Changes in row structure of extruded polyethylene film in grafting with styrene. II. Copolymer morphology

The morphology of extruded high-density polyethylene film grafted with styrene was studied by transmission electron microscopy of thin stained sections. Near the film surface grafted polystyrene was confined to amorphous layers between lamellar crystals of polyethylene. In the film interior separate polystyrene domains were also formed and became predominant in grafting in diluted styrene. The deciding factor for the location of grafted polystyrene is the chain length because only long chains can coalesce in large separate zones. The polystyrene zones expand by cracking the stacks of lamellae along the lamellar normals. Straightening of the twisted crystalline lamellae of polyethylene occurred in grafting. “Bubbles” of styrene homopolymer were formed under conditions of high monomer concentration. The effect of staining the graft by the Kanig method² was also discussed.     

Etching and the morphology of branched and cross-linked polyethylene

A permanganic acid etching technique was used to characterize the genuine morphologies of bulk crystallized samples of linear, branched, and crosslinked polyethylene. Four different kinds of artifacts as large as 15–20 m were detected. It was also noted that artifact density could be drastically reduced by proper selection of etching conditions. The morphologies of artifacts were independent of specimen crystallinity and the orientation of lamellar crystals; however, their rate of production was susceptible to the crystallinity of samples. The formation of a fresh surface involved the preferential etching of edge-on and secondary lamellae. As the growth features of cross-linked polyethylene were less than 6 m and were mainly sheaf-like structures, growth features could be readily distinguished from the artifacts by transmission electron microscopy. Another type of artifact (globules morphology) produced at angstrom scale was found to depend on the crystallinity and the surface structure of lamellar crystals. It is demonstrated that the fine lamellar details of branched and cross-linked polyethylene can be observed using transmission electron microscopy. Increasing the number of cross-links in polyethylene, modifies the size and nature of supermolecular structures, the periodic twisting of lamellar crystals, and the nature of the nucleation process. The study of a blend of branched and cross-linked polyethylene showed that the structurally dissimilar molecules co-crystallized at low crystallization temperatures, while there is a tendency for molecular fractionation at higher crystallization temperatures.     

Styrene and Polystyrene Modified Polyethylenes: Characterization and Properties

The initial structures of thin polyethylene films and of thin slices obtained from thicker specimens crystallized at temperature gradient in the modification process by styrene and polystyrene are studied. Comparison of the structures of these two types of samples shows clearly that the initial morphology and lamellar structure of the matrix has a basic influence on the modification process.     

Growth process and molecular packing of a self-assembled lipid nanotube: phase-contrast transmission electron microscopy and XRD analyses

Phase-contrast transmission electron microscopy (PC-TEM) and quick freezing method have been combined to study the initial growing process of a self-assembled lipid nanotube in water. The PC-TEM enabled us to detect thin lamellar edge structure and the very fast growth of the newborn edge to a thin tube with high contrast. The thin tube acts as a core structure for further growth into thick complete lipid nanotube. The initially formed nanotube structure is denoted as a "core tube". The core tube has uniform wall structure that consists of five lamellar layers and the inner and outer diameters of the core tube are 130 and 180 nm, respectively. The evaluated lamellar spacing of 4.6 nm is well compatible with that measured by X-ray diffraction. We also discussed the molecular packing of the nanotube from the pitch angle determined by the PC-TEM images, X-ray diffraction pattern in wide-angle region, and IR spectroscopy. The subcell structure of the nanotube is assigned to an orthorhombic type. The twisting angle between the neighboring lipid molecules is determined as ca. 0.26 degrees for the first time; it is a crucial parameter for the formation of a lipid nanotube in chiral packing but has not been elucidated before.     

A pyrrole-containing surfactant as a tecton for nanocomposite SiO2 films

A surfactant featuring a polymerizable pyrrole head group (dodecyl-dimethyl-(2-pyrrol-1-yl-ethyl)-ammonium bromide, DDPABr) was synthesized. The thermotropic behavior of the surfactant was investigated by differential scanning calorimetry (DSC) and X-ray scattering techniques, with small-angle X-ray scattering (SAXS) analysis revealing a highly ordered lamellar bilayer structure. After full characterization, DDPABr was used in the preparation of mesostructured SiO2 nanocomposite thin films via evaporation-induced self-assembly (EISA). Resulting thin SiO2-DDPABr films were studied by 1D and 2D small-angle X-ray scattering (SAXS) techniques, indicating a lamellar nanocomposite structure. Suitable theoretical SAXS models were applied to fit the experimental 1D SAXS data. The surfactant could be chemically polymerized within the lamellar domains.     

