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  • 1
    Electronic Resource
    Electronic Resource
    Oscillatory shear induced anisotropic domain growth and related rheological properties of binary mixtures (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 1575-1583 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Numerical simulation based on the modified time-dependent Ginzburg–Landau (TDGL) model has been performed on the domain growth and related rheological properties of binary mixtures under oscillatory shear. The simulation results reveal that the domain growth is anisotropic and depends on the quench depth. It is found that, in the deep quench case, the disclike domain with the normal parallel to the velocity gradient direction is observed, while in the shallow quench case, the rodlike domain with rod axis aligned along the flow direction is observed. The scattering functions for different light incident directions are calculated and suggest that the undulated rodlike morphology is formed in the shallow quench case. This undulated rodlike morphology shows the anomalous rheological response. A plausible interpretation for the anomalous rheological property is proposed based on the deformation of the undulated rodlike morphology under oscillatory shear. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476709
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  • 2
    Electronic Resource
    Electronic Resource
    Chain stretching effect on domain growth during spinodal decomposition of binary polymer mixtures under simple shear flow (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 9529-9536 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The chain stretching effect on domain growth during spinodal decomposition of binary polymer mixtures under simple shear flow is investigated by computer simulation. The simulation is based on a modified time-dependent Ginzburg–Landau equation, in which the chain stretching effect is introduced in the free energy functional. It is found that, for higher value of Rouse terminal relaxation time, the critical strain value for the burst of the domains is higher, thereby the domains are highly elongated. This may be responsible for the stringlike patterns observed experimentally under strong shear. When the chain stretching effect is introduced, the shear rate dependencies of the shear stress and first normal stress difference become stronger. The shear stress and first normal stress difference reach their maxima for the system of 1:1 mixture. The simulated results agree with the experimental observations qualitatively. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476400
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  • 3
    Electronic Resource
    Electronic Resource
    Microphase separation of diblock copolymer induced by directional quenching (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 784-792 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Computer simulation is carried out for studying the microphase separation of a two-dimensional diblock copolymer (DBCP) system under directional quenching. By setting the quenching boundary between the stable and the unstable phase, and shifting the boundary with a constant velocity, the time evolution of the domain morphologies is examined numerically on the basis of the time-dependent Ginzburg–Landau type equation with the free-energy functional for the DBCP. Three different types of morphologies are found for the symmetric (i.e., f=0.5) DBCP system. One is the irregular lamellar morphology and is essentially equivalent to that produced by homogeneous quenching. The other two are regular and are characteristics of directional quenching process. One of the regular lamellar morphologies is perpendicular to the quench boundary on the average, whereas the other one is parallel to the quench boundary. For the asymmetric DBCP system with f=0.4, which forms the equilibrium morphology of triangular phase, the mode of regular lamellar morphology with the normal of lamellae perpendicular to the quench boundary appears first under the condition of directional quenching when the initial thermal fluctuation is very small. The growth rate of the triangular phase gets faster when the initial thermal fluctuation increases. Therefore, our results reveal that the thermal fluctuation promotes the appearance of the mode of triangular morphology for the case of f=0.4. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473165
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  • 4
    Electronic Resource
    Electronic Resource
    The rheology and morphology of phase-separating fluids with viscosity contrast (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 7783-7792 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper, the effects of viscosity contrast between the components on the rheology and morphology of phase-separating binary fluids have been studied by numerically solving time-dependent Ginzburg–Landau equation and Navier–Stokes equation. It is found that, the viscosity contrast between the components strongly affects the bulk contribution to the overall rheological behavior. When the viscosity of the minor phase is higher, the trend of bulk contribution is contrary with that of interfacial contribution. Therefore, the non-Newtonian behavior is weakened. When the viscosity of the minor phases is lower, the evolution of bulk contribution is the same as interfacial contribution, and thus the non-Newtonian behavior is strengthened. However, the interfacial contribution still plays the crucial role in the overall rheological behavior. When the system contains two droplets or many domains, due to the merging of domains induced by shear flow, there is a decrease of interfacial volume fraction. Therefore, the interfacial contribution of rheology decreases and forms a peak at small shear strain. Correspondingly, the bulk contribution has also been altered. However, whether the bulk contribution increases or decreases will depend on the viscosity contrast. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1407294
