processes in polarization of the samples with x = 10 and 15 at% of Cu strongly affects the unusually high values of the real part of dielectric permittivity in low- and medium-frequency range.
关键词： AC impedance spectroscopy,electrical properties,thermal properties,Cu modification,DSC,As–Se glasses
更新于2025-09-10 09:29:36
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Improving the electroactive phase, thermal and dielectric properties of PVDF/graphene oxide composites by using methyl methacrylate-co-glycidyl methacrylate copolymers as compatibilizer
摘要： In this work, graphene oxide sheets (GO) filled polyvinylidene fluoride (PVDF) nanodielectric composites with methyl methacrylate-co-glycidyl methacrylate copolymer (MG) as compatibilizer were fabricated by solution blend process. MG improved the dispersion of GO and enhanced the interface strength between GO and PVDF matrix. The strong dipolar interaction between MG on the surface of GO and PVDF resulted in the crystal transformation of PVDF from a-phase to b/c-phase and nearly 81% b/c-phase PVDF formed for PVDF/MG@GO7.0 composite. The thermal stability, mechanical property, melting and crystallization behaviors of PVDF/MG@GO composites were improved obviously due to the enhanced interface strength between GO and PVDF matrix with the aid of MG. MG copolymers not only contributed to the uniform dispersion of GO in PVDF, but also prevented the direct connection of GO and effectively inhibited the occurrence of leakage current in composites. Therefore, the dielectric properties of PVDF/MG@GO composites were also enhanced significantly with the addition of MG compared with the PVDF/GO composites, which supported the fact that the dielectric properties of resulted composites could be tailored by using MG copolymer as compatibilizer.
关键词： thermal properties,PVDF,graphene oxide,compatibilizer,dielectric properties
更新于2025-09-10 09:29:36
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Synthesis, characterization, thermal and luminescent properties of thiophenol-functionalized platinum(II) bis(acetylide) complexes
摘要： Two thiophenol-functionalized trans-platinum(II) bis(acetylide) complexes, having one thiophenol moiety in each alkenyl backbone with general formula trans-[(PPh3)2Pt{C≡C–Ar–CH=CH(SC6H5)}2], (2a–2b), (Ar = phenylene or 2,5-dimethylphenylene), were synthesized in good yields and good regioselectivities. Compared to the absorption bands of the trans-platinum(II) bis(acetylide) complexes 1, the positions of the lowest energy absorption bands were redshifted by 17–18 nm, after functionalization with thiophenol. For both of the platinum(II) complexes 2, the lowest energy absorption bands in chloroform solution at room temperature were observed in the range 376–379 nm, and under excitation at the absorption maximum both complexes showed emission maxima in the range of 408–419 nm. All the new Pt complexes have been characterized by physico-chemical and spectroscopic methods.
关键词： thermal properties,thiophenol-functionalized,characterization,synthesis,platinum(II) bis(acetylide) complexes,luminescent properties
更新于2025-09-10 09:29:36
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Conductive and photoactive nature of conjugated polymer based on thiophene functionalized thiazole or benzothiadiazole
摘要： New poly (thiophene vinyl thiazole) (PTVT) and poly (thiophene vinyl benzothiadiazole) (PTVBT) was synthesized by Wittig condensation route. The absorption maximum of PTVT and PTVBT appeared at 376 and 410 nm in a solution state, and it was red-shifted to 417 and 510 nm in a thin film state. The optical band gaps were 1.7 and 1.5 eV calculated from thin film absorption edges of the polymer. The photoluminescence spectra of PTVT and PTVBT have an emission peak at 457 nm with bluish green and 487 nm with greenish-yellow fluorescence in THF solution. Both polymers showed a short fluorescence decay time (τ1) of 2.31 and 0.73 ns respectively. Furthermore, the aggregation-caused quenching (ACQ) phenomenon observed in both polymers in decreased fluorescence intensity with different water fractions. The lower electrochemical band gaps were achieved for both polymers (1.4, and 1.3 eV) from cyclic voltammetry. Both polymers have a granular shaped morphology with good surface roughness was observed using AFM. High thermal stability was observed with 8% weight loss at 400 °C for PTVT and 6% weight loss at 460°C for PTVBT. The highest electrical conductivity was observed from electrochemical impedance measurement which was 7.68·10–6 Ω–1·cm–1 for PTVBT.
关键词： poly(p-phenylenevinylene),thermal properties,band gap,photoluminescence,impedance
更新于2025-09-10 09:29:36