Orientation Of Molecular Chains Research Articles

Evolution of the Raman backscattered intensity used to analyze the micromechanisms of deformation of various polypropylene blends in situ during a uniaxial tensile test

This paper presents a study of the evolution of the Raman backscattered intensity used to follow the modifications of polymer microstructure in real time during a tensile test. The context of this study is the coupling of the VideoTraction™ system with a Raman spectrometer, which has already led to in‐situ measurements of molecular chains orientation and crystallinity. The polypropylene blends will be characterized optically at the same probing wavelength by incoherent light scattering to understand phenomena enlightened by Raman spectroscopy. Then, a discussion on the Raman intensity evolution is conducted, with the possible contribution of Raman spectroscopy to describe stages of the volume damage micromechanism. Copyright © 2014 John Wiley & Sons, Ltd.

High thermal conductivity of chain-oriented amorphous polythiophene

Polymers are usually considered thermal insulators, because the amorphous arrangement of the molecular chains reduces the mean free path of heat-conducting phonons. The most common method to increase thermal conductivity is to draw polymeric fibres, which increases chain alignment and crystallinity, but creates a material that currently has limited thermal applications. Here we show that pure polythiophene nanofibres can have a thermal conductivity up to ∼ 4.4 W m(-1) K(-1) (more than 20 times higher than the bulk polymer value) while remaining amorphous. This enhancement results from significant molecular chain orientation along the fibre axis that is obtained during electropolymerization using nanoscale templates. Thermal conductivity data suggest that, unlike in drawn crystalline fibres, in our fibres the dominant phonon-scattering process at room temperature is still related to structural disorder. Using vertically aligned arrays of nanofibres, we demonstrate effective heat transfer at critical contacts in electronic devices operating under high-power conditions at 200 °C over numerous cycles.

Evaluation of oriented amorphous regions in polymer films during uniaxial deformation; structural characterization of a poly(vinyl alcohol) film during stretching in boric acid aqueous solutions

We have improved the conventional analytical method of the scattering data obtained with in-situ synchrotron X-ray scattering experiments, which is applicable to the structural characterization of the film during stretching. Four components of molecular chains in the film are divided from two-dimensional wide-angle X-ray diffraction patterns. These components are the oriented crystals, the unoriented ones, the oriented amorphous chains, and the unoriented ones, respectively. This method allows to evaluate directly the degree of orientation of the amorphous chains and the amount of the oriented amorphous fraction in addition to each evaluation for the crystalline regions. This method is applied to the structural characterization of the poly(vinyl alcohol) (PVA) film during stretching in boric acid aqueous solutions, suggesting that boric acid accelerates orientation of molecular chains in the amorphous regions, and increases the oriented amorphous fraction by producing the cross-links between the PVA chains and hindering strain-induced crystallization. At a film break on stretching in the 3 wt% boric acid solution, the oriented amorphous fraction increases up to 70%, which is much higher compared to that in the film stretched in water, 45%. POLYM. ENG. SCI., 55:513–522, 2015. © 2014 Society of Plastics Engineers

Enhancement of Tensile Properties of Flax Filaments through Mercerization under Sustained Tension

In the present paper, the tensile properties of flax filaments were modified through mercerization under sustained tension forces. The tensile stress-strain curves of the treated filaments exhibit two stages. The slope of the first stage is much higher than the second one. The mercerization under sustained forces leads the two-stage characteristic to be more obvious. The effect of the sustained tension force on the tensile properties of filaments is dependent on the alkaline concentration. The tensile properties were only remarkably enhanced with high concentration of alkaline (e.g., > 10%) and sustained forces. Compared to the untreated filaments, the maximum tensile strength and modulus with optimum treatment conditions are improved by about 36% and 64% respectively. SEM and X-ray diffraction (XRD) analysis suggested that the enhancement of the tensile properties of the treated flax filaments comes from the orientation of amorphous cellulose molecular chains of micro fibrils and remove of the defects of the filament surfaces.

