Mechanical anisotropy in biaxially oriented polyvinyl chloride

The mechanical anisotropy of polyvinyl chloride oriented in two perpendicular directions with different draw ratios has been studied. The results are compared with the anisotropy of uniaxial samples oriented at a common draw ratio. The propagation velocities of ultrasonic pulses have been measured by an immersion technique. Longitudinal wave velocities have been measured in three principal planes over a wide range of propagation directions. The limitations of measuring velocities in the planes containing the draw axes were mitigated by use of a special slicing technique. Measurements were performed at 2 MH_z and 25°C. Velocities of the transverse waves were measured for incident wave angles greater than the critical angle. From these measurements, five elastic moduli were calculated for the uniaxially oriented samples, and nine elastic moduli were obtained for the biaxially oriented samples. In biaxially oriented samples, the moduli along the draw axes are directly proportional to the draw ratio in the same direction.     

Novel preferred orientation in injection-molded nylon 6-clay hybrid

Nylon 6-clay hybrid (NCH) is a molecular composite of Nylon 6 and uniformly dispersed silicate monolayers of montmorillonite. In this study the preferred orientation of montmorillonite and Nylon-6 crystallites in a thick (3 mm) injection-molded bar of NCH has been investigated using x-ray diffraction and electron micrography (TEM). It is clear that this bar has a triple layer structure consisting of surface, intermediate, and middle layers which have different preferred orientation. In the surface layer both the silicate monolayers and the chain axes of Nylon-6 crystallites are parallel to the bar surface though the latter are randomly oriented within the plane. In the intermediate layer the silicate monolayers remain parallel to the bar surface but the Nylon-6 crystallites rotate by 90° so that the chain axes would be perpendicular to the bar surface or the silicate monolayers. In the middle layer the silicate monolayers are randomly oriented around the flow axis of the NCH bar while remaining parallel to it, and the Nylon crystallites are randomly oriented around the flow axis while keeping their chain axes perpendicular to the silicate monolayers. It may be concluded that such preferred orientation of Nylon 6 crystallites is induced by the clay because the crystallites in the pure Nylon 6 bar have no preferred orientation. ©1995 John Wiley & Sons, Inc.     

A push/pull surface-mode liquid-crystal shutter: Technology and applications

The construction, operating principles and electro-optics of a surface-mode liquid-crystal shutter are reviewed. The shutter is composed of two glass plates, the inner surfaces of which are coated with a transparent electrically conductive layer. The substrates are treated to induce parallel director alignment. Polarizers are placed on the front and back of the cell oriented at right angles to each other and at 45° to the director. In the surface mode of operation a sustaining voltage is applied to the cell. This causes the director in the centre of the cell always to be oriented parallel to the electric field. The amplitude of the applied voltage determines the thickness of the surface layer-the layer in which the director orientation varies from parallel to the surface to parallel to the electric field. Light travelling through the cell will encounter retardation only in the surface layers. Hence the voltage controls the retardation of the cell, and by that means the polarization state of the light travelling through the cell. By adjusting the voltage so that the retardation is changed from 0λ to ½λ the shutter can switch from open to closed. It is possible to construct a faster-switching shutter. This so-called push/pull shutter is composed of three elements in optical series. The first two are surface-mode cells oriented such that their directors are perpendicular. The third element is a quarter-wave plate with its axes parallel to the directors. The three elements are placed between orthogonal polarizers, with the directors oriented at 45° to the polarizers axes. The closed state of the shutter is obtained by placing one shutter in the high-voltage 0λ state and the other in the low-voltage ¼λ state. The open state of the shutter is obtained by switching the voltage levels applied to the two cells. The operating principles and the electro-optics of this device are discussed in detail.     

Texture of injection-molded polypropylene

Injection-molded specimens of polypropylene were examined by x-ray diffraction for texture and orientation patterns as a function of the distance from the surface and of molding conditions. At least three distinct layers in the surface region whose texture patterns differ and an isotropic core of the moldings have been identified. These layers show preferred orientations; the axes of symmetry of the oriented textures lie in a plane passing through the direction of flow and perpendicular to the mold surface, but are inclined to the mold surface at a small angle. Some of these layers may be missing in conditions of either very high or very low shear during the injection-molding flow. A tentative explanation of the formation of the texture patterns is proposed.     

