Induction of Ring‐Shaped Calcium Oxalate Patterns by Boundaries between Liquid Expanded Phase and Liquid Condensed Phase in Langmuir‐Blodgett Film

The formation of calcium oxalate kidney stones was related to injuries of renal epithelial membranes. The liquid condensed (LC) domains in Langmuir‐Blodgett (LB) film of dipalmitoylphosphatidylcholine (DPPC) were used as a model system to induce crystal growth of urinary mineral calcium oxalate monohydrate (COM). The circular defective boundaries between the LC and liquid expanded (LE) phases of the DPPC monolayer could provide much more nucleating sites for crystallization of COM crystals. It induced ring‐shaped or solid circular patterns of COM crystals on hydrophobic quartz substrates depending on the crystallization time.     

层状复合氢氧化物对乙酰苯甲酸的负载与体外释放

共沉淀-微波晶化法合成层状复合氢氧化物(LDH)后, 用不同方式将乙酰苯甲酸(ASP)组装到LDH层间制成载药体LDH-ASP, 通过对合成及药物释放前后的液相分析与固相表征数据研究了LDH对ASP的负载及载药体LDH-ASP在磷酸盐介质的溶释现象. 结果表明: LDH层间通道是负载、贮存及控制药物释放的微观基础; 载体选择、药物配比、反应能量供给方式及搅拌强度是决定并影响LDH-ASP载药效率的基本因素, LDH-ASP结构参数可以反映药物负载情况、并与其释放性能明确相关; LDH对ASP的负载与释放均致晶胞参数改变、结晶度下降; 载药体与前体的晶态属性、热力学行为及表面特性相似, 而释放药物后固相的晶态性征减弱、无定形性增强、通道吸附活性降低, 有利于使命后载体在体内降解消除.     

Prediction of the induction period of crystallization of naproxen in solid dispersion using differential scanning calorimetry

The induction period of crystallization of amorphous naproxen in solid dispersion was measured by DSC. Hydroxypropylmethylcellulose acetate succinate LG (HPMCAS-LG) was selected as a polymer of solid dispersion, because of the excellent inhibitory effect of crystallization. Naproxen was chosen as a model drug having poor water solubility and poor physical stability of glassy state. The prediction of crystallization of amorphous naproxen in solid dispersion at the desired storage temperature or the desired polymer content was carried out. If the storage condition satisfied the requirement that was either more than 90% of HPMCAS-LG content at 333 K or below storage temperature of 301 K for 50% HPMCAS-LG content, the induction period of crystallization of naproxen in solid dispersion would be more than 1 year. The storage period of amorphous drug in solid dispersion of desired storage temperature and desired drug content might be predictable from measurement data of induction period of crystallization.     

Mechanochemical Synthesis of Urea Adducts with Long Chain Alkyl Derivatives

The adducts of urea and solid alkyl derivatives can beobtained mechanochemically in good yields. Theproducts synthesized by grinding the solid reagentshave identical IR spectra and XRD powder patterns tothose obtained by crystallization from ethanolicsolutions.     

A hierarchical model of crystallization in polymeric gels and porous solids

A kinetic model of the crystallization of substances in the volume of an agglomerate of many microparticles or in a polymeric gel in solution with a given composition and temperature was formulated. The model takes into account the diffusion of the crystallizing substance from outside into the space between microparticles in an agglomerate or between polymeric globules in a gel and then from this space into the volume of microparticles (globules) with the simultaneous nucleation and growth of microcrystals of the crystallizing substance. The possibility of simultaneous diffusion of several crystallizing substances, which chemically react with each other to produce product microcrystals, heating of the gel (solid) by the heat of crystallization, pushing the solution out from the space between microparticles, and changes in the volume of the gel (solid) as a result of crystallization is considered. The model was used to develop a classification of crystallization types in gels and porous solids and interpret several phenomena described in the literature. A hypothesis was advanced concerning some unknown phenomena related to crystallization.     

