Polymerization-induced cooperative assembly(PICA)is reported to efficiently access inverse bicontinuous mesophases within particles consisting of amphiphilic block copolymers(BCPs)and solvophobic copolymers.Reversible...Polymerization-induced cooperative assembly(PICA)is reported to efficiently access inverse bicontinuous mesophases within particles consisting of amphiphilic block copolymers(BCPs)and solvophobic copolymers.Reversible addition-fragmentation chain transfer(RAFT)dispersion alternating copolymerization of styrene and pentafluorostyrene is conducted in 2%v/v toluene/ethanol by simultaneously using poly(N,N-dimethylacrylamide)(PDMA29)as a macromolecular chain transfer agent(macro-CTA)and small molecule CTA.展开更多
The microstructures of carbon precursors significantly affect the electrochemical performance of Si/C composite anodes.However,the interaction between Si and carbon materials with different structures is still unclear...The microstructures of carbon precursors significantly affect the electrochemical performance of Si/C composite anodes.However,the interaction between Si and carbon materials with different structures is still unclear.Pitch-based materials undergoing different thermal treatments are superior sources for synthesizing carbons with different structures.Herein,different types of mesophase pitch(domain,flow-domain and mosaic structure) obtained from controllable thermal condensation are utilized to prepare Si/C composite materials and the corresponding models are established through finite element simulation to explore the correlation between the lithium storage properties of Si/C composites and the structures of carbon materials.The results indicate that the flow-domain texture pitch P2 has a better ability to buffer the volume expansion of silicon particles for its highly ordered arrangement of carbon crystallites inside could disperse the swelling stress uniformly alongside the particle surface.The sample Si@P2 exhibits the highest capacity of 1328 mA h/g after 200 cycles at a current density of 0.1 A/g as well as the best rate performance and stability.While sample Si@P3 in which the mosaic texture pitch P3 composed of random orientation of crystallites undergoes the fastest capacity decay.These findings suggest that highly ordered carbon materials are more suitable for the synthesis of Si/C composite anodes and provide insights for understanding the interaction between carbon and silicon during the charging/discharging process.展开更多
The Neoproterozoic-Lower Paleozoic dolostone gas reservoirs in the Chuanzhong Uplift in Southwestern China contain the mesophase pyrobitumen (pyrobitumen with mesophase). The mesophase in the pyrobitumen is mostly com...The Neoproterozoic-Lower Paleozoic dolostone gas reservoirs in the Chuanzhong Uplift in Southwestern China contain the mesophase pyrobitumen (pyrobitumen with mesophase). The mesophase in the pyrobitumen is mostly composed of a mixture of condensed macromolecule polycyclic aromatic hydrocarbons (PAH), and has been mostly converted to various grain, flow, and domain textures. The volcanic activity nearby the Chuanzhong Uplift may have generated very hot (over 300 °C) hydrothermal fluid, with migration of the fluid into the dolostone reservoir transforming the hydrocarbons in the reservoir into an anisotropic carbon by-product, which formed under high temperature and pressure conditions;over 300 °C and 200 MPa according to fluid inclusion analysis. The high temperature-pressure in reservoir was caused by sudden devolatilization of the hydrocarbons due to hydrothermal heating, which formed the unusual texture of the mesophase. The elliptical mesophase grains (EG), the honeycomb structure of pyrobitumen, and the occurrence of polarized classes of mesophase in single pyrobitumen deposits are all unusual textures. This study investigates the texture development of this pressure-affected pyrobitumen. Observation and study of the mesophase suggest that the class of mesophase in pyrobitumen is determined by temperature, while pressure (assessed from associated fluid inclusions) significantly affected the texture. Analysis of the texture of the pyrobitumen in conjunction with previous thermometry results from methane inclusions suggests that the high class mesophase of the pyrobitumen could be applied as a temperature indicator for geological conditions. Furthermore, the unusual textures of the pyrobitumen including elliptical mesophase grains (EG), the honeycomb structure of pyrobitumen, and the occurrence of polarized classes of mesophase in single pyrobitumen could reflect the abnormal high formation pressure.展开更多
