Spiralling optical morphologies in spherulites of poly(hydroxybutyrate)

Some rather unusual optical morphologies in thin films of poly(hydroxybutyrate) in which a temperature gradient is imposed across the thickness of the film are reported. Spherulites in which the Maltese cross degenerates into a continuous spiral grow under these conditions, and the direction of the rotation of the spirals depends on the direction of heating. These morphologies are explained with the existing understanding of spherulite optics. The helicoidally twisting crystallites are modeled as twisting around an axis at a fixed angle to the radius of the spherulite (and the plane of the film). The possible implications for future, inclusive models of banding in spherulites are discussed. Further observations on the temperature dependence of the optical banding pattern in poly(hydroxybutyrate) are also reported, and an unexpected minimum in band spacing and fine optically visible fibrillar texture is discussed. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1575–1583, 2000     

BTDA/m-PDA聚酰亚胺环带球晶形貌与生长影响因素的研究

综述了本课题组BTDA/m-PDA聚酰亚胺环带球晶研究的进展.通过偏光显微镜(PLM),透射电镜(TEM),和原子力显微镜(AFM),研究了球晶中片晶的生长形貌,并探讨了环带形成的机理.考察了环带球晶生长的影响因素,包括:(1)温度:在较低酰亚胺化温度下只能形成不规则的球晶,而在较高温度下形成中心环间距较大的球晶;(2)聚酰胺酸分子量:分子量较低聚酰胺酸不能形成环带球晶;(3)分子链的不对称性:通过不同比例单体共聚发现,分子链上间苯二胺和羰基的不对称性对环带的形成有着决定性的影响;(4)溶剂:随着溶剂含量的增加,环带球晶的环间距增大.     

Logistic Map三维耦合格子模型模拟环带球晶

应用Logistic map三维耦合格子模型对环带球晶进行了模拟. 利用数值计算的方法预测了与实验中环带球晶形貌一致的图案. 对于本体体系, 环带球晶形貌的带宽随Logistic map中可调参量μ的增大而变窄, 随耦合模型中的扩散项系数ε的增大而变宽; 对薄膜体系, 环带球晶形貌的带宽随格子厚度的增加而变宽, 模拟结果与实验结果一致. 同时, 还给出了螺旋状环带结构在三维空间中的形貌.     

Periodic structure during unidirectional solidification for peritectic Cd–Sn alloys

Unidirectional solidification for the peritectic Sn–1.0, 1.5, 2.0 at% Cd alloys was carried out under temperature gradients of 2.7×10³ K/m for 4 mm diameter specimens, and 5.3×10³ K/m for 2 mm diameter specimens. A banded structure in which the two constituent phases alternatively form perpendicular to the growth direction was observed in the 2 mm diameter specimens. On the other hand, a competitive microstructure was obtained in the 4 mm diameter specimens, in which the two phases interlace and the three-phase junction fluctuated in the radial direction during unidirectional solidification. Formation of the banded structure depended on the specimen diameter, while the transition from the cellular interface to the planar interface was not affected by the specimen diameter. In the high G/V region for peritectic alloys, the growth morphology in which the phases grow side by side is unstable, even if the pulling rate and temperature profile are constant. The banded structure and the competitive structure originate through the same mechanism; this is intrinsic for peritectic alloys with two-phase composition.     

甲壳素类液晶高分子的研究 Ⅰ侧基长度对羧酰化甲壳素的液晶性的影响

四种羧酰化甲壳素即乙酰化、丙酰化、丁酰化和己酰化甲壳素在二氯乙酸溶液中均呈现胆甾型溶致液晶相．临界浓度随侧基长度增加而略有增加,衍生物的临界浓度明显都比原甲壳素高许多,这些规律都可以用链刚性的变化来解释．四种羧酰化甲壳素在剪切时均能形成条带织构,而且能形成条带织构的最低浓度有明显差别,随侧基长度增加而提高,进一步表明侧基较长,液晶性减少．     

