A nucleation mechanism leading to stacking of lamellar crystals in polymer thin films

Systematic studies based on well‐controllable model systems aim at understanding how crystallization from a melt or solution of randomly coiled polymers leads to the formation of mono‐lamellar crystals. However, besides mono‐lamellar crystals also various other morphologically simple but yet not well understood structures are found. In particular, stacks of correlated lamellar crystals have been observed since the early days of the study of polymer crystallization. Here, we demonstrate that a recently proposed mechanism of self‐induced nucleation within lamellar crystals provides a possibility to explain how in such stacks lamellar crystals can be correlated. Examining various polymer systems, we show that the probability for generating self‐induced nuclei depends on the morphology of an initiating dendritic basal lamellar crystal. In addition, we provide evidence that this self‐induced nucleation mechanism, together with a high rate of transport of molten polymer to the fold surface, may allow the formation of polymer crystals with similar size in all three dimensions, containing a large number of superposed correlated lamellae. © 2019 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Surfactant Crystals as Stimulable Foam Stabilizers: Tuning Stability with Counterions

The demands on foam stability are variable and changing, which is why design of foams that are both ultrastable and stimulable is important. We study foams stabilized using surfactant particles made through precipitation of sodium dodecyl sulfate with alkali chlorides. We have previously shown that depending on the concentrations of surfactant and salt, the foams can be ultrastable or age like common surfactant foams. We now show that the adsorption of surfactant crystals changes with the type of salt added and how the crystals are made, as well as the surfactant concentration. We see differences in foam stability if the crystals are made prior to foaming or if they are formed concomitantly with foaming. The adsorption of the crystals is improved if the crystals are made during generation, possibly because of their smaller size. The foams destabilize when heated above the Krafft boundary. We show that through tuning the surfactant concentration and salt type or concentration, we can modulate the melting temperature, and hence the destruction temperature of foam between 22 and 50 °C. Precipitated surfactant particles are versatile alternatives to stabilize ultrastable and stimulable foams.     

Golden organic crystals of an azobenzene derivative containing two ester bonds

Recently we found while we were synthesising a cationic surfactant that a synthetic intermediate, 4,4′‐bis{1‐[2‐(N,N‐dimethylamino)]ethoxy}azobenzene, produced gold‐coloured crystals [Matsumoto et al., J. Oleo Sci., 59 , (2010) 151]. Here we describe how an azobenzene derivative, bis[4‐(ethoxycarbonylmethoxy)phenyl]diazene, also forms gold‐coloured crystals after recrystallisation from a mixture of acetone and water. The profile of the specular reflectance as a function of wavelength for the crystals is very similar to that for metallic gold plate, indicating that the crystals have a golden colour. The maximum specular reflectance of the crystals is 16%. Atomic force microscopy observation shows that the crystals have flat surfaces. X‐ray diffraction measurements demonstrate the presence of a periodic structure in the crystals, which indicates that monolayers (lamellar structure) consisting of azobenzene molecules with a thickness of 1.42 nm are stacked in the crystals. The gold‐coloured crystals are tolerant of ultraviolet light irradiation. The gold‐coloured crystals may be useful as a substitute for conventional metallic pigments in specific coating applications.     

The dihydrate-hemihydrate transformation in gypsum

A microscope study has been made of the development of crystals of calcium sulphate hemihydrate produced on, or in, sheets of the dihydrate in the form of selenite by calcining under controlled conditions. The crystal forms were shown to be strongly dependent upon both temperature and ambient water vapour pressure. A mechanism for the nucleation and growth of these crystals is propounded in terms of the diffusion of molecular vacancies. The relevant properties of the so-called α-and β-hemihydrates are discussed, and it is argued that these forms are due to incoherent and coherent growth, respectively, from the parent selenite; it is explained how it is possible to obtain incoherent growth in this solid transformation. The overall shape of the crystals is examined.     

Enhanced light extraction in ITO-free OLEDs using double-sided printed electrodes

We show how nanoimprint lithographic techniques are particularly suited for the realization of OLED device structures. We tested them to realize nanopatterned metallic electrodes containing photonic crystals to couple the light out and plasmonic crystals showing extraordinary transmission. At similar current densities, a two-fold electroluminescence is achieved with devices having double-sided structured metallic electrodes as compared to a control OLED with an ITO anode. The use of combined nanoimprint lithography processes has the potential to expand the performance range of various organic optoelectronic devices.     

