N-乙基壳聚糖的针状结晶

在N 乙基壳聚糖的甲酸溶液浇铸膜中观察到高分子少有的针状晶体 .从球晶经后结晶得到的针状晶体为长条矩形 ,典型尺寸为～ 5 0 μm× 2～ 5 μm× 1～ 2 μm ,高分子链平行于晶体长轴 .针状晶体首先出现在球晶的核心处 ,继而出现在球晶微纤每个树枝状分叉处 ,最后才遍布球晶各处 .针状晶体可以看成是高分子伸直链结晶的一种 .浇铸膜吸潮实际上形成了超浓溶液 (浓度 >80wt% ) ,从而分子链可以运动而后结晶成针状晶体     

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.     

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.     

聚ε-己内酯结晶形态的研究

采用DSC测试了聚ε-己内酯(PCL)的结晶温度(TC)和熔融温度(Tm)。同时采用偏光显微镜(POM)探讨了结晶时间的影响,发现结晶时间的改变只能够改变其晶体的尺寸,对其结晶形态并没有太大的影响。最后采用原子力显微镜(AFM)讨论了基底材料、溶剂和过冷度对PCL结晶形态的影响。结果表明:基底材料对PCL结晶形态的影响是比较显著的,PCL在硅片上呈棒状,在云母和涂有碳膜的云母上呈树枝状。溶剂对PCL结晶形态的影响明显,其结晶形态的差别与蒸汽压有关。在不同的温度下PCL结晶形态都成树枝状晶体,且分枝宽度随着过冷度的降低而增加。     

成膜溶剂对聚4-甲基戊烯-1膜的形态结构和透过行为的影响——Ⅰ.膜的结晶性质与表面形态

以聚4-甲基戊烯-1(PMP)为膜材质,分别以环己烷、三氯乙烯、四氯乙烯、环己烷/三氯乙烯及环己烷/四氯乙烯为溶剂,研究了这些溶液浇铸膜的结晶性质和表面形态。结果表明,溶剂对PMP的相对溶解能力和挥发速度同所成膜内PMP的结晶形式和结晶度密切相关;不同溶剂体系的PMP溶液浇铸膜的表面形态也不尽相同。并发现以四氯乙烯(或三氯乙烯)为溶剂或溶剂组分之一的PMP溶液浇铸膜存在未见报道的Ⅵ型结晶。     

晶体生长基元与晶体结晶习性

本文从结晶化学角度出发，结合晶体生长实际研究了ＡＯ２、Ａ２Ｏ３和ＡＢＯ３型晶体中ＡＯ６八面体的结晶方位和晶体方位和晶体结晶形貌之间的关系，通过ＢＢＯ、ＬＢＯ高温溶液结构的测定和对水热条件下ＳｉＯ２和ＢＴＯ溶液结构的分析，运用负离子配位多面体生长基元的理论模型解释了晶体的生长形态。     

水溶液体系中钐离子(III)对草酸钙结晶过程影响效应的研究

进行了水溶液体系中三价稀土离子(Sm3 )对草酸钙(CaC2O4)结晶过程影响效应的研究.采用微量热法、X射线衍射(XRD)以及扫描电镜(SEM)法,研究了Sm3 对草酸钙结晶过程动力学的影响效应及对草酸钙晶体晶型、形貌、尺寸的调控作用.微量热研究结果表明,Sm3 对草酸钙结晶过程的影响包括对晶体初期成核以及晶体生长过程的影响,在适宜的浓度(约2.50×10-5mol?L-1)下达到对晶体成核与生长的最佳抑制效果;XRD研究结果表明,Sm3 的加入有利于草酸钙二水合物(COD)的生成;SEM形貌研究表明,Sm3 对草酸钙晶体的形态、尺寸产生非常显著的调控作用.     

