自晶种方法宏量制备PS-b-PLLA单晶、复合单晶及其热力学稳定性

为了更好控制结晶的形态、大小以及产率,系统地研究了各种控制因素对自晶种方法制备PS-bPLLA嵌段共聚物单晶及复合单晶的影响,并考察了晶体在溶液和本体状态的热力学稳定性.通过调控成核温度(Ts)、成核时间(ts)和结晶温度(Tc)等参数,成功制备了不同尺寸、形状和厚度的单晶.随着Ts和ts的增加,晶体尺寸增加并且尺寸分布变窄.随着Tc的增加,单晶形状由菱形转变为截顶菱形.同时还利用两步法分别制备和表征了PS-b-PLLA/PLLA复合单晶.DSC热扫描实验表明,溶液生长的片状晶体在本体状态下处在热力学亚稳态,在升温熔融过程中出现明显的重结晶现象.但是晶体在不同温度下退火并不能增强其稳定性,从而证明了PLLA片晶厚度不能通过分子链在晶体内沿着链轴方向滑移而增厚.     

第一性原理和热力学计算预测a-Al_2O_3中缺陷的稳定性

基于第一性原理中的密度泛函理论(DFT)和热力学计算方法,利用VASP软件包和GULP程序,计算了a-Al_2O_3晶体的能带结构,并考虑振动熵对晶体中本征点缺陷的形成能的贡献,预测了不同温度和氧分压条件下a-Al_2O_3晶体中点缺陷的稳定性.缺陷热力学跃迁能级的计算表明,Al_i是浅施主能级,V_(Al)(除2-/3-之外)都是浅受主能级,这些浅热力学跃迁能级在价态的转换上比较容易.通过分析振动熵随温度变化情况,考虑振动熵对缺陷形成能的贡献是必要的,它使铝填隙和氧填隙的缺陷形成能增大,氧空位和铝空位的缺陷形成能减小(尤其在高温条件下).本文讨论了以费米(Fermi)能级、温度和氧分压为函数变化的最稳定点缺陷三维分布图,以便更清晰、直观地掌握晶体中稳定点缺陷随Fermi能级、温度和氧分压变化的分布关系.     

单分散扁平卤化银微晶成核过程的研究

多年来,卤化银乳剂微晶体制备的研究重点一直放在宏观相的结构与性能的关系上,已经发现卤化银照相乳剂的感光性能与晶体的结构和大小有很重要的关系^[1,2]。随着研究工作的深入,人们逐渐认识到:晶体的成核过程决定着宏观相微晶体的结构和形状,因此成核过程的研究日益受到人们的关注。Tanaka^[3,4]应用分光光度法从反应动力学角度入手研究AgX微晶的成核过程。     

片晶折叠表面成核机制与结晶温度的相关性研究

利用自晶种方法,在邻二氯苯稀溶液中培养聚丁二酸丁二醇酯(PBS)晶体,系统研究了结晶温度对其晶体形貌的影响.使用PBS单晶作为研究对象,有效避免小尺寸观察不具有统计意义的缺点.在结晶过程中,通过改变结晶温度和自晶种温度,可有效调控稀溶液中生长的PBS晶体尺寸大小和晶体中缺陷的数量,得到了单层无缺陷的单晶、双层晶体和多层晶体等一系列PBS片晶.基于对不同实验条件下得到片晶的形貌和表面粗糙度的统计结果,提出晶体中可容忍的缺陷数量与结晶温度和晶种温度密切相关这一结论,通过建立热力学模型,定性分析了晶体中缺陷数量和结晶温度的依赖关系,从片晶表面粗糙度统计结果出发,提出高分子片晶折叠表面成核机制,较好地解释了实验中观察到的不同PBS晶体的形貌.     

用XRD和TG技术研究明矾失水及复水过程

针对无机化学实验“明矾的制备”中存在明矾容易失水的问题进行探究。先用热重分析仪在不同温度下对分析纯明矾进行热处理分析，再取300℃热处理后的样品(KAl(SO₄)₂)进行复水实验；采用X射线粉末衍射技术(XRD)对样品进行物相表征，探究了热处理后明矾失水与复水之间的结构变化。通过理论计算并结合物质的晶体微观结构，阐明了明矾容易失水的原因，分析了明矾失水与复水的机理，为解释教学实验现象提供详实的理论依据。     

钾搀杂对叠氮化亚铜晶体能带结构影响的DFT研究

运用广义梯度近似(GGA)密度泛函理论（DFT）方法对钾搀杂叠氮化亚铜晶体的原子和电子结构以及缺陷形成能进行了研究。结果表明,钾搀杂破坏了叠氮酸根的对称性,导致不对称的原子位移。随着搀杂钾浓度的增加,搀杂叠氮化亚铜晶体的带隙逐渐增大。热力学上,杂质钾很容易被搀杂到叠氮化亚铜晶体中,而且钾还充当了缺陷团簇的成核中心。最后,从电子结构角度理解了搀杂钾浓度对叠氮化亚铜晶体感度的影响。     