废镍触媒的综合利用

本文采用酸溶，除渣，分离及蒸发浓缩，冷却，过滤等操作步骤，从废镍触媒中回收得有实用价值的硫酸镍，硫酸镁晶体，其回收率分别为７５％和９０％，经济效益也比较好。     

Mechanical and thermal properties of polyolefin thermoplastic elastomer blends

ABSTRACT

Polyolefin thermoplastic elastomers (POEs) are a class of thermoplastic elastomer (TPE) that can be easily processed. POEs have broad applications from automobiles to footwear and it is desirable to be able to alter the microstructure and properties. In this work, a systematic study of how blending and thermal processing of POEs affects mechanical and thermal properties is undertaken. Ethylene-octene copolymer POEs with different degrees of crystallinity are blended, compounded, and moulded and then slow cooled, quenched, or annealed. Differential scanning calorimetry (DSC) results show that the blends are immiscible and that quenching suppresses crystallinity while annealing thickens crystals. More crystals of the same thickness or thicker crystals of the same amount in the blends result in a higher modulus, lower elastic recovery, and more residual strain or permanent deformation after tensile testing. Microstructural control will allow for the optimal design of elastomeric materials with anticipated properties.     

Crystallization of polyamides under elevated pressure: 5.Pressure-induced crystallization from the melt and annealing of folded-chain crystals of nylon-11, poly(aminoundecaneamide) under pressure

High pressure dilatometry, differential scanning calorimetry, electron microscopy, X-ray diffraction, and infra-red spectroscopy to study how the crystallization of nylon-11 from the melt, as well as annealing of the folded-chain crystals, are affected by pressure in the range from 1 to 10 kbar (1 kbar = 100 MN/m²) and temperature in the range from 200° to 320°C. Pressures exceeding 3 kbar and temperatures higher than 230°C are sufficient for growth of the chain-extended crystals of nylon-11 either by pressure-induced crystallization from the melt or by annealing of the folded-chain crystals. Crystallization from the melt or annealing at 320°C or higher, and 10 kbar, resulted in crosslinking of the polymer. The highest melting temperature and heat of melting found for the chain-extended crystals of nylon-11 were 226°C and 35 cal/g respectively, as compared to 190°C and 13.6 cal/g for the folded-chain material. The texture of the chain-extended crystals of nylon-11 was found to be spherulitic with well developed striations forming circle patterns, and polymer chains passing through several lamellae. No sharp boundaries were found between the chain-extended lamellae. The alpha-crystalline modification, found for the folded-chain crystals of nylon-11, was preserved in the high pressure crystallization and annealing experiments. Infra-red absorption bands at 1420 and 1225 cm^?1 seem to be associated with the presence of folds in the nylon-11 crystals. It is suggested that, during the initial stage of crystallization under pressure, folded-chain crystals are formed, with a crystalline order and long spacing larger than that of the starting nylon-11.     

Melting behavior of high performance composite matrix polymers: Poly(phenylene sulfide)

We have been studying crystallization and melting behavior of high performance semicrystalline polymers to increase our understanding of the effects of processing on microstructure. Questions on development of morphology center around whether single or dual populations of crystals exist after melt processing, and how these crystals melt creating the multiple endotherms usually observed. We have used differential scanning calorimetry (DSC) to examine endothermic response in poly(phenylene sulfide), PPS, after various processing treatments. These include isothermal melt crystallization and crystallization from the rubbery amorphous state. For the first time, we report endothermic response of solution crystallized mats of single crystals. Our results on melt crystallized PPS are explained by a model in which different crystal populations exist in the material at room temperature prior to DSC scanning. Ability of the material to reorganize during the scan depends upon the initial state of perfection of the crystals.     