聚羟基丁酸酯环带球晶的形貌研究

聚羟基丁酸酯 ( PHB)是一种由细菌合成的手性高分子材料 ,其分子结构具有高度的规整性 [1] ,球晶比较大 (直径可达几毫米 ) ,是研究高分子结晶行为和形态的理想材料 [2 ] .在偏光显微镜下 ,Bauer[3]和 Martinez- Salazar等 [4 ] 曾在 PHB球晶上观察到消光带和同心的环线 .在聚环氧乙烷 [5] 和小分子液晶4-氰基 - 4 -癸氧基联苯的球晶上 [6 ] 也观察到了同心环线 .但这些工作都把同心环线归结为裂缝 ,并未提供证据 .事实上 ,偏光显微镜的低分辨率及其透视特点 [7] ,使之无法真实反映材料的表面形貌 ,因而也无法区分裂缝和台阶 .我们对光…     

BANDED TOEPLITZ PRECONDITIONERS FOR TOEPLITZ MATRICES FROM SINC METHODS

We give general expressions, analyze algebraic properties and derive eigenvalue bounds for a sequence of Toeplitz matrices associated with the sinc discretizations of various orders of differential operators. We demonstrate that these Toeplitz matrices can be satisfactorily preconditioned by certain banded Toeplitz matrices through showing that the spectra of the preconditioned matrices are uniformly bounded. In particular, we also derive eigenvalue bounds for the banded Toeplitz preconditioners. These results are elementary in constructing high-quality structured preconditioners for the systems of linear equations arising from the sinc discretizations of ordinary and partial differential equations, and are useful in analyzing algebraic properties and deriving eigenvalue bounds for the corresponding preconditioned matrices. Numerical examples are given to show effectiveness of the banded Toeplitz preconditioners.     

On clarification of haze in polypropylene

The mechanism of reducing light scattering in isotactic polypropylene (i‐PP), through the addition of so‐called clarifying agents, is studied with small‐angle light scattering (SALS) and scanning electron microscopy (SEM). The clarifying agents used in this study depict monotectic phase behavior with i‐PP, crystallizing in a relatively narrow concentration range in a nanofibrillar network, providing an ultrahigh nucleation density in the i‐PP melt. It is found that the clarifying effect, a dramatically increased transparency and reduced haze, that occurs within the aforementioned additive concentration range, coincides with a change in morphology from strongly scattering spherulites to shish‐kebab‐like crystalline structures, as evidenced by in situ SALS measurements and confirmed by SEM images. A simple scaling law, relating the diameter of the shish‐kebab structures to the fibril diameter and volume fraction of the clarifying agent is proposed, suggesting that the performance of a (fibril‐forming) clarifying agent will improve by reducing the fibril diameter and/or increasing the volume concentration of the clarifying agent. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 865–874     

含氧化偶氮苯介晶基元共聚醚的合成与液晶行为

以1,6-二溴己烷(A)和1,10-二溴癸烷(B)为共缩聚单体,按不同摩尔配比与4,4'-二羟基氧化偶氮苯经相转移催化共聚醚化反应,合成了一系列主链上含有氧化偶氮苯介晶基元的共聚醚,它们均有好的液晶性,其取向膜观察到条带织构,当A/B的摩尔比为1时液晶态范围最宽。     

Nature of the Ring‐Banded Spherulites in Blends of Aromatic Poly(ether ketone)s

Summary: The ring‐banded spherulites in liquid crystalline poly(aryl ether ketone) (LC‐PAEK) and poly(aryl ether ether ketone) (PEEK) blends with a higher content (>50%) of LC‐PAEK are investigated by polarizing light microscopy (PLM) and atomic force microscopy (AFM) techniques. The results indicate that the light core and rings of the ring‐banded spherulites under PLM are mainly composed of an LC‐PAEK phase, while the dark rings consist of coexisting phases of PEEK and a small amount of LC‐PAEK. The formation of the ring‐banded spherulites is attributable to structural discontinuity caused by a rhythmic radial growth.

PLM image of ring‐banded spherulites in a 70:30 LC‐PAEK/PEEK blend caused by rhythmic growth.