In order to obtain the microwave absorption(MA)materials with light weight,high efficiency and tunable properties,the carbonized mesophase pitch(CMP)with the variation in carbonization temperatures and particle sizes ...In order to obtain the microwave absorption(MA)materials with light weight,high efficiency and tunable properties,the carbonized mesophase pitch(CMP)with the variation in carbonization temperatures and particle sizes were prepared and characterized.The carbonization temperature mainly controlled the graphitization degree of the CMP to affect their conductive loss.The carbon residues were generated on the CMP surface when the temperature was higher than 700℃,which contributed significantly to the polarization loss of the CMP.For scale regulation,the segregation between the particles in the paraffin ring caused by the reduction particles of CMP carbonization at 750℃(750 CMP)resulted in a significant reduction in conductive losses while improving their impedance matching.The 750 CMP over 300 mesh sieved had the strongest MA properties of-53 d B at 3.4 GHz within 5.5 mm.Moreover,the prepared CMPs were multi-layer compounded and optimized by CST microwave studio.The synergistic effect derived from the improved impedance matching and the enhanced interfacial polarization resulted in significant reflection loss in multi-layer CMP.Overall,these findings lead to the systematically regulation of carbon-based materials for MA,showing an attractive application prospect for the preparation of high-performance MA materials.展开更多
The phase behaviour of lanthanide(Ⅲ) dodecylsulphates, Ln(C 12 H 25 SO 4) 3, by thermo optical microscopy using Lawrence penetration technique was investigated. The lyotropic phase behaviour of lanthanide(...The phase behaviour of lanthanide(Ⅲ) dodecylsulphates, Ln(C 12 H 25 SO 4) 3, by thermo optical microscopy using Lawrence penetration technique was investigated. The lyotropic phase behaviour of lanthanide(Ⅲ) dodecylsulphates in ethylene glycol water in mixtures hereof, depends on the composition of the solvent. For pure ethylene glycol and mixtures of ethylene glycol and water three different mesophases are formed, i.e. a lamellar, a cubic and a hexagonal phase, whereas when water is used as solvent no cubic phase is formed. The size of the lanthanide ion has no influence on the mesomorphism of these metallomesogens, although the smaller the lanthanide ion the lower the solubility.展开更多
Molecular simulations were performed to investigate the molecular structural effects on needle coke mesophase stacking.The simulation results showed that the stacking states of anthracene trimer and tetramer accumulat...Molecular simulations were performed to investigate the molecular structural effects on needle coke mesophase stacking.The simulation results showed that the stacking states of anthracene trimer and tetramer accumulations were orderly,while the stacking states of anthracene dimer,pentamer,and hexamer accumulations were disorderly.Anthracene trimer and tetramer in the model compounds were two of the most ideal needle coke mesophase constituents.It was also found that the introduction of methyl side chains in anthracene trimer derivatives was not conducive to the formation of a mesophase crystal.To sum up,the molecules which had similar structures to anthracene trimer or tetramer with no alkyl chains are ideal constituents of needle coke mesophase.展开更多
By a polarized light optical microscopy with a hot stage, liquid phase nuclear magnetic resonance 13 C NMR and 1 H NMR, X ray diffractometry and scanning electron microscopy (SEM), the factors that affect the formatio...By a polarized light optical microscopy with a hot stage, liquid phase nuclear magnetic resonance 13 C NMR and 1 H NMR, X ray diffractometry and scanning electron microscopy (SEM), the factors that affect the formation of mesophase in C/C composites, such as pressure, quinoline insolubles (QI) and heterocylic compounds, were analyzed. Further, the graphitizability of the resultant carbon was discussed. The results indicate that to some degree, QI contents accelerate the formation of mesophase at atmospheric pressure; while at high pressure, the coalescence and growth of mesophase spherules are impeded and the resultant coke produced from higher QI content pitch is harder to be graphitized. This is in agreement with the transfer of microstructure from domain anisotropy to fine grained mosaics.展开更多
The cerium-modified cubic mobil composition of matters 48 (MCM-48) molecular sieves were synthesized using cetyltrimethylammonium bromide (CTAB) as templates at low molar ratio of surfactant to inorganic precursor...The cerium-modified cubic mobil composition of matters 48 (MCM-48) molecular sieves were synthesized using cetyltrimethylammonium bromide (CTAB) as templates at low molar ratio of surfactant to inorganic precursor. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results show that the well-ordered cubic mesostructure was obtained when the Ce/Si molar ratio is less than 0.05. With the increase of Ce/Si molar ratio, the increase of unit cell parameters and the change of Fourier transform infrared spectroscopy (FTIR) provide powerful evidences for the incorporation of cerium in the framework of mesoporous molecular sieves. Nitrogen sorption data indicate that the Brunauer-Emmett-Teller (BET) surface area and the average pore diameter of Ce(Ⅲ)-MCM-48 are 1288 m 2·g -1 and 4.2 nm, and those of Ce(Ⅳ)-MCM-48 are 1228 m 2·g -1 and 3.7 nm, respectively. Diffuse reflectance UV-visible (UV-vis) spectroscopy confirms the presence of Ce(Ⅲ) in the octahedral position and Ce(Ⅳ) in the fluorite structure. X-ray photoelectron spectroscopy (XPS) studies further reveal that Ce(Ⅲ) and Ce(Ⅳ) coexist in the framework of mesoporous molecular sieves.展开更多
