扫描电子显微镜对样品的要求及样品的制备

扫描电子显微镜对样品的要求很严,要求样品必须是固体,且做到五无:无毒、无放射性、无污染、无磁、无水分,成分稳定,块状样品大小要适中,粉末样品要进行特殊处理,对不导电和导电性能差的样品要进行镀膜,且要选择适当的镀膜仪,方能达到理想的分析效果.     

高分子/石墨复合材料的制备与导电性能的研究进展

介绍了近年来高分子/石墨复合材料制备方法和导电机理的研究进展。通过氧化、插层以及插层后加热可以在石墨碳层上引入极性基团,提高其比表面积,有利于高分子进行插层。用处理后比表面积高的石墨制备复合材料可以降低材料的渗滤值,提高材料的导电性能。复合材料的导电机理可以用渗滤理论来解释。     

液体样品对核磁图谱质量影响因素探讨

结合样品核磁测试结果,以具体实例的形式,总结了核磁样品分析的基本要求,分析了核磁管和氘代试剂的选择、样品制备及pH值等因素对核磁测试结果的影响,并提出了样品最优测试条件:核磁管管体内外表面要足够光洁均匀,在高温条件下,优先选用升温核磁管.尽量选择小支封装氘代试剂,降低水峰的影响,并且应考虑样品的性质,避免试剂与测试样品发生反应.样品必须与溶剂充分混合均匀,样品量要在溶液粘度与灵敏度之间做好平衡.在分析与氧、氮和硫共价相连的氢原子时,应该选择恰当的pH溶液.以上研究结果可以为其它样品核磁测试提供借鉴指导.     

Über ein neues Verfahren zur Ermittlung des Endpunktes bei registrierten potentiometrischen Titrationen

Among all straight lines originating from one point and intersecting the titration curve three times, there is only one to be bisected by the inner point of intersection or to be divided in proportion to asymmetry factors. This point is to be considered as a more correct approximate value of the equivalence point than that obtained by previous methods. Practicable results are available, because in this way the qualities of asymmetrical titration curves can be taken into consideration. The asymmetry factors can be calculated and taken from tables or can be determined experimentally.     

Supercritical-fluid chromatography: Open columns vs packed columns

Supercritical-fluid chromatography (SFC) may be performed either in open (capillary) columns or in packed columns. Both approaches have been demonstrated numerous times in the literature. In this contribution it will be attempted to discuss some aspects of columns for SFC. Some advantages of both types of columns will be identified. Attention is paid to the stationary phase film thickness, the speed of analysis, and to the maximum number of theoretical plates (effect of column pressure drop). In this brief contribution many questions will be left unanswered and many significant aspects will be left undiscussed, illustrating that much research remains to be done in this area.     

染料结合2μm无孔硅胶亲和填料的制备与应用

在２μｍ无孔硅胶表面键合３ 氨丙基 三乙氧基硅烷（ＡＰＳ）,并与三嗪染料活性蓝Ｆ３ＧＡ（ＣｉｂａｃｒｏｎＢｌｕｅＦ３ＧＡ,ＣＢ）反应,制得亲和色谱填料,并采用扫描电镜、元素分析、ｐＨ稳定性测试对此填料进行鉴定与表征。该填料具有良好的色谱性能,且对生物大分子有一定的亲和选择性,改变ｐＨ值及离子强度对溶菌酶的结合量有明显影响,可用于分离卵清蛋白（Ｏｖａｌ）和溶菌酶（Ｌｙｓ）,且对α ,β ,γ 球蛋白有不同的亲和作用,并可从鸡蛋清中制备少量溶菌酶。     

Neue verfahren zur jodometrischen mikrobestimmung von jodid- bzw. Bromidion

The methods described above are based on the fact, that iodide can be determined as iodate on iodometric way after oxidation with freshly prepared chlorine water and after removal of excess of free chlorine by means of potassium cyanide. However oxidation may be carried out by adding of hypobromite the excess of which can be removed by adding of phenol water.Bromide can be transformed to BrCl by means of an excess of chlorine water. BrCl reacts with potassium cyanide under formation of cyanogen bromide and chloride. The excess of free chlorine would be removed as cyanogen chlorine and chloride. The cyanogen bromide formed can be measured on the usual iodometric way.     

Development and applications of time-of-flight neutron depth profiling (TOF-NDP)

Neutron depth profiling (NDP) is a surface analysis technique based on the irradiation of samples with thermal or sub-thermal neutrons, and subsequent release of charged particles. Emitted particles rapidly lose kinetic energy primarily through interactions with the electrons of the substrate material. The depth of the reaction site can be found by using stopping power correlations. In conventional NDP, particle residual energy is measured by using a silicon semiconductor detector. In time-of-flight NDP (TOF-NDP), the energy can be determined by particle flight time. Time measurement can be made more sensitively than the energy measurement. Silicon semiconductor detectors can be replaced by microchannel plates (MCP). In this study, TOF-NDP concept will be briefly explained; Penn State TOF-NDP facility will be introduced; preliminary measurements performed with an alpha-source will be presented.     