Molecular chain orientation in polycarbonate during equal channel angular extrusion: Experiments and simulations

The objective of this contribution is to provide some insights of the molecular chain orientation in polycarbonate (PC) during an equal channel angular extrusion (ECAE) process. Experimentally, wide-angle X-ray scattering was carried out to characterize the microstructure of the ECAE-deformed glassy amorphous polymer. The deformation behavior of the PC specimen in the ECAE process was simulated using a physically-based viscohyperelastic–viscoplastic constitutive model that was implemented into a finite element code. The large inelastic deformation response of the glassy amorphous polymer was modeled by assuming that the deformation mechanisms are split into an intermolecular resistance and a molecular network resistance. The intermolecular resistance captures the initial response and the yielding rate-dependence due to the isotropic resistance to deformation resulting from intermolecular barriers to chain-segment rotation. The molecular network resistance reproduces the anisotropic strain hardening response at large strains due to stretching and chain orientation. The progressive molecular chain orientation during the ECAE process and its distribution were analyzed. The predicted results, favorably compared with the experimental observations, show a high degree of anisotropy and heterogeneity in orientation of polymer molecular chains in the ECAE-deformed PC.

OS0601 ポリ乳酸スクリューの力学的特性及び破壊挙動に及ぼす配向の影響

Effects of extrusion ratio (ER) and lubricant during extruding on mechanical properties and fracture behavior of poly(lactic acid) (PLA) screws were investigated in terms of shear strength and acoustic emission (AE). Self-reinforced PLA screws were manufactured from axially extruded PLA billets by forging. Shear strength for PLA screw increased by drawing. The result suggested that drawing is effective method to improve shear strength for PLA screws. This might be due to orientation of molecular chains during drawing. Shear strength did not increase linearly with ER, and shear strengths for screw extruded at low ER were slightly higher than that for screw extruded at high ER. This might be due to molecular orientations for screw extruded at high ER were lower than that for screw extruded at low ER. From AE measurement, AE event occurred in the specimens with extrusion was lower compared to that without extrusion, whereas AE energy was higher. This suggested that the number of micro-damages which occurred in extruded specimen was fewer and the size of micro-damages was larger.

Pattern transfer and molecular chain orientation modulation by soft template during the nanoimprint lithography

The templates for the nanoimprinting are fabricated usually through a series of steps, such as E-beam lithography, E-beam deposition, liftoff and reactive ion etching. Any mistake during these steps would lead to the failure of the fabrication, so the template is always expensive and difficult to make. Under this circumstance, it is really important to find an effective way to build the template. In this report, the patterned photoresist layer is used as a mother set of the pattern definition of the soft template polydimethylsiloxane. The grating structure of conjugated polymer poly (9,9-dioctylfluorene) film is successfully obtained by this template in the nanoimprinting process. In addition, we also find the anisotropy of molecular chain distribution. Both the transmission electron microscope diffraction pattern and the polarized absorption spectrum are used to prove that this anisotropy is induced by the molecular chain alignment, which would be really helpful in future applications in organic emission equipment. Moreover, this result is also applicable to the poly (9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(1,4-benzo-2,1',3-thiadiazole) film system.

Study of PE and iPP orientations on the surface of carbon nanotubes by using molecular dynamic simulations

In this study, the early stage of interfacial crystallisation behaviour of low molecular weight polyethylene (PE) and isotactic polypropylene (iPP) oligomer on the surface of carbon nanotubes (CNTs) with different diameters, chiralities and topography structures was studied using MD simulations. We started to simulate the effect of CNTs chirality and diameter on PE molecular chain orientation, and then the effect of CNTs topography structure on PE and iPP molecular chain orientation was investigated. Finally, some experiments were carried out to prove the simulated results. Our study shows that for CNTs with a diameter comparable with the radius of gyration (Rg) of a polymer chain, an easy orientation of PE chains along CNTs axis is observed for all the systems of the CNTs with different chiralities due to a geometric confinement effect. For CNTs with a much larger diameter, multiple orientation of PE chains is induced on its surface due to the lattice matching between graphite lattice and PE molecular chains. In this case, the chirality of CNTs dominates the orientation of graphite lattice, which determines the orientation of PE chains arrangement on CNTs surface. More importantly, it was found that the groove structure formed by CNT bundles is very useful for the stabilisation of polymer chain, and thus facilitates the orientation of molecular chain along the long axis of CNTs. As a result, a novel nanohybrid shish–kebab (NHSK) structure with CNTs acting as central shish while polymer lamellae as kebab can be successfully obtained for both PE with zigzag conformation and iPP with helical conformation. This simulation result was well supported by the experimental observation. Our study could provide not only a deep understanding of the origin of the polymer chain orientation on CNTs surface but also the guidance for the preparation of polymer/CNTs nanocomposites with novel NHSK structure.

