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Crosslink network and phenyl content on the optical, hardness, and thermal aging of PDMS LED encapsulant
摘要： This work aims to synthesize new series of polysiloxane copolymer through hydrosilylation reaction based on different level of crosslink densities and phenyl content. The results revealed that polysiloxanes resins with phenyl rings increased viscosity up to 3800 cps while displaying a relatively high refractive index of 1.531. The asymmetric phenyl substitution onto chain backbone led to formation of densely packed structure resulting in reduced water absorption and gas permeability of PDMS resins. High level of crosslinking contributed to a high shore A hardness and adhesion strength. It displayed transparency of 97% whose percentage reduction was 1.6% under thermal and 0.6% UV aging. No obvious discoloration was observed during accelerated thermal aging up to 210 min at 80 (cid:1)C. These results are key attributes that make the synthesized polysiloxane series as ideal candidate for high brightness LED encapsulant. ? 2019 Wiley Periodicals, Inc. ? 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47895.
关键词： copolymers,thermal properties,ring-opening polymerization,optical properties,synthesis and processing techniques
更新于2025-11-19 16:56:42
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Improvement of Optical and Thermal Properties for Quantum Dots WLEDs by Controlling Layer Location
摘要： The inorganic halide perovskite quantum dots (QDs) have been considered as a promising substitute for white light-emitting diodes (WLEDs). In this article, the green CsPbBr3 QDs and red K2SiF6:Mn4+ (KSF) phosphor were used to fabricate the conversion layers. Because the layers location is fundamental to the absorption priority of blue light, the location of KSF and QDs were controlled and the QDs-up type and QDs-down type WLEDs were made. The optical power, luminous efficiency, CCE and luminous intensity in the middle of QDs-up type are 13.83 mW, 13.54 lm/W, 11.94% and 2.65 cd, meaning 24.26%, 25.72%, 2.63% and 23.83% higher than those of QDs-down type, respectively. In addition, the QDs-up type has a lower correlated color temperature (CCT) shift of 734 K and a decreased highest temperature of 56.8℃ (51.5% and 14.9% lower). These key property differences indicate that the QDs-up type is more suitable for the application in display and backlight. In order to explore the reasons for these differences, the emission spectra, CCE, reflection rate, absorption rate and temperature curves of QDs or KSF films were also analyzed, which provided a better understanding of designing package structures.
关键词： layer location,thermal properties,quantum dots WLEDs,optical properties
更新于2025-11-19 16:46:39
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A Wide Temperature Insensitive Piezoceramics for High-Temperature Energy Harvesting
摘要： One of the key challenges in the development of high-temperature energy harvesting (HTEH) technology is to clarify the relationship between temperature-dependent material parameters and device power generation capabilities. However, at present, the research on temperature stability of piezoceramics mainly relies on thermal annealing technology, which cannot follow the actual temperature dependence of the piezoelectricity, and it is even more difficult to predict the temperature stability of HTEH. To shed light on this field, here, (1-x)BiScO3-xPbTiO3 system was chosen for building HTEH material, and the temperature dependent electrical parameters, such as d33, εr, and g33, have been measured by multiple in-situ techniques. It was found that the synergistic effect of d33 and εr with temperature helps to obtain a stable g33 value in a wide temperature range. Moreover, in the mode of the cantilever-type energy harvester, a stable output voltage was obtained at x=0.64 harvester with less than 20% change over a broad temperature range of 100-250 oC, and it was verified that the temperature stability of g33 is crucial to the operation stability of HTEH devices.
关键词： in-situ techniques,piezoelectric materials/properties,energy harvesting,thermal properties
更新于2025-11-14 17:28:48
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Revealing the correlation between molecular structure and dielectric properties of carbonyl‐containing polyimide dielectrics
摘要： Polymer dielectrics with outstanding heat resistance and advanced dielectric properties are of great importance for high-temperature capacitors in the applications of hostile circumstances. In this work, a series of aromatic carbonyl-containing polyimides (CPI) are prepared from the carbonyl dianhydride and different diamines. The correlation between molecular structure (i.e., different linked structure ( O , CH2 , SO2 ) in diamines, the length of repeating unit and the linked position (para-para or meta-meta), and properties is revealed in detail to obtain CPI dielectrics with excellent thermal resistance (glass transition temperature, Tg: 241~352°C), reasonably high dielectric constant (3.99~5.23), low dissipation factor (0.00307~0.00395), and admirable breakdown strength (425~552 MV/m) simultaneously. Particularly, CPI-5 with carbonyl structure in dianhydride and sulfonyl group in diamine proves to exhibit discharged energy density and charge–discharge efficiency of 6.34 J/cm3 and 92.3% at 500 MV/m, respectively. In addition, CPI-5 also displays stable dielectric properties in temperature range of ?50?200°C. ? 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47883.