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  • 5
    Electronic Resource
    Electronic Resource
    The effect of shear flow on morphology and rheology of phase separating binary mixtures (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 8348-8361 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The morphology and the corresponding rheological properties of phase separating binary mixtures under shear flow are studied by computer simulation based on the modified time-dependent Ginzburg–Landau (TDGL) model. In order to investigate the hydrodynamic effect, model H in three dimensions has been used to simulate the phase separation of binary fluids under shear flow. For the sake of comparison, the simulation has also been performed based on simple binary solid model (model B). It is found that, for deep and critical quench, the domain grows faster and the domain anisotropy is lower in binary fluids due to the internal flow field induced by hydrodynamic interaction. For deep and off-critical quench, the internal flow field makes the elongated domain quickly relax to their original spherical shape before they are mutually contacted each other. Thus, it reduces the domain merging probability. It is also found that, for deep and critical quench, there are two peaks appeared in the shear viscosity as a function of shear strain at low shear rate, which agrees with the experimentally observations quite well. For shallow quenching, the broader interfaces suppress the internal flow caused by hydrodynamic interaction and thus the difference between binary solids and binary fluids is small. All these observed unique characters have been explained according to the hydrodynamic interaction and the relaxation rate of the deformed interface.© 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1313553
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  • 6
    Electronic Resource
    Electronic Resource
    Surface enrichment effect on the morphological transitions induced by directional quenching for binary mixtures (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 719-727 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The morphological transitions during directional quenching-induced spinodal decomposition in binary mixtures are investigated by computer simulation. By setting the quenching front between the stable and unstable phases, and shifting the front with a constant velocity, the evolution of the domain morphologies is examined numerically on the basis of the time-dependent Ginzburg–Landau (TDGL) equation. Three different types of morphologies are found for the critical quenching. One is irregular morphology (IM), which is essentially equivalent to that produced by homogeneous quenching. The other two are regular, representing the characteristics of the directional quenching process. One is regular lamellar morphology (RLM) and the other is regular column morphology (RCM). By varying the shifting velocity of the cooling front, two morphological transition velocities, va from IM to RLM, and vi from RLM to RCM, are observed. In contrast to that, for the case of off-critical quenching, a new transition velocity vb from RCM back to RLM can be found if the cooling front is further shifted slower. This characteristic morphological transition is attributed to the surface enrichment effect appearing in the nonequal volume fraction system, which competes with linear instability triggered by initial thermal fluctuation in the early stage of spinodal decomposition. Detailed studies reveal that RLM can be easily formed and thus the region of RCM is reduced when the surface enrichment effect is stronger. On the other hand, RCM will be preferred if the initial thermal fluctuation is stronger. The quantitative relation between lamella width and shifting velocity of the cooling front is also presented. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481847
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  • 7
    Electronic Resource
    Electronic Resource
    Monte Carlo simulation of kinetics and chain-length distribution in radical polymerization (1993)
    Basel : Wiley-Blackwell
    Die Makromolekulare Chemie, Theory and Simulations 2 (1993), S. 747-760 
    Details
    ISSN: 1018-5054
