高分子共混物梯度相结构形成过程中的界面效应

通过在高分子共混物内部引入不同的第三相界面,系统地研究了退火热处理条件下该界面对于共混物梯度相形态形成的影响.对具有一定初始粒径的共混物体系或初始近似为均相的共混体系,在第三相界面的诱导下,均能形成梯度相形态.探讨了诱导界面间距与体系相结构的关系.结果表明,当两个诱导界面间距小于所生成梯度层厚度的两倍时,梯度结构趋于交叠.继续减小诱导界面间距,则梯度结构趋于消失,诱导界面间共混物中分散相粒子快速长大,界面的诱导作用遍布整个样片,证实了我们所提出的“高分子共混物中二维条件下界面诱导加速分散相粒子粗化凝聚”的结论.     

Coupling between lysozyme and glycerol dynamics: microscopic insights from molecular-dynamics simulations

We explore possible molecular mechanisms behind the coupling of protein and solvent dynamics using atomistic molecular-dynamics simulations. For this purpose, we analyze the model protein lysozyme in glycerol, a well-known protein-preserving agent. We find that the dynamics of the hydrogen bond network between the solvent molecules in the first shell and the surface residues of the protein controls the structural relaxation (dynamics) of the whole protein. Specifically, we find a power-law relationship between the relaxation time of the aforementioned hydrogen bond network and the structural relaxation time of the protein obtained from the incoherent intermediate scattering function. We demonstrate that the relationship between the dynamics of the hydrogen bonds and the dynamics of the protein appears also in the dynamic transition temperature of the protein. A study of the dynamics of glycerol as a function of the distance from the surface of the protein indicates that the viscosity seen by the protein is not the one of the bulk solvent. The presence of the protein suppresses the dynamics of the surrounding solvent. This implies that the protein sees an effective viscosity higher than the one of the bulk solvent. We also found significant differences in the dynamics of surface and core residues of the protein. The former is found to follow the dynamics of the solvent more closely than the latter. These results allowed us to propose a molecular mechanism for the coupling of the solvent-protein dynamics.     

Untersuchungen der Temperaturbedingungen in der Graphitlaserdampfwolke

With the goal to obtain information on the evaporation and atomization conditions in the vapour cloud produced by laser impact on graphite (‘graphite laser torch’) the authors determined the spatial distribution of the gas temperature of the atomic vapour and the vibrational temperature of the CN molecules. The gas temperature was determined as the colour temperature of the ‘torch’. The applied method permits measurements not only in the vicinity of the target but also at a large distance from both the target and the axis of the torch. The distribution of the ‘effective’ temperature along the axis of symmetry of the torch and the local temperature distribution along the radius were used to derive the mean temperature of the atomic vapour. It was found that about 70% of the material ejected from the crater has a mean temperature of about 3400 K in the region between the target and the analytical zone. In order to determine the local vibrational temperature of the CN molecules in the analytical zone, the authors modulated the radiation from the torch electromechanically so that the radiation from the torch was recorded during the same period of time as analytical signals. The vibrational temperature of the CN molecules in the analytical region was found to be in a range between 3100 and 3600 K.     

Analysis of self-electrophoretic motion of a spherical particle in a nanotube: effect of nonuniform surface charge density

Autonomous motions of a spherical nanoparticle in a nanotube filled with an electrolyte solution were investigated using a continuum theory, which consisted of the Nernst-Planck equations for the ionic concentrations, the Poisson equation for the electric potential in the solution, and the Stokes equation for the hydrodynamic field. Contrary to the usual electrophoresis, in which an external electric field is imposed to direct the motion of charged particles, the autonomous motion originates from the self-generated electric field due to the ionic concentration polarization of the liquid medium surrounding an asymmetrically charged particle. In addition to the particle motion, the interaction between the electric field generated and the free charges of the polarized solution induces electroosmotic flows. These autonomous motions of the fluid as well as the particle were examined with focus on the effects of the surface-charge distribution of the particle, the size of the nanotube, and the thickness of the electric double layer, which affected the direction and the speed of the particle significantly.     

