Machine learning(ML)has emerged as a powerful tool for predicting polymer properties,including glass transition temperature(Tg),which is a critical factor influencing polymer applications.In this study,a dataset of po...Machine learning(ML)has emerged as a powerful tool for predicting polymer properties,including glass transition temperature(Tg),which is a critical factor influencing polymer applications.In this study,a dataset of polymer structures and their Tg values were created and represented as adjacency matrices based on molecular graph theory.Four key structural descriptors,flexibility,side chain occupancy length,polarity,and hydrogen bonding capacity,were extracted and used as inputs for ML models:Extra Trees(ET),Random Forest(RF),Gaussian Process Regression(GPR),and Gradient Boosting(GB).Among these,ET and GPR achieved the highest predictive performance,with R2 values of 0.97,and mean absolute errors(MAE)of approximately 7–7.5 K.The use of these extracted features significantly improved the prediction accuracy compared to previous studies.Feature importance analysis revealed that flexibility had the strongest influence on Tg,followed by side-chain occupancy length,hydrogen bonding,and polarity.This work demonstrates the potential of data-driven approaches in polymer science,providing a fast and reliable method for Tg prediction that does not require experimental inputs.展开更多
Purpose:This study investigates the physics of annual fractional citation growth and its impact on journal bibliographic metrics,focusing on the interplay between journal publication growth and citation dynamics.Desig...Purpose:This study investigates the physics of annual fractional citation growth and its impact on journal bibliographic metrics,focusing on the interplay between journal publication growth and citation dynamics.Design/methodology/approach:We analyze bibliometric data from three prominent fluids journals-Physics of Fluids,Journal of Fluid Mechanics,and Physical Review Fluids-over the period 1999-2023.The analysis examines the relations among annual fractional journal publication growth,citation growth,and bibliographic metric suppressions.Findings:Our findings reveal that the suppression of impact factor growth is significantly influenced by annual fractional journal publication growth rather than citation growth.All three journals exhibit similar responses to publication growth with minimal scatter,following a consistent functional relation.We also identify narrow,nearly Gaussian distributions for annual fractional journal publication growth.Furthermore,we introduce a new growth-independent dimensionless bibliometric metric,journal urgency,the ratio of annual fractional citation growth to the 4-year running average immediacy index.This metric captures effectively the dependency of citation growth on urgency and reveals consistent distributions across the journals analyzed.Research limitations:The study is limited to three major fluids journals and to the availability of bibliometric data from 1999 to 2023.Future work could extend the analysis to other disciplines and journals.Practical implications:Understanding the relation between publication growth and bibliometric suppressions can inform editorial and strategic decisions in journal management.The proposed journal urgency metric offers a novel tool for assessing and comparing journal performance independent of growth rates.Originality/value:This study introduces a new bibliometric metric-journal urgency-that provides fresh insights into citation dynamics and bibliographic metric behavior.It highlights the critical role of publication growth in shaping journal impact factors and CiteScores,offering a unified framework applicable across multiple journals.展开更多
Two novel heterogeneous nickel a-diimine based polymerization catalysts, containing MWCNT as the main ligand, were synthesized by novel in situ catalyst preparation technique. The in situ synthesis was performed by co...Two novel heterogeneous nickel a-diimine based polymerization catalysts, containing MWCNT as the main ligand, were synthesized by novel in situ catalyst preparation technique. The in situ synthesis was performed by covalent attachment of the acenaphthenic ligand core to amine functionalized MWCNT ligand arms through diimine bonding and further nickel dibromide chelation. The prepared catalysts were fully characterized and their structures and supporting efficiencies were determined. Single or double introduction of the MWCNTs through their ends or sidewall（s） in the catalytic system, as a ligand, influenced the catalytic performance, microstructure and morphology of obtained polyethylenes. MWCNT sidewall bonding to para-aryl position of the tetramethylphenyl moiety performed as more electron-donating ligand than MWCNT ends linked to the imine bond and protected the catalytic system to retain its activity. This character resulted in the maintenance of the resulting polymer topology at elevated temperatures so that the catalytic activity and the obtained polymer melting points remained around 110 g PE·mmol^-1 Ni·h^-1 and 123 ℃ in all polymerization temperatures respectively. In polymerization trials, molecular weight fall against temperature was not as sharp as what had been observed in sequentially prepared catalysts insofar as the molecular weight of resultant polymer at 60 ℃ reached to 310000 g·mol^-1 which was close to the highest value had been reported at 30 ℃ for sequentially prepared catalysts. TEM observations showed the presence of the stopped-growth polymer chains due to geometrical constrains or ligand debonding for both catalytic systems.展开更多
Ethylene polymerization was carried out by immobilization of rac-ethylenebis（1-indenyl）zirconium dichloride （Et（Ind）2ZrCl2） and rac-dimethylsilylbis（1-indenyl）zirconium dichloride （Me2Si（Ind）2ZrCl2） preact...Ethylene polymerization was carried out by immobilization of rac-ethylenebis（1-indenyl）zirconium dichloride （Et（Ind）2ZrCl2） and rac-dimethylsilylbis（1-indenyl）zirconium dichloride （Me2Si（Ind）2ZrCl2） preactivated with methylaluminoxane （MAO） on calcinated silica at different temperatures. Polymerizations of ethylene were conducted at different temperatures to find the optimized polymerization temperature for maximum activity of the catalyst. The Me2Si bridge catalyst showed higher activity at the lower polymerization temperature compared to the Et bridge catalyst. The highest catalytic activities were obtained at temperatures about 50 ~C and 70 ~C for Me2Si（Ind）2ZrC1JMAO and Et（Ind）zZrCI2/MAO catalysts systems, respectively. Inductively coupled plasma-atomic emission spectroscopy results and polymerization activity results confirmed that the best temperature for calcinating silica was about 450 ℃ for both catalysts systems. The melting points of the produced polyethylene were about 130 ℃, which could be attributed to the linear structure of HDPE.展开更多