In the ethyl-cyanoethylcellulose ((E-CE)C)/dichloroacetic acid (DCA) cholesteric liquid crystalline solution, the hand-like texture is formed when the mesophase aggregates with the disk-like texture grow to big enough...In the ethyl-cyanoethylcellulose ((E-CE)C)/dichloroacetic acid (DCA) cholesteric liquid crystalline solution, the hand-like texture is formed when the mesophase aggregates with the disk-like texture grow to big enough and merge with each other with increasing concentration. The band-like texture is composed of parallel equidistant bright and dark alternative strips which are about 0.2-2.0 μm in width. In the band-like texture, the layers of ordered polymer chains are perpendicular to the solution film and the axes of helicoids are parallel to it. The width of the strips is different in different zones. Under the effect of an external magnetic field, the strips in the band-like texture first become wider and then narrower gradually.Moreover, the axes of helicoids in the (E-CE) C/DCA mesomorphic solution change from the direction normal to the magnetic field to the agreement with the magnetic field direction.展开更多
There was phase separation between the anisotropic and isotropic phases in the ethyl-acetyl cellulose/dichloroacetic acid cholesteric liquid crystalline solutions .The textures of mesophase varied with the concentrati...There was phase separation between the anisotropic and isotropic phases in the ethyl-acetyl cellulose/dichloroacetic acid cholesteric liquid crystalline solutions .The textures of mesophase varied with the concentration. The mesophases could form the disc-like texture, oily streaks texture and texture of domains gathered randomly. In the first two textures the layers of the ordered molecular chain were perpendicular to the slide surface and the axes of the helical structure were parallel to the slide surface.展开更多
The kinetics of mesophase formation of a thermotropic hydroxyethyl cellulose acetate from isotropic phase to cholesteric mesophase has been studied by means of depolarizing transmittance method. Avrami type analysis o...The kinetics of mesophase formation of a thermotropic hydroxyethyl cellulose acetate from isotropic phase to cholesteric mesophase has been studied by means of depolarizing transmittance method. Avrami type analysis of the data gives an exponent n close to 1, which suggests the nucleation followed by rod-like growth. It means that the kinetic behavior of phase transition from isotropic to cholesteric mesophase is very similar to that of the mesophase formation from isotropic to nematic mesophase.展开更多
The morphological changes of a side-chain liquid-crystalline polymethacrylate during isotropization and liquid-crystallization transitions were studied by means of polarizing microscopy. These transitions were found t...The morphological changes of a side-chain liquid-crystalline polymethacrylate during isotropization and liquid-crystallization transitions were studied by means of polarizing microscopy. These transitions were found to be composed of the initiation of a new phase at local places of the old phase matrix and the growth of the new phase: domains. The kinetics of the liquid-crystallization of the polymer from an isotropic melt to a smectic mesophase was also investigated. The isothermal process of the transition can be described by the Avrami equation. The values of the Avrami exponent were found to be around 2.6. which is lower than the value usually obtained for crystallization transition of polymers, but larger than that reported for liquid-crystallization transition of main-chain polymers. These results may indicate the difference in growth geometry of new phase during transition between crystallization and liquid-crystallization in general and between liquid-crystallization of main-chain and side-chain polymers. It was found that the liquid-crystallization of the used side-chain polymethacrylate may occur at small undercoolings with high transformation rate similar to that of main-chain polymers and small-molecule liquid crystals, while the crystallization of polymers can only proceed at large undercoolings. These phenomena can be explained by the idea that the surface free energy of nucleus during liquid-crystallization transition is less than that for crystallization, and evidence was obtained from analysis of the temperature dependence of the transformation rate.展开更多
The macro-and micro-structure of two groups(high modulus and high thermalconductivity)of MP-based carbon fibres were studied using X-ray diffraction,and both scanningand transmission electron microscopy.The dominant m...The macro-and micro-structure of two groups(high modulus and high thermalconductivity)of MP-based carbon fibres were studied using X-ray diffraction,and both scanningand transmission electron microscopy.The dominant macrostructure in cross section is of foldedpseudo-radial layers which have a tendency to form a quasi-uniform domain as the fibre modulusincreases.It is found that high thermal conductivity fibres have both missimg sector and circularcross sections(possessed predominantly by the high modulus fibre group).The microstructuralstudy indicates that apart from the fibre C700,which has a three-dimensional graphite structure,these two groups of carbon fibres all exhibit a turbostratic stacking order.Furthermore it is foundthat the turbostratic stacking thickness as determined from dark-field measurement is much largerthan the classical crystallite thickness L_c as measured from X-ray diffraction.展开更多