Proton character of the peptide unit in the Ca2+-binding sites of calcium pump

The effect of forming calcium pump structures in biological systems on the proton character of the peptide unit has been studied theoretically using the density-functional theory calculations with a large basis set. One acetic acid, one acetate, and three acetamide molecules as well as the modeling peptide unit (MPU) have been employed to mimic the amino acid residues forming the Ca2+-binding sites. To highlight the limiting case of the Ca2+-binding effect on the proton property and the proton countertransport possibility in the direction opposite to the ion, the MPU bounded by the bare or the hydrated Ca2+ has also been investigated. The natural bond orbital (NBO) analysis indicates that the increase of the p-character of the (N-H) sigma orbital results in weakening of the N-H bond which is lengthened when a Ca2+ ion is introduced to the MPU. Calculated NMR shielding sigma(H1) of the MPU shifts upfield upon the Ca2+ ion combination, which reveals the donating of the electron from the amide H as represented by the increase of the calculated positive natural charge for amide H of the MPU. Moreover, the proton affinities (PA) and gas-phase basicities (GB) for the amide nitrogen active site of the MPU are reduced; that is, the acidity of the amide hydrogen gets stronger because of the influence of the Ca2+ ion. To prove the transport possibility of the N-H proton in the direction opposite to the Ca2+ ion along the N-H...O=C hydrogen bond in the helical peptide linkage, NH3 and H2O are used here to assist the dissociation of the amide H of the MPU, and the calculated results show the notable decrease of the deprotonation energies compared to that of the case without this assistance. Moreover, calculated results also reveal that the variation of the quantities discussed here for amide H of the MPU gets smaller when the acidity of Ca2+ ion decreases. Ionization states of the acidic residues forming the Ca2+-binding sites may influence the activity of the amide H of the MPU and further affect the transport tendency of the peptide unit proton in the direction opposite to Ca2+.     

柱吸附容量对蔗糖还原糖色谱分离过程产率和回收率的影响

本文采用了能反映流体轴向扩散的大型液相色谱分离过程数学模型,应用计算机模拟分析蔗糖和还原糖的色谱分离过程,从吸附剂吸附容量和柱装填密度两个方面;考察柱吸附容量对大型色谱分离的产率和回收率的影响。研究结果表明：在色谱柱中流体线速度恒定的条件下对多组分分离,回收率是随吸附剂吸附容量以及床层装填密度的增大而增大的;产率先随吸附剂吸附容量的增大而增大,而在出现峰值后下降;随着床层装填密度的增大,产率增加,但与此同时轴向扩散系数也增大,从而降低分离效率,导致在较高装填密度的范围内产率增力。的幅度减少。在相同的吸附剂用量下,采用短柱高装填密度的色谱柱将比长柱低装填密度色谱柱能获得更高的回收率和产率。     

晶种数量对MOR分子筛上烷基转移反应的影响及反应机理研究

以丝光沸石(MOR)分子筛为催化剂,甲苯与三甲苯烷基转移反应为探针反应,系统考察了晶种数量变化对分子筛物化性能和催化性能的影响。研究表明,合成过程中晶种添加量的不同会显著影响催化剂的酸性、比表面积和孔体积,进而影响其催化剂活性和稳定性。当晶种添加量为8%时,MOR分子筛具有最多的B酸含量、最大的比表面积和孔体积,同时对应的催化剂活性和稳定性也最好。本研究还对甲苯和三甲苯烷基转移反应机理进行了深入研究,结果表明,发生在MOR分子筛上的烷基转移反应通过双分子中间体机理进行,并应用实验手段捕捉到了中间体的存在,证实了双分子中间体机理的合理性,同时推导出可能的反应机理路线图。     

内给电子体对Ziegler-Natta催化剂性能的影响

研究了5种新型内给电子体对Ziegler-Natta催化剂结构和催化性能的影响.结果表明,使用两种不同制备工艺制备的氯化镁载体均为δ晶型,而不同的内给电子体的加入使得催化剂的氯化镁载体具有不同的微晶结构和形态.在催化剂制备阶段中,内给电子体的加入方式对催化剂的性能有很大的影响.在5种内给电子体中,以cis-1,2-环己二甲酸二异丁酯为内给电子体时,催化剂的聚合活性和PP等规度最高,性能与工业催化剂相当;当选用cis-1,2-环己二甲酸二异丁酯为内给电子体,CMMS为外给电子体,硅钛物质的量之比为10及铝钛物质的量之比为100时,催化剂的聚合活性和PP等规度达到最高.     