The penta-ether compound was synthesized by the reaction of di（trimethylolpropane） with sodium hydride as the strong base and methyl iodide as the alkyl halide. This compound was characterized by NMR, FTIR, and GC t...The penta-ether compound was synthesized by the reaction of di（trimethylolpropane） with sodium hydride as the strong base and methyl iodide as the alkyl halide. This compound was characterized by NMR, FTIR, and GC techniques. The MgCl_2-supported titanium catalysts were incorporated with varying amounts of penta-ether compound as the internal donor and also the catalysts without the internal donor were synthesized. The synthesized catalysts and the conventional ZieglerNatta catalyst were characterized. The titanium contents were determined by spectrophotometry, magnesium by complexometric titration and chloride by argentometric titration. The effects of the new internal donor on propylene polymerization with the prepared MgCl_2-supported Ziegler-Natta catalysts were investigated and then these results were compared to the results obtained using the conventional diisobutyl phthalate-besed-Ziegler-Natta catalyst. The highest crystallinity degree, melting temperature, and isotacticity of polypropylene were obtained using the catalyst with a pentaether/Mg molar ratio equal to 0.21.展开更多
In this study, we report narrow-size distribution Zn_2SnO_4（ZSO） nanoparticles, which are produced by low-temperature solution-processed used as the electron extraction layer（EEL） in the inverted polymer solar ce...In this study, we report narrow-size distribution Zn_2SnO_4（ZSO） nanoparticles, which are produced by low-temperature solution-processed used as the electron extraction layer（EEL） in the inverted polymer solar cells（i-PSCs）. Moreover, poly[（9,9-bis（30-（N,N-dimethylamino）propyl）-2,7-fluorene）-alt-2,7-（9,9-dioctylfluorene）]（PFN） is used to modify the surface properties of ZSO thin film. By using the ZSO NPs/PFN as the EEL, the i-PSCs fabricated by poly[4,8-bis（2-ethylhexyloxyl）benzo[1,2-b：4,5-b0] dithio-phene-2,6-diyl-altethylhexyl-3-fluorothithieno [3,4-b]thiophene-2-carboxylate-4,6-diyl]（PTB7） blended with（6,6）-phenyl-C_（71）-butyric acid methylester（PC_（71）BM） bulk heterojunction（BHJ） composite, exhibits a power conversion efficiency（PCE） of 8.44%, which is nearly 10% enhancement as compared with that of7.75% observed from the i-PSCs by PTB7：PC_（71）BM BHJ composite using the ZnO/PFN EEL. The enhanced PCE is originated from improved interfacial contact between the EEL with BHJ active layer and good energy level alignment between BHJ active layer and the EEL. Our results indicate that we provide a simple way to boost efficiency of i-PSCs.展开更多
Poly(methyl methacrylate)/poly(methacrylamide) copolymer (PMMA-co-PMAA) was synthesized by a free radical copolymerization of MMA and MAA monomers in methylethyl ketone using AIBN as radical initiator. Multi-wall carb...Poly(methyl methacrylate)/poly(methacrylamide) copolymer (PMMA-co-PMAA) was synthesized by a free radical copolymerization of MMA and MAA monomers in methylethyl ketone using AIBN as radical initiator. Multi-wall carbon nanotubes (MWCNT) were oxidized in KMnO4 acidic suspension. Carboxyl groups on the surface oxidized MWCNT were reacted with primary amide group of PMMA-co-PMAA copolymer in MEK solution under ultrasound to form polymer brush on the surface of MWCNT. With the help of TG analyses the amount of covalently grafted PMMA-co-PMAA copolymer onto MWCNT surface was determined as ?47 wt%. TEM analyses identified thin co-polymer layer adhered onto MWCNT surface with average thickness ?5 nm.展开更多
We developed flame retarded polyimine type vitrimers and carbon fibre reinforced composites using two additive and a reactive flame retardant containing phosphorus:ammonium polyphosphate(APP),resorcinol bis(diphenyl p...We developed flame retarded polyimine type vitrimers and carbon fibre reinforced composites using two additive and a reactive flame retardant containing phosphorus:ammonium polyphosphate(APP),resorcinol bis(diphenyl phosphate)(RDP);and N,N’,N’’-tris(2-aminoethyl)-phosphoric acid triamide(TEDAP).We characterised the vitrimer matrix materials by differential scanning calorimetry(DSC),thermal analysis(TGA),limiting oxygen index(LOI),UL-94 test and mass loss calorimetry(MLC),while the vitrimer composites by LOI,UL-94 test,MLC and dynamic mechanical analysis(DMA).We compared the performance of the vitrimer systems to a benchmark pentaerythritol-based aliphatic epoxy resin system(PER).The vitrimer reference had higher thermal stability but lower fire performance than the PER aliphatic reference epoxy.At lower phosphorus content,the vitrimer systems exhibited a melting above their vitrimer transition temperature,which negatively affected their LOI and UL-94 results.From 2%phosphorus content,rapid charring and extinguishing of vitrimers prevented the softening and deforming.The superior performance of these same flame retardants in vitrimer systems could be attributed to the high nitrogen content of imine-based vitrimers in combination with phosphorus flame retardants,exploiting nitrogen-phosphorus synergism.In both matrices,flame retardants with solid phase action lead to better fire performance,while in composites,the lowest peak heat release rates(152 kW/m2 in vitrimer composite)were achieved with RDP acting predominantly in the gas phase,as carbon fibres hindered the intumescent phenomenon.展开更多
The effect of carbon black(CB),carbon nanotube(CNT),and graphene(G)on foaming,electrical conductivity(EC),and electromagnetic interference(EMI)shielding of polystyrene(PS)foam that has been produced via microwave heat...The effect of carbon black(CB),carbon nanotube(CNT),and graphene(G)on foaming,electrical conductivity(EC),and electromagnetic interference(EMI)shielding of polystyrene(PS)foam that has been produced via microwave heating operation and supercritical carbon dioxide(CO_(2))was studied.Foams containing 1 wt%,CNT,and G reached over 90%porosity after 30 s and 3 min radiation time,respectively;however,PS/CB foam did not expand properly even after 3.5 min.In addition,the expansion ratio of PS/CB and PS/G was one-sixth and one-half of PS/CNT,respectively-due to the great CNT’s ability to convert microwave radiation to heat.EC of solid and porous nanocomposites has been increased via raising filler content;however,PS/CNT displayed the highest value at the same volume fractions.This ascending trend could not endure during foaming,so a remarkable optimum-point has been observed for nanocomposite foams.Eventually,EMI-shielding properties of solid and foam nanocomposites were discussed.展开更多