The first TEMPO-mediated 'living' free radical polymerization of liquid crystalline monomer, 2, 5-bis[(4-methoxyphenyl)oxycarbonyl]styrene (MPCS), was carried out at 130 degrees C with BPO as an initiator. The...The first TEMPO-mediated 'living' free radical polymerization of liquid crystalline monomer, 2, 5-bis[(4-methoxyphenyl)oxycarbonyl]styrene (MPCS), was carried out at 130 degrees C with BPO as an initiator. The molecular weight of the polymer can be varied from rather low values to high values while maintaining narrow polydispersity. It was observed that the polymerization of MPCS proceeded much faster than that of styrene. A tentative explanation for this fast polymerization was suggested.展开更多
The thermotropic liquid crystalline behavior of a fusible polydiacetylene has been studied by using polarizing optical microscopy and wide angle X-ray diffraction. It was found that the typical threaded texture can ex...The thermotropic liquid crystalline behavior of a fusible polydiacetylene has been studied by using polarizing optical microscopy and wide angle X-ray diffraction. It was found that the typical threaded texture can exhibit in the melt and the banded texture can be observed when applied a gentle shear to the melt. The results indicate that this polydiacetylene is really a thermotropic liquid crystalline polymer.展开更多
A series of novel mesogenic polyamides containing a flexible pendent side group was synthesized by solution condensation polymerization. The new monomers, diacids and diamines containing flexible elements of different...A series of novel mesogenic polyamides containing a flexible pendent side group was synthesized by solution condensation polymerization. The new monomers, diacids and diamines containing flexible elements of different lengths, were also synthesized and characterized by H-1 NMR, mass spectroscopy and elemental analysis. The polymers were characterized by viscosity measurements, differential scanning calorimetry (DSC), X-ray diffraction and polarizing optical microscopy. These studies revealed that polyamides containing flexible elements of a sufficient length exhibited thermotropic liquid crystalline (LC) properties. The melting temperatures of this series of polymers were: particularly sensitive to the length of the flexible segment on the main chain and that of the flexible pendent ester side chain. Lyotropic LC behaviours were also observed in solution.展开更多
The morphological features of a side-chain liquid crystalline polymer during the mesophase transitions were investigated by using the DSC technique. The polymer used was polyacrylate with mesogens of three benzene rin...The morphological features of a side-chain liquid crystalline polymer during the mesophase transitions were investigated by using the DSC technique. The polymer used was polyacrylate with mesogens of three benzene rings attached to the main chain through a flexible spacer. A special two-phase texture was observed in the transition temperature range. Similar to main-chain liquid crystalline polymers the transition process of the side-chain liquid crystalline polymer was composed of an initiation of the new phase at local places of the old phase matrix and a growth process of the new phase domains.展开更多
An Abbe refractometer with a rotatable polarizer mounted on the eyepiece is used for determining the two principal refractive indices of methyl-cyanoethyl cellulose/dichloroacetic acid liquid crystalline solutions. Th...An Abbe refractometer with a rotatable polarizer mounted on the eyepiece is used for determining the two principal refractive indices of methyl-cyanoethyl cellulose/dichloroacetic acid liquid crystalline solutions. The critical concentration where the mesophase appears can be determined according to the variation of the increment of the refractive index with the concentration. Mesophase textures of the liquid crystalline solutions are observed and the influence of the concentration on mesophase textures is also discussed.展开更多
The kinetics of mesophase formation of a lyotropic aromatic polyamide from isotropic state has been studied by means of depolarized light intensity. Avrami type analysis of the data gives an exponent close to 1, which...The kinetics of mesophase formation of a lyotropic aromatic polyamide from isotropic state has been studied by means of depolarized light intensity. Avrami type analysis of the data gives an exponent close to 1, which suggests the nucleation followed by one-dimensional growth. No influence of blending flexible chain from nylon 6 to the aromatic polyamide on the kinetics of mesophase formation was observed.展开更多
基金support by the National Natural Science Foundation of China(nos.51733003 and 21674059)the Fundamental Research Funds for the Central Universities are thanked.
