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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 2254-2260 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new method is presented to simulate the motion of concentrated fiber suspensions in shear flow at low Reynolds numbers without Brownian motion. The hydrodynamic interaction among fibers is considered in a particle simulation method (PSM), in which a fiber is modeled by arrays of spheres. The motion of each constituent sphere of a fiber, which are dispersed into a unit cell with periodic boundaries, is followed to predict the microstructure and the rheological properties. The hydrodynamic interaction is decomposed into two parts, intra- and interfiber ones. In the former, the many-body problem is solved by calculating the mobility matrix for each fiber to obtain the hydrodynamic force and torque exerted on each sphere. In the latter, only the near-field lubrication force is considered between spheres of one fiber and another. The validity of this approximate treatment was first examined for the sphere dispersed system. The simulated microstructure and the rheological properties were in very good agreement with results of both experiments and the Stokesian dynamics. The methodology was then applied to concentrated rigid and flexible fiber suspensions. The overshoot of suspension viscosity was observed at the early stage for rigid fiber suspensions, but not for flexible ones. This was because of the transient change of the microstructure from the flow-directional orientation to the planar orientation of rigid fibers. The normal stress was calculated for the flexible fiber suspension and clearly showed that the elasticity of fiber suspensions was due to the deformation of fibers. The proposed simulation method can predict the effect of such parameters as the aspect ratio, flexibility, and volume fraction of fibers on the microstructure and the rheological properties of fiber suspensions. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 3317-3324 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The recently developed simulation method, named as the particle simulation method (PSM), is extended to predict the viscosity of dilute suspensions of rodlike particles. In this method a rodlike particle is modeled by bonded spheres. Each bond has three types of springs for stretching, bending, and twisting deformation. The rod model can therefore deform by changing the bond distance, bond angle, and torsion angle between paired spheres. The rod model can represent a variety of rigidity by modifying the bond parameters related to Young's modulus and the shear modulus of the real particle. The time evolution of each constituent sphere of the rod model is followed by molecular-dynamics-type approach. The intrinsic viscosity of a suspension of rodlike particles is derived from calculating an increased energy dissipation for each sphere of the rod model in a viscous fluid. With and without deformation of the particle, the motion of the rodlike particle was numerically simulated in a three-dimensional simple shear flow at a low particle Reynolds number and without Brownian motion of particles. The intrinsic viscosity of the suspension of rodlike particles was investigated on orientation angle, rotation orbit, deformation, and aspect ratio of the particle. For the rigid rodlike particle, the simulated rotation orbit compared extremely well with theoretical one which was obtained for a rigid ellipsoidal particle by use of Jeffery's equation. The simulated dependence of the intrinsic viscosity on various factors was also identical with that of theories for suspensions of rigid rodlike particles. For the flexible rodlike particle, the rotation orbit could be obtained by the particle simulation method and it was also cleared that the intrinsic viscosity decreased as occurring of recoverable deformation of the rodlike particle induced by flow.
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  • 3
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Macromolecules 27 (1994), S. 3735-3738 
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Macromolecules 28 (1995), S. 2893-2896 
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Macromolecules 28 (1995), S. 8868-8869 
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 644-650 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A method is proposed for simulating the dynamic behavior of rigid and flexible fibers in a flow field. The fiber is regarded as made up of spheres that are lined up and bonded to each neighbor. Each pair of bonded spheres can stretch, bend, and twist, by changing bond distance, bond angle, and torsion angle between spheres, respectively. The strength of bonding, or flexibility of the fiber model, is defined by three parameters of stretching, bending, and twisting constants. By altering these parameters, the property of the fiber model can be changed to be rigid to flexible. The motion of the fiber model in a flow field is determined by solving the translational and rotational equations for individual spheres under the hydrodynamic force and torque exerting on. This method was applied to simulate rotational motions with and without bending deformation of the fiber in a simple shear flow under the conditions of infinitely dilute system, no hydrodynamic interaction and low Reynolds number of a particle. For the rigid fiber, the computed period of rotation and the computed distribution of orientation angle agree with those calculated by Jeffery's equation with an equivalent ellipsoidal aspect ratio. For the flexible fiber, the period of rotation decreases rapidly with the growth of bending deformation of the fiber and rotation orbits deviate from a circular one of the rigid fiber. These tendencies are similar to experimental ones described by Forgacs and Mason. These results show that the proposed method using bonded spheres' model can reproduce the dynamic behavior of rigid and flexible fibers in a flow field successfully.
