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Molecular dynamics simulation study on the structure and properties of polyimide/silica hybrid materials
摘要： A type of polyimide/silica (PI/SiO2) copolymer model was established through the dehydration of tetraethyl orthosilicate molecules (TEOS) and bonding to a silane coupling agent. The content of SiO2 was controlled by adjusting the number of molecules which bound to the TEOS. Finally, the silica was formed into a hybrid model (hybrid PI/SiO2) with a small molecule embedded in the PI. The model was optimized by geometric and molecular dynamics and the changes in the model structure, Young’s modulus, shear modulus, and glass-transition temperature (Tg) were analyzed. The results showed that the density and cohesive energy density of the composites could be improved by doping SiO2 in PI. Young’s modulus and shear modulus of PI/SiO2 hybrid materials were higher than undoped PI. The tensile strength reached 568.15 MPa when the doping content was 9%. Therefore, the structure design and content control of SiO2 was an effective way to improve the performance of a PI/SiO2 composite. The variation of Tg and tensile strength of PI/SiO2 hybrid composites is consistent with that of PI/SiO2 composite synthesized in real experiment, which will be a convenient method for new material design and performance prediction. ? 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 136, 47335.
关键词： molecular dynamics,shear modulus,Young’s modulus,polyimide/silica,glass-transition temperature
更新于2025-09-23 15:23:52
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Facile synthesis of thermal responsive fluorescent poly(imino ether sulfone): Nondestructive detection of Tg and erasable thermal imaging
摘要： A novel heat-resistant fluorescent polymer poly(imino ether sulfone) (PIES) as thermally erasable and writable imaging material has been synthesized via a facile nucleophilic substitution polycondensation reaction. Taking advantage of the tenability of the 'push-pull' π-electron mode by changing temperatures, the Tg of PIES film can be 'naked eye' nondestructively detected by taking advantage of the visual fluorescence quenching.
关键词： Nondestructive detection,Poly(imino ether sulfone),High performance polymer,Glass transition temperature
更新于2025-09-23 15:23:52
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Viscosity of chalcogenide glass-formers
摘要： Chalcogenide glass-formers are being used in a remarkable range of various optoelectronic, photonics, photoconducting, sensing and memory device applications. The knowledge of viscosity is essential for the processing of any glass-forming material, in particular for the fabrication of precise optical elements, which is the main application field of chalcogenide glasses. This work presents an extensive collection of all available viscosity data for chalcogenides, including the measurement methods. The Mauro–Yue–Ellison–Gupta–Allan (MYEGA), Arrhenius and VFT equations are used to fit the temperature dependences of viscosity. The viscosity glass transition temperatures, fragilities and apparent activation energies are calculated from these fits. Consequently, these parameters are discussed with regard to the compositional evolution of the respective chalcogenide systems.
关键词： glass transition,chalcogenide,viscous flow,fragility,Viscosity
更新于2025-09-23 15:23:52
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Influence of Sm2O3 Ion Concentration on Structural and Thermal Modification of TeO2-Na2O Glasses
摘要： The effect of Sm+3 ions concentration doped TeO2-Na2O glasses on structural and thermal parameters have been discussed. Glass samples with molar composition (80-x) TeO2-20Na2O-xSm2O3 glasses (x=0, 0.3, 0.6, 1, 1.2, 1.5) are prepared by melt quenching technique. Crystallization temperature (Tc), melting temperature (Tm) and glass transition temperature (Tg) are measured by using differential thermal analysis (DTA), it is found that the stability factor (ΔT) increases from (58.5-97.8) oC with the increasing of Sm2O3. The amorphous phase nature of the glass samples are observed by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive x-ray (EDX) spectrometer are applied to study the structural properties of the glass samples. Values of density (ρ), molar volume (VM), and ionic packing density (Vt) were calculated for each of the glass compositions. The effect of the Sm2O3 on the glass structure have been investigated by using FTIR and Raman spectroscopies, the FTIR spectra are characterized by a band of 637 cm-1 for the telluride glass, high frequency peak at 668 cm-1 presented by Raman spectra which indicates that these glasses network are basically consists of TeO4 and TeO3/TeO3+1 structural units. The spectra of Raman shows the presence of Sm-O bond, Na-O bond, Te-O-Te bridging configurations, vibrations of Te-O-Te bonds and stretching modes of non-bonding oxygen found on the TeO3/TeO3+1 structural unit.