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In this paper, the Monte Carlo method for numerically simulating the kinetics and chain-length distribution in radical polymerization is described. Because the Monte Carlo method is not subject to the assumption of steady-state, it is particularly suitable for studying the kinetic behaviour before the steady-state has been reached and for systems in which the steady-state assumption may be violated. Illustrative applications of the algorithm given in this paper not only demonstrate convincingly both the feasibility and usefulness of the algorithm, but also provide some new insight into the illustrative examples. For the case of pseudostationary radical polymerization such as rotating-sector and pulsed-laser initiations, we have found that the pseudostationary radical concentration can be reached after two or three initiation periods. However, the number-average chain-length x̄n reaches the pseudostationary value much slower than the radical concentration. It is oscillatively reaching the pseudostationary value, and the amplitudes of the oscillations are decreasing with time. We have also found that the chain-length distribution of the resulting polymer in the case of pseudostationary radical polymerization with termination by combination has stronger periodic modulation. Hence, it should be easier to locate the points of inflection in practice. Therefore, the rate constant of propagation, kp, can be determined precisely for systems which are dominated by a combination-type of termination.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mats.1993.040020511
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  • 8
    Electronic Resource
    Electronic Resource
    Narrow molecular weight distribution of condensation polymers achieved by adding monomers in many batches (1995)
    Weinheim : Wiley-Blackwell
    Macromolecular Theory and Simulations 4 (1995), S. 953-965 
    Details
    ISSN: 1022-1344
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The Z transform method has been used to calculate the molecular weight distribution (MWD) of condensation polymers. The MWD obtained by using Z transform is explicitly discrete. The method is illustrated for two cases: (1) further polycondensation of AB prepolymers with certain initial MWD, and (2) polycondensation of AB and Ar (r is the number of A type functional groups) monomers where AB monomers are added in several batches. In the latter case, it is found that the resulting MWD is much narrower than that of one-batch polycondensation. The trick of producing narrow MWDs of condensation polymers is merely a consequence of keeping AB monomer concentration as low as possible during the reaction in order to suppress the condensation reaction between monomeric AB molecules. The theoretical prediction has been confirmed by Monte Carlo simulation. Therefore, it provides a new possible technique for obtaining narrow MWD polymers through polycondensation reactions.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mats.1995.040040508
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  • 9
    Electronic Resource
    Electronic Resource
    Kinetics of spinodal decomposition in mixtures of low molecular weight liquid crystals and flexible polymers (1997)
    Weinheim : Wiley-Blackwell
    Macromolecular Theory and Simulations 6 (1997), S. 1153-1168 
    Details
    ISSN: 1022-1344
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In this paper, the time-dependent Ginzburg-Landau model for mixtures containing nematogens has been applied to mixtures of low molecular weight liquid crystals and flexible polymers. Dynamic equations for the time evolution of concentration and orientation fluctuations and the structure factors for these fluctuations are given. It is shown that the coupling between concentration and orientation fluctuations is absent in the isotropic spinodal region, thus the evolution of the structure factors for the concentration fluctuations falls into the Cahn-Hilliard classic category and it exhibits no maximum in the structure factors of orientation fluctuations. We should emphasize that, in the anisotropic spinodal region, both concentration and orientation structure factors possess a maximum but not coincide with each other and both are shifting to smaller wave numbers according to the scaling relation, qmax ˜ τ-α, as time increases. The value of a closely correlates to the interfacial free-energy parameters.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mats.1997.040060607
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  • 10
    Electronic Resource
    Electronic Resource
    Monte Carlo simulation of chain length distribution in radical polymerization with transfer reaction (1995)
    Weinheim : Wiley-Blackwell
    Macromolecular Theory and Simulations 4 (1995), S. 811-819 
    Details
    ISSN: 1022-1344
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In this paper, the basic principle and a Monte Carlo method are described for numerically simulating the chain-length distribution in radical polymerization with transfer reaction to monomer. The agreement between the simulated and analytical results shows that our algorithm is suitable for systems with transfer reaction. With the simulation algorithm, we confirm that transfer reaction has a similar effect as disproportionation on the molecular weight distribution in radical polymerization with continuous initiation. In the pulsed laser (PL) initiated radical polymerization with transfer reaction, the ‘waves’ on the chain-length distribution profile become weaker as the ratio of transfer reaction rate constant, ktr, to the propagation rate constant, kp, is increased in the case with either combination-type or disproportionation-type termination. Moreover, it seems that the combination termination has a broadening effect on the waves. Therefore, kp can also be determined by precisely locating the inflection point Lo on the chain-length distribution profile for radical polymerization with transfer reaction, unless ktr is large enough to smear out the waves on the chain-length distribution.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mats.1995.040040414
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