The entry of substances into the plasma of a d.c. arc from the top surface area of an electrode

Using neutron activation analysis the variation with time of the amounts of Cu, Co and Cd left on the top surface area of the electrode were determined when these elements enter the arc in the presence of the additives KCl, KNO₃, K₂SO₄ as well as in the absence of additives. The additives studied lower the rates with which the elements leave the electrode surface, this effect being greater the lower the boiling point of the element. Additive compounds with varying anions affect the rate of evaporation of the elements from the surface of the electrode to different extents due to the effect of the anionic component of the additive on the electrode temperature. The value of the electrode temperature is not the only factor which determines the escape process of the substance from the electrode surface.     

脉冲激光溅射下固液界面生长的碳纳米管及其机理初探

以脉冲激光束直接溅射浸在水中的单质碳样品，发现在固液界面也能产生的碳纳米管，实验还发现碳纳米管的形成与样品的结构有密切的关联：石墨的层状结构越完整，碳纳米管的形成越容易，而且石墨层面相对于激光束的取向也会显著地影响碳的生成。     

Electrothermal atomization—the way toward absolute methods of atomic absorption analysis

Considering the currently prevailing opinion that electrothermal atomizers are very susceptible to matrix interferences, an opinion which is contradictory to the optimistic forecasts of the first publications, the general status of the problem to date has been investigated.The first part of the paper deals with the ideal models of the two basic types of electrothermal atomizers, viz., those of the semi-enclosed and those of open type. The graphite cuvette and the Massmann furnace have been selected for discussion in their two commercial versions—the HGA and the CRA—of the first type of atomizers; the West filament and the combined atomizers—rod-in-flame and capsule-in-flame—of the second type. The models describing the distribution of atoms in the absorbing zone have been compared and the data obtained have been used to interpret the experimentally observed differences in the sensitivity of real atomizers.The second section of the paper discusses the conformity of real atomizers relative to ideal models and to the requirement of correctly recording the absorption by means of integrating the pulses. A marked time and space non-isothermality of the commercial atomizers has been established which makes it impossible to measure the integral absorption correctly. The graphite cuvette and the combined atomizers best meet the requirements of the ideal models. On the basis of the data obtained, the possible ways of bringing the semi-enclosed atomizers closer to ideal models have been explored. In this connection, the possibility of using a graphite platform for vaporizing samples in tube furnaces as well as using the temperature-controlled furnace and the pulse heated graphite furnace with a capacitance power supply has been examined. The application of the last method ensures time and space isothermality of the absorbing layer and reduces by 10–100 times the electric power input.The third section of the paper examines the thermochemical laws governing the possible chemical effects arising from the interaction between the analytes, on the one hand, and the furnace walls, the gaseous atmosphere and the matrix, on the other. A critical review has been carried out of the results of some recent publications on investigation of sample vaporization in graphite furnaces, which reveals the fact that the temperature of absorption appearance is rarely connected with the heat of vaporization of the free element. In most instances it is determined by the sum of the heat of decomposition of the non-volatile carbide and the heat of vaporization of the free element. Thermochemical examination of the stability of the compounds formed in the gaseous phase revealed the fact that besides forming monoxides, there is the possibility of forming monocyanides. In addition, the presence of large quantities of halogens causes partial binding of the analyte as gaseous monohalides, mainly monochlorides. In order to eliminate the latter effect, it has been suggested to employ higher atomization temperatures or to bind chlorine in a stable lithium monochloride. The efficiency of the proposed methods has been tested by experiment.Our research has shown that the main reasons for the unsatisfactory status of the problem concerning the matrix effects, are connected with the use of the amplitude (peak) method of recording the absorption, with the time and space non-isothermality of the absorbing layer of the commercial atomizers, and with the formation of gaseous monohalides. All these problems may be eliminated on the basis of theoretically proved and tested methods, some of which are discussed in this paper.     