The growing environmental awareness,the search for alternatives to fossil resources,and the goal of achieving a circular economy have all contributed to the increasing valorization of biowaste to produce bio-based pol...The growing environmental awareness,the search for alternatives to fossil resources,and the goal of achieving a circular economy have all contributed to the increasing valorization of biowaste to produce bio-based polymers and other high-value products.Among the various biowaste materials,lignin has gained significant attention due to its high aromatic carbon content,low cost,and abundance.Lignin is predominantly sourced as a byproduct from the paper industry,available in large quantities from hardwood and softwood,with variations in chemical structure and susceptibility to hydrolysis.This study focuses on softwood lignin obtained through the LignoForce^(TM) technology,comparing the thermal and chemical characteristics,and stability,of a recently produced batch with that of a batch that has been stored for four years.Additionally,the development of lignin-based thermoplastic polymer mixtures using Polyethylene Terephthalate Glycol(PET-G)and a blend of Polycarbonate and Acrylonitrile-Butadiene-Styrene(PC/ABS)with high lignin content(50–60 wt%)is explored,as well as the production of filaments for carbon fiber production.For this purpose,following melt mixing,the lignin-based mixtures were spun into filaments,which were subsequently subjected to thermal stabilization in an oxidative atmosphere.The lignin phase was well distributed in the PET-Gmatrix and the twomaterials presented a good interface,which further improved after thermal treatment under an oxidative atmosphere.After thermal treatment an increase in tensile modulus,tensile strength,and elongation at break of approximately 160%,200%,and 100%,respectively,was observed,confirming the good interface established,and consistent with structural changes such as cross-linking.Conversely,the PC/ABS blend did not form a good interface with the lignin domains after melt mixing.Although the interactions improved after thermal treatment,the tensile strength and elongation at break decreased by approximately 30%,while themodulus increased by approximately 20%.Overall,the good processability of the lignin/polymer mixtures into filaments,and their physical,chemical,and mechanical characterization before and after thermal oxidation are good indicators of the potential as precursors for carbon fiber production.展开更多
An oil-based drilling fluid should be stable and tolerant to high temperatures for use in deep drilling. An invert emulsion of water in oil is a good choice as an oil- based drilling fluid which is a mixture of a soli...An oil-based drilling fluid should be stable and tolerant to high temperatures for use in deep drilling. An invert emulsion of water in oil is a good choice as an oil- based drilling fluid which is a mixture of a solid phase and two immiscible liquid phases stabilized by a polymeric surfactant. In deep drilling, due to high temperatures, the polymeric surfactant degrades and a phase separation occurs. Here, octadecyltrimethoxysilane-modified silica nanoparticles were used to form a stable invert emulsion of water in oil for the drilling fluid model which resulted in a milky fluid with the formation of 60 gm water droplets. In addition, rheological study showed that using hydrophobic silica nanoparticles resulted in a stable water in oil invert emulsion with desired properties for a drilling fluid that can be modified by adjusting the nanoparticle nature and content. Aging experiments at 120 ℃ indicated that they also have good stability at high temperatures for challenging drilling operations.展开更多
To improve creep resistance of directional polytetrafluoroethylene （PTFE） films, epoxy grafted nano-SiO2 is mixed with PTFE powder before sintering and calender rolling. The aligned macromolecular chains （especiall...To improve creep resistance of directional polytetrafluoroethylene （PTFE） films, epoxy grafted nano-SiO2 is mixed with PTFE powder before sintering and calender rolling. The aligned macromolecular chains （especially those in amorphous region） of the composite films can be bundled up by the nanoparticles to share the applied stress together. In addition, incorporation of silica nanoparticles increases crystallinity of PTFE and favors microfibrillation of PTFE in the course of large deformation. As result, PTFE films exhibit lower creep strain and creep rate, and higher tensile strength and hardness. The work is believed to open an avenue for manufacturing high performance fluoropolymers by nano-inclusions.展开更多
In this investigation,the structural and electrical properties of nanocomposites of polyaniline(PANI) and cobalt ferrite synthesized by hydrothermal route are reported for the first time(with weight ratios of CoFe_2O_...In this investigation,the structural and electrical properties of nanocomposites of polyaniline(PANI) and cobalt ferrite synthesized by hydrothermal route are reported for the first time(with weight ratios of CoFe_2O_4/PANI 1:2 and 2:1).Synthesized nanomaterials have been characterized by XRD,FT-IR,SEM and TEM techniques.FT-IR results confirm the presence of CoFe_2O_4 and PANI in the samples.Their detailed conductivity measurements have been investigated.It has been found that PANI has a more effective conducting mechanism in CoFe_2O_4-PANI composites.These results are also consistent with the change in AC conductivity orders in composites.展开更多