Review of Mesoscopic Modeling of Liquids in Materials Science

Mesoscopic theories can be used in the field of materials science to derive local average properties of relevance to the engineer such as flux, pressure, average density or composition. In the following density functional theory will be described and applied to different systems of interest and in particular, to materials formed from complex liquids as characterized by atomic structure and the type of interaction between the individual particles. The calculation of the solid to liquid transition will be explained in detail as a prototype for other order disorder transitions. The theory of polymers in solution will be revisited and used to calculate phase separation in mixtures. An extension of the theory to include the orientation of rodlike, long molecules will be applied to liquid crystals. In the presence of an interface, the system properties depend strongly on position in space and can be predicted from parameters obtained in the bulk in a square gradient approximation for sufficiently smooth and small deviations from the uniform distribution. A phase transition is often used to prepare heterogeneous materials by nucleation and growth. It will be shown how the equilibrium theory can be extended to study the dynamics of nonequilibrium phenomena.     

Reaction force constant and projected force constants of vibrational modes along the path of an intramolecular proton transfer reaction

We have explored the relationships between the reaction force F(ξ), the reaction force constant κ(ξ) and the projected force constants of the intramolecular proton transfer HO−NS → ON−SH along the intrinsic reaction coordinate ξ. The structural changes and energetics associated with the reaction are analyzed in terms of the three regions defined by F(ξ): reactant, transition and product. The significance of the similarity between κ(ξ) and the variation of the force constant associated to the reaction coordinate mode, k_ξ(ξ), is discussed in detail.     

Measurement of near zero concentration: recording and reporting results that fall close to or below the detection limit

Issues relating to the recording and reporting of analytical data obtained where the concentration of analyte is around or below the detection limit are discussed. The following recommendations are proposed. Analytical results should be recorded by the analyst exactly as they occur, including any negative results, and such records retained for an appropriate length of time. For the purposes of quality assurance in the laboratory (including method validation, internal quality control, and proficiency testing), negative results should be used as they stand. Analytical results reported to a customer should be accompanied by a statement of uncertainty including, in the present context, uncertainty at low concentrations of analyte. The method of editing of reported results must be a contractual matter between the analyst and the customer, but a statement of the procedure used should accompany the results and should be explicit. Normally such editing should be restricted to setting negative results to zero. The customer should be encouraged to pass on the statement to all end users. Data intended for the public domain should be accompanied by a statement detailing the uncertainty, the method of editing, and the location of the unedited data. Most types of statistical processing of datasets containing low concentrations of analyte should be undertaken on the unedited data.     

电化学噪声测量分析系统设计与实现

根据电化学噪声原理,利用微机技术设计实现了电化学噪声测量分析系统。该系统具有高灵敏度,自动选择量程,多回路自动测量,可调整采样参数等功能,并在时／频域内对所测量的电化学噪声进行分析。     

问题、项目引领式教学法在高校有机化学教学中的应用

问题、项目引领式教学法可分为问题引领式与项目引领式教学两个部分。问题引领式教学法可用于课程的基础部分教学;项目引领教学法主要用于学生已掌握一定的基础知识之后,教师有针对性地提出一些目前亟待解决的小的项目让学生提出思路及解决办法。通过两种方法的互相补充,可显著提高学生对有机化学这门课程的学习兴趣,也能使有机化学的理论知识与实践能力更紧密地联系在一起,从而提高该课程的教学效果,同时也激发学生创新的潜能。     

Controlling nanoparticle formation via sizable cages of supramolecular soft materials

We present a new generic strategy to fabricate nanoparticles in the "cages" within the fibrous networks of supramolecular soft materials. As the cages can be acquired by a design-and-production manner, the size of nanoparticles synthesized within the cages can be tuned accordingly. To implement this idea, both selenium and silver were chosen for the detailed investigation. It follows that the sizes of selenium and silver nanoparticles can be controlled by tuning the pore size of the fiber networks in the material. When the concentration of the gelator is high enough, monodisperse nanoparticles can be prepared. More interestingly, the morphology of the nanoparticles can be altered: silver disks can be formed when the concentrations of both the gelator and silver nitrate are sufficiently low. As the fiber network serves as a physical barrier and semisolid support for the nanoparticles, the stability in the aqueous media and the ease of application of these nanoparticles can be substantially enhanced. This robust surfactant-free approach will not only allow the controlled fabrication of nanoparticles, but also can be applied to the fabrication of composite materials for robust applications.     

Light activated patterning of dye-labeled molecules on surfaces

This Communication describes a novel method for patterning proteins, ligands, or other organic/inorganic species onto solid substrates. The process works by linking the moiety of interest to a fluorophore that can be subsequently photobleached and bound to the interface. The technique can be performed in aqueous solution and allows several species to be addressed onto the surface simultaneously by using different frequencies of light. Because the method can be used with fluorophores excited by visible light, shorter and more damaging wavelengths can be avoided.     