Crystallization of poly-p-oxybenzoate on mica

Thin film polymerization/crystallization of poly-4-oxybenzoate (P-4-OB) from melt or dilute solutions yields on mica cleavage surface an epitaxial overgrowth with crystal blocks oriented in 1 to 3 substrate directions rotated by 60°. The b and c crystal axes of P-4-OB lie in the mica cleavage plane, with the a axis being perpendicular to it. At higher polymerization temperatures a different type of P-4-OB orientation on mica was also observed: two P-4-temperatures a different type of P-4-OB orientation on mica was also observed: two P-4-OB phase I crystals, again with b- and c-axes lying parallel to mica cleavage plane, were oriented perpendicular to each other. There is a pronounced tendency of the relatively thick P-4-OB overgrowth to form complex crystal structures involving both phase I and II with different types of orientation on mica substrate. © 1996 John Wiley & Sons, Inc.     

Molecular orientation study of uniaxially drawn nafion polymer electrolyte membranes utilizing polarized UV–Raman spectra

Nafion® perfluorosulfonic acid polymer electrolyte membranes were uniaxially drawn at a temperature where the α‐relaxation is active. Polarized UV–Raman spectra revealed the anisotropy developed. They strongly suggest that, upon uniaxial drawing, Nafion macromolecular chains are oriented parallel to the drawing axis, while the perfluorinated side chains exhibit a tendency to be oriented perpendicular to the draw axis. The drawing process resulted in the reduction of the membrane thickness in addition to an enhanced mechanical strength along the draw direction, measured with dynamic mechanical analysis. In a parallel study, a preliminary molecular orientation study of uniaxially drawn Teflon samples allowed a better assignment of the Raman bands of Nafion. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2509–2517, 2007     

Atomic force microscopy measurements of topography and friction on dotriacontane films adsorbed on a SiO2 surface

We report comprehensive atomic force microscopy (AFM) measurements at room temperature of the nanoscale topography and lateral friction on the surface of thin solid films of an intermediate-length normal alkane, dotriacontane (n-C32H66), adsorbed onto a SiO2 surface. Our topographic and frictional images, recorded simultaneously in the contact mode, reveal a multilayer structure in which one to two layers of molecules adsorb adjacent to the SiO2 surface oriented with their long axis parallel to the interface followed by partial layers of molecules oriented perpendicular to the surface. The thicknesses of the parallel and perpendicular layers that we measured with the AFM agree with those inferred from previous x-ray specular reflectivity measurements on similarly prepared samples. We also observe bulk dotriacontane particles and, in contrast with our previous measurements, are able to determine their location. Above a minimum size, the bulk particles are separated from islands of perpendicularly oriented molecules by regions of exposed parallel layers that most likely extend underneath the particles. We find that the lateral friction is sensitive to the molecular orientation in the underlying crystalline film and can be used effectively with topographic measurements to resolve uncertainties in the film structure. We measure the same lateral friction on top of the bulk particles as on the perpendicular layers, a value that is about 2.5 times smaller than on a parallel layer. Scans on top of parallel layers indicate a constant height but reveal domains having different sublevels of friction. We explain this by the domains having different azimuthal orientations of the molecules.     