The spatial arrangement of the cell is important and considered as underlying mechanism for mathematical modeling of cell to cell interaction.The ability of cells to take on the characteristics of other cells in an or...The spatial arrangement of the cell is important and considered as underlying mechanism for mathematical modeling of cell to cell interaction.The ability of cells to take on the characteristics of other cells in an organism,it is important to understand the dynamical behavior of the cells.This method implements experimental parameters of the cell-cell interaction into the mathematical simulation of cell arrangement.The purpose of this research was to explore the three-dimensional spatial distribution of anterior horn cells in the rat spinal cord to examine differences after sciatic nerve injury.Sixteen Sprague-Dawley male rats were assigned to control and axotomy groups.Twelve weeks after surgery,the anterior horn was removed for first-and second-order stereological studies.Second-order stereological techniques were applied to estimate the pair correlation and cross-correlation functions using a dipole probe superimposed onto the spinal cord sections.The findings revealed 7% and 36% reductions in the mean volume and total number of motoneurons,respectively,and a25% increase in the neuroglial cell number in the axotomized rats compared to the control rats.In contrast,the anterior horn volume remained unchanged.The results also indicated a broader gap in the pair correlation curve for the motoneurons and neuroglial cells in the axotomized rats compared to the control rats.This finding shows a negative correlation for the distribution of motoneurons and neuroglial cells in the axotomized rats.The cross-correlation curve shows a negative correlation between the motoneurons and neuroglial cells in the axotomized rats.These findings suggest that cellular structural and functional changes after sciatic nerve injury lead to the alterations in the spatial arrangement of motoneurons and neuroglial cells,finally affecting the normal function of the central nervous system.The experimental protocol was reviewed and approved by the Animal Ethics Committee of Shahid Beheshti University of Medical Sciences(approval No.IR.SBMU.MSP.REC1395.375) on October 17,2016.展开更多
The application of natural fibers as reinforcement in composite material has increased due to environmental concerns,low cost,degradability and health concerns.The purpose of this study is to identify the best type of...The application of natural fibers as reinforcement in composite material has increased due to environmental concerns,low cost,degradability and health concerns.The purpose of this study is to identify the best type of bamboo fibers to be used as reinforcement for kenaf(K)/bamboo hybrid composite.There were three types of bamboo fibers evaluated in this study which include bamboo mat(B),bamboo fabric(BF)and bamboo powder(BP).Chemical composition of B,BF,BP and K fibers were analyzed in this study.The effect of different types of bamboo fibers on tensile,impact,and morphological properties were investigated.The B/epoxy composites displayed the highest tensile strength(53.03 MPa)while K/epoxy composite had the highest tensile modulus(4.71 GPa).Scanning electron micrographs of B/epoxy composites displayed better fiber/matrix interfacial bonding in comparison to other studied composites.Results showed that impact strength of BF-based composite was highest(45.70 J/m).In conclusion,the tensile strength of B/epoxy composite is superior to the other bamboo reinforced composites and will be further evaluated in the next study.展开更多
The multi-walled carbon nanotube was introduced into the polymer matrix (PANI) to improve the electric conductivity as well as mechanical properties of the original polymer matrix.PANI/multi-walled carbon nanotube (MW...The multi-walled carbon nanotube was introduced into the polymer matrix (PANI) to improve the electric conductivity as well as mechanical properties of the original polymer matrix.PANI/multi-walled carbon nanotube (MWCNT) composites were synthesized via ex-situ and in-situ polymerization to improve their electrical property.And the DC conductivities of PANI/MWCNT according to content and diameter of MWCNT were measured by four-point probe.The highest electric conductivity of PANI/MWCNT composite is 20 S/cm when 0.3% (mass fraction) MWCNTs with 10 nm in diameter and 15 μm in length are added in composite.展开更多
Graphene oxide was prepared by ultrasonication of completely oxidized graphite and used to improve the flame retardancy of epoxy. The epoxy/graphene oxide nanocomposite was studied in terms of exfoliation/dispersion, ...Graphene oxide was prepared by ultrasonication of completely oxidized graphite and used to improve the flame retardancy of epoxy. The epoxy/graphene oxide nanocomposite was studied in terms of exfoliation/dispersion, thermal stability and flame retardancy. X-ray diffraction and transmission electron microscopy confirmed the exfoliation of the graphene oxide nanosheets in epoxy matrix. Cone calorimeter measurements showed that the time to ignition of the epoxy/graphene oxide nanocomposite was longer than that of neat epoxy. The heat release rate curve of the nanocomposite was broadened compared to that of neat epoxy and the peak heat release rate decreased as well.展开更多
Simultaneous functionalization and reduction of graphene oxide （GO） is realized by refluxing of GO suspension with polyetheramine （D2000） followed by thermal treatment at 120℃. Compared to GO, the D2000-treated ...Simultaneous functionalization and reduction of graphene oxide （GO） is realized by refluxing of GO suspension with polyetheramine （D2000） followed by thermal treatment at 120℃. Compared to GO, the D2000-treated GO （GO- D2000） becomes hydrophobic, thermally stable and highly conductive with an electrical conductivity of 11 S/m, which is almost 8 orders of magnitude higher than that of GO. Due to the high conductivity and improved dispersion of GO-D2000, its epoxy nanocomposites exhibit a sharp transition from electrically insulating to conducting with a low percolation threshold of 0.71 vol%. With 3.6 wt% GO-D2000, the glass transition temperature of the epoxy nanocomposite is 27 K higher than that of neat epoxy.展开更多
文摘Machine learning(ML)has emerged as a powerful tool for predicting polymer properties,including glass transition temperature(Tg),which is a critical factor influencing polymer applications.In this study,a dataset of polymer structures and their Tg values were created and represented as adjacency matrices based on molecular graph theory.Four key structural descriptors,flexibility,side chain occupancy length,polarity,and hydrogen bonding capacity,were extracted and used as inputs for ML models:Extra Trees(ET),Random Forest(RF),Gaussian Process Regression(GPR),and Gradient Boosting(GB).Among these,ET and GPR achieved the highest predictive performance,with R2 values of 0.97,and mean absolute errors(MAE)of approximately 7–7.5 K.The use of these extracted features significantly improved the prediction accuracy compared to previous studies.Feature importance analysis revealed that flexibility had the strongest influence on Tg,followed by side-chain occupancy length,hydrogen bonding,and polarity.This work demonstrates the potential of data-driven approaches in polymer science,providing a fast and reliable method for Tg prediction that does not require experimental inputs.