Switching the emission of di(4-ethoxyphenyl)dibenzofulvene among multiple colors in the solid state

Luminescent materials exhibiting emission switching in the solid state have drawn much attention though there is still no clear design strategy for such materials. In this letter, we reported the crystallization induced emission enhancement (CIEE) of di(4-ethoxyphenyl)dibenzofulvene (1), and achieved switching its emission among four different colors through modulation of its molecular packing patterns. We have investigated its potential application as optical recording materials. The twisted conformations of CIEE compounds afford morphology dependent emission and facilitate tuning their emission through modulation of molecular packing patterns. Thus we provide a possible design strategy for solid stimulus responsive luminescent materials.     

The influence of minor components on the structural reorganization in glassforming materials

Correlation of structure parameters of glasses and related crystals formed in homogeneous or heterogeneous nucleation processes by thermal treatment is discussed on the basis of DTA, TG and EGA measurements in relation to the textural patterns of the materials. For cordierite glass, crystallization of metastable disordered cordierite polymorphs is related to an exothermic heat evolution and simultaneous with a small weight loss (appr. 0.025%). By MS-EGA, evolution of water was determined during the transformation of the metastable melt to a metastable intermediate crystalline phase. Interpretation of the crystallization by comparing the available structure parameters of cordierite glasses and crystals alone is insufficient to explain the role of water in the kinetics of crystallization. Optical and electron microscopy of the primary crystallization phenomena show the metastable solid solution with low quartz-type structure. Interpretation of the crystallization behaviour in terms of conventional theory of nucleation and crystal growth is impossible.     

Circular patterns of calcium oxalate crystals induced by defective Langmuir-Blodgett film

The injury of the renal epithelial cell membrane can promote the nucleation of nascent crystals, as well as adhesion of crystals on it. It thus accelerates the formation of renal calculi. In this paper, the defective Langmuir-Blodgett (LB) films were used as a model system to simulate the injured renal epithelial cell membrane. The microcosmic structure of the defective LB film and the molecular mechanism of the effect of this film on nucleation, growth, deposited patterns and adhesion of calcium oxalate monohydrate (COM) were investigated. The circular defective domains were formed in dipalmitoylphosphatidylcholine (DPPC) LB film after the film was treated by potassium oxalate. These domains could induce ring-shaped patterns of COM crystals. In comparison, the LB film without pretreatment by potassium oxalate only induced random growth of hexagonal COM crystals. As the crystallization time increased, the size of COM crystals in the patterns increased, the crystal patterns changed from empty circles to solid circles, and the number of the circular patterns with small size (5-20 μm) increased. The results would shed light on the molecular mechanism of urolithiasis induced by injury of the renal epithelial membrane at the molecular and supramolecular level.     

固相缩聚PET等温结晶动力学

高聚物等温结晶动力学方面的研究者甚多,由熔融缩聚制备的不同分子量PET的等温结晶动力学及几种不同缩聚催化体系固相缩聚PET的等温结晶动力学已有报道.本文采用一个修正的Avrami方程对固相缩聚PET样品进行系统的等温结晶动力学研究.     

未添加晶种结晶过程的中后期动力学模拟

以KNO₃-H₂O为模型体系, 考察了未添加晶种的间歇结晶过程动力学, 将历经爆发成核后的结晶体系近似为添加晶种的结晶体系. 并结合光学关联方法, 推导了可描述历经爆发成核后的晶体形成和生长速率模型. 模型中含有可反映结晶固相信息的透光率变量, 从而避免了以往模型仅靠液相浓度数据求解模型参数的不便. 运用该模型拟合未添加晶种结晶过程的中后期实验数据, 得到了KNO₃晶体的二次成核和生长动力学参数, 参数结果与文献中报道的添加晶种结晶过程的参数值相近. 在此基础上, 针对添加晶种的结晶过程, 提出了晶种添加量的定量设计方法, 并得到了实验的初步验证.     

Physical stability of amorphous acetanilide derivatives improved by polymer excipients

Crystallization rates of drug-polymer solid dispersions prepared with acetaminophen (ACA) and p-aminoacetanilide (AAA) as model drugs, and polyvinylpyrrolidone and polyacrylic acid (PAA) as model polymers were measured in order to further examine the significance of drug-polymer interactions. The crystallization of AAA and ACA was inhibited by mixing those polymers. The most effective inhibition was observed with solid dispersions of AAA and PAA. The combination of AAA and PAA showed a markedly longer enthalpy relaxation time relative to drug alone as well as a higher T(g) than predicted by the Gordon-Taylor equation, indicating the existence of a strong interaction between the two components. These observations suggest that crystallization is effectively inhibited by combinations of drug and polymer that show a strong intermolecular interaction due to proton transfer between acidic and basic functional groups.     