文摘Polymerization-induced cooperative assembly(PICA)is reported to efficiently access inverse bicontinuous mesophases within particles consisting of amphiphilic block copolymers(BCPs)and solvophobic copolymers.Reversible addition-fragmentation chain transfer(RAFT)dispersion alternating copolymerization of styrene and pentafluorostyrene is conducted in 2%v/v toluene/ethanol by simultaneously using poly(N,N-dimethylacrylamide)(PDMA29)as a macromolecular chain transfer agent(macro-CTA)and small molecule CTA.
基金financial support from the National Key Research and Development Programme (2018YFC1801901)the National Natural Science Foundation of China (21808115, 22108309, 52172093)+1 种基金the Key Research and Development Project (Major Project of Scientific and Technological Innovation) of Shandong Province (2020CXGC010308)the Taishan Scholar Program of Shandong (ts20190919)。
文摘The microstructures of carbon precursors significantly affect the electrochemical performance of Si/C composite anodes.However,the interaction between Si and carbon materials with different structures is still unclear.Pitch-based materials undergoing different thermal treatments are superior sources for synthesizing carbons with different structures.Herein,different types of mesophase pitch(domain,flow-domain and mosaic structure) obtained from controllable thermal condensation are utilized to prepare Si/C composite materials and the corresponding models are established through finite element simulation to explore the correlation between the lithium storage properties of Si/C composites and the structures of carbon materials.The results indicate that the flow-domain texture pitch P2 has a better ability to buffer the volume expansion of silicon particles for its highly ordered arrangement of carbon crystallites inside could disperse the swelling stress uniformly alongside the particle surface.The sample Si@P2 exhibits the highest capacity of 1328 mA h/g after 200 cycles at a current density of 0.1 A/g as well as the best rate performance and stability.While sample Si@P3 in which the mosaic texture pitch P3 composed of random orientation of crystallites undergoes the fastest capacity decay.These findings suggest that highly ordered carbon materials are more suitable for the synthesis of Si/C composite anodes and provide insights for understanding the interaction between carbon and silicon during the charging/discharging process.
基金funded by the National Natural Science Foundation of China for Young Scholars(No.41903059).
文摘The Neoproterozoic-Lower Paleozoic dolostone gas reservoirs in the Chuanzhong Uplift in Southwestern China contain the mesophase pyrobitumen (pyrobitumen with mesophase). The mesophase in the pyrobitumen is mostly composed of a mixture of condensed macromolecule polycyclic aromatic hydrocarbons (PAH), and has been mostly converted to various grain, flow, and domain textures. The volcanic activity nearby the Chuanzhong Uplift may have generated very hot (over 300 °C) hydrothermal fluid, with migration of the fluid into the dolostone reservoir transforming the hydrocarbons in the reservoir into an anisotropic carbon by-product, which formed under high temperature and pressure conditions;over 300 °C and 200 MPa according to fluid inclusion analysis. The high temperature-pressure in reservoir was caused by sudden devolatilization of the hydrocarbons due to hydrothermal heating, which formed the unusual texture of the mesophase. The elliptical mesophase grains (EG), the honeycomb structure of pyrobitumen, and the occurrence of polarized classes of mesophase in single pyrobitumen deposits are all unusual textures. This study investigates the texture development of this pressure-affected pyrobitumen. Observation and study of the mesophase suggest that the class of mesophase in pyrobitumen is determined by temperature, while pressure (assessed from associated fluid inclusions) significantly affected the texture. Analysis of the texture of the pyrobitumen in conjunction with previous thermometry results from methane inclusions suggests that the high class mesophase of the pyrobitumen could be applied as a temperature indicator for geological conditions. Furthermore, the unusual textures of the pyrobitumen including elliptical mesophase grains (EG), the honeycomb structure of pyrobitumen, and the occurrence of polarized classes of mesophase in single pyrobitumen could reflect the abnormal high formation pressure.