文摘Purpose:This study investigates the physics of annual fractional citation growth and its impact on journal bibliographic metrics,focusing on the interplay between journal publication growth and citation dynamics.Design/methodology/approach:We analyze bibliometric data from three prominent fluids journals-Physics of Fluids,Journal of Fluid Mechanics,and Physical Review Fluids-over the period 1999-2023.The analysis examines the relations among annual fractional journal publication growth,citation growth,and bibliographic metric suppressions.Findings:Our findings reveal that the suppression of impact factor growth is significantly influenced by annual fractional journal publication growth rather than citation growth.All three journals exhibit similar responses to publication growth with minimal scatter,following a consistent functional relation.We also identify narrow,nearly Gaussian distributions for annual fractional journal publication growth.Furthermore,we introduce a new growth-independent dimensionless bibliometric metric,journal urgency,the ratio of annual fractional citation growth to the 4-year running average immediacy index.This metric captures effectively the dependency of citation growth on urgency and reveals consistent distributions across the journals analyzed.Research limitations:The study is limited to three major fluids journals and to the availability of bibliometric data from 1999 to 2023.Future work could extend the analysis to other disciplines and journals.Practical implications:Understanding the relation between publication growth and bibliometric suppressions can inform editorial and strategic decisions in journal management.The proposed journal urgency metric offers a novel tool for assessing and comparing journal performance independent of growth rates.Originality/value:This study introduces a new bibliometric metric-journal urgency-that provides fresh insights into citation dynamics and bibliographic metric behavior.It highlights the critical role of publication growth in shaping journal impact factors and CiteScores,offering a unified framework applicable across multiple journals.
文摘Two novel heterogeneous nickel a-diimine based polymerization catalysts, containing MWCNT as the main ligand, were synthesized by novel in situ catalyst preparation technique. The in situ synthesis was performed by covalent attachment of the acenaphthenic ligand core to amine functionalized MWCNT ligand arms through diimine bonding and further nickel dibromide chelation. The prepared catalysts were fully characterized and their structures and supporting efficiencies were determined. Single or double introduction of the MWCNTs through their ends or sidewall（s） in the catalytic system, as a ligand, influenced the catalytic performance, microstructure and morphology of obtained polyethylenes. MWCNT sidewall bonding to para-aryl position of the tetramethylphenyl moiety performed as more electron-donating ligand than MWCNT ends linked to the imine bond and protected the catalytic system to retain its activity. This character resulted in the maintenance of the resulting polymer topology at elevated temperatures so that the catalytic activity and the obtained polymer melting points remained around 110 g PE·mmol^-1 Ni·h^-1 and 123 ℃ in all polymerization temperatures respectively. In polymerization trials, molecular weight fall against temperature was not as sharp as what had been observed in sequentially prepared catalysts insofar as the molecular weight of resultant polymer at 60 ℃ reached to 310000 g·mol^-1 which was close to the highest value had been reported at 30 ℃ for sequentially prepared catalysts. TEM observations showed the presence of the stopped-growth polymer chains due to geometrical constrains or ligand debonding for both catalytic systems.
基金financially supported by the National Iranian Petrochemical Company Research and Technology(NIPC-RT)
文摘Ethylene polymerization was carried out by immobilization of rac-ethylenebis（1-indenyl）zirconium dichloride （Et（Ind）2ZrCl2） and rac-dimethylsilylbis（1-indenyl）zirconium dichloride （Me2Si（Ind）2ZrCl2） preactivated with methylaluminoxane （MAO） on calcinated silica at different temperatures. Polymerizations of ethylene were conducted at different temperatures to find the optimized polymerization temperature for maximum activity of the catalyst. The Me2Si bridge catalyst showed higher activity at the lower polymerization temperature compared to the Et bridge catalyst. The highest catalytic activities were obtained at temperatures about 50 ~C and 70 ~C for Me2Si（Ind）2ZrC1JMAO and Et（Ind）zZrCI2/MAO catalysts systems, respectively. Inductively coupled plasma-atomic emission spectroscopy results and polymerization activity results confirmed that the best temperature for calcinating silica was about 450 ℃ for both catalysts systems. The melting points of the produced polyethylene were about 130 ℃, which could be attributed to the linear structure of HDPE.