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 3300-3308 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A numerical method for computing the dynamics of a platelike particle dispersed system is presented. The particle simulation method (PSM) for fiber suspensions is extended to handle a platelike particle, which is modeled with an array of spheres. Each pair of adjacent spheres is connected and deformed by three types of springs; stretch, bend, and twist. The motion of the platelike particles in flow is followed by solving the translational and rotational equations of motion for each constituent sphere. The mobility matrix for each particle is calculated to obtain the hydrodynamic force and torque exerted on each sphere. For the hydrodynamic interaction among particles, the near-field lubrication force is considered when the separation between spheres belonging to different particles is close, but the far-field part is neglected. The method was applied to the dilute and concentrated system. For the dilute system, the motion of isolated square and rectangular platelike particles was calculated in a simple shear flow. The computed rotation orbits of a rigid square platelike particle were in good agreement with those calculated by Jeffery's equation for an oblate spheroid (disk). The characteristic behavior, which is unknown from the classical theory, of the rigid rectangular particle and the soft square particle was revealed. For the concentrated system, transient behavior of the platelike particles in a simple shear flow was calculated by dispersing them into a unit cell with periodic boundaries. The planar orientation of particles was observed in the microstructure of the concentrated system, and furthermore the orientation of the major axis of particles in the shear direction appeared in the rectangular platelike particle dispersed system. © 1997 American Institute of Physics.
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  • 8
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Fiber orientation induced by injection mold filling of short-fiber-reinforced thermoplastics (FRTP) causes anisotropy in material properties and warps molded parts. Predicting fiber orientation is important for part and mold design to produce sound molded parts. A numerical scheme is presented to predict fiber orientation in three-dimensional thin-walled molded parts of FRTP. Folgar and Tucker's orientation equation is used to represent planar orientation behavior of rigid cylindrical fibers in concentrated suspensions. The equation is solved about a distribution function of fiber orientation by using a finite difference method with input of velocity data from a mold filling analysis. The mold filling is assumed to be nonisothermal Hele-Shaw flow of a non-Newtonian fluid and analyzed by using a finite element method. To define a degree of fiber orientation, an orientation parameter is calculated from the distribution function against a typical orientation angle. Computed orientation parameters were compared with measured thermal expansion coefficients for molded square plates of glass-fiber-reinforced polypropylene. A good correlation was found.
    Additional Material: 14 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 36 (1988), S. 1821-1831 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Originally incompatible blends of SAN 30% and PC 70% were extruded with extremely high shear rate up to 107 s-1 as a typical example of the blends. The materials were examined with a scanning electron microscope (SEM), a pulsed NMR, etc. The molecular weight of the blends was also measured with gel permeation chromatography. The blends are of binary systems microscopically in the first run of extruding, in which the minor constituent is present as small spherical particles in the major constituent. The apparent volume fraction of the spherical minor constituent estimated from the microscopic photographs decreases with the shear rate. The fraction is decreased also with the repeated runs. SEM observation reveals that dimple fracture of microsize takes place on SAN sphere dispersed in PC matrix. And at the bottom of the dimple, a small particle, which would be composed of PC, is present. From these, SAN in the blend is thought to be partly ductile even at the temperature of liquid nitrogen. At the fifth run, the blend appears uniform or structureless. Dynamic loss tangent gives two peaks corresponding to that of SAN and that possibly attributed to PC. The latter shifts to lower temperatures with the number of extruding run. These show that some of SAN is mixed with PC in a compatible form. The pulsed NMR analysis supports the conclusion. Furthermore, the analysis suggests that some of SAN is mixed in PC. This result shows the compatibility of SAN with PC is enhanced in extremely high shear rate processing.
    Additional Material: 10 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1371-1376 
    ISSN: 0887-624X
    Keywords: diphenyldiacetylene ; pressure ; reaction ; condensed polycyclic aromatic compound ; oligomer ; polyacene ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of diphenyldiacetylene (1,4-diphenylbutadiyne) by annealing under elevated pressure (0.1-500 MPa) was carried out. Diphenyldiacetylene reacted at 210°C with appearance of gas, and this temperature was independent of the pressure. The measurement of high pressure differential thermal analysis (DTA) revealed that the reaction temperature under elevated pressure was below 24-42°C of the exothermic peak temperature. This implied that exothermic reaction occurred under elevated pressure. Elementary analysis, gel permeation chromatography (GPC), FTIR, Raman scattering, and high resolution 13CNMR experiments were performed to characterize the structure of the product. It was indicated that the product was a mixture of derivative of condensed polycyclic aromatic compound with phenyl group and diphenyldiacetylene oligomer. The fraction of the derivatives increased with increasing pressure, and pressure accelerated the dehydrogenation of the derivatives. The number-averaged molecular weight (Mn) of the diphenyldiacetylene oligomer was 470-610 and the weight-averaged molecular weight (Mw) was 1700-2300. It was considered that the oligomer had a polyacene-based structure. © 1994 John Wiley & Sons, Inc.
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