关键词： dielectric properties,films,thermal properties,polyimides
更新于2025-11-14 14:48:53
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Reinforcing effect of amine-functionalized and carboxylated porous graphene on toughness, thermal stability, and electrical conductivity of epoxy-based nanocomposites
摘要： Epoxy-based nanocomposites reinforced with nonfunctionalized porous graphene (NPG), carboxylated porous graphene (CNPG), and amine-functionalized porous graphene (ANPG) were investigated with regard to mechanical properties, thermal stability, and electrical conductivity. Nanomaterials were added to the epoxy matrix in varying contents of 0.5, 1, and 2 wt %. Generally, mechanical properties were improved as a result of introducing nanomaterials into the epoxy resin. However, the amelioration of toughness was only observed in functionalized NPGs/epoxy nanocomposites. Field emission scanning electron microscopy images showed that functionalized nanomaterials induced a rougher fracture surface compared to the neat epoxy. Dynamic mechanical analysis along with differential scanning calorimetry confirmed an increment in the glass-transition temperature (Tg) of the reinforced nanocomposites. Also, they proved that functionalization made the epoxy network tougher and more flexible. The electrical conductivity and thermal stability of the epoxy resin were also improved when loaded with nanomaterials.
关键词： toughness,electrical properties,thermal properties,nanocomposites
更新于2025-09-23 15:23:52
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Preparation of graphene oxide with large lateral size and graphene/polyimide hybrid film via in situ “molecular welding” strategy
摘要： In this letter, we report an "ultrasonication-free" direct exfoliation method to obtain graphene oxide with large lateral size (LGO). The average size of LGO sheets is about 50 lm * 50 lm. The g-LGO film shows a superior in-plane thermal conductivity after the graphitization treatment. Furthermore, the in situ "molecular welding", using polyimide (PI) to weld up the GO sheets, is conducted to improve the performance of hybrid thermal conducting film. The thermal conductivity of g-LGO/PI film is 1053.975 ± 8.762 W m-1 K-1, superior to that of the g-LGO film and g-SGO/PI. The direct preparation method to obtain GO with large lateral size, followed by such an in situ "molecular welding" strategy by PI, provides a promising way to fabricate graphene-based film for efficient thermal management.
关键词： Molecular welding,In situ polymerization,Large lateral size,Thermal properties,Carbon material
更新于2025-09-23 15:23:52
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Tuneable thermal expansion of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate
摘要： The linear coefficient of thermal expansion for a mixture of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonate (PEDOT:PSS) is calculated using density functional theory and the Debye-Grüneisen model. The linear coefficient of thermal expansion is a key factor in thermal management (thermal conductivity, thermal stress and thermal fatigue) of microelectronic and energy devices, being common applications of the conjugated polymeric PEDOT:PSS system. The obtained value of 53×10-6 K-1 at room temperature can be rationalised based on the electronic structure analysis. The PEDOT and PSS units are bonded by a dipole-dipole interaction between S in PEDOT and H in PSS. A C-C bond in a benzene ring (PSS) or thiophene (PEDOT) is up to 13 times stronger than the S-H bond. By adjusting the population of the S-H bonds by deprotonating PSS, the linear coefficient of thermal expansion can be enhanced by 57%. This allows for tuning the thermal properties of PEDOT:PSS in cutting-edge devices.