基金supported by Sichuan Science and Technology Program,Grant No.2022YFG0111the Postdoctoral Innovative Talent Support Program(Grant No.BX20190220)the State Key Laboratory of Polymer Materials Engineering(Grant No.sklpme2019-2-02)for financial support。
文摘In order to obtain the microwave absorption(MA)materials with light weight,high efficiency and tunable properties,the carbonized mesophase pitch(CMP)with the variation in carbonization temperatures and particle sizes were prepared and characterized.The carbonization temperature mainly controlled the graphitization degree of the CMP to affect their conductive loss.The carbon residues were generated on the CMP surface when the temperature was higher than 700℃,which contributed significantly to the polarization loss of the CMP.For scale regulation,the segregation between the particles in the paraffin ring caused by the reduction particles of CMP carbonization at 750℃(750 CMP)resulted in a significant reduction in conductive losses while improving their impedance matching.The 750 CMP over 300 mesh sieved had the strongest MA properties of-53 d B at 3.4 GHz within 5.5 mm.Moreover,the prepared CMPs were multi-layer compounded and optimized by CST microwave studio.The synergistic effect derived from the improved impedance matching and the enhanced interfacial polarization resulted in significant reflection loss in multi-layer CMP.Overall,these findings lead to the systematically regulation of carbon-based materials for MA,showing an attractive application prospect for the preparation of high-performance MA materials.
文摘The phase behaviour of lanthanide(Ⅲ) dodecylsulphates, Ln(C 12 H 25 SO 4) 3, by thermo optical microscopy using Lawrence penetration technique was investigated. The lyotropic phase behaviour of lanthanide(Ⅲ) dodecylsulphates in ethylene glycol water in mixtures hereof, depends on the composition of the solvent. For pure ethylene glycol and mixtures of ethylene glycol and water three different mesophases are formed, i.e. a lamellar, a cubic and a hexagonal phase, whereas when water is used as solvent no cubic phase is formed. The size of the lanthanide ion has no influence on the mesomorphism of these metallomesogens, although the smaller the lanthanide ion the lower the solubility.
基金Funding provided by the Molecular Simulation Key Laboratory at SINOPEC Research Institute of Petroleum Processing is gratefully acknowledged.
文摘Molecular simulations were performed to investigate the molecular structural effects on needle coke mesophase stacking.The simulation results showed that the stacking states of anthracene trimer and tetramer accumulations were orderly,while the stacking states of anthracene dimer,pentamer,and hexamer accumulations were disorderly.Anthracene trimer and tetramer in the model compounds were two of the most ideal needle coke mesophase constituents.It was also found that the introduction of methyl side chains in anthracene trimer derivatives was not conducive to the formation of a mesophase crystal.To sum up,the molecules which had similar structures to anthracene trimer or tetramer with no alkyl chains are ideal constituents of needle coke mesophase.
文摘By a polarized light optical microscopy with a hot stage, liquid phase nuclear magnetic resonance 13 C NMR and 1 H NMR, X ray diffractometry and scanning electron microscopy (SEM), the factors that affect the formation of mesophase in C/C composites, such as pressure, quinoline insolubles (QI) and heterocylic compounds, were analyzed. Further, the graphitizability of the resultant carbon was discussed. The results indicate that to some degree, QI contents accelerate the formation of mesophase at atmospheric pressure; while at high pressure, the coalescence and growth of mesophase spherules are impeded and the resultant coke produced from higher QI content pitch is harder to be graphitized. This is in agreement with the transfer of microstructure from domain anisotropy to fine grained mosaics.