纳米材料及其水热法制备（上）

简述了纳米材料的特性及纳米材料科学；介绍了水热法制备纳米晶的技术，提出了在水热条件下如何控制纳米晶的颗粒度。用负离子配位多面体生长基元理论模型合理地解释了水热条件下纳米晶的取向连生，配向附生和枝蔓晶的形成机理。     

Micromechanical approach to modeling damage in crystalline polyethylene

The purpose of this article is to describe how the concepts of continuum damage mechanics can be applied to modeling of polyethylene materials under different loading conditions. The increasing use of polyethylene in diverse applications motivates the need for understanding how its molecular properties relate to the overall behavior of the material. Although microstructure and mechanical properties of polymers have been the subject of several studies, the irreversible microstructural rearrangements occurring at large deformations are not completely understood. In this work, a three‐dimensional damage constitutive model for polyethylene is proposed. The material is analyzed from a microscopic viewpoint and considered as an aggregate of crystals. The model regards the crystals as rigid‐viscoplastic and incorporates the effects of atomic debonding on the overall mechanical behavior. To illustrate the capability of the proposed model, two simulations are carried out to capture the macroscopic stress–strain behavior and texture evolution under uniaxial tension and simple shear loading conditions. The results are compared with experimental data and numerical simulations from other references. POLYM. ENG. SCI., 47:410–420, 2007. © 2007 Society of Plastics Engineers.     

Structural analysis of poly(butylene adipate) banded spherulites from their biodegradation behavior

Poly(butylene adipate) (PBA) has been reported to have polymorphic crystal structures and only the mixture of two crystal modifications (α and β crystals) forms banded spherulites. However, how the two crystals coexist in banded spherulites remains to be solved. In this work, the morphological structure of PBA banded spherulites was analyzed from their biodegradation behavior by means of polarized optical microscopy (POM), scanning electron microscopy (SEM), atomic force microscopy (AFM) and wide-angle X-ray diffraction (WAXD). It was found that the banded spherulites were made up of alternate flat-on and edge-on domains in lamellar crystals along the radiating direction. To determine the distribution of two crystal modifications in banded spherulites and the interrelationships between the alternate domains with polymorphic crystal structures, the relative contents of two crystal modifications in banded spherulites were first quantified, and their changes were then correlated to the morphological changes of banded spherulites in the course of biodegradation in terms of the difference in biodegradation kinetics of two crystal modifications. It was found that the flat-on domains show a slower crystal growth rate but a faster biodegradation rate than the edge-on domains. The analysis indicates that the flat-on domains in spherulites are composed of α crystals, while the edge-on domains are composed of β crystals. The primary growth mechanism of PBA banded spherulite was proposed based on the difference in crystallization heat and kinetics of two crystal modifications.     

Confocal Scanning Laser Microscopic Study of the RDX Defect Structure in Deformed Polymer‐Bonded Explosives

The influence of an explosion‐driven deformation on the defect structure in RDX crystals embedded in a polymer‐bonded explosive was investigated by means of confocal scanning laser microscopy. The images were compared to the defect structure in the as‐received RDX grades, embedded in an epoxy resin. In this way it is possible to qualitatively analyze the changes in defect structure of the RDX crystals that were induced by the explosion‐driven deformation. For the first time, these data therefore provide experimental confirmation of how shock waves mechanically interact with energetic crystals – a topic that, up to now, was only explored by means of simulations.     

Floating Zone Crystal Growth and Phase Equilibria: A Review

The thermal-imaging floating zone technique can be used to grow crystals of yttrium iron garnet (Y₃Fe₅O₁₂), aluminum-doped yttrium orthoferrite (YFe_0.88Al_0.12O₁₂), and magnetite (Fe₃O₄), which represent peritectic compounds, solid-solution crystals, and atmosphere-sensitive materials, respectively. The reactions involved in floating zone crystal growth are explained on the basis of phase diagrams. A review of crystal growth reports, including unpublished findings by the present authors, demonstrates how the crystallization processes, the reaction with the ambient atmosphere, and the composition variation in the obtained crystals can be explained or controlled on the basis of phase equilibrium. The floating zone technique is applicable to a variety of materials and remains a handy tool for materials research; however, its industrial application may be limited.     