关键词： electronic structure,thermal properties,density functional theory,conjugated polymers
更新于2025-09-23 15:23:52
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Ab-initio study of electronic, optical, thermal, and transport properties of Cr <sub/>4</sub> AlB <sub/>6</sub>
摘要： Theoretical investigation of different physical parameters of Cr4AlB6 have been done within the framework of density functional theory. Cr4AlB6 is a no band gap material. Its Cr-3d states contributes the most at the Fermi level. Thermal properties are investigated using quasi-harmonic Debye model as implemented in Gibbs code for different values of pressure and temperature. Study of transport property suggests that its electrical conductivity increases nonlinearly with increase in temperature but the relative change in its value is very low whereas its thermal conductivity increases linearly with the increase in temperature and relative increase in thermal conductivity is very high. The behavior of Cr4AlB6 is anisotropic and property is ceramic. It has potential applications in making ceramic capacitors. Its reflectivity is high in low energy region. It suggests that material can be used as coating material for far-infrared radiation. Study of the transport property suggests that because of very high value of thermal conductivity, it can be used for heat sink applications.
关键词： optical properties,first principles,electronic properties,thermal properties,thermoelectric transport properties,structural properties
更新于2025-09-23 15:22:29
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Materials containing benzocyclobutene units with low dielectric constant and good thermostability prepared from star-shaped molecules
摘要： With the development of ultralarge-scale integrated circuits, polymers with low dielectric constant and high thermal stability have aroused great interest. We prepared two novel bridged siloxane-based benzocyclobutene (BCB) star-shaped monomers, tetrakis[dimethyl siloxy-4-(10,10-dimethyl-10-ethyl silicon)-benzocyclobutene] (TDSDES-BCB) and tetrakis(hexamethyl siloxane vinyl-benzocyclobutene) (THSV-BCB), and the corresponding resins were obtained by curing. The structures of TDSDES-BCB and THSV-BCB were confirmed by 1H-NMR, 13C-NMR, and 29Si-NMR spectra and time-of-flight mass spectrometry analysis. The curing behavior of these monomers was investigated by Fourier transform infrared spectroscopy and differential scanning calorimetry. The dielectric constant of cured TDSDES-BCB is only 2.43 at 10 MHz (that of THSV-BCB is 2.46). In addition, these resins display high thermal stability: the 5 wt % weight loss temperature of cured TDSDES-BCB is about 467 °C (454 °C for THSV-BCB resin). The excellent low dielectric property is attributable to the free volume created by the star-shaped structure and crosslinked network structure of BCB after curing.
关键词： thermosets,structure–property relationships,resins,dielectric properties,thermal properties
更新于2025-09-23 15:22:29
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Optical, thermal and gas separation properties of acetate-containing copoly(ether-imide)s based on 6FDA and fluorenyl diamines
摘要： The diamine, 9,9-bis[4-(4-amino-3-hydroxylphenoxy)phenyl]fluorene (BAHPPF) was synthesized by the modified two-step method. Then, a series of acetate-containing copoly(ether-imide)s were prepared by the copolymerization of BAHPPF, 9,9-bis(4-aminophenyl)fluorene (BAF) and 2,20-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) followed by chemical imidization. The structures and properties of the BAHPPF and copoly(ether-imide)s were characterized by nuclear magnetic resonance spectrometer (NMR), Fourier transform infrared spectrometer (FTIR), X-ray diffractometer (XRD), differential scanning calorimeter (DSC), thermogravimetric analyzer (TGA), ultraviolet-visible spectrophotometer (UV-VIS), and tensile testing. Single gas permeation performances of these copoly(ether-imide)s were also studied for five representative gases of interest including H2, O2, N2, CO2, and CH4. The experimental results showed that the copoly(ether-imide)s showed excellent optical properties with high light transmittance above 80.2% at 450 nm. The glass transition temperature of these copolymers were higher than 333°C. Their tensile strength and Young’s module also increased, and the elongation decreased with the decrease of BAHPPF. High gas permeabilities of copoly(ether-imide)s were obtained, and the ideal selectivity of CO2/CH4 was improved due to the introduction of acetate group and flexible ether linkage. These copoly(ether-imide)s could be applied to the field of optics and gas separation.
关键词： gas separation,acetate-containing,Copoly(ether-imide)s,thermal properties,light-colored and transparent
更新于2025-09-23 15:22:29