Degree Of Orientation Increases Research Articles

All-optical orientation of linear molecules with combined linearly and elliptically polarized two-color laser fields.

We show that a combination of a fundamental pulse with linear polarization along the vertical direction and an elliptically polarized second harmonic pulse with both vertical and horizontal electric field components can be used to orient linear molecules efficiently, leading to higher degrees of orientation. Due to this specific combination of polarizations, the asymmetric hyperpolarizability interaction potential, which remains the same as that in a linearly polarized two-color laser field, is created along the vertical component of the elliptically polarized second harmonic pulse. On the other hand, the horizontal component suppresses the otherwise strong symmetric polarizability potential responsible for alignment, increasing the tunneling probability from the shallower potential well to the deeper one. As a result, the degree of orientation increases and can be controlled by changing the intensity of the horizontal component of the elliptically polarized second harmonic pulse. This study is the generalization of the all-optical molecular orientation technique based on the anisotropic hyperpolarizability interaction.

Temperature and deformation dependence of structural evolution in polyamide 1010

Polyamide 1010 (PA1010) is a representative of long-chain polyamides, used in applications requiring good mechanical, thermal and chemical properties. It has a lower melting point and slightly higher flexible properties compared to nylon 66. Very few reports have been focused on the structures and properties of long-chain polyamides, which brings some troubles on their processing and applications. For the purpose of understanding mechanical changes within different temperature interval, dynamic structure transition of PA1010 was investigated by wide-angle X-ray diffractometer (WAXD) equipped with a hot stretching stage. During the process of the simultaneous thermal stretched, in addition to the Brill transition phenomenon, it was also accompanied by changes in crystallinity, orientation and tensile force. Both annealing and stretching can promote crystallization, in addition, stretching can also induce and destroy crystallization. With stretch ratios increasing, the crystallinity increases firstly, reaches the maximum when stretch ratio is 2.25 times and then decreases. The degree of orientation increase firstly but increase poorly after 2.50 times. The stretch force increase gradually too. The stretch force has a stronger ability than temperature to induce the PA1010 undergo the Brill transition. The presented results show that Brill transition is completed and the α-crystal structure completely transformed into γ-crystal structure when the stretch ratio is 2.50 times.

Effects of orientation on the transport of d‐limonene in polypropylene

AbstractKinetics and equilibria of sorption and desorption of d‐limonene in three polypropylene films (unoriented polypropylene [UN], uniaxially oriented polypropylene [UA], and biaxially oriented polypropylene [BA]) were studied at 30°C and various penetrant activities. The weight percent uptake of a saturated vapor of limonene in UN, BA, and UA films ranged ranged from 12.5 to 19.0%. The kinetics of sorption of a saturated vapor of limonene in these polymers exhibits an increasing tendency toward Fickian transport as the degree of orientation increases, with the highly oriented BA approaching a Fickian response. As the penetrant activity is lowered, sorption kinetics tends to show a Fickian response more closely even for the UN and the UA films. Desorption of limonene from the three samples appears to be Fickian and considerably faster than sorption in the initial stages; however, the process decelarates after roughly half of the penetrant has desorbed. Subsequent exposure of the three oriented films to a saturated vapor of limonene resulted in identical sorption kinetics, suggesting the absence of crazing or other irreversible damage often associated with anomalous sorption in glassy polymers. These results illustrate that the concentration dependent anomalies in kinetics of sorption of a large penetrant such as limonene in the unoriented polypropylene film may be influenced by orientation to yield Fickian transport even at the highest external surface concentration. Thus, the orientation processes appear to affect large‐scale swelling‐induced relaxations to a larger degree than it does the diffusional processes which are dependent on smaller‐scale segmental motions. © 1995 John Wiley & Sons, Inc.

Dynamic mechanical analysis of fibers. II. Estimation of fiber orientation and characterization of heat set PET yarns

AbstractA drawn PET yarn was heat set (annealed) at temperatures between 110°C and 245°C in an unconstrained mode and the samples characterized by dynamic mechanical analysis (DMA). A method for estimating the fiber orientation factor (α) is proposed using DMA and shown to be more sensitive than the crystalline orientation (x‐ray diffraction) or total orientation (birefringence) measurements of the heat set yarns. The extension/shrinkage behavior of the heat set yarns has been discussed in the light of morphological changes, e.g., degree of orientation and the micro‐crystallite formation. Unlike in the unconstrained mode, heat setting under constraint does not lead to the formation of micro‐crystallites as revealed by differential scanning calorimetry. As a consequence, although the modulus and degree of orientation increase upon constrained annealing, the thermal stability, i.e., loss of orientation (reflected by shrinkage) could not be improved.

Orientational order near the boundaries of glassy diane-based oligomers with the surrounding phases

Spontaneous birefringence and IR spectroscopy were used as methods for studying a homologous series of diane-based oligomeric polyhydroxyethers. Orientational order has been found to appear near the spherical or planar interfaces between films prepared from oligomers with M n ⩾ 1500 and a solid substrate or air. Both the thickness of the oriented layer and the degree of orientation increase with increasing M n . The thickness also increases with increasing radius of curvature of the oriented surface, levelling off as the surface becomes planar. With rising molar mass the relative content of hydrogen-bonded hydroxyl groups declines. The observed rise in the degree of orientation with increasing molar mass has been attributed to the diminishing plasticizing effect of low-molar-mass fractions, combined with changes in the interaction between the terminal epoxide groups and hydroxyls situated in the central regions of the chain.