Photochemical instability of CdSe nanocrystals coated by hydrophilic thiols

The photochemical instability of CdSe nanocrystals coated by hydrophilic thiols was studied nondestructively and systematically in water. The results revealed that the photochemical instability of the nanocrystals actually included three distinguishable processes, namely the photocatalytic oxidation of the thiol ligands on the surface of nanocrystals, the photooxidation of the nanocrystals, and the precipitation of the nanocrystals. At first, the thiol ligands on the surface of a nanocrystal were gradually photocatalytically oxidized using the CdSe nanocrystal core as the photocatalyst. This photocatalytic oxidation process was observed as a zero-order reaction in terms of the concentration of the free thiols in the solution. The photogenerated holes in a nanocrystal were trapped onto the thiol ligands bound on the surface of the nanocrystal, which initiated the photooxidation of the ligands and protected the nanocrystal from any photooxidation. After nearly all of the thiol ligands on the surface of the nanocrystals were converted into disulfides, the system underwent several different pathways. If the disulfides were soluble in water, then all of the disulfides fell into the solution at the end of this initial process, and the nanocrystals precipitated out of the solution without much variation over their size and size distribution. When the disulfides were insoluble in water, they likely formed a micelle-like structure around the nanocrystal core and kept it soluble in the solution. In this case, the nanocrystals only precipitated after severe oxidation, which took a long period of time. If the system contained excess free thiol ligands, they replaced the photochemically generated disulfides and maintained the stability and solubility of the nanocrystals. The initiation stage of the photooxidation of CdSe nanocrystals themselves increased as the thickness and packing density of the ligand shell increased. This was explained by considering the ligand shell on the surface of a nanocrystal as the diffusion barrier of the oxygen species from the bulk solution into the interface between the nanocrystal and the surface ligands. Experimental results clearly indicated that the initiation stage of the photooxidation was not caused by the chemical oxidation of the system kept in air under dark conditions or the hydrolysis of the cadmium-thiol bonds on the surface of the nanocrystals, both of which were magnitudes slower than the photocatalytic oxidation of the surface ligands if they occurred at all. The results described in this contribution have already been applied for designing new types of thiol ligands which dramatically improved the photochemical stability of CdSe nanocrystals with a ligand shell that is as thin as approximately 1 nm.     

Properties of free surface of water-methanol mixtures. Analysis of the truly interfacial molecular layer in computer simulation

Molecular dynamics simulations of the vapor-liquid interface of water-methanol mixtures of five different compositions were performed on the canonical (N,V,T) ensemble at 298 K. In addition, the vapor-liquid interface of the two neat systems was simulated, as well. The obtained configurations were analyzed by means of the novel identification of truly interfacial molecules method, which provides a full list of the molecules that are right at the surface (i.e., at the boundary of the two phases). The molecular level roughness of the surface, the adsorption of the methanol molecules at the surface layer, the orientation of the surface molecules, the residence time of the molecules at the surface layer, as well as the surface aggregation of the molecules were analyzed in detail. Both the frequency and the amplitude of the surface roughness were found to become larger with an increasing methanol content. This effect was found to be stronger for the amplitude, which falls in the range of 2-4 A, depending on the composition of the system. Methanol was found to be adsorbed at the surface layer, being preferentially at the humps of the molecularly rough surface. Surface methanol prefers to orient in such a way that the O-CH(3) bond remains perpendicular to the macroscopic plane of the surface, pointing the methyl group to the vapor phase. The main orientational preference of the water molecules is to lie parallel to the surface. Methanol was found to remain considerably longer at the surface layer of the mixed systems than water. Thus, contrary to the fact that the residence times of the two molecules were found to be rather similar to each other at the surface of their neat liquids, the residence time of the methanol molecules was an order of magnitude larger than that of water molecules at the surface of their mixtures. A strong lateral microscopic segregation of the molecules was observed at the surface layer; the minor component of the system (irrespective of whether it was water or methanol) was found to form two-dimensional aggregates, leaving the rest of the surface empty for the major component. The effect of the vicinity of the vapor phase on the properties of the molecules was found to vanish very quickly: the composition of the second layer as well as the properties of the molecules of this layer (e.g., dynamics and orientation) did not differ considerably from those in the bulk liquid phase.     