基金financially supported by the Marun Petrochemical Co.,Mahshahr,Iran
文摘The penta-ether compound was synthesized by the reaction of di（trimethylolpropane） with sodium hydride as the strong base and methyl iodide as the alkyl halide. This compound was characterized by NMR, FTIR, and GC techniques. The MgCl_2-supported titanium catalysts were incorporated with varying amounts of penta-ether compound as the internal donor and also the catalysts without the internal donor were synthesized. The synthesized catalysts and the conventional ZieglerNatta catalyst were characterized. The titanium contents were determined by spectrophotometry, magnesium by complexometric titration and chloride by argentometric titration. The effects of the new internal donor on propylene polymerization with the prepared MgCl_2-supported Ziegler-Natta catalysts were investigated and then these results were compared to the results obtained using the conventional diisobutyl phthalate-besed-Ziegler-Natta catalyst. The highest crystallinity degree, melting temperature, and isotacticity of polypropylene were obtained using the catalyst with a pentaether/Mg molar ratio equal to 0.21.
基金supported by National Natural Science Foundation of China (No. 51329301)
文摘In this study, we report narrow-size distribution Zn_2SnO_4（ZSO） nanoparticles, which are produced by low-temperature solution-processed used as the electron extraction layer（EEL） in the inverted polymer solar cells（i-PSCs）. Moreover, poly[（9,9-bis（30-（N,N-dimethylamino）propyl）-2,7-fluorene）-alt-2,7-（9,9-dioctylfluorene）]（PFN） is used to modify the surface properties of ZSO thin film. By using the ZSO NPs/PFN as the EEL, the i-PSCs fabricated by poly[4,8-bis（2-ethylhexyloxyl）benzo[1,2-b：4,5-b0] dithio-phene-2,6-diyl-altethylhexyl-3-fluorothithieno [3,4-b]thiophene-2-carboxylate-4,6-diyl]（PTB7） blended with（6,6）-phenyl-C_（71）-butyric acid methylester（PC_（71）BM） bulk heterojunction（BHJ） composite, exhibits a power conversion efficiency（PCE） of 8.44%, which is nearly 10% enhancement as compared with that of7.75% observed from the i-PSCs by PTB7：PC_（71）BM BHJ composite using the ZnO/PFN EEL. The enhanced PCE is originated from improved interfacial contact between the EEL with BHJ active layer and good energy level alignment between BHJ active layer and the EEL. Our results indicate that we provide a simple way to boost efficiency of i-PSCs.
文摘Poly(methyl methacrylate)/poly(methacrylamide) copolymer (PMMA-co-PMAA) was synthesized by a free radical copolymerization of MMA and MAA monomers in methylethyl ketone using AIBN as radical initiator. Multi-wall carbon nanotubes (MWCNT) were oxidized in KMnO4 acidic suspension. Carboxyl groups on the surface oxidized MWCNT were reacted with primary amide group of PMMA-co-PMAA copolymer in MEK solution under ultrasound to form polymer brush on the surface of MWCNT. With the help of TG analyses the amount of covalently grafted PMMA-co-PMAA copolymer onto MWCNT surface was determined as ?47 wt%. TEM analyses identified thin co-polymer layer adhered onto MWCNT surface with average thickness ?5 nm.
基金Project no.TKP-6-6/PALY-2021 has been implemented with the support provided by the Ministry of CultureInnovation of Hungary from the National Research,Development and Innovation Fund,financed under the TKP2021-NVA funding scheme+4 种基金funded by the National Research,Development and In-novation Office(NKFIH K142517)This research has been imple-mented with the support of the 2021-1.2.4-TÉT-2021-00050,which encourages scientific and technological cooperation between USA and HungarySupport from theÚNKP-23-3-II-BME-227,ÚNKP-23-5-BME-409 andÚNKP-23-5-BME-417 New National Excellence Pro-gram of the Ministry for Culture and Innovation from the source of the National Research,Development and Innovation Fund is acknowledgedsupported by the János Bolyai Research Scholarship of the Hungarian Academy of Sci-ences No.BO/00508/22/6 and No BO/00980/23/7support of Bertalan Papp in preparation works.
文摘We developed flame retarded polyimine type vitrimers and carbon fibre reinforced composites using two additive and a reactive flame retardant containing phosphorus:ammonium polyphosphate(APP),resorcinol bis(diphenyl phosphate)(RDP);and N,N’,N’’-tris(2-aminoethyl)-phosphoric acid triamide(TEDAP).We characterised the vitrimer matrix materials by differential scanning calorimetry(DSC),thermal analysis(TGA),limiting oxygen index(LOI),UL-94 test and mass loss calorimetry(MLC),while the vitrimer composites by LOI,UL-94 test,MLC and dynamic mechanical analysis(DMA).We compared the performance of the vitrimer systems to a benchmark pentaerythritol-based aliphatic epoxy resin system(PER).The vitrimer reference had higher thermal stability but lower fire performance than the PER aliphatic reference epoxy.At lower phosphorus content,the vitrimer systems exhibited a melting above their vitrimer transition temperature,which negatively affected their LOI and UL-94 results.From 2%phosphorus content,rapid charring and extinguishing of vitrimers prevented the softening and deforming.The superior performance of these same flame retardants in vitrimer systems could be attributed to the high nitrogen content of imine-based vitrimers in combination with phosphorus flame retardants,exploiting nitrogen-phosphorus synergism.In both matrices,flame retardants with solid phase action lead to better fire performance,while in composites,the lowest peak heat release rates(152 kW/m2 in vitrimer composite)were achieved with RDP acting predominantly in the gas phase,as carbon fibres hindered the intumescent phenomenon.
