尼龙1010环状球晶的研究

利用偏光显微镜研究了尼龙1010环状球晶的生成条件、形态特征和光学性质,发现在等温结晶过程中只可生成环状球晶;在降温过程中可由相同光性的放射状球晶转变成正、负、混合光性环状球晶;在升温过程中正光性和混合光性环状球晶分别转变成不对称四瓣形和六瓣形环状球晶,负放射球晶可转变成另一种负环状球晶。     

尼龙1010等温结晶球晶形态与生成条件研究

 本文利用偏光显微镜研究了等温结晶时尼龙1010球晶的形态与生成条件,发现在原始样品熔点附近或高于原始熔点以上温度结晶,主要生成暗、亮与带正环的负光性放射状球晶;熔点以下至195℃主要生成正放射状球晶;在较宽的温度范围内可生成混合光性放射状球晶,与少量的六瓣、两瓣、不对称四瓣形三种异常光性球晶;181℃以下主要生成正环状球晶.     

尼龙1010等温结晶球晶形态与生成条件研究

本文利用偏光显微镜研究了等温结晶时尼龙1010球晶的形态与生成条件,发现在原始样品熔点附近或高于原始熔点以上温度结晶,主要生成暗、亮与带正环的负光性放射状球晶;熔点以下至195℃主要生成正放射状球晶;在较宽的温度范围内可生成混合光性放射状球晶,与少量的六瓣、两瓣、不对称四瓣形三种异常光性球晶;181℃以下主要生成正环状球晶.     

尼龙1010球晶的熔融

本文利用偏光显微镜研究了尼龙1010等温结晶所生成的几类球晶的熔融现象,测得正环状球晶的熔点(T_m)为182℃,正放射球晶T_m=203℃;混合放射球晶T_m=202～205℃;暗负放射球晶T_m=204～210℃;亮负放射球晶T_m=205～210℃。利用Hoffman T_m-T_ε外推法测得其平衡熔点T_m~0=215℃。     

间规聚苯乙烯晶体结构的研究——等温结晶球晶形态及生成条件研究

用偏光显微镜研究了 2 0 0℃～Tm 等温熔体结晶间规聚苯乙烯 (s PS)的球晶形态及其生成条件 ,发现s PS共可生成八类球晶 .在较低温度 (Tc<2 40℃ )下 ,生成大量晶片排列疏散的羽毛状球晶 ;而Tc>2 40℃时 ,生成大量晶片堆砌紧密的八瓣球晶及少量四瓣球晶 ;此外 ,2 30℃附近还有带螺旋消光环的正球晶和串晶生成     

尼龙1010结晶与熔融行为的研究

用DSC研究了降温速率R对尼龙10 10结晶与熔融的影响,以及室温(RT)和液氮(LN)骤冷退火样品的熔融.降温时结晶温度随R增大线性降低;T_g以上可完成结晶时结晶度相同;结晶起始温度>181℃生成的晶体有三个熔融峰,对应于环状和放射状球晶的转化与熔融;在181℃和T_g间结晶,无放射球晶转化峰;T_g下有结晶放热峰样品加热时有冷结晶发生.RT未退火样品三个熔融峰,退火温度T_α≥180℃样品两个峰,结晶度C∝T_a;LN未退火样品单一熔融峰,T_a>160℃双峰,T_a≤160℃三峰,低温峰温与C均∝T.     

聚醚醚酮球晶结构的形态特征研究

本文借助热台偏光显微镜,扫描电子显微镜,红外光谱等技术研究了聚醚醚酮(PEEK)球晶结构的形态特征。发现PEEK的同-球晶可在不同条件下呈现放射状及带状的形态,而这两种形态可相互进行可逆的热转变。对这两种球晶的相互转变规律及球晶的微观结构作了分析,提出了PEEK球晶结构的模型。     

聚对苯二甲酸丁二酯熔融结晶形态的扫描电镜观察

本文利用扫描电镜和离子蚀刻技术研究了PBT熔融结晶的形态结构。结果表明,PBT根据其结晶条件的不同可产生非常结晶、正球晶、螺旋状球晶及树枝晶。非常球晶呈放射状织构,但晶的中部是由约0.2μ的晶带交织而成网状结构。正球晶呈放射状织构,结构比较紧密。螺旋状球晶虽然也有放射状织构,但放射状的片晶已有一定程度的扭曲,球晶的中部为不规则螺旋扭曲,这类球晶在偏光显微镜下没有观察到典型的黑十字消光图。     