Effects of T-tubules on dielectric spectra of skeletal muscle simulated by boundary element method with two-dimensional models

In order to investigate the origin of large intensity the alpha-relaxation in skeletal muscles observed in dielectric measurements with extracellular electrode methods, effects of the interfacial polarization in the T-tubules on dielectric spectra were evaluated with the boundary-element method using two-dimensional models in which the structure of the T-tubules were represented explicitly. Each model consisted of a circular inclusion surrounded by a thin shell corresponding to the sarcolemma. The T-tubules were represented by simplified two types of invagination of the shell: straight invagination along the radial directions, and branched one. Each of the models was subjected to two kinds of calculations relevant to experiments with the extracellular and the intracellular electrode methods. Electrical interactions between the cells were omitted in the calculations. Both calculations showed that the dielectric spectra of the models contained two relaxation terms. The low-frequency relaxation term assigned to the alpha-relaxation depended on the structure of the T-tubules. Values of the relaxation frequency of the alpha-relaxation obtained from the two types of calculations agreed with each other. At the low-frequency limit, the permittivity obtained from the extracellular-electrode-type calculations varied in proportion to the capacitance obtained from the intracellular-electrode-type ones. These results were consistent with conventional lumped and distributed circuit models for the T-tubules. This confirms that the interfacial polarization in the T-tubules in a single muscle cell is not sufficient to explain the experimental results in which the intensity of the alpha-relaxation in the extracellular-electrode-type experiments exceeded the intensity expected from the results of the intracellular-electrode-type experiments. The high-frequency relaxation term that was assigned to the beta-relaxation was also affected by the T-tubule structure in the calculations relevant to the extracellular-electrode-type experiments.     

Electrophoresis of a colloidal sphere in a spherical cavity with arbitrary zeta potential distributions

An analytical study is presented for the quasi-steady electrophoretic motion of a dielectric sphere situated at the center of a spherical cavity when the surface potentials are arbitrarily nonuniform. The applied electric field is constant, and the electric double layers adjacent to the solid surfaces are assumed to be much thinner than the particle radius and the gap width between the surfaces. The presence of the cavity wall causes three basic effects on the particle velocity: (1) the local electric field on the particle surface is enhanced or reduced by the wall; (2) the wall increases the viscous retardation of the moving particle; and (3) a circulating electroosmotic flow of the suspending fluid exists because of the interaction between the electric field and the charged wall. The Laplace and Stokes equations are solved analytically for the electric potential and velocity fields, respectively, in the fluid phase, and explicit formulas for the electrophoretic and angular velocities of the particle are obtained. To apply these formulas, one has to calculate only the monopole, dipole, and quadrupole moments of the zeta-potential distributions at the particle and cavity surfaces. It is found that the contribution from the electroosmotic flow developing from the interaction of the imposed electric field with the thin double layer adjacent to the cavity wall and the contribution from the wall-corrected electrophoretic driving force to the particle velocities can be superimposed as a result of the linearity of the problem.     

Electrophoresis of a spherical particle along the axis of a cylindrical pore filled with a Carreau fluid

The electrophoresis of a spherical particle along the axis of a cylindrical pore filled with a Carreau fluid is investigated theoretically. In addition to the boundary effect due to the presence of the pore, the influences of the thickness of double layer surrounding a particle and the properties of the fluid on the electrophoretic behavior of the particle are also examined. We show that, in general, the presence of the pore has the effect of retarding the movement of a particle. On the other hand, the shear-thinning nature of the liquid phase is advantageous to its movement. For both Newtonian and Carreau fluids, the mobility of a particle increases monotonically with the decrease in the thickness of double layer, but the mobility is more sensitive to the variation of the thickness of double layer in the latter. The mobility of a particle in a Carreau fluid is larger than that in the corresponding Newtonian fluid, and the difference between the two increases with the decrease in double-layer thickness; in addition, depending upon the values of the parameters assumed, the percentage difference can be in the order of 50%.     