Hg~1~-~xCd~xTe平衡蒸汽压的热力学研究

Hg~1~-~xCd~xTe熔体组元平衡蒸汽分压是晶体制备中必须考虑的重要热力学参数, 文献报道中数据差别很大, 影响对该材料进一步研究。本文根据光吸收原理, 系统测定x=0-0.4的Hg~1~-~xCd~xTe系熔体平衡汞和碲分压, 运用热力学关系计算镉分压, 讨论p~H~g-x关系, 并将所得结果与文献报道数据进行比较与分析。     

结晶生长的化学键合理论及其在稀土晶体快速生长中的应用

高温稀土晶体的快速生长能够在很大程度上降低晶体的生长成本,然而过快的生长速度会造成熔体上方过冷,带来晶体开裂等严重的质量问题.本文从生长界面处的微观化学键合结构出发研究晶体的可控生长过程,理论上证明了结晶热力学和动力学协同控制晶体生长界面处的化学键合过程.计算结果表明界面处化学键合结构在单晶生长中具有决定性作用.本文还从轨道杂化的角度研究了稀土离子的成键特性,可用于研究稀土离子在生长界面处的化学键合结构.针对大尺寸稀土氧化物晶体,结晶生长的化学键合理论可以定量优化晶体的系列生长参数,将各向异性的结晶热力学表达和各向同性的结晶动力学表达控制在不同尺度区间,实现高品质稀土晶体快速生长.     

在缺乏仪器和药品时的几个代用实验

1.讲到初中化学第一章第七节作晶体样品时可作胆矾与明矾的晶体,为了得到较大而有规则的晶体。最好用较粗的头发栓好一块晶体浸在各该物质的过饱和溶液里,等晶体不能再长大的时候。把晶体拿出再将该溶液制成过饱和溶液,继而把已经长大的晶体放在里边,使晶体继续结晶,这样反复三、五次即可得到较大而有规则的晶体。     

物理化学学报

正化学平衡与热力学参数、量热学、非平衡态热力学与耗散结构、统计热力学、宏观动力学、分子动态学、超快动力学、激发态、溶液化学、复杂流体、溶液结构、大气化学、动态结构、分子结构、体相结构、簇、谱学。量子化学、统计力学、模拟方法与应用、计算化学、化学信息学。     

Thermodynamics of alternating copolymer of ethylene and carbon monoxide in the 0–600 K region

The temperature dependence of the heat capacity of the alternating copolymer (ACP) of carbon monoxide with ethylene was studied, and temperatures and enthalpies of its phase transformations were measured by adiabatic vacuum, dynamic, and isothermal calorimetry in the temperature range from 8 to 600 K. The energy of burning of ACP was measured at 298.15 K in a calorimeter with the static bomb and isothermal shell. The thermodynamic parameters of transformation of the α-form of ACP crystals into the β-form and fusion of the β-form were determined. The thermodynamic functions for the 0–507 K range and thermodynamic characteristics atT=298.15 K andp=101.325 kPa were calculated. The thermodynamic parameters of the alternating copolymerization of ethylene and CO at 0–507 K and standard pressure were calculated for the bulk reaction. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 284–288, February, 1998.     

The Specific Heat of Tetramethylammonium Salts

New measurements of the (N(CH₃ )₄ )₂ MnBr₄ specific heat by adiabatic calorimetry around the ferro- paraelastic phase transition shown by the crystal around 276 K are compared with previous calorimetric studies on similar tetramethylammonium bromide compounds. The thermodynamic behaviour of the tribromides and tetrabromides derivatives together with the influence on the phase transition parameters of the cation and halogen molecular substitutions are examined. The thermal relaxation experiments permit to study the behaviour of the crystals thermal conduction as a function of the temperature. Finally, the Landau theory for second order phase transitions is used to describe the thermodynamic behaviour of some of these crystals. This revised version was published online in July 2006 with corrections to the Cover Date.     

Structure-ionization relationship of tyrosine-containing peptides

The arid-base chemistry of tyrosine-containing peptides such as enkephalin, tyrosylglycylglycine, tyrosylglycine and analogous peptides is described. For each peptide and tyrosine derivative, microscopic and macroscopic acid dissociation constants and the thermodynamic parameters for proton dissociations were determined from pH-titrations and ultraviolet absorption spectra. The relative concentrations of various ionic forms for the peptides were calculated from the microscopic constants. The concentration ratio, represented by the tautomeric equilibrium constant (K(t)), showed a definite relationship to structure.     