Photo-orientation in a freshwater Cryptomonas species

Phototactic orientation is characterized in a freshwater species of the flagellate Cryptomonas. In contrast to the marine species, C. maculata, which shows both pronounced positive and negative phototaxis, and an unidentified red tide Cryptomonas species, which is restricted to positive phototaxis, this limnetic species possesses an unusual phototactic response: at all effective fluence rates it orients perpendicular to the direction of the light beam (diaphototaxis). When grown under nitrogen and phosphorus deficiency, the absorption spectrum does not change considerably but the degree of orientation increases. Addition of p-quinone, a quencher of free radical formation, at concentrations of up to 10 −5 M does not alter the phototactic behaviour at either high or low fluence rates, while 1,4-diazobicyclo [2.2.2] octane (DABCO) as well as other scavengers of singlet oxygen, affects photo-orientation at high fluence rates using a concentration of 10 −4 M, but not at low fluencerates. These results indicate that the high fluence rate response may be mediated by a type II ( 1O 2 production) photodynamic effect.

The microfabric of deformed kaolin

SUMMARYSamples of remoulded kaolin have been subjected to varying consolidation and shearing stress conditions, and the resulting microfabric has been examined using a scanning electron microscopy and an X‐ray texture diffractometer. Preparation of samples for observation in the SEM involved both freeze‐drying and critical point drying methods. In consolidation experiments, a significant regional variation in the degree of orientation is observed in each sample. An increase in orientation is seen near drainage surfaces. Observations from areas remote from these surfaces on samples consolidated one‐dimensionally show that from 0 kPa to 100 kPa there is little increase in the general degree of orientation. However, the large decrease in voids ratio associated with this change of stress level is achieved by aggregation of particles into domains, the latter being randomly orientated with respect to one another. Above 100 kPa, the degree of orientation increases, as the particles show a tendency to align with their normal vectors parallel to the principal stress direction.These findings are in agreement with the X‐ray texture goniometer studies on impregnated specimens cut from parts of the consolidated samples adjacent to those for scanning electron microscopy studies. The surfaces of specimens for the X‐ray studies were cut orthogonal either to the major principal stress direction or to the space diagonal in σ1, σ2, σ3 space.Micrographs of kaolin consolidated one‐dimensionally in one direction and then to a higher stress level in an orthogonal direction show a closely packed near random fabrics. Examination of samples deformed in shear reveal narrow zones, although regular herring‐bone‐shaped kink bands have been seen in the region between two parallel shear zones.

The thermal expansion of reinforced nylon‐6 composites through the matrix glass transition temperature

AbstractThe coefficient of thermal expansion (CTE) of nylon‐6 reinforced with particulate filler, short glass fibers, and long‐to‐continuous glass fibers was measured between −30 and 170°C. As the reinforcement level, the reinforcement aspect ratio, or degree of orientation increases, the linear CTE decreases. The Tg range for the composite system is equal to the Tg for the pure nylon‐6 matrix. An unexpected result is observed when the nylon‐6 is reinforced with long or continuous glass fibers in random planar orientation and the weight fraction of reinforcement exceeds 10 percent. In this case, the longitudinal linear CTE (parallel to the plane of the fibers) above the Tg is lower than the longitudinal linear CTE below the Tg. Analysis of the mathematical descriptions of composite thermal behavior indicates that an extremely low composite modulus in the transverse direction above the Tg may be a cause for this low CTE. The differences in CTE between short fiber and long fiber reinforced compositions indicate that the critical fiber length for thermal stress transfer may be higher than the critical fiber length for mechanical stress transfer.

Effects of Imperfect Orientation on Natural Ferromagnetic Resonance of Polycrystalline Hexagonal Ferrites

Effects of imperfect orientation on natural ferromagnetic resonance of oriented polycrystalline hexagonal ferrites are investigated theoretically and experimentally. It has been shown that absorption peak values increase and linewidths decrease as the degree of orientation increases. An assumption that the distribution of crystallites obeys canonical distribution is made. Numerical calculations are made of the resonance curves as a function of frequency under the condition that individual crystallite behaves independently. Effects of the degree of orientation on the backward characteristics of the resonance isolator are investigated experimentally at 50 GHz band.

Flow orientation and fracture strength of a model linear hard polymer solid

AbstractA mathematical analysis is given to describe the effect of prior large flow orientation on the variation of the fracture strength of a model linear hard polymer solid. For the simple state of uniaxial orientation, the fracture strengths in the direction of orientation and that perpendicular to the direction of orientation are evaluated as functions of the strain change and the strength of the unoriented material. The results indicate an increase of strength in the direction of orientation and a decrease of strength perpendicular to the direction of orientation as the degree of orientation increases.