“CLASSIC NMR”: An In‐Situ NMR Strategy for Mapping the Time‐Evolution of Crystallization Processes by Combined Liquid‐State and Solid‐State Measurements

A new in‐situ NMR strategy (termed CLASSIC NMR) for mapping the evolution of crystallization processes is reported, involving simultaneous measurement of both liquid‐state and solid‐state NMR spectra as a function of time. This combined strategy allows complementary information to be obtained on the evolution of both the solid and liquid phases during the crystallization process. In particular, as crystallization proceeds (monitored by solid‐state NMR), the solution state becomes more dilute, leading to changes in solution‐state speciation and the modes of molecular aggregation in solution, which are monitored by liquid‐state NMR. The CLASSIC NMR experiment is applied here to yield new insights into the crystallization of m‐aminobenzoic acid.     

Coupling between kinetics and rheological parameters in the flow-induced crystallization of thermoplastic polymers

Flow Induced Crystallization (FIC) is the common term to indicate the acceleration in polymer crystallization kinetics due to the action of flow. FIC is expected to be the result of the coupling between the intrinsic (quiescent) crystallization kinetics and the rheological response of the polymer. The choice of a suitable rheological model, therefore, is a crucial requirement for a successful FIC model. Recent work of our group^[1] has demonstrated that the Doi-Edwards rheological model (DE), based on the concept of chain reptation, can be easily incorporated into classical crystallization models to successful predict the enhancement in nucleation rate under the action of a steady shear flow. In this paper, the interaction between the rheological parameters of the DE model and the crystallization kinetics parameters is investigated in more details. In particular, the effect of the crystallization temperature, which acts on both the polymer relaxation time and the free energy jump between liquid and solid phase, is determined and discussed.     

The influence of micro- and nanoparticles on model atomically flat surfaces on crystallization of polyethylene

Crystallization of high density polyethylene (PE) from the melt on model atomically flat solid surfaces decorated with micro- and nanoparticles of gold or NaCl of different size and densities is investigated. The morphology of the contact layer of PE after its detachment from the support is studied using atomic force microscopy (AFM). It is shown that the nucleating and ordering effect of the solid on PE crystallization depends to a large extend on the nanostructure of its surface, in particular on the size of the atomically flat domains and on the presence of nanoscopic obstacles. The minimum size of the flat domain which can significantly influence the PE crystallization is estimated to be of the order of 150 nm.     

A technique for in situ monitoring of crystallization from solution by solid-state 13C CPMAS NMR spectroscopy

We report a technique for carrying out in situ solid-state NMR studies of crystallization from solution, allowing the evolution of different solid state structures (polymorphs) produced during the crystallization process to be identified. The technique exploits selectivity in NMR properties (specifically, the efficiency of cross-polarization from (1)H to (13)C) between molecules in the solid and solution states, such that the first solid particles produced during the crystallization process are observed selectively, without detecting any signal from dissolved solute (or solvent) molecules. The application of the technique is demonstrated to reveal new insights concerning an isotope effect on the polymorphic outcome of crystallization of glycine from water. As revealed by this example, the in situ solid-state NMR approach reported here creates significant new opportunities for probing and understanding details of the evolution of solid state structures produced during crystallization from solution.     

Single crystal growth of Bi1−xSrxMnO3—Thermodynamics and experiment

The primary crystallization field of a perovskite solid solution Bi_1−xSr_xMnO_3−δ was delimited by calculating the respective phase equilibria in the quaternary Bi–Sr–Mn–O system. The calculations are based on the recent assessment involving all three ternary subsystems, a quaternary liquid approximated as a mixture of Mn, MnO, Mn₂O₃, SrO and Bi₂O₃ species with binary Redlich–Kister coefficients and the perovskite phase described in terms of a point defect model allowing Sr²⁺ for Bi³⁺ substitution, oxygen vacancy formation and the related Mn³⁺/Mn⁴⁺ mixing on Mn-sublattice. The crystallization path and the composition of the crystallized solid solution are compared with single crystal growth experiments performed by self-flux method from a Bi-rich melt. The crystallization path obtained for a selected feed composition for which the largest and high quality single crystal have been grown, turns out to end very close to the global eutectic point.     