Quiescent and strain-induced crystallization of poly(p-phenylene terephthalamide) from sulfuric acid solution

Quiescent and strain-induced crystallization of poly(p-phenylene terephthalamide) (PPTA) from sulfuric acid solution has been studied. Negative spherulites (SA-PPTA spherulites) are formed from hot concentrated solutions by cooling. The spherulite consists of radiating fibrous lamellae several hundred angstroms wide. The electron diffraction pattern indicates that PPTA molecules are oriented perpendicular to the long axes of the fibrous lamellae and that the [010] or [110] direction of the modification I crystal and [010] direction of the modification II crystal are parallel to the long axes of the fibrous lamellae. The width of the lamellae is much smaller than the chain length of the starting PPTA. It appears that hydrolysis of PPTA during melting crystallization determines the chain length, i.e., the width of the fibrous lamella. Stacked, lamellar structures like “row structures” are formed under shear. The longer axes of the fibrous lamellae are oriented perpendicular to the shear direction. It is confirmed by electron diffraction studies that the PPTA molecules are oriented parallel to the shear direction. Well-developed fibrils with the PPTA molecules oriented to the fibril axis, are formed by adding the SA-PPTA spherulites to water with vigorous stirring.     

Morphology of cold-drawn nylon 66

A nylon 66 composed of uniformly sized spherulites approximately 50 μ in diameter was examined before and after cold drawing by light and electron microscopy of thin sections and by low-angle x-ray diffraction. Spherulites retained their identity through drawing, but the spherulites elongated less than the bulk specimen indicating that relative motion of spherulities must have occurred. The observation of dilations (0.3 μ long) at interspherulitic boundaries support this contention. The thin-section electron micrographs indicated that the spherulites were composed of radiating lamellae approximately 95 A. thick. After drawing, the lamellae were preferentially oriented both parallel and perpendicular to the draw direction. Lamellae parallel to draw had thinned to approximately 70 A. While lamellae perpendicular to the draw had apparently thickened to 150 A. Three low-angle x-ray diffraction patterns yielded quantitative agreement with the electron-micrograph data. The pattern form the undrawn nylon was a diffuse ring corresponding to a 95 A. spacing. On the drawn specimen, with the beam parallel to draw, a ring corresponding to the 150 A. spacing was obtained, while with the beam perpendicular to draw two arcs were recorded at spacings of 70 and 150 A. The drawing was done at room temperature and proceeded by neck formation and propagation, yielding a 4:1 draw ratio.     

Polarization of the monomer and excimer fluorescence of pyrene derivatives in liquid-crystalline hosts

The monomer and excimer fluorescence polarization of 4,9-disubstituted pyrenes with molecular long axes nearly perpendicu- lar to the pyrene skeleton were measured in a nematic liquid crystal. By comparison with unsubstituted pyrene it is found that the excimer transition moment is oriented parallel to the sandwich plane and perpendicular to the pyrene long axis.     

Liquid crystalline cellulose derivative elastomer films under uniaxial strain

Mesogenic cellulose derivative chains cross-linked into free-standing thin films were prepared by a shear-casting technique from anisotropic precursor solutions of thermotropic (acetoxypropyl)cellulose. After shear cessation a macroscopically oriented serpentine structure with the director in average along the shear direction is locked resulting in anisotropic optical and mechanical properties of the material. These films were submitted to an external uniaxial mechanical field perpendicular and parallel to the shear direction. Stretching perpendicular to the shear direction produced significant director rotations and a reset of order of the director order parameter for a deformation in the range 2–3 as detected by X-rays and optical microscopy. The different response found for strains imposed parallel and perpendicular to the initial average director orientation indicates that even though our system shows a serpentine director modulation that is either attenuated or reinforced by deformations parallel or perpendicular to the shear direction, its behaviour is similar to theoretical predictions for monodomain nematic elastomers described in the literature.     

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.     

Small-angle Hv light scattering from deformed spherulites with orientational fluctuation of optical axes

Mathematical evaluation was done for small-angle light scattering from disordered spherulites under Hv polarization conditions. The calculation was carried out for a two-dimensional deformed spherulite whose major optical axes are oriented at 0 or 45° with respect to the radial direction. The calculated results were compared with the scattering patterns observed for polypropylene (PP) spherulites, whose optical axes are oriented parallel to the radial direction, and poly(butylene terephthalate) (PBT) spherulites, whose optical axes are oriented at 45° with respect to the radial direction. The degree of disorder for PBT was much larger than that for PP. By selecting a parameter associated with the degree of disorder of the optical axes with respect to the radial direction, the patterns calculated as a function of draw ratios were in good agreement with the observed patterns, which changed from four leaves to streaks extended in the horizontal direction. Through a series of observed and calculated patterns, it turns out that an increase in the disorder under the deformation process occurs drastically even for perfect spherulites in an undeformed state.     