基金financially supported by the National Natural Science Foundation of China(Grant No.51703083).
文摘The effect of carbon black(CB),carbon nanotube(CNT),and graphene(G)on foaming,electrical conductivity(EC),and electromagnetic interference(EMI)shielding of polystyrene(PS)foam that has been produced via microwave heating operation and supercritical carbon dioxide(CO_(2))was studied.Foams containing 1 wt%,CNT,and G reached over 90%porosity after 30 s and 3 min radiation time,respectively;however,PS/CB foam did not expand properly even after 3.5 min.In addition,the expansion ratio of PS/CB and PS/G was one-sixth and one-half of PS/CNT,respectively-due to the great CNT’s ability to convert microwave radiation to heat.EC of solid and porous nanocomposites has been increased via raising filler content;however,PS/CNT displayed the highest value at the same volume fractions.This ascending trend could not endure during foaming,so a remarkable optimum-point has been observed for nanocomposite foams.Eventually,EMI-shielding properties of solid and foam nanocomposites were discussed.
基金funded by Project Better Plastics—Plastics in a Circular Economy—PPS4(Circularity by Alternative Feedstocks)Grant agreement ID:POCI-01-0247-FEDER-046091RR was funded by FCT through the PhD grant with reference UI/BD/154446/2022.
文摘The growing environmental awareness,the search for alternatives to fossil resources,and the goal of achieving a circular economy have all contributed to the increasing valorization of biowaste to produce bio-based polymers and other high-value products.Among the various biowaste materials,lignin has gained significant attention due to its high aromatic carbon content,low cost,and abundance.Lignin is predominantly sourced as a byproduct from the paper industry,available in large quantities from hardwood and softwood,with variations in chemical structure and susceptibility to hydrolysis.This study focuses on softwood lignin obtained through the LignoForce^(TM) technology,comparing the thermal and chemical characteristics,and stability,of a recently produced batch with that of a batch that has been stored for four years.Additionally,the development of lignin-based thermoplastic polymer mixtures using Polyethylene Terephthalate Glycol(PET-G)and a blend of Polycarbonate and Acrylonitrile-Butadiene-Styrene(PC/ABS)with high lignin content(50–60 wt%)is explored,as well as the production of filaments for carbon fiber production.For this purpose,following melt mixing,the lignin-based mixtures were spun into filaments,which were subsequently subjected to thermal stabilization in an oxidative atmosphere.The lignin phase was well distributed in the PET-Gmatrix and the twomaterials presented a good interface,which further improved after thermal treatment under an oxidative atmosphere.After thermal treatment an increase in tensile modulus,tensile strength,and elongation at break of approximately 160%,200%,and 100%,respectively,was observed,confirming the good interface established,and consistent with structural changes such as cross-linking.Conversely,the PC/ABS blend did not form a good interface with the lignin domains after melt mixing.Although the interactions improved after thermal treatment,the tensile strength and elongation at break decreased by approximately 30%,while themodulus increased by approximately 20%.Overall,the good processability of the lignin/polymer mixtures into filaments,and their physical,chemical,and mechanical characterization before and after thermal oxidation are good indicators of the potential as precursors for carbon fiber production.
文摘An oil-based drilling fluid should be stable and tolerant to high temperatures for use in deep drilling. An invert emulsion of water in oil is a good choice as an oil- based drilling fluid which is a mixture of a solid phase and two immiscible liquid phases stabilized by a polymeric surfactant. In deep drilling, due to high temperatures, the polymeric surfactant degrades and a phase separation occurs. Here, octadecyltrimethoxysilane-modified silica nanoparticles were used to form a stable invert emulsion of water in oil for the drilling fluid model which resulted in a milky fluid with the formation of 60 gm water droplets. In addition, rheological study showed that using hydrophobic silica nanoparticles resulted in a stable water in oil invert emulsion with desired properties for a drilling fluid that can be modified by adjusting the nanoparticle nature and content. Aging experiments at 120 ℃ indicated that they also have good stability at high temperatures for challenging drilling operations.
基金financially supported by the National Natural Science Foundation of China (No.51173207)Sino-Hungarian Scientific and Technological Cooperation Project (No.2009DFA52660)+1 种基金Key projects of Guangdong Education Office (No.cxzd1101)Natural Science Foundation of Guangdong (Nos.2010B010800020,2011B090500004,2011BZ100051)
文摘To improve creep resistance of directional polytetrafluoroethylene （PTFE） films, epoxy grafted nano-SiO2 is mixed with PTFE powder before sintering and calender rolling. The aligned macromolecular chains （especially those in amorphous region） of the composite films can be bundled up by the nanoparticles to share the applied stress together. In addition, incorporation of silica nanoparticles increases crystallinity of PTFE and favors microfibrillation of PTFE in the course of large deformation. As result, PTFE films exhibit lower creep strain and creep rate, and higher tensile strength and hardness. The work is believed to open an avenue for manufacturing high performance fluoropolymers by nano-inclusions.