关键词： Telluride glass,FTIR,Raman spectra,Rare Earth,Glass transition
更新于2025-09-23 15:22:29
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Assessing Physical Stability of Colloidal Dispersions Using Turbiscan Optical Analyzer
摘要： The physical stability of aqueous colloidal dispersions containing highly concentrated droplets of poorly water-soluble drugs has recently been identified as one of the main considerations in developing amorphous solid dispersions (ASDs). Turbiscan, an instrument based on multiple light scattering technology, was employed for the first time to assess colloidal dispersions with ritonavir as the model compound. The physical instability of ritonavir-rich droplets was monitored directly with and without the presence of candidate polymer additives at different drug concentrations and temperatures. The mechanism of the observed instability was confirmed to be coalescence of liquid droplets, based on the low glass transition temperature of water-saturated amorphous ritonavir determined using a newly developed experimental procedure. Temperature and solvent composition, within the range studied, have little influence on the kinetics of ritonavir coalescence. On the contrary, higher concentration of drug, i.e., more droplets per unit volume, greatly accelerates the coalescence process. In addition, polymers with varying degrees of hydrophobicity resulted in different levels of effectiveness in stabilization which is likely related to the strength of drug-polymer interactions and the corresponding differences in surface adsorption. This work demonstrates that the Turbiscan optical analyzer can be used as a rapid screening tool that provides a first-pass, high-throughput feasibility ranking of different excipients and additives to support the development of ASD formulations.
关键词： nanodroplets,coalescence,glass transition temperature,physical stability,stabilization,amorphous,ritonavir,colloidal dispersions,Turbiscan
更新于2025-09-23 15:22:29
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Modifying the thermomechanical properties of electrospun fibres of poly-vinyl cinnamate by photo-cross-linking
摘要： We explore the effects of cross-linking on some thermal and mechanical properties of polymer nanofibers of poly-vinyl cinnamate which were electro-spun from 1,2 dichloroethane. Scanning electron microscopy performed on the fibres revealed smooth fibres which were devoid of beading or ribbon-type features. When cross-linked, the Young’s moduli and glass transition temperatures of the fibres increase, owing to the formation of new covalent bonds which leads to higher overall binding energies. The glass transition temperatures increased by 20 K after 1 h of photo-polymerization while the Young’s modulus increased by 50% for the same exposure time. The glass transition temperatures as well as the heats of enthalpy indicate that a significant portion of cross-linking occurs within the first 10 min of exposure.
关键词： Photo-polymer,Young’s modulus,Enthalpy,Glass transition,Electro-spinning,Cross-linking
更新于2025-09-23 15:21:01
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The Phase Behavior in the Active Layer of Small Molecule Organic Photovoltaics: The State Diagram of p-DTS(FBTTh <sub/>2</sub> ) <sub/>2</sub> :PC <sub/>71</sub> BM
摘要： A comprehensive study was undertaken to obtain a more fundamental understanding of the phase behavior of the p-DTS(FBTTh2)2:PC71BM system, used in small molecule organic solar cells, with a strong focus on the amorphous phase and its influence on crystallinity. Three dedicated thermal protocols were used in combination with advanced thermal analysis, solid-state NMR, and wide angle X-ray diffraction. Rapid cooling, to avoid structure formation and gain insight in the amorphous phase, and slow cooling, to promote structure formation, were used as limiting cases to explain the intermediate behavior after device processing from solution. A complete state diagram was developed and the glass transition (Tg) - composition relationship was determined. In the case of slow cooling and the procedure used for device processing, the rapid crystallization of p-DTS(FBTTh2)2 leads to an enrichment of the amorphous phase in PC71BM, increasing its Tg and causing vitrification of the mixed amorphous phase before crystallization when the total amount of PC71BM exceeds 70 wt%. The common processing additive 1,8-diiodooctane (DIO) was found to lead to a lower p-DTS(FBTTh2)2 crystallinity and smaller average crystal size. More importantly, it acts as a strong plasticizer, lowering Tg significantly and thus reducing the morphological stability of the p-DTS(FBTTh2)2:PC71BM mixtures.