Melt‐extensional properties and orientation behaviors of polypropylene‐layered silicate nanocomposites

Polypropylene‐layered silicate nanocomposites consisting of three components—pure polypropylene, maleated polypropylene, and organically modified silicate—were prepared by the melt‐intercalation method to investigate melt‐extensional properties such as melt strength, neck‐in test, and orientation behavior. The nanocomposites showed an enhanced tensile modulus, enhanced storage modulus, much enhanced melt tension, and reduced neck‐in during the melt processing as compared with neat polymer. The uniaxial drawing induced the silicate surface to align parallel to the sheet surface. The c and a* axes of the polypropylene crystals were bimodally oriented to the flow direction, and the b axes were oriented to the thickness direction. The bimodal orientation of the polypropylene crystal was enhanced with the concentration of silicates. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 158–167, 2005     

Nanostructure and crystallization phenomena in multilayered films of alternating iPP and PA6 semicrystalline polymers

The present work is concerned with the study of the crystalline morphology and the nanostructure of a multilayered system of two alternating immiscible semicrystalline polymers: isotactic polypropylene (iPP) and polyamide 6 (PA6). Films with a volume ratio of 70/30 were prepared by means of layer multiplying coextrusion. Contrary to previous experiments, performed with semicrystalline/amorphous and amorphous/amorphous nanolayered systems, the studied iPP/PA6 film does not exhibit a well defined maximum in the USAXS patterns. This result accounts for an irregular layered structure, as further confirmed by means of TEM images. Nevertheless, such a layered assembly still influences the crystallization behaviour of both constituent polymers. On the one hand, the crystallization of PA6 within the multilayered material is substantially hindered as evidenced by its weak scattering intensity. Real time studies as a function of temperature undoubtedly detect the presence of a WAXS peak and a SAXS maximum associated to PA6 above the melting temperature of iPP. Room temperature AFM studies also confirm the occurrence of crystalline structures within the PA6 layers. On the other hand, SAXS and WAXS measurements at room temperature reveal the occurrence of an oriented lamellar morphology within the iPP layers bearing uniaxial symmetry around an axis perpendicular to the layers surface. Results show that the crystalline molecular chains are placed mainly parallel to the layer surfaces forming edge-on lamellae. Moreover, X-ray scattering results are in agreement with the occurrence of two populations of lamellae, both edge-on and perpendicular to each other, in agreement with the crosshatched morphology observed by AFM.     

Preparation of Oriented Liquid‐Crystalline/Isotropic Block Copolymer Films with Parallel or Perpendicular Arrangement of Smectic Layers and Lamellar Microdomains

Films of a symmetric liquid‐crystalline/isotropic block copolymer consisting of a smectic LC side‐chain polymer and polystyrene were prepared by solvent casting from solution and from the isotropic melt. By annealing the solvent‐cast film in the S_A phase an oriented microphase‐separated film of lamellar morphology was obtained in which both the lamellae of the block copolymer and the smectic layers of the LC block were oriented parallel to the film surface. A lamellar morphology with perpendicular orientation of lamellae and smectic layers was generated by cooling the block copolymer from the melt.     

Microdielectrometric monitoring of film preparation process with oriented domains for hydroxypropyl cellulose cast from isotropic aqueous solution under the sinusoidal electric field with large amplitude