聚氧乙烯球晶上彩色环状条纹的形成

用自然白光代替偏振光在显微镜下观察聚氧乙烯球晶的生长过程, 可以更清晰地看到彩色环形条纹的形成. 当成长中的二维球晶相互碰撞后, 被挤出的熔体改变球晶的原有结晶方向, 流向饼形球晶中央而在其表面上逆向结晶, 由于被挤出的熔体数量有限, 晶层的厚度逐渐减小, 在盖玻片下方形成一个盘状的楔形真空间隙. 此间隙导致彩色环状干涉条纹的形成. 实验用肉眼直接观察到二维球晶在生长过程中结晶方式的变化, 为二次结晶理论的发展提供了实验依据.     

聚对苯二甲酸乙二酯形态结构的光散射研究

在不同结晶条件下,聚对苯二甲酸乙二酯样品出现了三种不同的光散射图形(正常球晶、异常球晶和混合球晶散射图形)。并假定正常球晶的光轴方向与半径垂直;异常球晶的光轴方向与半径夹+45°角或-45°角;混合球晶则是正常球晶与异常球晶叠加的结果。基于这些假定,按照Clough的计算公式,用二维球晶模型分别对具有上述各种光轴取向的球晶进行了计算。结果表明,计算出的H_v、V_v散射图形与实验所得的散射图形符合得很好。偏光显微镜的观察结果也进一步证实了这些模型的假定。     

Lyotropic mesophase of cellulose in ammonia/ammonium thiocyanate solution

Solutions of cellulose in a mixture of 27:73 (w/w) of liquid ammonia and ammonium thiocyanate become liquid crystalline at room temperature above a certain critical concentration which depends on the degree of polymerization of the dissolved cellulose. The high optical rotations of the solution suggest that the cellulose mesophase is cholesteric in nature. In the two-phase region, the cellulose solutions exhibit negatively birefringent spherulites that possess both ringed and nonringed internal structures. The anisotropic solutions can be oriented by shear, indicating high potential for spinning them into useful fibers.     

MULTIPLE MELTING AND CRYSTALLIZATION BEHAVIOR OF NYLON 1212

The wide-angle X-ray diffraction (WAXD) patterns of isothermally crystallized Nylon 1212 show that γ-form crystals form below 90℃ and the α-form crystals can exist above 140℃. In the temperature range of 90-140℃, the α-form and γ-form crystals coexist. Variable-temperature WAXD exhibits that the nylon 1212 γ-form does not show crystal transition on heating, while α-form isothermally crystallized at 160℃ exhibits Brill transition at a little higher than 180℃ on heating. The multiple melting behaviors of Nylon 1212 isothermally crystallized from melt come from a complex mechanism of different crystal structures, dual lamellar population and melting-recrystallization. In polarized optical microscope (POM) observations, Nylon 1212 isothermally crystallized at 175℃ shows the ringed banded spherulites. However, at temperatures below 160℃ the ringed banded image disappears, and cross-extinct spherulites are formed.     

Isothermal crystallization kinetics and spherulitic morphology of poly(4‐hydroxybutyric acid‐alt‐glycolic acid)

Isothermal crystallization behavior of a new regular polyester constituted by glycolic acid and 4‐hydroxybutyric acid units is studied by means of differential scanning calorimetry and hot‐stage optical microscopy. A wide range of crystallization conditions were experimentally accessible, allowing various morphological features to be observed and accurate estimates made of characteristic growth parameters, including radial growth and nucleation rates. Three‐dimensional spherulitic growth from heterogeneous nuclei is deduced from the Avrami analysis, whereas optical micrographs reveal two different spherulitic textures that agree with the existence of two crystallization regimes. These can be well distinguished from the breaks observed in the Lauritzen and Hoffman plots when the linear crystal growth rate or the overall crystallization rate is considered. Ringed and nonringed spherulites with negative and positive birefringence, respectively, can be obtained depending on crystallization conditions and regimes. The studied polyester shows rather complex melting behavior which is interpreted in terms of a recrystallization process involving the two different kinds of spherulites. This study allows polymorphism to be discounted. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2640–2653, 2007     

Morphology and interference color in spherulite of poly(trimethylene terephthalate) copolyester with bulky linking pendent group