Effect of sericin blending on molecular orientation of regenerated silk fiber

The use of regenerated silk fiber is limited due to its inferior mechanical properties in spite of high potential in a wide variety of applications. Many studies have been conducted in order to improve the mechanical properties of the regenerated silk materials, but no one has so far suggested an obvious solution. Meanwhile, some reports showed evidence that structural development of silk protein can be manipulated by physical interactions between silk fibroin (SF) and silk sericin (SS) during the regeneration process, especially in recrystallization process of SF. Such a hypothesis suggests a promising clue to enhance the mechanical properties of silk-based materials. Therefore, in this study, we tried to elucidate how SS can promote developing the molecular chain orientation of SF, resulting in an improvement of mechanical properties of regenerated silk fiber during spinning process. The tensile properties of the regenerated silk fiber were significantly improved compared to those of pure SF fiber when a proper amount of SS was blend with SF; both tenacity and breaking elongation increased by approximately 30 % and 70 % at three fold draw ratio, respectively. Quantitative analysis of X-ray diffraction and Herman’s orientation coefficient confirmed that such an improvement of tensile property was mainly caused by an increase of molecular orientation induced by sericin during the drawing process.

The variability of mechanical properties and molecular conformation among different spider dragline fibers

Spider dragline fiber is a high-performance biomaterial that has received much attention. To screen the outstanding spider dragline fibers, the mechanical properties and microstructures of dragline fibers collected from Nephia clavata, Nephia pilipes, Argiope bruennichi and Argiope amoena were investigated. It was found that the mechanical properties of spider dragline fiber were variable. Among the four different species, the larger spiders did not always extrude thicker dragline fibers and produce fibers with the maximum breaking force. The dragline fibers could sustain one to three times the body weight of the spider at a reeling speed of 20 mm/s. N. clavata dragline fiber showed a stronger breaking stress and initial modulus than that of N. pilipes, A. bruennichi and A. amoena. With an increasing reeling speed, the breaking strain decreased; the initial modulus increased in N. clavata, N. pilipes and A. bruennichi, but the breaking stress exhibited a different tendency. The results also revealed that dragline fiber of N. clavata contained the most β-sheet polypeptides and an excellent orientation of β-sheet molecular chains.

Polyamide 6–Cellulose Composites: Effect of Cellulose Composition on Melt Rheology and Crystallization Behavior

Melt rheology and crystallization behavior of polyamide 6 (PA 6) and microcrystalline cellulose (MCC) composites were systematically studied in this research. The incorporation of MCC into the PA 6 matrix resulted in higher complex viscosities (|η*|), storage modulus (G′), and shear viscosities than those of neat PA 6, especially at low frequencies. The orientation of rigid molecular chains in the composites introduced by the addition of MCC induced a strong shear thinning behavior with an increase in MCC loading. The non‐isothermal crystallization kinetics of PA 6 and MCC composites were investigated by differential scanning calorimetry. The Avrami and Tobin model were applied to describe the process of non‐isothermal crystallization and to determine the crystallization parameters of the composites. Analysis of the crystallization kinetics indicated that the Avrami (na) and Tobin exponent (nt) was altered by the MCC. It was also found that the Avrami and Tobin equations fit the empirical data well. POLYM. ENG. SCI., 54:739–746, 2014. © 2013 Society of Plastics Engineers

Three-dimensional culture of epidermal cells on ordered cellulose scaffolds

An ordered cellulose film scaffold, termed a nematic ordered cellulose (NOC) template, had unique surface properties and successfully induced the establishment of a three-dimensional (3D), hierarchical structure of epidermal cells by cell attachment and subsequent culture. Initially, the scaffold surface properties were characterized through contact angle measurements and atomic force microscopy to evaluate appropriate hydrophobicity and orientation of molecular chains for 3D culture. The template surfaces exhibited higher hydrophobicity, in the range of 70–75°, than usual cellulose films and appeared suitable for surface cell adhesion. In fact, epidermal cells successfully attached and proliferated favorably on the NOC templates, similar to development in normal culture flasks. Furthermore, the NOC film, as a semipermeable template, was also employed to allow 3D proliferation of epidermal cell layers in the perpendicular direction. The template proved to be suitable as a 3D cell culture device, resulting in the proposal that the construction processes of these 3D cell layers followed the basic concept of skin formation.

