共查询到18条相似文献,搜索用时 203 毫秒
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采用原子转移自由基方法(ATRP)合成窄分布的末端基为巯基的四臂星型聚苯乙烯(4-PS-SH).巯基容易被空气中的氧气氧化生成二硫键,会引起四臂星型聚苯乙烯分子间交联.利用激光光散射研究了四臂聚苯乙烯在亚浓溶液中氧化交联生成大的胶束进而生成宏观化学凝胶的过程.静态激光光散射测量结果表明四臂聚苯乙烯亚浓溶液以及凝胶样品的时间平均散射光强不随测量位置的变化而涨落,说明此凝胶是结构均一的化学凝胶.动态光散射结果表明在四臂聚苯乙烯亚浓溶液氧化生成凝胶的过程中,动态强度-强度时间相关函数的慢运动衰减的贡献最初随着氧化时间的增加逐渐增强,当氧化反应进行到一定程度时慢运动的贡献又逐渐减弱,最终慢运动消失.生成的化学凝胶的相关函数与最初亚浓溶液的相关函数几乎重合.静态和动态激光光散射结果表明生成的四臂聚苯乙烯凝胶是结构均匀的化学凝胶. 相似文献
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电解质溶液中牛血清白蛋白分子相互作用的动态光散射研究 总被引:2,自引:0,他引:2
溶液中粒子斥与吸引作用力,这种依赖关系可以通过作用参数λ来的扩散系数对浓度的依赖关系主要取决于粒子在溶液中所占的体积分数和粒子间的排表示。本研究利用动态光散射技术测量了不同离子强度下牛血清白蛋白分子的扩散系数,求出了相应条件下的λ值。结果表明,在低离子强度下,λ是正值,蛋白质分子间的作用以排斥力为主,随着离子强度的逐渐增大,λ变为负值,蛋白质分子间的作用以吸引力为主,当离子强度大于0.5mol/L的时候,蛋白质开始发生聚集。利用DLVO理论的两体硬球相互作用模型解释了蛋白质分子间相互作用的变化规律:随着离子强度的增加,静电斥力被屏蔽,范德华分子作用力起主要作用。根据值与离子强度变化的相关性,回归出了蛋白质参数:在实验条件下,蛋白质所带的有效电荷Zr=-9.0e、Hamaker常量AH=2.8kBT。实验结果表明:动态光散射技术可以有效地用来研究蛋白质分子间的相互作用。 相似文献
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采用配液结晶法制取了溶菌酶蛋白质晶体, 使用动态光散射测量了溶液中聚集体的颗粒度几率分布; 使用Zeiss显微镜测定了溶菌酶(110)晶面的生长速度. 实验表明: 随着蛋白质和NaCl浓度的增加, 溶液中聚集体的颗粒尺寸也相应增加. 随着反应时间的增加, 溶菌酶分子在溶液中的聚集反应, 逐渐达到平衡; 在蛋白质和NaCl浓度较高时, 溶菌酶晶体的(110)面生长较快, 而在蛋白质和NaCl浓度较低时, 该晶面生长较慢. 基于二维成核生长机理, 从晶体生长动力学理论方程出发, 计算了二维成核的形成能α=4.01×10-8 J•cm-2. 相似文献
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In a previous paper (Vivarès, D.; Bonneté, F. Acta Crystallogr., Sect. D 2002, 58, 472), protein-protein interactions of Aspergillus flavus urate oxidase (Uox) in solution were determined by small-angle X-ray scattering in the presence of different poly(ethylene glycol)s (PEG) in order to correlate second virial coefficient measurements with crystallization conditions. In this paper, we have characterized the experimental phase diagram of urate oxidase in the case of PEG 8000 by determining the solubility curve and the dilute part of the liquid-liquid phase separation (LLPS). Within this phase diagram, different mechanisms of urate oxidase crystal growth and LLPS can be observed by optical video microscopy. The influence of the LLPS on both the mechanisms and kinetics of urate oxidase crystal growth was observed by optical microscopy and small-angle X-ray scattering (SAXS). Interactions between the macromolecules were studied by SAXS in the dilute and dense phases of the demixed solution. It was observed that the LLPS precedes and slows down the crystallization. This study shows that urate oxidase is a good model to study protein/PEG mixtures in the general context of protein crystallization. 相似文献
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The kinetics of crystallization of a number of salts from aqueous solutions of ethanol was studiedunder isothermal conditions on a setup enabling simultaneous automated recording of the electrical conduc-tivity, optical transmission, light scattering (at an angle of 90° to the incident light beam) of a super-saturated solution in salt crystallization. The rate coefficients of crystal growth were determined. 相似文献
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A new criterion based on surface and volume diffusion kinetics was established to predict protein crystallization. Similar to the layer-by-layer crystal growth process of protein, the kinetics of the two-dimensional self-assembly of protein at the aqueous solution surface provides a convenient and reliable way to estimate the surface integration and the volume transport during protein crystallization. Both the surface and diffusion kinetics were estimated based on the protein self-assembly at the air/solution interface, which can be obtained by measuring the surface tension. A crystallization coefficient is found to provide an effective and reliable criterion to predict protein crystallization conditions. This criterion has been applied to lysozyme, concanavalin A and BSA crystallization, and it turns out to be very successful and more reliable than the second virial coefficient criterion. 相似文献