文摘The cerium-modified cubic mobil composition of matters 48 (MCM-48) molecular sieves were synthesized using cetyltrimethylammonium bromide (CTAB) as templates at low molar ratio of surfactant to inorganic precursor. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results show that the well-ordered cubic mesostructure was obtained when the Ce/Si molar ratio is less than 0.05. With the increase of Ce/Si molar ratio, the increase of unit cell parameters and the change of Fourier transform infrared spectroscopy (FTIR) provide powerful evidences for the incorporation of cerium in the framework of mesoporous molecular sieves. Nitrogen sorption data indicate that the Brunauer-Emmett-Teller (BET) surface area and the average pore diameter of Ce(Ⅲ)-MCM-48 are 1288 m 2·g -1 and 4.2 nm, and those of Ce(Ⅳ)-MCM-48 are 1228 m 2·g -1 and 3.7 nm, respectively. Diffuse reflectance UV-visible (UV-vis) spectroscopy confirms the presence of Ce(Ⅲ) in the octahedral position and Ce(Ⅳ) in the fluorite structure. X-ray photoelectron spectroscopy (XPS) studies further reveal that Ce(Ⅲ) and Ce(Ⅳ) coexist in the framework of mesoporous molecular sieves.
基金This work was supported by Academia Sinica Selected Research Program.
文摘In the ethyl-cyanoethylcellulose ((E-CE)C)/dichloroacetic acid (DCA) cholesteric liquid crystalline solution, the hand-like texture is formed when the mesophase aggregates with the disk-like texture grow to big enough and merge with each other with increasing concentration. The band-like texture is composed of parallel equidistant bright and dark alternative strips which are about 0.2-2.0 μm in width. In the band-like texture, the layers of ordered polymer chains are perpendicular to the solution film and the axes of helicoids are parallel to it. The width of the strips is different in different zones. Under the effect of an external magnetic field, the strips in the band-like texture first become wider and then narrower gradually.Moreover, the axes of helicoids in the (E-CE) C/DCA mesomorphic solution change from the direction normal to the magnetic field to the agreement with the magnetic field direction.
基金Projects supported by the Science Fund of the Chinese Academy of Sciences.
文摘There was phase separation between the anisotropic and isotropic phases in the ethyl-acetyl cellulose/dichloroacetic acid cholesteric liquid crystalline solutions .The textures of mesophase varied with the concentration. The mesophases could form the disc-like texture, oily streaks texture and texture of domains gathered randomly. In the first two textures the layers of the ordered molecular chain were perpendicular to the slide surface and the axes of the helical structure were parallel to the slide surface.
基金This work supported by the National Basic Research Project-Macromolecular Condensed State
文摘The kinetics of mesophase formation of a thermotropic hydroxyethyl cellulose acetate from isotropic phase to cholesteric mesophase has been studied by means of depolarizing transmittance method. Avrami type analysis of the data gives an exponent n close to 1, which suggests the nucleation followed by rod-like growth. It means that the kinetic behavior of phase transition from isotropic to cholesteric mesophase is very similar to that of the mesophase formation from isotropic to nematic mesophase.
文摘The morphological changes of a side-chain liquid-crystalline polymethacrylate during isotropization and liquid-crystallization transitions were studied by means of polarizing microscopy. These transitions were found to be composed of the initiation of a new phase at local places of the old phase matrix and the growth of the new phase: domains. The kinetics of the liquid-crystallization of the polymer from an isotropic melt to a smectic mesophase was also investigated. The isothermal process of the transition can be described by the Avrami equation. The values of the Avrami exponent were found to be around 2.6. which is lower than the value usually obtained for crystallization transition of polymers, but larger than that reported for liquid-crystallization transition of main-chain polymers. These results may indicate the difference in growth geometry of new phase during transition between crystallization and liquid-crystallization in general and between liquid-crystallization of main-chain and side-chain polymers. It was found that the liquid-crystallization of the used side-chain polymethacrylate may occur at small undercoolings with high transformation rate similar to that of main-chain polymers and small-molecule liquid crystals, while the crystallization of polymers can only proceed at large undercoolings. These phenomena can be explained by the idea that the surface free energy of nucleus during liquid-crystallization transition is less than that for crystallization, and evidence was obtained from analysis of the temperature dependence of the transformation rate.