A novel phosphorus-containing copolyester (PTTP), poly(trimethylene terephthalate) (PTT) copolyester with a bulky linking pendent group of 9,10-dihydro-10-[2,3-di(hydroxycarbonyl) propyl]-10-phosphaphenanthrene-10-oxide (DDP) was prepared, and its crystallization, crystal morphology and interference color were investigated in this article for the first time. Differential scanning calorimeter (DSC) results showed that with the increase of DDP content, the melting point (T(m)) and crystallization ability of PTTP decreased. WAXD results suggests that the three samples share one crystal structure, however the crystallinity decreases with increasing DDP content. Polarized optical microscope (POM) observation indicated that the samples showed non-banded spherulites at a lower and higher temperature, and banded spherulites at the middle temperature range. From the micrographs obtained from scanning electronic microscopy (SEM) and atomic force microscopy (AFM), ringed patterns with many defects could be found for samples with higher DDP contents, which crystallized at a lower temperature, and a transformation from square-shaped spherulites to circular spherulites was noted for samples with higher DDP contents, which crystallized at a higher temperature. The interference color of the spherulites was also studied and it was shown that with the increase of film thickness or decrease of DDP content, the spherulites became more colorful under POM observation, indicating that the hindering effect and randomness caused by incorporating the DDP monomer with a bulky pendent group into the PTT molecular chain exhibited a negative influence on the molecular mobility and crystallization ability of the copolyester, and led to the formation of the defective band morphology and the less colorful interference color of the PTTP spherulites.     

聚(ε-己内酯)/苯乙烯-丙烯腈共聚物共混物的形态研究

本文研究了聚(ε-己内酯)(PCI/苯乙烯-丙烯腈共聚物(SAN)共混物的形态。采用差示扫描量热计(DSC)测量了PCL/SAN共混物中的PCL结晶度随着SAN含量的增加而下降;当SAN浓度达到60wt％。以上时,PCI的结晶度趋于零。通过偏光显微镜可以观察到在含高浓度PCI的共混物中,PCL是以球晶形式存在的。样品是由PCL球晶充满的,但是随着SAN含量的增加,PCL球晶半径减小,球晶结构逐渐变得不规整,而X-射线衍射测试了不同组成的PCL/SAN共混物中PCL的晶胞参数没有改变,说明SAN没有进入到PCL的晶胞内。以小角X-射线散射结果发现PCI片晶之间的距离随着SAN含量的增加而增大。以上说明SAN分子与没有结晶的PCL形成无定形相夹在PCL的片晶之间。     

Unusual Spherulitic Morphology of Poly(propylene fumarate)

Spherulites are the most common crystalline morphology and thus the visual expression of crystal structures for polymers. The diversified patterns have provided intuitive morphology probes for various crystallization behaviors, while the correlations between them are still needed to be enriched. In this work, the complicated spherulitic morphology of poly(propylene fumarate)(PPF), which is sensitive to crystallization temperature, is investigated. PPF melt, respectively, crystallizes into rough spherulites, regularly banded spherulites, and spherulites containing both two kinds of morphology at low, high, and mediate temperatures. By systematically assaying, it is clear that the growth axis along the radial direction changes from a-axis to b-axis as the crystallization temperature increases, which leads to the formation of unique crystallization-temperature-dependent spherulites. Based on detailed characterization of Fourier transform infrared spectroscopy, the packing state of the specific hydrogen bonds of "C=C―H···O=C―C=C" in PPF crystal lattices is determined, and furthermore, the mechanism for temperature-dependent selection of growth axes for PPF spherulites in melt is reasonably speculated.     

Formation of ringed spherulites in polyethylenes

The effects of molecular weight, molecular weight distribution, crystallization temperature, quenching medium, and sample preparation on the formation of ringed spherulites in linear polyethylenes were studied by polarized light microscopy and small-angle light scattering. When the samples were crystallized at a predetermined temperature, ringed spherulites were formed over a narrow range of temperature and molecular weight with both fractionated and unfractionated polymer samples. Quenching the samples in air at room temperature considerably extended the range of molecular weights for the formation of ringed spherulites. Minor modification of an airquench method further extended the range and yielded better-defined structures. The results are interpreted in terms of the anisotropy of the melt, the thermal conductivity of the quenching medium, and the shear stress applied during the crystallization process. That highly specific conditions are necessary for spherulite formation, of both the conventional and ringed type, is a major conclusion of this study.