A new nebulizer for atomic spectrometry

The rotating disc nebulizer has been redesigned with respect to the principle parameters that determines its analytical performance. The flow pattern of the aerosol attained has been optimized by altering the shape of the inner chamber of the nebulizer to obtain optimum aerodynamic characteristics. The optimum angle of impact and "free flight" distance has been established using particle size distribution and mass transport efficiency as criteria. Analytical characteristics have been determined by monitoring the emission signal from aqueous standards. The accuracy has been assessed by using reference steel samples. Using standard solutions of different viscosity the performance of the nebulizer with respect to viscosity changes of the sample has been compared with that of a commercial Meinhardt nebulizer. The rotating disc nebulizer has been less affected by changes in viscosity making it possible to use this nebulizer with slurry and oil samples.     

Solvent dependent analysis of isotropic Raman band shape of C=O stretching vibration

The isotropic Raman band shape corresponding to C=O stretching vibration of some molecules has been studied in neat liquids and as a function of solvent concentration using both polar and non-polar solvents. The Raman band shape was analyzed on the basis of correlation with the Lorentzian line shape by employinga simple method of linear curve fitting. In neat liquids and in low solvent concentration region, the band shape was found to be non-Lorentzian. With the gradual increase in solvent concentration the band shape approaches a Lorentzian function. The plot of the correlation coefficient for a Lorentzian shape shows a discontinuity in the intermediate range of solvent concentration. The influence of the structural characteristics of the solute and the solvent systems on the reference mode and various multipolar interactions together with the time varying spatial distribution of solvent molecules with respect to the reference molecule are expected to govern the microenvironmental fluctuations. This may be responsible for the discontinuity in the intermediate solvent concentration region.     

Facile solution synthesis of hexagonal Alq3 nanorods and their field emission properties

A facile self-assembly growth route assisted by surfactant has been developed to synthesize tris(8-hydroxyquinoline)aluminium (Alq(3)) nanorods with regular hexagonal shape and good crystallinity, which exhibit field-emission characteristics with a very low turn-on field of ca. 3.1 V microm(-1) and a high field-enhancement factor of ca. 1300.     

Coherent radiation from high-current electron beams of linear accelerators and its applications

The characteristics of the far-infrared light source using the coherent radiation emitted from a high-energy short electron bunch have been investigated. The coherent radiation has a continuous spectrum in a submillimeter to millimeter wavelength range and the brightness is relatively high. The spectrum of the radiation is determined by the longitudinal form factor of the electron bunch. The operational conditions of a high-current linear accelerator have been optimized using an electron bunch shape monitor. The coherent transition radiation light source has been applied to absorption spectroscopy for liquid water and to an imaging experiment for a leaf of rose.     

A new nebulizer for atomic spectrometry

The rotating disc nebulizer has been redesigned with respect to the principle parameters that determines its analytical performance. The flow pattern of the aerosol attained has been optimized by altering the shape of the inner chamber of the nebulizer to obtain optimum aerodynamic characteristics. The optimum angle of impact and free flight distance has been established using particle size distribution and mass transport efficiency as criteria. Analytical characteristics have been determined by monitoring the emission signal from aqueous standards. The accuracy has been assessed by using reference steel samples. Using standard solutions of different viscosity the performance of the nebulizer with respect to viscosity changes of the sample has been compared with that of a commercial Meinhardt nebulizer. The rotating disc nebulizer has been less affected by changes in viscosity making it possible to use this nebulizer with slurry and oil samples.     

均分散氯化氧铋胶体粒子制备

近年来均分散体系发展很快,在催化剂、功能陶瓷、传感器、超导体、涂料以及医药和化妆品等方面都有广泛的应用.Matijevic 等人曾对均分散体系制备作过系统研究,关键在于有效地控制晶核生长速率.我们曾对均分散体系制备作过多种研究.本文研制的BiOCl 均分散粒子可作为医药、化妆品方面的增白收敛剂、精细陶瓷的原料等.本工作是利用铋盐水解生成碱式铋盐沉淀.因此利用控制酸度抑制水解.水解时加入其它物质使其有效地控制品核生长.在水解过程中,我们加入烷基苯磺酸和硫酸钠来改变固液之间的界面性质,有利于晶核一次性生长和晶核稳定生成.     