关于物理化学课程基本内容教学改革的建议

对物理化学教学改革提出以下4条建议：(1)教学内容要适应科学发展;(2)内容构架要以解决科学问题为主线;(3)教学要注重沟通知识模块间的科学联系;(4)明确指出各知识模块的科学应用。     

Biocompatibility of nanofilm-encapsulated silicone and silicone-hydrogel contact lenses

A material placed in or in contact with a biological system, that causes the minimum perturbation that can be tolerated by the host biological system, can be considered to be biocompatible. The major effects caused by a contact lens can be considered to be 1) the blocking of the natural supply of oxygen to the epithelium cells of the cornea, 2) interference with the normal evaporation of water from the tear fluid layer, and 3) hindrance of the normal functions of blinking for replenishing oxygen-saturated tear fluid and removing dead epithelium cells, which result from apoptosis. The encapsulation of a highly oxygen-permeable contact lens by a nanofilm with an imperturbable surface state minimizes all these terms. The encapsulated contact lens can be worn safely in extended wear.     

The Morphology of Liquid-Crystalline Polymers and the Possible Consequences for their Rheological Behaviour

Abstract

Polymer liquid crystals can occur as polydomain materials where the domain size may be tens of microns. While the material within each domain may be characterized by a common order parameter, the directors of the domains can be more or less randomly distributed. Since the transition from polydomain to monodomain material only involves the removal of grain boundaries and the alignment of directors, the free energy change must necessarily be small. Such a transition can readily be achieved, therefore, by the action of any external field: electrical, magnetic, stress or surface. In this work optical photomicrographs of polymeric liquid crystals with widely varying and in some cases well controlled morphologies are presented. Probable dependence of rheological behaviour on morphology is also discussed. Such dependence is expected to be considerable under certain conditions. Due to experimental and sample limitations, however, direct correlations of rheology and morphology are sparse. Morphological consequences for the rheology of liquid-crystalline materials can be exemplified by the following possibilities. In contrast to the case of isotropic melts, wall effects can be non-negligible. Zero shear rate rheological parameters are not expected to be uniquely defined quantities since the domain sizes are large and the director may not be effectively averaged over typical sample dimensions. Non-zero shear-rate measurements of rheological parameters is effected by the propensity of: (1) individual domain directors to align under the influence of a stress field and (2) flow alignment to dominate surface-induced alignment above some critical shear rate. The effects might be manifested by a non-newtonian regime as well as yield stress behaviour and thixotropy. The kinetics of relaxation from mono- to poly-domain material has implications for the dynamic response and rheological hysterises of the material.     

The Morphology of Liquid-Crystalline Polymers and the Possible Consequences for their Rheological Behaviour

Polymer liquid crystals can occur as polydomain materials where the domain size may be tens of microns. While the material within each domain may be characterized by a common order parameter, the directors of the domains can be more or less randomly distributed. Since the transition from polydomain to monodomain material only involves the removal of grain boundaries and the alignment of directors, the free energy change must necessarily be small. Such a transition can readily be achieved, therefore, by the action of any external field: electrical, magnetic, stress or surface. In this work optical photomicrographs of polymeric liquid crystals with widely varying and in some cases well controlled morphologies are presented. Probable dependence of rheological behaviour on morphology is also discussed. Such dependence is expected to be considerable under certain conditions. Due to experimental and sample limitations, however, direct correlations of rheology and morphology are sparse. Morphological consequences for the rheology of liquid-crystalline materials can be exemplified by the following possibilities. In contrast to the case of isotropic melts, wall effects can be non-negligible. Zero shear rate rheological parameters are not expected to be uniquely defined quantities since the domain sizes are large and the director may not be effectively averaged over typical sample dimensions. Non-zero shear-rate measurements of rheological parameters is effected by the propensity of: (1) individual domain directors to align under the influence of a stress field and (2) flow alignment to dominate surface-induced alignment above some critical shear rate. The effects might be manifested by a non-newtonian regime as well as yield stress behaviour and thixotropy. The kinetics of relaxation from mono- to poly-domain material has implications for the dynamic response and rheological hysterises of the material.     

Four-arm oligonucleotide Ni(II)-cyclam-centered complexes as precursors for the generation of supramolecular periodic assemblies

The development of a multiarm metal-centered DNA building block as a precursor for the construction of supramolecular assemblies has relied upon the preparation of a Ni(II)-1,4,8,11-tetrazacyclotetradecane ligand (cyclam) functionalized with four linkers. This complex can be incorporated into a support-bound DNA sequence and the remaining three linkers can then be elongated by DNA synthesis. The result is a Ni(II)-cyclam complex tethering four 20-mer DNA strands. This building block, designed to be tetrahedral in nature, can in principle be used to form tetrahedral assemblies. These assemblies can be designed to be of known size and composition or permitted to grow into complexes of essentially infinite size, ideally the macroscopic version of a crystal.