成膜溶剂对聚4-甲基戊烯-1膜的形态结构和透过行为的影响——Ⅰ.膜的结晶性质与表面形态

以聚4－甲基戊烯－1（PMP）为膜材质，分别以环己烷、三氯乙烯、四氯乙烯、环己烷／三氯乙烯及环己烷／四氯乙烯为溶,他这些溶液浇铸膜垢结晶性质和表面形态。结果表明，溶剂对PMP的相对溶解能力和挥发速度同所成膜内PMP的结晶形式和结晶度密切相关；不同溶剂体系的PMP溶液浇铸膜的表面形态也不尽相同。并发现以四氯乙烯（或三氯乙烯）为溶剂或溶剂组分之一的PMP溶液浇铸膜存在未见报道的Ⅵ型结晶。     

聚电解质膜PDAC/PSS诱导CaCO3结晶的研究

以模拟软体动物珍珠层的周期性基质控制形成过程制备仿生层状复合材料. 将聚苯乙烯磺酸钠(PSS)与聚二烯二甲基氯化铵(PDAC)用逐层浸渍的方法使其组装成多层膜, 用于诱导过饱和溶液中CaCO₃的结晶, 详细研究了膜紫外吸收随组装层数增加的线性变化. 扫描电镜和X射线衍射表征了晶体的形貌和结构. (PDAC/PSS)₁₅PDAC膜诱导获得的CaCO₃晶体为六面体结构, 晶体尺寸为30～40 μm; (PDAC/PSS)₁₅膜诱导CaCO₃结晶, 可以在膜表面获得形貌与珍珠层非常相似的CaCO₃晶体, 结晶10 h获得的晶片结构呈规则的六边形, 片尺寸约为10～20 μm. X射线衍射结果表明两种晶体的晶格结构与天然珍珠层差异明显, 说明静电作用为晶体形貌的主控因素之一, 但不是晶格结构的决定因素. 复合材料断面电镜照片表明其为层状结构.     

聚电解质膜PDAC/PSS诱导CaCO3结晶的研究

以模拟软体动物珍珠层的周期性基质控制形成过程制备仿生层状复合材料．将聚苯乙烯磺酸钠(PSS)与聚二烯二甲基氯化铵(PDAC)用逐层浸渍的方法使其组装成多层膜,用于诱导过饱和溶液中CaCO3的结晶,详细研究了膜紫外吸收随组装层数增加的线性变化．扫描电镜和X射线衍射表征了晶体的形貌和结构,(PDAC/PSS)15PDAC膜诱导获得的CaCO3晶体为六面体结构,晶体尺寸为30～40μm;(PDAC/PSS)15膜诱导CaCO3结晶,可以在膜表面获得形貌与珍珠层非常相似的CaCO3晶体,结晶10h获得的晶片结构呈规则的六边形,片尺寸约为10～20μm,X射线衍射结果表明两种晶体的晶格结构与天然珍珠层差异明显,说明静电作用为晶体形貌的主控因素之一,但不是晶格结构的决定因素．复合材料断面电镜照片表明其为层状结构。     

Crystal structure and morphology of phenyl‐capped tetraaniline in the leucoemeraldine oxidation state

A series of crystals of phenyl‐capped tetraaniline in the leucoemeraldine oxidation state were obtained at different isothermal temperatures and were observed directly under transmission electron microscope. The crystals obtained at higher temperatures exhibit more perfect structures than those obtained at lower temperatures. Both the lamella thickness and the crystal size increase with crystallization temperature. The tetraaniline is apt to form larger scale crystals under lower degree of supercooling. However, their crystal structures keep steady with the crystallization temperature. The tetramer was found to adopt a monoclinic lattice with unit cell parameter of a = 13.93 Å, b = 8.82 Å, c = 23.20 Å, and β = 95.03°, as determined using electron diffraction tilting method combined with wide‐angle X‐ray diffraction experiment. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 764–769, 2006     