Comparative study on the lamellar structure of polyethylene foams

A comparative study on the lamellar morphology of a collection of polyethylene foam (LDPE) has been performed in order to obtain a better understanding of the morphology of the crystalline phase of these materials. The lamellar structure was measured by small-angle X-ray scattering (SAXS), differential scanning calorimetric (DSC) and Raman spectroscopy. The results have shown that the lamellar structure of the foams is different to that of a LDPE solid sheet. Moreover, the different sensitivity of the three experimental techniques to the lamellar structure has also been analyzed.     

PE/PEO/PE-PEO 对称三元共混体系相行为的耗散粒子动力学模拟研究

建立了对应实验体系聚乙烯/聚氧化乙烯/聚乙烯-聚氧化乙烯嵌段共聚物(PE/PEO/PE-PEO)的对称三元共混模型,并采用耗散粒子动力学(DPD)模拟方法对其相行为进行了理论研究.研究结果表明,随着均聚物体积分数的增加,体系的平衡相态发生由层状相(LAM)到双连续微乳液(BME)再到相分离(PS)的转变,相态演化规律和...     

Lamellar orientation in thin films of symmetric semicrytalline polystyrene-b-poly(ethylene-co-butene) block copolymers: effects of molar mass, temperature of solvent evaporation, and annealing

Orientation of the lamellar microdomains in thin films of three symmetric polystyrene-b-poly(ethylene-co-butylene) block copolymers (S65E155, S156E358, and S199E452) on mica was investigated via atomic force microscopy (AFM), grazing incidence X-ray diffraction (GIXRD) and X-ray photoelectron spectroscopy (XPS). The results show that lamellar orientation in the SxEy block copolymers greatly depends on the molar mass of the block copolymers, the temperature of solvent evaporation, and annealing. The nascent thin film of the low molar mass block copolymer, S65E155, shows a multilayered structure parallel to the mica surface with the PS block at both polymer/mica and polymer/air interfaces, but the high molar mass block copolymers, S156E358 and S199E452, exhibit a structure with lamellar microdomains perpendicular to the mica surface. When the solvent is evaporated at a lower temperature, the crystallization rate is fast and a two-dimensional spherulite structure with the lamellar microdomains perpendicular to the mica surface is observed. Annealing of all the thin films with lamellar microdomains perpendicular to the mica surface leads to morphological transformation into a multilayered structure parallel to the mica surface. In all SxEy thin films on mica, the stems of PE crystals are always perpendicular to the interface between the lamellar PE and PS microdomains. A mechanism is proposed for the formation of different microdomain orientations in the thin films of semicrystalline block copolymers. When the thin film is prepared from a homogeneous solution, microdomains perpendicular to the substrate surface are formed rapidly for strongly segregated block copolymers or at a lower crystallization temperature and kinetically trapped by the strong segregation strength or solidification of crystallization, while for weakly segregated block copolymers or at slower crystallization rate, the orientation of the microdomains is dominated by surface selectivity.     

Cleavage of branched polyethylene by chemical filling

Branched polyethylene, melt-crystallized in commercial fabrication processes, cleaves into two layers when exposed to a prolonged “chemical filling” treatment (i.e., formation of filler in situ by interdiffusion of two reactive permeants). Cleavage has been observed in film and blown bottles. With film, progressive changes in experimental conditions from one sample to another, shifted the cleavage plane from near the surface to deeper lying planes. Separation of a thin surface layer requires more filler deposit than does separation into layers of more equal thickness. These observations suggest that a well defined layer structure may exist in branched polyethylene and that cohesive bonding is stronger between layers near the surface of the film than it is between deeper lying layers. Linear polyethylene showed slight layer separation after prolonged chemical filling, but clean cut separation of large areas was not achieved. This behavior may indicate that the cohesive bonding between layers is much stronger in linear polyethylene than in branched polyethylene.     

聚甲基丙烯酸β羟乙酯在聚乙烯膜上辐射接枝物的形态结构

本文用透射电子显微镜(TEM),光学显微镜(OM),小角X射线散射(SAXS)等方法研究了聚甲基丙烯酸β羟乙酯(HEMA)在聚乙烯(PE)膜上辐射接枝物的形态结构.观察了微相结构随接枝条件变化规律.HEMA为支链的接枝共聚物的基本形态是高度分散的HEMA微区(约几百A)存在于PE连续相中的两相体系.随接枝量增加,微区形态发生变化.SAXS结果进一步证实了接枝共聚物相分离的形态结构,并利用Tsvankin-Buchanan公式计算了共聚物的长周期、无定形层厚及一维结晶度.     