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Stephen Z. D. Cheng Jianhua Chen Anqiu Zhang Daniel P. Heberer 《Journal of Polymer Science.Polymer Physics》1991,29(3):299-310
Differential scanning calorimetry (DSC) and in situ small-angle x-ray scattering (SAXS) indicate that in an α ω-methoxy-poly(ethylene oxide) (MPEO) fraction (MW 3000) a transient nonintegral folding (NIF) crystal initially forms during crystallization throughout a wide range of crystallization temperatures. Subsequent transformations of the NIF to IF (integral folding) crystals at low temperatures occur mainly through isothermal thickening or thinning via perfection processes or, at higher temperatures, through primary crystal formation. The NIF crystal is thermodynamically the least stable state among the crystal forms, but its growth is the most rapid. The overall crystallization and crystal melting of this MPEO fraction reveal that the NIF crystal and the NIF → IF crystal transformations are common to low-molecular mass PEO fractions without regard to the end group. Nevertheless, diffusion coefficient and viscosity measurements provide clear evidence of an end-group effect in PEO and MPEO fractions. The difference in the overall crystallization and isothermal thickening and thinning kinetics of low-molecular mass PEO and MPEO fractions can lead to further understanding of end-group effects. 相似文献
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The crystal growth of dense and almost monodisperse colloids has been investigated during recent years, but less is known about the melting behavior. The current study thus focuses on this topic. Monodisperse hard spheres were found to crystallize for certain concentrations (49-58 vol %), after sufficiently long times. The characteristics of the crystal growth change when the colloidal particles are polydisperse. Finally, when the size distribution function of the particles is broad enough, the crystallization no longer took place. Dense oil-in-water emulsions with polydispersities of around 10% were successfully produced, and in a first approximation, these emulsions behaved like hard spheres. The polydispersity of the emulsions was sufficiently high to avoid crystallization in equilibrium but low enough to induce a disorder-to-order transition under shear. The formed crystals started to melt once the shear was discontinued. The melting behavior of these "oil droplet crystals" was investigated by means of time-resolved static light scattering experiments, and it was found that crystallization could be induced in a concentration regime between 46 and approximately 74 vol %. The melting behavior of these crystals depended strongly on the concentration. The typical melting times ranged from a few seconds to several hours or days when the concentration was increased. It was speculated that this phenomenon could be explained by the strong dependence of the mobility of the oil droplets on the volume fraction, as verified by dynamic light scattering experiments on oil-in-water emulsions in a similar concentration regime. 相似文献
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Crystallization kinetics of syndiotactic polypropylene(sPP)was observed by light attenuation measurements. The initial stages of temperature dependent sPP crystallization fall in the range of Rayleigh scattering and Rayleigh-Debye- Gans scattering.Initial time and growth time of crystallization were obtained,and the trend of crystallization temperature dependent linear attenuation coefficient on the radius and the index of the refraction of the spherulite were evaluated. 相似文献
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聚合物的结晶是高分子链由无序转变为在三维空间中有规则排列的过程。实现转变的外界条件主要是温度和时间。近年来,人们借助偏光显微镜法(PLM)、小角激光光散射法(SALS)等研究聚对苯二甲酸乙二酯(PET)的结晶形态已有不少报导。 相似文献