Effect of Emulsifier Type on the Crystallization Kinetics of Oil-in-Water Emulsions Containing a Mixture of Solid and Liquid Droplets

Measurements of the ultrasonic velocity as a function of time (at 6.0°C) have been used to monitor the kinetics of crystallization of oil droplets in n -hexadecane-in-water emulsions containing a mixture of solid and liquid droplets. Crystallization is induced in liquid droplets when solid droplets are present. Induced crystallization is probably caused by crystals, protruding from solid droplets, penetrating into liquid droplets during collisions and thus acting as nucleation sites for crystal growth. The rate of induced crystallization depends strongly on the type of emulsifier used to stabilize the emulsion droplets. For the series of emulsifiers used in this study the rate decreased in the following order: Tween 20 > SDS > β-lactoglobulin > β-casein. Differences in rate can be explained by considering the influence the emulsifiers have on the interactions between droplets.     

Microstructural Exploration of the High Capacitance in RuO_2-ZrO_2 Coating

A high capacitance RuO₂-ZrO₂ coating was prepared by thermal decomposition method.Extended X-ray absorption fine structure(EXAFS),X-ray diffraction(XRD),high-resolution transmission electron microscope(HRTEM)and ab initio calculations were applied to understand the role of the microstructure in the acquisition of high specific capacitance of RuO₂-based oxides.The results show that the RuO₂-ZrO₂ oxide prepared at critical crystallization temperature can be considered to be quasi-amorphous or microcrystalline(A short-range ordered crystal structure can be seen from the TEM image,but no diffraction peaks can be seen from the XRD diffraction patterns).And this RuO₂-ZrO₂ was identified as a solid solution with high solid solubility.It referred to herein as a quasi-amorphous solid solution.Such a special microstructure was conducive for"synergistic catalysis"owing to the cationic interaction and thus could gain high"active site density"and high"active surface",thus developing high specific capacitance.     

Effect of methyl substitution of the ethylene unit on the physical properties of poly(butylene succinate)

A series of poly(butylene succinate‐co‐butylene 2‐methyl succinate)s were prepared through variations in the molar fraction of succinic acid to 2‐methyl succinic acid, and the effects of methyl substitution on the shear‐induced crystallization, nonisothermal crystallization behavior, dynamic rheological properties, crystal morphology, and mechanical properties were investigated. Introducing 2‐methyl succinic units reduced the melting temperature and crystallization temperature; this indicated that the substituted units retarded crystallization of the polymer. The Avrami exponents, estimated by modified Avrami plots, ranged from 2.1 to 3.5 and were a little diminished by the substitution. The substitution also reduced the rate of crystallization under shear. However, the effect was diminished with an increasing shear rate because most polymer chains were more regularly arranged at higher shear rates. Dynamic experiments in the solid state revealed that the peak on a plot of the loss tangent against the temperature became sharper at higher contents of the substituted unit, and the peak temperature, the glass‐transition temperature, was reduced as the content of 2‐methyl succinic acid increased. Wide‐angle X‐ray diffraction patterns showed that there was little effect of the 2‐methyl succinic acid unit on the crystal morphology. The toughness of the polymer was abruptly increased up to 350% at the expense of the tensile modulus. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1759–1766, 2004     

Crystallization kinetics and excess free energy of H2O and D2O nanoscale films of amorphous solid water

Temperature-programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS) are used to investigate the crystallization kinetics and measure the excess free energy of metastable amorphous solid water films (ASW) of H(2)O and D(2)O grown using molecular beams. The desorption rates from the amorphous and crystalline phases of ASW are distinct, and as such, crystallization manifests can be observed in the TPD spectrum. The crystallization kinetics were studied by varying the TPD heating rate from 0.001 to 3 K/s. A coupled desorption-crystallization kinetic model accurately simulates the desorption spectra and accurately predicts the observed temperature shifts in the crystallization. Isothermal crystallization studies using RAIRS are in agreement with the TPD results. Furthermore, highly sensitive measurements of the desorption rates were used to determine the excess free energy of ASW near 150 K. The excess entropy obtained from these data is consistent with there being a thermodynamic continuity between ASW and supercooled liquid water.