文摘The macro-and micro-structure of two groups(high modulus and high thermalconductivity)of MP-based carbon fibres were studied using X-ray diffraction,and both scanningand transmission electron microscopy.The dominant macrostructure in cross section is of foldedpseudo-radial layers which have a tendency to form a quasi-uniform domain as the fibre modulusincreases.It is found that high thermal conductivity fibres have both missimg sector and circularcross sections(possessed predominantly by the high modulus fibre group).The microstructuralstudy indicates that apart from the fibre C700,which has a three-dimensional graphite structure,these two groups of carbon fibres all exhibit a turbostratic stacking order.Furthermore it is foundthat the turbostratic stacking thickness as determined from dark-field measurement is much largerthan the classical crystallite thickness L_c as measured from X-ray diffraction.
基金This work was supported by the Foundation of Peking University for Young Scientist and the National Natural Science Foundation of China(Grant No.29874003).
文摘The first TEMPO-mediated 'living' free radical polymerization of liquid crystalline monomer, 2, 5-bis[(4-methoxyphenyl)oxycarbonyl]styrene (MPCS), was carried out at 130 degrees C with BPO as an initiator. The molecular weight of the polymer can be varied from rather low values to high values while maintaining narrow polydispersity. It was observed that the polymerization of MPCS proceeded much faster than that of styrene. A tentative explanation for this fast polymerization was suggested.
基金This work was supported by the National Basic Research Project-Macromolecular Condensed State
文摘The thermotropic liquid crystalline behavior of a fusible polydiacetylene has been studied by using polarizing optical microscopy and wide angle X-ray diffraction. It was found that the typical threaded texture can exhibit in the melt and the banded texture can be observed when applied a gentle shear to the melt. The results indicate that this polydiacetylene is really a thermotropic liquid crystalline polymer.
基金This work is supported by the National Natural Science Foundation of China
文摘A series of novel mesogenic polyamides containing a flexible pendent side group was synthesized by solution condensation polymerization. The new monomers, diacids and diamines containing flexible elements of different lengths, were also synthesized and characterized by H-1 NMR, mass spectroscopy and elemental analysis. The polymers were characterized by viscosity measurements, differential scanning calorimetry (DSC), X-ray diffraction and polarizing optical microscopy. These studies revealed that polyamides containing flexible elements of a sufficient length exhibited thermotropic liquid crystalline (LC) properties. The melting temperatures of this series of polymers were: particularly sensitive to the length of the flexible segment on the main chain and that of the flexible pendent ester side chain. Lyotropic LC behaviours were also observed in solution.
基金The authors are grateful to the Director Foundation of Institute of Chemistry,Chinese Academy of Sciences and Science Foundation of Polymer Physics Laboratory,Chinese Academy of Sciences for supporting this work
文摘The morphological features of a side-chain liquid crystalline polymer during the mesophase transitions were investigated by using the DSC technique. The polymer used was polyacrylate with mesogens of three benzene rings attached to the main chain through a flexible spacer. A special two-phase texture was observed in the transition temperature range. Similar to main-chain liquid crystalline polymers the transition process of the side-chain liquid crystalline polymer was composed of an initiation of the new phase at local places of the old phase matrix and a growth process of the new phase domains.
基金Projects supported by Academia Sinica Selected Research Program and The National Natural Science Foundation of China.
文摘An Abbe refractometer with a rotatable polarizer mounted on the eyepiece is used for determining the two principal refractive indices of methyl-cyanoethyl cellulose/dichloroacetic acid liquid crystalline solutions. The critical concentration where the mesophase appears can be determined according to the variation of the increment of the refractive index with the concentration. Mesophase textures of the liquid crystalline solutions are observed and the influence of the concentration on mesophase textures is also discussed.
基金This work was supported by Academia Sinica selected Research Program and National Natural Science Foundation of China
文摘The kinetics of mesophase formation of a lyotropic aromatic polyamide from isotropic state has been studied by means of depolarized light intensity. Avrami type analysis of the data gives an exponent close to 1, which suggests the nucleation followed by one-dimensional growth. No influence of blending flexible chain from nylon 6 to the aromatic polyamide on the kinetics of mesophase formation was observed.