Structural modifications induced by compressive plastic deformation in single-step and sequentially irradiated UHMWPE for hip joint components

Structural modifications were studied at the molecular scale in two highly crosslinked UHMWPE materials for hip-joint acetabular components, as induced upon application of (uniaxial) compressive strain to the as-manufactured microstructures. The two materials, quite different in their starting resins and belonging to different manufacturing generations, were a single-step irradiated and a sequentially irradiated polyethylene. The latter material represents the most recently launched gamma-ray-irradiated polyethylene material in the global hip implant market. Confocal/polarized Raman spectroscopy was systematically applied to characterize the initial microstructures and the microstructural response of the materials to plastic deformation. Crystallinity fractions and preferential orientation of molecular chains have been followed up during in vitro deformation tests on unused cups and correlated to plastic strain magnitude and to the recovery capacity of the material. Moreover, analyses of the in vivo deformation behavior of two short-term retrieved hip cups are also presented. Trends of preferential orientation of molecular chains as a function of residual strain were similar for both materials, but distinctly different in their extents. The sequentially irradiated material was more resistant to plastic deformation and, for the same magnitude of residual plastic strain, possessed a higher capacity of recovery as compared to the single-step irradiated one.

Wavenumber Dependence of FT-IR Image of Molecular Orientation in Banded Spherulites of Poly(3-hydroxybutyrate) and Poly(l-lactic acid)

The chemical and the molecular chain orientation image of a banded spherulite of crystalline polymers, poly(l-lactic acid) (PLLA) and poly(3-hydroxybutyrate) (PHB), are visualized using FT-IR imaging with a newly proposed multipolarization calculation method. The vector representation of FT-IR image at different absorption spectral peaks visualizes the magnitude and direction of molecular chain orientation directly in comparison with the retardation and the slow-axis azimuthal images obtained by birefringence imaging. We found for the first time that the wavenumber dependence of in-plane orientation function in the band structure of a PHB spherulite, which is known as a double-band structure originated from a biaxial refractive index ellipsoid. The 15 absorption peaks in the IR spectrum of PHB can be classified into three groups by a different appearance of a band structure in view of the magnitude of molecular chain orientation. The azimuthal image of birefringence also shows the double-band structure; however, the FT-IR azimuthal images of orientation axis indicate the completely different distribution in which there is no band structure at any IR absorption peaks. By contrast, a good correspondence between the azimuthal image of the slow axis of birefringence and the orientation axis of FT-IR is observed in the spherulite of PLLA, which has a uniaxial refractive index ellipsoid. The advanced FT-IR imaging method clarifies the wavenumber-dependent two-types single-band structures of PHB, indicating the local molecular chain orientation along the crystallographic axes in a unit cell.

3-dimensional anisotropic thermal transport in microscale poly(3-hexylthiophene) thin films

Anisotropy in material structure leads to distinct anisotropy in mechanical and thermal properties for polymer materials. In this work, poly(3-hexylthiophene) (P3HT) thin films are fabricated using the spin coating technique for investigation of anisotropic thermal transport. Raman spectroscopy study of spin-coated P3HT films confirms the partially aligned molecular structure. Based on the main orientation of molecular chains, 3-dimensional thermal characterization is performed to understand the anisotropic thermal transport. The thermal conductivity varies from 0.1 to 3.18 W/m K and presents strong orientation-dependent feature. The anisotropy factor for in-plane thermal conductivity spans in the range of 2–4, lower than the factor for perfectly aligned structure. For thermal diffusivity, strong anisotropy is also observed. Particularly, for the out-of-plane direction, the thermal diffusivity is found almost one order of magnitude lower than that in the in-plane direction.

Thermo-optic coefficient of Ormocomp and comparison of polymer materials in athermal replicated subwavelength resonant waveguide gratings

We study the thermo-optic coefficient (dn/dT) of UV-curable Ormocomp® thin films by three methods, based on calculations using analytical models and data measured by ellipsometry, fitted with the Cauchy model in the wavelength range 380<λ<1000nm. The obtained values of dn/dT by the three methods are −1.02×10−4°C−1, −0.81×10−4°C−1, and −1.27×10−4°C−1. These values are employed to achieve an athermal operation of resonant waveguide gratings (RWGs). We describe the design, fabrication and characterization of three RWGs with different polymer materials (polycarbonate, cyclic olefin copolymer and Ormocomp®) and investigate athermal filtering device operation over a wide range of temperatures. The thermal spectral shifts of RWGs are described in terms of thermal expansion and thermo-optic coefficients of the selected materials. Furthermore, the spectral shifts are explained on the basis of shrinkage strains, frozen-in stresses and the molecular chain orientation in polymeric materials.