Mechanical properties of oriented low‐density polyethylene with an oriented lamellar‐stack morphology

A quantitative study was undertaken of the anisotropy of low‐strain mechanical behavior for specially oriented polyethylene with controlled crystalline and lamellar orientation. The samples were prepared by the die drawing of injection‐molded rods of polyethylene and annealing. This produced a parallel lamellar structure for which a simple, three‐dimensional composite laminate model could be used to calculate the expected anisotropy. Experimental data, including X‐ray strain measurements of the lateral crystalline elastic constants, showed good quantitative agreement with the model prediction. The X‐ray strain measurements confirmed that the amorphous regions exert large constraints on the crystalline phase in the lateral directions, where an order of magnitude difference was found between the measured apparent lateral crystalline compliances in the lamellar‐stack sample and the expected values for a perfect crystal. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 755–764, 2000     

A permanganic etchant for polyolefines

A permanganic etchant has been developed which reveals lamellar and other fine detail in surfaces of at least three crystalline polyolefines, viz., polyethylene (of both high and low density), isotactic polypropylene, and isotactic poly(4-methylpentene-1). In typical treatments of high-density polyethylene ca. 2 μm of material is removed with defective regions suffering preferential attack. The etchant also discriminates between lamellar orientations, eating deeper where side surfaces of laminae are exposed than on fold surfaces, and between different polymers, attacking isotactic polypropylene more strongly than polyethylene. Comparison with other techniques authenticates the detail exposed and samples appear to be otherwise unaltered by their treatment. Besides normal imaging, it is also possible to use etched samples for transmission diffraction studies in the electron microscope. The method has very considerable application for revealing lamellar details in crystalline polyolefines (which can be chosen to be representative or selective according to the nature of the surface used). Examples are given of a wide variety of melt-crystallized morphologies for the three polymers cited and also of lamellae in a drawn polyethylene sample. It is pointed out that permanganic etching is complementary to the technique of chlorosulfonation used to stain polyethylene in a similar way as bright field microscopy is to dark field.     

Scanning electron microscopy of oriented high density polyethylene

Summary The microfibrillar and lamellar morphologies in cold-drawn and cold-drawn/annealed high-density polyethylene sheets were observed by means of scanning electron microscopy. Differences in contrast on fracture surfaces for cold-drawn sheet are interpreted in terms of a preferential orientation of inter-microfibrillar tie molecules in the plane of the sheet brought about by the drawing mechanism. In annealed, cold-drawn sheet, stacks of lamellae were observed which showed twinned orientations of inclined lamellae. This roof-top structure is interpreted in terms of shear within the individual microfibrils during micronecking, and corresponds to the well-known 4-point small-angle X-ray pattern for this type of specimen. Light etching with fuming nitric acid was necessary in order to resolve the individual lamellar texture.With 9 figures     

Self-assembly of rod-coil molecules into molecular length-dependent organization

A series of rod-coil molecules (n-x, where n represents the number of repeating units in a PPO coil and x the number of phenyl groups in a rod segment) with variation in the molecular length, but an identical rod to coil volume ratio was synthesized, and their self-assembling behavior was investigated by using DSC and X-ray scatterings. The molecule with a short rod-coil molecule (16-4) shows a 3-D tetragonal structure based on a body-centered symmetry of the discrete bundles in addition to a lamellar structure. This 3-D lattice, on heating, collapses to generate a disordered micellar structure. Remarkably, the molecules based on longer molecular length (21-5 and 24-6) were observed to self-organize into, on heating, lamellar, tetagonally perforated lamellar, 2-D hexagonal columnar and finally disordered micellar structures. Further increase in the molecular length as in the case of 29-7 and 32-8 induces a 3-D hexagonally perforated lamellar structure as an intermediate structure between the lamellar and tetragonally perforated lamellar structures. Consequently, these systems demonstrate the ability to regulate the domain nanostructure, from 2-dimensionally continuous layers, long strips to discrete bundles via periodic perforated layers by small changes in the molecular length, at an identical rod-to-coil volume fraction.     

Cryo-fracture TEM: direct imaging of a random mesh phase

A novel and a simple method that allows direct imaging of viscous samples by cryo-TEM (cryo-transmission electron microscopy) is presented. A fracture on the vitrified sample is created in a controlled way. In the fracture, some edges are thin enough to allow direct imaging in transmission mode. The method was used to directly image a nonionic surfactant lamellar phase where a random mesh structure is formed at lower temperatures (<10 degrees C). A so-called random mesh phase, characterized by the presence of perforated surfactant bilayers, is imaged here for the first time. Images from the mesh structure are compared with images from the classical lamellar structure formed at room temperature.     