基金the Fatih University,Research Project Foundation (Contract No.P50020902-2)TUBITAK (Contract No.110T487) for financial support of this study
文摘In this investigation,the structural and electrical properties of nanocomposites of polyaniline(PANI) and cobalt ferrite synthesized by hydrothermal route are reported for the first time(with weight ratios of CoFe_2O_4/PANI 1:2 and 2:1).Synthesized nanomaterials have been characterized by XRD,FT-IR,SEM and TEM techniques.FT-IR results confirm the presence of CoFe_2O_4 and PANI in the samples.Their detailed conductivity measurements have been investigated.It has been found that PANI has a more effective conducting mechanism in CoFe_2O_4-PANI composites.These results are also consistent with the change in AC conductivity orders in composites.
基金supported by the Research Vice-chancellor of Shahid Beheshti University of Medical Sciences,Tehran,Iran(No.1394-373 to RMF)
文摘The spatial arrangement of the cell is important and considered as underlying mechanism for mathematical modeling of cell to cell interaction.The ability of cells to take on the characteristics of other cells in an organism,it is important to understand the dynamical behavior of the cells.This method implements experimental parameters of the cell-cell interaction into the mathematical simulation of cell arrangement.The purpose of this research was to explore the three-dimensional spatial distribution of anterior horn cells in the rat spinal cord to examine differences after sciatic nerve injury.Sixteen Sprague-Dawley male rats were assigned to control and axotomy groups.Twelve weeks after surgery,the anterior horn was removed for first-and second-order stereological studies.Second-order stereological techniques were applied to estimate the pair correlation and cross-correlation functions using a dipole probe superimposed onto the spinal cord sections.The findings revealed 7% and 36% reductions in the mean volume and total number of motoneurons,respectively,and a25% increase in the neuroglial cell number in the axotomized rats compared to the control rats.In contrast,the anterior horn volume remained unchanged.The results also indicated a broader gap in the pair correlation curve for the motoneurons and neuroglial cells in the axotomized rats compared to the control rats.This finding shows a negative correlation for the distribution of motoneurons and neuroglial cells in the axotomized rats.The cross-correlation curve shows a negative correlation between the motoneurons and neuroglial cells in the axotomized rats.These findings suggest that cellular structural and functional changes after sciatic nerve injury lead to the alterations in the spatial arrangement of motoneurons and neuroglial cells,finally affecting the normal function of the central nervous system.The experimental protocol was reviewed and approved by the Animal Ethics Committee of Shahid Beheshti University of Medical Sciences(approval No.IR.SBMU.MSP.REC1395.375) on October 17,2016.
文摘The application of natural fibers as reinforcement in composite material has increased due to environmental concerns,low cost,degradability and health concerns.The purpose of this study is to identify the best type of bamboo fibers to be used as reinforcement for kenaf(K)/bamboo hybrid composite.There were three types of bamboo fibers evaluated in this study which include bamboo mat(B),bamboo fabric(BF)and bamboo powder(BP).Chemical composition of B,BF,BP and K fibers were analyzed in this study.The effect of different types of bamboo fibers on tensile,impact,and morphological properties were investigated.The B/epoxy composites displayed the highest tensile strength(53.03 MPa)while K/epoxy composite had the highest tensile modulus(4.71 GPa).Scanning electron micrographs of B/epoxy composites displayed better fiber/matrix interfacial bonding in comparison to other studied composites.Results showed that impact strength of BF-based composite was highest(45.70 J/m).In conclusion,the tensile strength of B/epoxy composite is superior to the other bamboo reinforced composites and will be further evaluated in the next study.
基金project(2012-0007594)supported by Basic Science Research Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Education,Science and Technology
文摘The multi-walled carbon nanotube was introduced into the polymer matrix (PANI) to improve the electric conductivity as well as mechanical properties of the original polymer matrix.PANI/multi-walled carbon nanotube (MWCNT) composites were synthesized via ex-situ and in-situ polymerization to improve their electrical property.And the DC conductivities of PANI/MWCNT according to content and diameter of MWCNT were measured by four-point probe.The highest electric conductivity of PANI/MWCNT composite is 20 S/cm when 0.3% (mass fraction) MWCNTs with 10 nm in diameter and 15 μm in length are added in composite.
基金supported by the National Natural Science Foundation of China(No.50873006)Program for New Century Excellent Talents in Universities,Ministry of Education of China(NCET-08-0711)
文摘Graphene oxide was prepared by ultrasonication of completely oxidized graphite and used to improve the flame retardancy of epoxy. The epoxy/graphene oxide nanocomposite was studied in terms of exfoliation/dispersion, thermal stability and flame retardancy. X-ray diffraction and transmission electron microscopy confirmed the exfoliation of the graphene oxide nanosheets in epoxy matrix. Cone calorimeter measurements showed that the time to ignition of the epoxy/graphene oxide nanocomposite was longer than that of neat epoxy. The heat release rate curve of the nanocomposite was broadened compared to that of neat epoxy and the peak heat release rate decreased as well.
基金financially supported by the National Natural Science Foundation of China(Nos.51125010 and 51221002)the Specialized Research Fund for the Doctoral Program of Higher Education of China(No.20100010110006)
文摘Simultaneous functionalization and reduction of graphene oxide （GO） is realized by refluxing of GO suspension with polyetheramine （D2000） followed by thermal treatment at 120℃. Compared to GO, the D2000-treated GO （GO- D2000） becomes hydrophobic, thermally stable and highly conductive with an electrical conductivity of 11 S/m, which is almost 8 orders of magnitude higher than that of GO. Due to the high conductivity and improved dispersion of GO-D2000, its epoxy nanocomposites exhibit a sharp transition from electrically insulating to conducting with a low percolation threshold of 0.71 vol%. With 3.6 wt% GO-D2000, the glass transition temperature of the epoxy nanocomposite is 27 K higher than that of neat epoxy.