Laser-induced incandescence study on the metal aerosol particles as the effect of the surrounding gas medium

The fundamental heat transfer phenomena caused by the 1064 nm pulsed laser irradiations on the molybdenum aerosol particles were investigated by monitoring the time evolutions of the incandescence spectra using an ICCD detector with a multichannel spectrograph. The particle temperatures were evaluated from the incandescence spectra with the Planck function, and the cooling processes of the laser-heated particles were investigated. By measuring the decrease in the laser-heated particle temperatures with different surrounding media, the roles of the heat transfer processes such as vaporization, thermal radiation, and heat conduction to the surrounding media were discussed. The influences of the vaporization processes on the total heat transfer phenomena were investigated by monitoring the emissions of the constituent molybdenum atoms in the laser-induced incandescence spectra of the aerosol particles and also by investigating the relationships between the intensity of the incandescence and the fluence of the 1064 nm pulsed laser. The calculations using the theory of heat conduction suggested that the diameters of the particles produced by the photolysis of Mo(CO)6 depended on the nature of the surrounding gases.     

Precise construction on the structure of zeolite microcapsules

In this paper, the precise construction on the structure of silicalite-1 microcapsules (S1) was specifically described. The interior carbon modifications and the outside mesoporous functionalizations were successfully conducted and each sample was characterized in detail. It was found that the carbon networks could be formed inside the zeolite microcapsules via the pretreatment of sugar injections. The uniformity of the distinct microcapsule could be regulated by adjusting the sugar concentrations. With the encapsulated Pt species inside the MSSs, the nano-particles could be dispersed well within the carbon network. On the other hand, during the fabrication of the mesoporous materials outside the microcapsules, the template and the acidity of the system could play an important role in determining the morphology of S1. Besides, the PDDA modification on the shell of S1 could help the combination of the meso-layer and the shell of S1 at nano-scale. The thickness of the outside mesopore could be modulated through the controlling of the silica content.     

Inclusion complexes between beta-cyclodextrin and a Gemini surfactant in aqueous solution: an NMR study

(1)H NMR spectra, diffusion-ordered NMR (DOSY), and 2D rotating-frame Overhauser enhancement spectroscopy (ROESY) experiments for aqueous solutions at 298 K containing the gemini surfactant, bis (dodecyl dimethylammonium)diethyl ether dibromide (12-EO(1)-12), in the absence and presence of beta-cyclodextrin (beta-CD) were used to characterize the surfactant and to determine the effects of the complexation in the micellization. For the binary system, the critical micelle concentration (cmc), the aggregation number, the stepwise micellization constant, and the size of the monomer have been obtained by studying the dependence of the chemical shifts and the self-diffusion coefficients with the concentration of surfactant. For the ternary system, the analysis of the (1)H NMR spectra and the self-diffusion coefficients reveal the formation of complexes of 1:1 and 2:1 stoichiometry (beta-CD:gemini), with a calculated stability constant for the second binding step higher than that of the first. The values of the hydrodynamic radii of the complexes were obtained from the calculated diffusion coefficients. The presence of beta-CD modifies the cmc in an extension that indicates mainly the formation of a 2:1 complex. The analysis of the chemical shifts of the surfactant indicates the nonparticipation of the complexes into the micelles. ROE enhancements depend substantially on the amount of the macrocycle added and therefore on the stoichiometry; at low concentrations of beta-CD, one of the hydrocarbon chains binds favorably with the cavity whereas the other interacts with the outer face. By contrast, at higher concentrations of beta-CD, the two hydrocarbon tails are included in two different macrocycles.