关键词： p-DTS(FBTTh2)2:PC71BM,glass transition temperature,wide angle X-ray diffraction,phase behavior,crystallinity,amorphous phase,small molecule organic photovoltaics,thermal analysis,solid-state NMR,1,8-diiodooctane (DIO)
更新于2025-09-23 15:19:57
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Insulating Polymers for Enhancing the Efficiency of Nonfullerene Organic Solar Cells
摘要： A series of insulating polymers are used as additives in nonfullerene organic solar cells (OSCs) for the first time. A significant relative power conversion efficiency (PCE) enhancement of up to 16% is observed with an introduction of polystyrene for only 5.0 wt% into the active layer of OSCs. Other insulating polymers possessing linear nonconjugated backbones with different side chains are also incorporated into OSCs and the resultant PCE enhancement decreases with the decrease in the side chain size. Another important issue that is noted is the glass transition temperature of the polymer additive. When the glass transition temperature is higher than the thermal annealing temperature of the active layer, the polymer additive plays a negative effect on the device performance and the device efficiency decreases monotonically with the increase in addition amount. So the effect of the insulating polymer additives in nonfullerene OSCs can be attributed to the reconstruction of the active layer films, which increases the crystallinity, carrier mobility, and carrier lifetime of the organic semiconductors in the bulk heterojunction of the devices. This work provides a guideline for the selection of polymer additives in OSCs apart from the consideration on the optoelectronic property of the additives.
关键词： nonfullerenes,insulating polymers,organic solar cells,additives,glass transition temperatures
更新于2025-09-23 15:19:57
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Investigations of physical parameters of Ge doped binary Se-As chalcogenide glassy alloys for optical fiber application
摘要： Germanium doped chalcogenide glasses have potential applications in non- linear and optoelectronic devices. Ternary Ge-Se-As system has been considered to study the different important physical parameters. The impact of deviation of Ge on the cost of As in Ge-Se-As glassy system has been discussed in terms of average coordination number, cohesive energy, heat of atomization, and the theoretical optical band gap of the system. Almost all the physical parameters are found to change linearly with the variation in Ge content. The physical properties approximated in the present study can reveal the structural details for optical fibers.
关键词： Chalcogenide glasses,cohesive energy,mean bond energy,glass transition temperature,lone pair electrons
更新于2025-09-16 10:30:52
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Dynamical processes related to viscous flow in a supercooled arsenic selenide glass-forming liquid: Results from high-temperature 77Se NMR spectroscopy
摘要： Dynamical processes in supercooled AsSe9 liquid are studied using 1D and 2D 77Se NMR spectroscopic techniques. The results demonstrate the coexistence of two distinct dynamical processes: one is a slow process related to the chemical exchange between the various Se environments by bond scission/renewal and the other is the fast Se chain segmental motion, which leads to the rapid averaging of the chemical shift anisotropy. The timescales of these two processes become increasingly similar as the glass transition is approached from above. The slow process is found to be closely coupled to viscosity over the entire temperature range of investigation and its activation energy is consistent with the Se-Se/As bond energies. On the other hand, the activation energy of the fast process is significantly higher, which may be indicative of its cooperative nature. This process becomes coupled to viscosity only in the immediate vicinity of the glass transition.
关键词： Supercooled liquid,Relaxation,Chalcogenide,Viscous flow,Glass transition,NMR spectroscopy
更新于2025-09-11 14:15:04