A facile design for multifunctional AIEgen based on tetraaniline derivatives

Aniline oligomers have been widely used in many fields due to their excellent physicochemical properties. Owing to strong intermolecular interactions, their emission is always weakened or quenched when they are in high concentration or aggregated state, which greatly limits their fluorescent applications. Inspired by the concept of aggregation-induced emission(AIE), herein we introduced large steric groups onto the aniline oligomer to prevent the formation of packing structure. In particular, diphenyl vinyl group was bonded with oligomeric tetraaniline by a facile synthetic procedure with high yield. The obtained aniline oligomer derivative exhibited typical AIE features, which was also confirmed by density functional theoretical calculation. More importantly, this AIE oligomer was able to detect Fe~(3+) ions selectively and quantitatively. The fluorescence intensity decreased linearly along with the increment of Fe~(3+) concentration. Moreover, we demonstrated that this AIE oligomer could stain live bacteria, such as E. coli and S. aureus efficiently. All these results suggest that such a readily accessible and multifunctional tetraaniline derivative provides a new platform for the construction of fluorescent materials.     

Crystalline lanthanum hydroxycarbonates with controlled phases and varied morphologies prepared on non-crystalline substrates

Lanthanum hydroxycarbonate crystals with controlled phases and varied morphologies were prepared on the surface of a non-crystalline substrate, glass. The phases and morphologies of the crystals were controlled conveniently by varying the reaction temperature and the quantity of starting materials. Orthorhombic crystals were obtained at 160 °C, distributed individually on the substrate and had a flaky rhombic shape. Hexagonal crystals were obtained at 180 °C. The crystals had a rhomboidal shape, were uniform and continuous enough to form a solid film on the substrate. The substrates were corroded under the hydrothermal conditions and offered a coarse surface for the crystal growth. The hexagonal lanthanum hydroxycarbonate was discovered to show significant second harmonic generation, which would be of interest for developing novel optical materials.     

Statistical Theory of Stable and Meta stable Transition for Crystallization and Fusion of Homopolymers ⅣStatistical Dynamics of Polymeric Crystallization by Molecular Segregation-Division of Crystal Grow-rate Regimes and Their Temperature and Grown Mechan

First a short review on the crystal growth theories and the experimental data was presented. Then a set of quantitative expressions for the size growth-rate of crystals produced by four different micro-growth mechanisms (folding, extending and two types of combination for folding and extending) was derived by a general evaluating method. A set of quantitative expressions for the correlations between the crystal size growth-rate and the product of crystalline temperature and super-cooling temperature at four different micro-growth mechanisms was obtained. Three growth-rate regimes were divided, the variations of the morphology for the crystals in the three types of regimes with the crystalline and super-cooling temperatures were discussed. They showed that these theoretical correlations between the morphology of crystals and the crystalline and super-cooling temperatures are in agreement with the later important observation on the lateral shape of crystals.     

Control of n-alkanes crystallization by ethylene-vinyl acetate copolymers

The crystallization of paraffins from their solution at low temperature was investigated in the presence of ethylene-vinyl acetate (EVA) copolymers that allow the control of the size of the crystals. Depending on the type of solvent and distribution of the paraffin lengths, the mechanisms of crystal formation and growth are different. Precipitation of the EVA prior to the paraffins leads to the nucleation of a large number of crystals, whereas the adsorption of EVA on the surface of the growing crystals slows down the crystal growth. EVA can act either as a nucleating agent or as a growth inhibitor. These two mechanisms were identified from the analysis of the temperature of crystallization (cloud point), the chemical composition of the crystals, and the observations of the crystal habit. The EVA was able to co-crystallize with the paraffins in crystals of an orthorhombic structure and the melting enthalpies of the crystalline paraffin did not depend significantly on their neighborhood. The energies of interaction between the different paraffinlike components are close to each other, so that minor changes of the experimental conditions may lead to dramatic effects. This is the basic rationale for the large behavioral diversity observed in these systems.     