Microdielectrometry was applied to macroscopically anisotropic media. The distribution and effective portion of the electrostatic energy density, w ₁₄ and J ₁₄, respectively, were calculated, considering the additive contributions of four pairs of microelectrodes. The electric field lines were calculated numerically and investigated experimentally with polarised optical microscopy using thin layers of a nematic liquid crystal with a positive dielectric anisotropy. The applicability of microdielectrometry was investigated using the nematic liquid crystal. Microdielectrometric monitoring was also performed during the preparation process for a solid film with oriented domains with long axes perpendicular to the electric filed cast from an isotropic aqueous solution of hydroxypropyl cellulose under the sinusoidal electric field with large amplitude of 2.0 kV mm^?1 and frequency of 10⁵ Hz. In the logarithmic relation between the dielectric constant and loss factor divided by J ₁₄, the two dielectric parameters measured for different film thicknesses at 2.0 kV mm^?1 were superposed on a single curve. The curve for the electrically oriented domains was considrably different from that for a randomly oriented polydomain texture found under the electric field with small amplitude of 0.05 kV mm^?1 and the same frequency.     

Orientation of chromonic liquid crystals by topographic linear channels: multi-stable alignment and tactoid structure

We study the alignment behaviour of the chromonic liquid crystal phases of sunset yellow (SSY)/water, disodium cromoglycate (DSCG)/water and their mixtures when confined in cells by polymer films topographically imprinted with linear channels of 250 nm width, depth and spacing. A variety of novel alignment effects are generated by contact with such a patterned surface, as follows. Nematic DSCG and nematic SSY at low concentration and their nematic mixtures orient with the long axes of stacked chromonic aggregates on average parallel to the channels, that is, with the molecular planes normal to the channel axis. These oriented nematics exhibit isotropic/nematic tactoids aligned with their major axes along the channels. Two geometries of the tactoids, elliptic cylinder and rectangular cuboid with hemi cylindrical ends are observed. Additionally, a transition of DSCG tactoids from a three-dimensional (3D) director configuration to a two-dimensional one is observed when the tactoids on one surface of a cell touch the other surface of the cell. In SSY solutions of sufficiently high concentration, multi-stable alignment is found, including preferential in-plane orientation of the director parallel to, perpendicular to and 45° rotated from the channels.     

A dielectric study of the amorphous fraction in oriented nylon 610

Since some dielectric loss peaks can be assigned to amorphous phase motions, it would appear that dielectric measurements should be a good probe to study the effects of macroscopic plastic deformation on the structure of the amorphous phase. We report here results of measurements of dielectric constant and loss in nylon 610 measured both parallel (∥) to and perpendicular (⊥) to the extrusion direction in specimens prepared by extrusion through a die at 160°. It is found that the intensity of the (∥) loss was nearly zero and the (⊥) loss intensity was greatly reduced compared to unoriented material. The other relaxation parameters (loss width and location) were largely unaffected. Since the amide dipole is nearly perpendicular to the chain axis and alternates in direction in the extended conformation, a considerable degree of chain alignment parallel to the draw direction is indicated. These results therefore show considerable permanent amorphous phase orientation even though the deformation was carried out 100° above its glass temperature.     

Crystal and molecular structure of monomeric yttrium(III) dipivalylmethanate. Arrangement of adsorbed layers

Crystal structure of monomeric yttrium(III) dipivalylmethanate, YO₆C₃₃H₅₇, has been studied by X-ray diffraction. Crystal data: a=17.868(3), b=9.977(2), c=10.633(2) Å, V=1895.7 ų, space group Pmn2₁, Z=2, d_calc=1.116, d_exp=1.119 g/cm³. The compound has a molecular structure and consists of monomeric molecules with a proper symmetry plane m. In the metallocycle lying in this plane, Y-O interatomic distances and O?Y?O bond angles markedly differ from the similar distances and angles in the other two planes. The average Y?O, O?C, and C?C distances are 2.22, 1.25, and 1.46 Å, respectively. As a result of comparative crystal-chemical analysis carried out for related compounds, the coordination polyhedra around the yttrium atoms were found to be trigonal prisms formed by six oxygen atoms of three bidentate ligands. Layers ～1 μm thick were obtained by vapor condensation of the complex on different supports; the layers were investigated by XRD. Irrespective of the type of support, the layers are oriented polycrystalline films with [001] texture axes. Arrangement of the adsorbed molecules of the complex is analyzed. The layers are self-organized into close-packed structures with C(CH₃)₃ groups oriented toward supports.