Growth of polyethylene single crystals from the melt: Morphology

Three-dimensional shape of polyethylene single crystals grown from the melt has been studied. Two distinct types of lateral habit have been obtained: lenticular shape (type A) and truncated lozenge (type B) in the range of regime I and II. Electron microscopy has revealed chair-like shape of type B crystal and reconfirmed the planar shape of type A crystal. In the type B crystal, spiral growth has occurred frequently in the {110} sectors and the sense of the handedness of spiral terraces has been maintained. It has been, suggested that the frequens occurrence of spiral growth is responsible for a morphological change (axialite-spherulite) accompanying the regime I–II transition. The origin of the chair-like crystals has been discussed and, a possible mechanism has been suggested for the formation of spiral terraces; the mechanism is based on a distortion caused by the three-dimensional shape of chair-like crystals. It has been found that the chair-like crystals are curved in the opposite way to S-shaped lamellae observed by Bassett and Hodge in banded spherulites. In fact, the present work has led to the recognition of further classes of crystal with curving cross-sections and of distinctions between them. In final analysis, a unifying thread has been identified between lateral habits, growth kinetics and three-dimensional shape of lamellae, in turn, leading to some rationalization of multilayer developments including twisting in banded spherulites, the latter based on existing suggestions in the literature.     

A new perspective of shape recognition to discover the phase transition of finite‐size clusters

An ultrafast shape‐recognition technique was used to analyze the phase transition of finite‐size clusters, which, according to our research, has not yet been accomplished. The shape of clusters is the unique property that distinguishes clusters from bulk systems and is comprehensive and natural for structural analysis. In this study, an isothermal molecular dynamics simulation was performed to generate a structural database for shape recognition of Ag? Cu metallic clusters using empirical many‐body potential. The probability contour of the shape similarity exhibits the characteristics of both the specific heat and Lindemann index (bond‐length fluctuation) of clusters. Moreover, our implementation of the substructure to the probability of shapes provides a detailed observation of the atom/shell‐resolved analysis, and the behaviors of the clusters were reconstructed based on the statistical information. The method is efficient, flexible, and applicable in any type of finite‐size system, including polymers and nanostructures. © 2014 Wiley Periodicals, Inc.     

Molecular shape diversity of combinatorial libraries: a prerequisite for broad bioactivity

A computational method to rapidly assess and visualize the diversity in molecular shape associated with a given compound set has been developed. Normalized ratios of principal moments of inertia are plotted into two-dimensional triangular graphs and then used to compare the shape space covered by different compound sets, such as combinatorial libraries of varying size and composition. We have further developed a computational method to analyze interset similarity in terms of shape space coverage, which allows the shape redundancy between the different subsets of a given compound collection to be analyzed in a quantitative way. The shape space coverage has been found to originate mainly from the nature and the 3D-geometry (but not the size) of the central scaffold, while the number and nature of the peripheral substituents and conformational aspects were shown to be of minor importance. Substantial shape space coverage has been correlated with broad biological activity by applying the same shape analysis to collections of known bioactive compounds, such as MDDR and the GOLD-set. The aggregate of our results corroborates the intuitive notion that molecular shape is intimately linked to biological activity and that a high degree of shape (hence scaffold) diversity in screening collections will increase the odds of addressing a broad range of biological targets.     

Predicting shape memory characteristics of polyurethane in three‐point bending deformation

As a kind of an exceptional material, the temperature‐responding shape memory polymer can fix a temporary shape when cooled down and recover to its original shape when reheated up. Several models have been developed to describe the process. In the present work, we use the generalized Maxwell model to predict the shape memory characteristics of polyurethane in three‐point bending deformation by means of three‐dimensional finite element simulation. The deformation–temperature–stress behavior is obtained numerically. The results reveal that under the condition of accelerating reheating rates at the stage of stress‐free recovery, the maximum recovery rate occurs at higher temperature whereas the recovery ratio decreases. When the deformation degree enlarges, the maximum recovery stress increases in the situation of constrained recovery. The micro‐motion theory of polymer segments is used to explain the characteristics in the shape memory cycle. The simulated results agree well with previous researches, which demonstrate that the simplified model and the numerical simulation method are helpful for both scientific research and engineering development about shape memory polymers. Copyright © 2014 John Wiley & Sons, Ltd.     

Is molecular rotation really influenced by subtle changes in molecular shape?

In an attempt to seek out whether the reorientation time of a solute molecule is influenced by marginal changes to its shape, rotational relaxation of four coumarin solutes that are almost identical in size but subtly distinct in shape has been investigated in a viscous nonpolar solvent as a function of temperature. It has been observed that the reorientation times of the four coumarins differ significantly from one another. The four solutes have been treated as asymmetric ellipsoids and Stokes-Einstein-Debye hydrodynamic theory has been employed to calculate the shape factors and boundary condition parameters. The measured reorientation times when normalized by respective shape factors and boundary condition parameters can be scaled on a common curve, which is an indication that ellipsoid based hydrodynamic theory is adequate to model the reorientation times even when the differences in the shapes of the solute molecules are minimal.     