Imaging of Two-Dimensional Distribution of Molecular Orientation in Poly(ethylene oxide) Spherulite Using IR Spectrum and Birefringence

The two-dimensional quantitative imaging of molecular chain orientation is presented together with a chemical FT-IR imaging, in comparison with the optical birefringence imaging. The molecular chain orientation of the spherulite of poly(ethylene oxide) (PEO) is visualized using the four polarizations method of FT-IR imaging. The magnitude of orientation function and the azimuth angle of orientation axis are calculated with the FT-IR absorbance measured with a linear polarizer settled at four different angles. Retardation and the slow axis in a refractive index ellipsoid are calculated using transmission intensity measured with an electrical-controlled variable elliptical analyzer and a circular polarizer. In spite of the 6 times difference of the spatial resolution, the azimuth angle image determined from FT-IR imaging detects the change of molecular chain orientation, giving the similar line profiles of azimuth angle to that of slow axis determined from birefringence on the spherulite interface. A good c...

Morphological aspects of injected polypropylene/clay nanocomposite materials

AbstractPolypropylene (PP) clay nanocomposites were injection‐molded using two different coupling agents based on maleic anhydride‐grafted PP (MA‐g‐PP) and two clay loadings. The morphological aspects of these materials were studied by depth profiling. Molecular chain and clay orientations were characterized using attenuated total reflectance‐infrared analysis and transmission electron microscopy (TEM). Both clay platelets and PP molecular chain orientations were found to decrease from the surface toward the core of the injection–molded specimens. Clay intercalation, characterized by both complementary X‐ray diffraction and TEM, was found to be significantly influenced by both the characteristics of the coupling agent used and the type of residual stresses generated at each layer across the thickness of the injection‐molded parts. The use of low‐molecular weight (Mw) MA‐g‐PP led to a uniform intercalation but with no further exfoliation. The use of higher molecular weight MA‐g‐PP led to a heterogeneous intercalation with some signs of exfoliation. The crystallization behavior of PP clay nanocomposites studied by differential scanning calorimetry showed an increase in the level of crystallinity from the surface to the core of the specimens; these results were also confirmed by scanning electron microscopy. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

Orientation of poly(vinyl alcohol) nanofiber and crystallites in non-woven electrospun nanofiber mats under uniaxial stretching

The development of macroscopic nanofiber orientation and microscopic crystallite and molecular chain orientation have been investigated during uniaxial stretching of electrospun poly(vinyl alcohol) (PVA) non-woven nanofiber mats. Scanning electron microscopy and stress-strain/small-angle X-ray scattering show that the macroscopic nanofiber orientation significantly increases during the initial stage of deformation, and approaches a plateau on the way of stretching. Detailed analyses of the stress-strain/wide-angle X-ray diffraction measurement and polarized Fourier transform infrared spectroscopy indicate that the microscopic crystallite and molecular chain orientation rapidly increase at the initial stage of stretching due to macroscopic nanofiber orientation. At higher deformation, the microscopic modes of orientation continuously develop as a result of the nanofiber stretching. The complicated deformation process of non-woven nanofiber mats is discussed in terms of macroscopic nanofiber orientation and the microscopic crystallite and molecular chain orientation.

Investigation of Rheological Properties and Conformation of Silk Fibroin in the Solution of AmimCl

The conformation and eventual morphology of silk fibroin (SF) chains are crucial for the mechanical properties of SF materials, and are strongly related to the solvation step as a key stage in their processing conditions. In this work, a novel SF/AmimCl (1-allyl-3-methylimidazolium chloride) solution with unique properties is reported and compared with conventional regenerated SF aqueous solutions, based on an investigation of its rheological properties. The steady shearing behavior suggested that AmimCl is a good solvent for SF molecules, and shear thinning of semidiluted SF/AmimCl solution at high shear rates showed behavior similar to that in native spinning, which is due to the rearrangement and orientation of SF molecular chains. Fitting of experimental dynamic viscoelastic data to the Rouse model provided an effective method to estimate the molecular weight of SF. We believe that this work not only provides a better understanding of the relationship between properties of silk protein and aggregation states of their molecular chains, but also provides tools to fabricate high-performance SF-based materials.