Chiral Cooperativity in Helical Polymers

Human experience informs us of the two extreme consequences of crowding: random behavior of the individuals, in which each takes a singular path; and cooperative behavior, in which the individuals in the crowd act in a predictable uniform manner, such as in a military organization These extremes find parallels in the crowded situations encountered at the molecular level, exemplified for the former by glassy states, such as often encountered in polymeric materials, 1 or for the latter, in the uniform archetypal arrangements of crystals or liquid crystals. Here we review the cooperative characteristics of uniform arrangements that take a chiral form and explore how these characteristics lead to left- and right-handedness. These studies lead us to understand the basis of amplification of chirality in regular arrays, in which small influences have large consequences, and how chiral cooperativity acts in the resolution of conflict between influences favoring left- and right-handedness. 2     

The role of hydrothermal pathways in the evolution of the morphology of ZnO crystals

Understanding growth mechanisms usually leads to the successful preparation of a targeted microstructure. However, the large number of parameters that influence the shape and the size of nanostructures often make it difficult to predict the outcome. We investigated the growth of wurtzite-type ZnO by closely following such a multistage process. We associated the diverse morphology of the precipitated crystals, prepared under the same hydrothermal conditions, to the differences in the transient crystallization processes during the precipitation. By altering the pH of the suspension after the precipitation, we gain control over the resulting morphology of the ZnO and show how to grow identical crystallites with different shapes and crystal sizes. Here we report, for the first time, on how ZnO platelets grow in a certain Zn²⁺/OH⁻ ratio along the basal and one of the prismatic directions to form sphalerites with very high surface area. We also offer an explanation as to how sphere-like hierarchical structures composed of plate- or rod-like ZnO crystals form through self-assembly driven processes.     

Back to the future: Fatty acids,the green genie to design smart soft materials

Fatty acids are widely used in industries for various applications as soaps or in their crystalline form. Fatty acid soaps are used as surface-active agent to stabilize foams and emulsions, for detergency, and surface wetting. Fatty acid molecules in organic solvents are used as low-molecular-mass organic gelators. Currently, there is a renewed interest in using fatty acids in industrial applications instead of petrochemical surfactants since fatty acid soaps are green surfactants. Fatty acids exhibit also many advantages, including the design of responsive soft-materials. Fatty acid soaps are natural pH and thermoresponsive surfactants, which can lead to responsive foams and emulsions. In their crystalline form, fatty acid crystals in both aqueous and non-aqueous solvents stabilize liquid foams. These crystals are also efficient in the production of liquid marbles. Fatty acids are solvosurfactants with the ability to form microemulsions and capillary suspensions. In this review, we illustrate how fatty acid molecules can be used in the manufacture of multiresponsive soft-materials ranging from aqueous and non-aqueous foams, emulsions, nanoemulsions, microemulsions, liquid marbles and capillary suspensions.     

Nano-Segregation and Directed Self-Assembly in the Formation of Functional Liquid Crystals

It is often a question that is asked: “How can you predict from the molecular architecture of a material the structure of the condensed phases it forms, and what properties would you expect the phase to exhibit?” For liquid crystals, knowing how to design materials for particular applications requires precision molecular engineering. In this article we examine how molecular topology and interactions influence phase formation and report on material design.     

寡聚核苷酸对茶碱晶型的调节作用

有机晶体多晶型调控的规律研究对于医药、燃料、农药等行业具有重要意义。茶碱是一种甲基嘌呤类似物,具有I、II、III、IV和M 5种多晶型。由于腺嘌呤核苷与茶碱结构具有相似性,研究了腺嘌呤核苷组成的寡聚核苷酸对茶碱溶液结晶过程的影响。结果表明采用寡聚核苷酸d（A₁₀）、d（A₂₀）为添加剂,能够显著影响乙醇-水体系降温结晶过程中茶碱多晶型的形成,促进M晶型生成。分子模拟计算揭示了腺嘌呤碱基组成的核苷酸片段与茶碱M晶型重要晶面之间的相互作用能最强,正是这种强相互作用促进了茶碱结晶过程中M晶型的生长。     

碘化铅单晶体生长工艺分析

在坩埚下降法生长PbI2单晶体的过程中,如何解决晶体中的富碘问题是一个研究关键.本文采用坩埚下降法生长出了三种不同颜色的富碘PbI2单晶体.实验中发现:通过合理的选择坩埚在温场中的生长位置,可最大限度的减轻晶体富碘现象,分析了相关工艺,得出了最优工艺方案.结果表明:在适当的工艺条件下,坩埚下降法设备简单,易于操作,是生长PbI2单晶体的优良方法.