Model shape transitions of micelles: spheres to cylinders and disks

We present a microscopic analysis of shape transitions of micelles of model linear nonionic surfactants. In particular, symmetric H(4)T(4) and asymmetric H(3)T(6) surfactants have been chosen for the study. In a previous work, it has been observed that symmetric surfactants have a strong tendency to prefer spherical micelles over a wide range of chemical potentials, while asymmetric surfactants undergo shape transitions between a spherical micelle at low concentration to other forms, mainly finite cylindrical micelles. This study combines the application of a two-dimensional single-chain mean-field theory (SCMFT) with Monte Carlo (MC) simulations of exactly the same systems. On the one hand, the characteristics of the SCMFT make this method suitable for free energy calculations, especially for small surfactants, due to the incorporation of relevant microscopic details in the model. On the other hand, MC simulations permit us to obtain a complete picture of the statistical mechanical problem, for the purpose of validation of the mean-field calculations. Our results reveal that the spherical shape for the symmetric surfactant is stable over a large range of surfactant concentrations. However, the asymmetric surfactant undergoes a complex shape transition that we have followed by calculating the standard chemical potential as a function of the aggregation number. The results indicate that the system forms prolate spheroids prior to developing short capped cylinders that gradually grow in length, with some oscillations in the energy of formation. The most important result of our work is the evidence of a bifurcation where, together with the elongated objects, the system can develop oblate aggregates and finally a torus shape similar to a red blood cell.     

Ethane adsorption in slit-shaped micropores: influence of molecule orientation on adsorption capacity

Adsorption of ethane in a slit shaped micropore system has been studied by Monte Carlo molecular simulation by considering this hydrocarbon as a two interacting sites molecule. Ethane adsorption in pore sizes from 0.41 to 1.66 nm was simulated at 303 K. Microscopic characteristics of the adsorbed phase have been studied for pores of different size, comparing two density profiles: the molecule centre of mass profile and the molecular interaction site profile. Averaged angle distribution of molecule positions with respect to the slit plane across the pore width has been also obtained by simulation. These results were related to ethane molecule packing efficiency, which is also related to the adsorption capacity in terms of the adsorbed phase density. Packing efficiency presents an oscillation shape as the result of the adsorbate disorder inside the pore. Pressure influence on the adsorption has been studied by following pore filling by simulation. When pore condensation takes place and for pressures above condensation, fluid-fluid interactions are determinant in molecule disorder observed between the two adsorbed layers.     

热适性形状记忆聚合物

动态共价交联聚合物的研究具有悠久的历史,其早期的工作着眼于如何解决应力松弛带来的聚合物材料力学性能降低的问题.20世纪90年代以来,利用动态共价键来主动设计聚合物网络的特殊可适性逐渐成为研究主流,其中包括自修复和重加工性.然而,受到动态共价键的种类、通用性及所实现功能的特异性等限制,对于动态共价交联聚合物网络的研究尚停留在基础阶段.本文以本课题组近期在动态共价交联形状记忆聚合物的研究为基础,结合其他相关工作,展示了通用共价键(酯键及氨酯键)的动态可逆性,并利用其设计了具有特殊性能和潜在商业化价值的形状记忆聚合物.在此基础上,我们提出分子结构设计及宏观性能均不同于传统热塑性和热固性形状记忆聚合物的第3类形状记忆聚合物,即热适性形状记忆聚合物.     

Synthesis and characterisation of biodegradable liquid crystal elastomer with the property of shape recovery

Novel shape recovery biodegradable liquid crystal (LC) elastomer is reported here for the first time. The method of synthesis of the shape memory biodegradable LC elastomer has been explored. During the reaction, the LC molecules are added to form LC polymers, and then cross-linking agent is added to form a cross-linked LC elastomer. The LC elastomer in this work is hydrophilic. In vitro degradation of the LC elastomer films in a buffer of pH 7.4 at 37°C shows that the LC elastomer has good degradability. The biodegradable LC elastomer exhibits liquid crystalline behaviour and has shape memory ability. Its shape memory and actuating properties also have been studied. The reversible transition from liquid crystalline phase to isotropic phase is utilised as the switching mechanism for these stimuli-responsive materials. When reheating the LC elastomer to 120°C, the shape will recover.     

Continuous flow nano-technology: manipulating the size, shape, agglomeration, defects and phases of silver nano-particles

Spinning disc processing (SDP) is an instantaneously scalable, continuous flow and high throughput flash nano-fabrication technology which embraces green chemistry metrics. It has been used to prepare silver nano-particles with remarkable control in size (5-200 nm), shape (spheroidal, acicular or agglomerate rosettes), surface characteristics, and phase (cubic versus hexagonal), along with imparting defects for particles >10 nm diameters. The control is associated with changing the nature of the stabilising surfactant (respectively, starch, polyethylene glycol and poly(4-vinylpyridine)), the concentration of the reactants, and flow rates.     