A systematic examination of the morphogenesis of calcium carbonate in the presence of a double-hydrophilic block copolymer

In this paper, a systematic study of the influence of various experimental parameters on the morphology and size of CaCO3 crystals after room-temperature crystallization from water in the presence of poly(ethylene glycol)-block-poly(methacrylic acid) (PEG-b-PMAA) is presented. The pH of the solution, the block copolymer concentration, and the ratio [polymer]/[CaCO3] turned out to be important parameters for the morphogenesis of CaCO3, whereas a moderate increase of the ionic strength (0.016 M) had no influence. Depending on the experimental conditions, the crystal morphologies can be tuned from calcite rhombohedra via rods, ellipsoids or dumbbells to spheres. A morphology map is presented which allows the prediction of the crystal morphology from a combination of pH, and CaCO3 and polymer concentration. Morphologies reported in literature for the same system but under different crystallization conditions agree well with the predictions from the morphology map. A closer examination of the growth of polycrystalline macroscopic CaCO3 spheres by TEM and time-resolved dynamic light scattering showed that CaCO3 macrocrystals are formed from strings of aggregated amorphous nanoparticles and then recrystallize as dumbbell-shaped or spherical calcite macrocrystal.     

Thermodynamics of the solution equilibria of 3-hydroxypyridine and pyridoxine in water-dioxane mixtures

The thermodynamics of tautomeric and microscopic ionization equilibrium constants of 3-hydroxypyridine and pyridoxine have been determined in waterdioxane mixtures (0–70% weight fraction in dioxane) ranging from 10°C to 50°C. Generally, for both types of processes, the entropic contributions to the Gibbs energy predominate and this tendency increase concomitantly with the dioxane content in the media. The thermodynamic parameters are consistent with the corresponding values obtained from macroscopic ionization processes. An equation for the equilibrium constant K as a function of temperature and a solvent characteristic parameter is proposed to predict the K values throughout the whole range of the temperature and solvent compositions studied.     

Reversible melting and crystallization of high‐molar‐mass poly(oxyethylene)

The heat capacity of poly(oxyethylene) (POE) with a molar mass of 900,000 Da has been analyzed with differential scanning calorimetry and quasi‐isothermal, temperature‐modulated differential scanning calorimetry. The crystal structure, lattice parameters, and coherently scattering domain sizes have been measured with wide‐angle X‐ray diffraction as a function of temperature. The high‐molar‐mass POE crystals are in a folded‐chain macroconformation and show some locally reversible melting starting already at about 250 K. At 335 K, the thermodynamic heat capacity reaches the level of the melt. The reversible crystallinity depends on the modulation amplitude and has been varied in the melting range from ±0.2 to ±3.0 K. Before melting, there is neither a change in the crystal structure nor a change in the domain size, but the expansivity of the crystals increases at about 320 K. These observations support the interpretation that the monoclinic POE crystals possess a glass transition temperature with a midpoint at about 324 K, whereas the maximum melting temperature is 341 K. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 475–489, 2007     

State variables in calorimetric investigations: Experimental results and their theoretical impact

Use of state variables (p, V, T) in scanning calorimetric measurements is demonstrated by results obtained for various condensed systems, such as dense liquids of various physicochemical natures, polymers, and liquid crystals. The simultaneous determination of thermal and mechanical responses of the investigated system, perturbed by a variation of an independent thermodynamic variable while the other independent variable is kept automatically constant, allows the determination of thermodynamic derivatives over wide ranges of pressure and temperature, impossible to obtain by other known techniques. It is demonstrated that through appropriate molecular models for respective thermodynamic derivatives or models on which the respective EOS are constructed, the pVT-controlled scanning calorimetry is a useful means of relating microscopic molecular properties with macroscopic observations.     

Stereospecific morphogenesis of aspartic acid helical crystals through molecular recognition

Helical morphologies were generated from aspartic acid (Asp) crystals in agar gel matrix. The morphogenesis stereospecifically proceeded in the helical crystal growth: D- and L-Asp provided left- and right-handed structures, respectively. The backbone of the helical morphology was twisted twins of tilted unit crystals, as was the case with inorganic helical crystals. The molecular recognition between the Asp crystals and agar matrix molecules resulted in the stereospecific morphogenesis. The chirality in Asp and agar molecules, the enantiomorph of unit crystals, and the resultant macroscopic helix were exquisitely associated with each other.     

Hierarchical structures,surface morphology and mechanical elasticity of lamellar crystals dominated by halogen effects

To understand the deformation mechanism of molecular crystals under mechanical forces will accelerate the molecular design and preparation of deformable crystals. Herein, the relationship between structural halogenation and molecular-level stacking, micro/nanoscale surface morphology, and macroscopic mechanical properties are investigated. Elastic crystals of halo-pyrimidinyl carbazoles (CzM-Cl, CzM-Br and CzM-I) with lamellar structure and brittle crystal (CzM-F) were quantitatively analyzed by crystal energy framework (CEF) providing the inter/intralayer interaction energy (Inter/Intra-IE). It is revealed that the elastic crystals bend under external force as a result from stronger Intra-IE to prevent cleavage and weaker Inter-IE for the short-range movement of molecules on the slip plane. This research will provide an insight for the molecular design of flexible crystals and facilitate the development of next-generation smart crystal materials.     

Thermal properties of xenon adsorbed on graphite

We report theoretical results for dynamical and thermodynamic properties of the bare graphite (0001) surface, and with a physisorbed monolayer of xenon. The surface vibrations of graphite are less pronounced than those in more isotropic crystals. The surface-excess specific heat of the bare surface peaks at 45 K, that of the xenon at 13.5 K.