纳米级聚乙烯和聚丙烯微晶的高分辨透射电子显微学研究

用高分辨电子显微学方法对从极稀的二甲苯溶液中得到的纳米级聚乙烯(PE)和聚丙烯(PP)微晶进行了研究,发现这种纳米级微晶是分子堆砌不完善,但可以独立存在的一种亚稳态结构,其晶格存在着大量的弯曲、分叉、位错等缺陷,经热处理后有序程度大大提高.表明高分辨电子显微学方法是研究PE和PP纳米级微晶的亚稳态结构和稳定性的有效手段.     

The Ambiguous Origin of Thermochromism in Molecular Crystals of Dichalcogenides: Chalcogen Bonds versus Dynamic Se−Se/Te−Te Bonds

We report thermochromism in crystals of diphenyl diselenide (dpdSe) and diphenyl ditelluride (dpdTe), which is at variance with the commonly known mechanisms of thermochromism in molecular crystals. Variable temperature neutron diffraction studies indicated no conformational change, tautomerization or phase transition between 100 K and 295 K. High-pressure crystallography studies indicated no associated piezochromism in dpdSe and dpdTe crystals. The evolution of the crystal structures and their electronic band structure with pressure and temperature reveal the contributions of intramolecular and intermolecular factors towards the origin of thermochromism—especially the intermolecular Se⋅⋅⋅Se and Te⋅⋅⋅Te chalcogen bonds and torsional modes of vibrations around the dynamic Se−Se and Te−Te bonds. Further, a co-crystal of dpdSe with iodine (dpdSe-I₂) and an alloy crystal of dpdSe and dpdTe implied a predominantly intramolecular origin of the observed thermochromism associated with vibronic coupling.     

Four-center type photopolymerization in the crystalline state. V. X-ray crystallographic study of the polymerization of 2,5-distyrylpyrazine

Changes in crystal structure during polymerization and oligomerization of 2,5-distyrylpyrazine have been investigated by x-ray crystallography. The polymer and the oligomer as obtained are three-dimensionally oriented, and the directions of the three axes of the resultant crystals coincide with those of the original crystal. The space group of the products also agrees with that of the monomer. It is concluded that the polymer and the oligomer crystals approximately duplicate the molecular arrangement in the monomer crystal. The polymerization mechanism is discussed on the basis of the crystal structures.     

Electrocrystallization of Metals under Ideal and Real Conditions

Ideal conditions during electrocrystallization, which are only approximately attainable, would lead to a perfect single crystal, whereas real conditions yield a monocrystalline or polycrystalline product containing many structural defects. The electrolytic production of quasi-ideal single crystals requires an overpotential that supplies at least the activation energy necessary for the formation of two-dimensional nuclei, since growth otherwise proceeds via screw dislocations with formation of a “real” crystal. The potential deviation in electrocrystallization under real conditions is due to electrochemical and/or crystallization overpotential, which can be determined separately. The investigation of electrocrystallization also offers possibilities for a systematic study of the formation of imperfections in real crystals.     

Quantitative analysis of crystallization kinetics by light depolarization technique. Possibilities and limitations

The kinetics of isothermal crystallization of various polymers was investigated by light depolarization technique (LDT) using the new setup with direct registration of depolarization ratio. Experimental data were analyzed using new method proposed by Ziabicki who shown that degree of crystallinity is a non-linear function of degree of depolarization, crystal thickness, and its birefringence. Other experimental methods were involved providing supplementary information on crystal thickness (SAXS) and allowing comparison of crystallization kinetics (WAXS, DSC). The advantage of LDT relies on high sampling rate allowing on-line measurements and lack of inertia effects that exist in other methods like calorimetry. The limitations of the applicability of the method are discussed. The method needs supplementary information not only on crystal thickness but also on variable optical birefringence of real crystals. Our results show that LDT can be used in a simple way for investigation of crystallization kinetics at relatively high temperatures, providing large and perfect crystals. In such a case it is sufficient to use crystal intrinsic birefringence and final crystal thickness typical at particular temperature of crystallization. On the other hand, depolarization ratio combined with measurements by other methods (crystallinity and crystal thickness) can be used for estimation of crystal birefringence.