HDPE,LLDPE或LDPE高取向薄膜微结构的电子显微学研究

木工作用透射电子显微术及电子衍射技术研究3种PE(HDPE,LLDPE或LDPE)均聚物高取向薄膜的微结构。定量测定了它们的结晶尺寸。通过倾斜样品电子显微学研究确定了不同种PE纤维结构的对称性。     

Structure of ultrathin polyethylene layers in multilayer films

The crystalline structures of “microlayer” and “nanolayer” polyethylene have been examined in coextruded films comprised of alternating layers of high-density polyethylene and polystyrene. Transmission electron microscopy (TEM), small-angle x-ray scattering (SAXS), and wide-angle x-ray scattering (WAXS) reveal that microlayer polyethylene, where the layer thickness is on the order of several microns, crystallizes with the normal unoriented lamellar morphology. In nanolayer films, where the film thickness of tens of nanometers is on the size scale of molecular dimensions, lamellae are oriented with the long axes perpendicular to the extrusion direction in a row-nucleated morphology similar to structures described in the literature. The lamellae are partially twisted about the long axes. The preferred twist angles of ±40° orient the lamellar surfaces normal to the layer surface. The row-nucleated morphology imparts highly anisotropic mechanical properties to the nanolayer polyethylene.     

Phase behavior and interfacial properties of diblock copolymer-homopolymer ternary mixtures: Influence of volume fraction of copolymers and interaction energy

We use a Monte Carlo method to study the phase and interfacial behaviors of A-b-B diblocks in a blend of homopolymers, A and B, which are confined between two asymmetric hard and impenetrable walls. Our results show that, when the interaction strength is weak, the block copolymersare uniformly distributed in the ternary mixtures under considered concentrations. Under strong interaction strength, distribution region of the block copolymers changes from a single smooth interface to a curved interface or multi-layer interface in the ternary mixtures. Furthermore, our findings show that with increasing volume fraction of A-b-B diblock copolymer(фC), copolymer profiles broaden while фC≥ 0.4, a lamellar phase is formed and by further increasing фC, more thinner layers are observed. Moreover, the results show that, with the increase of фC, the phase interface first gradually transforms from plane to a curved surface rather than micelle or lamellar phase while with the increase of the interaction between A and B segments(ε_(AB)), the copolymer chains not only get stretched in the direction perpendicular to the interface, but also are oriented. The simulations also revealthat the difference between symmetric and asymmetric copolymers is negligible in statistics if the lengths of two blocksare comparable.     

Theory of curved interfaces and membranes: Mechanical and thermodynamical approaches

The mechanical and thermodynamical approaches to the theory of the general curved interfaces are presented and compared. In the mechanical approach a curved interface or membrane is characterized by the tensors of surface stresses and moments. They are connected by the surface balances of the linear and angular momentum. On the other hand, in the thermodynamical approach the surface is characterized by the scalar dilation and shear tensions as well as by the bending and torsion moments. In this review we investigate the problem about the relationships connecting the mechanical and thermodynamical approaches. We find that these two approaches are in a good agreement, that they are complementary to each other and represent the two parts of a self-consistent theory. The latter can be applied to any system where curved interfaces, thin films or membranes are present: microemulsions, lamellar and sponge phases, lipid vesicles and cell membranes, capillary waves at interfaces, undulation and peristaltic surface forces, lateral capillary forces between particles in thin liquid films, etc.     

Mechanism of the transition between lamellar and gyroid phases formed by a diblock copolymer in aqueous solution

The mechanism of the transition from a lamellar phase to a gyroid phase in an aqueous solution of a diblock copolymer has been studied by time-resolved synchrotron small-angle X-ray scattering. The transition occurs via a metastable perforated lamellar structure. The perforations initially have liquidlike ordering before developing hexagonal packing. The transient phase of irregularly perforated layers is revealed by the development of diffuse scattering peaks, just below the Bragg peaks of the lamellar structure. The diffuse scattering is modeled by Monte Carlo simulations of perforated layers. Following the formation of perforations, Bragg peaks characteristic of a hexagonal structure signal an ordering into a hexagonal lattice (with the concomitant loss of diffuse scattering). Computer simulations based on a dynamic density functional model reproduce these features. The hexagonal perforated lamellar phase is rapidly replaced by the gyroid phase. The domain spacing of the gyroid phase is larger than that of the perforated lamellar structure. The perforated lamellar and gyroid phases coexist for a defined period. The reverse transition from gyroid to lamellae occurs directly, with no transient or metastable intermediates.