4,5-环氧环己烷1,2-二甲酸二缩水甘油酯与2-甲基咪唑的固化特征

用扭辫分析法(TBA)、示差扫描量热法(DSC)对4,5-环氧环己烷1,2-二甲酸二缩水甘油酯、二甲基咪唑体系的固化特征作了研究;由TBA法测得的玻璃化时间、固化温度的关系曲线呈W型,表明本体系整个固化过程系通过两个交联反应阶段完成的,即其玻璃化曲线在80℃通过最小值后的向上延伸为交联反应第一阶段,在120℃以上,玻璃化时间又趋缩短,并在180℃通过第二个最小值后又向上急剧延伸为交联反应的第二阶段。第一、二阶段反应趋近完全时试样的玻璃化温度分别为130℃、190℃。参照Farkas等的工作对本体系的交联反应过程作了讨论。     

Oscillatory shear response of moisture barrier coatings containing clay of different shape factor

Oscillatory shear rheology of barrier coatings based on dispersed styrene-butadiene latex and clay of various shape factors or aspect ratio has been explored. Barrier performance of these coatings when applied to paperboard has been assessed in terms of water vapour transmission rates and the results related to shape factor, dewatering and critical strain. It has been shown that a system based on clay with high shape factor gives a lower critical strain, dewatering and water vapour transmission rate compared with clays of lower shape factor. The dissipated energy, as calculated from an amplitude sweep, indicated no attractive interaction between clay and latex implying a critical strain that appears to be solely dependent on the shape factor at a constant volume fraction. Particle size distribution was shown to have no effect on the critical strain while coatings of high elasticity exhibited high yield strains as expected. The loss modulus demonstrated strain hardening before the elastic to viscous transition. The loss modulus peak was identified by a maximum strain which was significantly lower for a coating based on clay with a high shape factor. The characteristic elastic time was found to vary between 0.6 and 1.3s. The zero shear viscosity of barrier dispersion coatings were estimated from the characteristic elastic time and the characteristic modulus to be of the order of 25-100 Pa s.     

An investigation into compressive responses of shape memory polymeric cellular lattice structures fabricated by vat polymerization additive manufacturing

A combination of additive manufacturing techniques with shape memory materials, so that the shape, property, or functionality of a 3D printed structure can change as a function of time, has recently created new progress in 4D printing. Low-density lattice structures, due to their unique mechanical properties and engineering characteristics, have been candidates for lightweight structures and energy absorbing applications. In the present work, Rhombic and Body-Centered Cubic (BCC) cellular lattice structures, as well as cylindrical bulk samples, were designed and fabricated with Digital Light Process (DLP) by using shape memory resin. The energy absorption of SMP samples was studied in terms of the capabilities of absorption and recovery. In addition, deformation mechanisms of the structures, the influence of strain rate, cyclic behavior and the strain recovery of the structures after each cycle were investigated. All the studies were done in three different cold, warm and hot programming schemes to evaluate the effects of temperature on shape memory effect of the products. Although both structures showed nearly the same strain recovery rates at all conditions, Rhombic structure was found to possess better functional and structural behaviors than BCC lattice in terms of strength, stiffness, and absorption as well as recovery of the induced energy.     

Radiation crosslinked Polyolefinic blends: exploring thermally tuned dual Shape Memory character

Shape memory behavior of thermally triggered polymeric materials based on ethylene octene copolymer (EOC) and ethylene propylene diene rubber (EPDM) has been studied in details. Investigation of the shape memory behavior of uncrosslinked EOC–EPDM and electron beam crosslinked EOC–EPDM blends have been pursued thoroughly. Shape memory study has been carried out at 60°C, which shows that with the effect of electron beam radiation shape fixity behavior of the crosslinked blends becomes poor as compared with its uncrosslinked blend system whereas the improvement in shape recovery behavior takes place after the exposure to electron beam radiation. Morphology study by Atomic Force Microscopy (AFM) and crystallinity study by X‐ray diffraction analysis also give the clear idea regarding the formation of crosslinked network structure. Improvement in gel content with increasing radiation dose supports the formation of network structure. Even after the crosslinking in presence of electron beam radiation also, it has been found that crosslinked EPDM rich blends is superior in terms of shape memory behavior point of view. Lower decay of stress value coupled with lower relaxation ratio of crosslinked EPDM rich blend support its superior shape memory behavior. Copyright © 2016 John Wiley & Sons, Ltd.