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Kell Mortensen - One of the best experts on this subject based on the ideXlab platform.

  • effect of Planar Extension on the structure and mechanical properties of polystyrene poly ethylene co butylene polystyrene triblock copolymers
    Polymer, 2000
    Co-Authors: Christophe Daniel, Ian W. Hamley, Kell Mortensen
    Abstract:

    Abstract Two thermoplastic poly(styrene)–poly(ethylene- co -butylene)–poly(styrene) triblock copolymers containing either spherical or cylindrical poly(styrene) microdomains were pre-oriented through Extensional flow. Small angle neutron scattering (SANS) measurements revealed that the pre-oriented triblock with a spherical microstructure adopts a body-centred cubic (bcc) structure with a [111] orientation along the flow direction. For the pre-oriented triblock with a cylindrical microstructure, the cylinder axis is aligned along the Extensional flow direction. Investigation of the mechanical properties showed that Young's moduli of the pre-oriented copolymers are highly anisotropic. Specimens were then subject to uniaxial deformation along the Extensional flow direction and at the same time microstructural changes induced by the deformation were investigated by SANS. It was found that the deformation of the bcc lattice is affine, and that the deformation of the microstructure is reversible. For the triblock copolymer with a cylindrical microdomain structure the deformation of the lattice was found to be non-affine. In this case, SANS patterns suggest a “micronecking” and a breaking of the cylindrical domains without any change in the domain spacing.

  • Effect of Planar Extension on the structure and mechanical properties of polystyrene–poly(ethylene-co-butylene)–polystyrene triblock copolymers
    Polymer, 2000
    Co-Authors: Christophe Daniel, Ian W. Hamley, Kell Mortensen
    Abstract:

    Abstract Two thermoplastic poly(styrene)–poly(ethylene- co -butylene)–poly(styrene) triblock copolymers containing either spherical or cylindrical poly(styrene) microdomains were pre-oriented through Extensional flow. Small angle neutron scattering (SANS) measurements revealed that the pre-oriented triblock with a spherical microstructure adopts a body-centred cubic (bcc) structure with a [111] orientation along the flow direction. For the pre-oriented triblock with a cylindrical microstructure, the cylinder axis is aligned along the Extensional flow direction. Investigation of the mechanical properties showed that Young's moduli of the pre-oriented copolymers are highly anisotropic. Specimens were then subject to uniaxial deformation along the Extensional flow direction and at the same time microstructural changes induced by the deformation were investigated by SANS. It was found that the deformation of the bcc lattice is affine, and that the deformation of the microstructure is reversible. For the triblock copolymer with a cylindrical microdomain structure the deformation of the lattice was found to be non-affine. In this case, SANS patterns suggest a “micronecking” and a breaking of the cylindrical domains without any change in the domain spacing.

Christophe Daniel - One of the best experts on this subject based on the ideXlab platform.

  • effect of Planar Extension on the structure and mechanical properties of polystyrene poly ethylene co butylene polystyrene triblock copolymers
    Polymer, 2000
    Co-Authors: Christophe Daniel, Ian W. Hamley, Kell Mortensen
    Abstract:

    Abstract Two thermoplastic poly(styrene)–poly(ethylene- co -butylene)–poly(styrene) triblock copolymers containing either spherical or cylindrical poly(styrene) microdomains were pre-oriented through Extensional flow. Small angle neutron scattering (SANS) measurements revealed that the pre-oriented triblock with a spherical microstructure adopts a body-centred cubic (bcc) structure with a [111] orientation along the flow direction. For the pre-oriented triblock with a cylindrical microstructure, the cylinder axis is aligned along the Extensional flow direction. Investigation of the mechanical properties showed that Young's moduli of the pre-oriented copolymers are highly anisotropic. Specimens were then subject to uniaxial deformation along the Extensional flow direction and at the same time microstructural changes induced by the deformation were investigated by SANS. It was found that the deformation of the bcc lattice is affine, and that the deformation of the microstructure is reversible. For the triblock copolymer with a cylindrical microdomain structure the deformation of the lattice was found to be non-affine. In this case, SANS patterns suggest a “micronecking” and a breaking of the cylindrical domains without any change in the domain spacing.

  • Effect of Planar Extension on the structure and mechanical properties of polystyrene–poly(ethylene-co-butylene)–polystyrene triblock copolymers
    Polymer, 2000
    Co-Authors: Christophe Daniel, Ian W. Hamley, Kell Mortensen
    Abstract:

    Abstract Two thermoplastic poly(styrene)–poly(ethylene- co -butylene)–poly(styrene) triblock copolymers containing either spherical or cylindrical poly(styrene) microdomains were pre-oriented through Extensional flow. Small angle neutron scattering (SANS) measurements revealed that the pre-oriented triblock with a spherical microstructure adopts a body-centred cubic (bcc) structure with a [111] orientation along the flow direction. For the pre-oriented triblock with a cylindrical microstructure, the cylinder axis is aligned along the Extensional flow direction. Investigation of the mechanical properties showed that Young's moduli of the pre-oriented copolymers are highly anisotropic. Specimens were then subject to uniaxial deformation along the Extensional flow direction and at the same time microstructural changes induced by the deformation were investigated by SANS. It was found that the deformation of the bcc lattice is affine, and that the deformation of the microstructure is reversible. For the triblock copolymer with a cylindrical microdomain structure the deformation of the lattice was found to be non-affine. In this case, SANS patterns suggest a “micronecking” and a breaking of the cylindrical domains without any change in the domain spacing.

Ian W. Hamley - One of the best experts on this subject based on the ideXlab platform.

  • effect of Planar Extension on the structure and mechanical properties of polystyrene poly ethylene co butylene polystyrene triblock copolymers
    Polymer, 2000
    Co-Authors: Christophe Daniel, Ian W. Hamley, Kell Mortensen
    Abstract:

    Abstract Two thermoplastic poly(styrene)–poly(ethylene- co -butylene)–poly(styrene) triblock copolymers containing either spherical or cylindrical poly(styrene) microdomains were pre-oriented through Extensional flow. Small angle neutron scattering (SANS) measurements revealed that the pre-oriented triblock with a spherical microstructure adopts a body-centred cubic (bcc) structure with a [111] orientation along the flow direction. For the pre-oriented triblock with a cylindrical microstructure, the cylinder axis is aligned along the Extensional flow direction. Investigation of the mechanical properties showed that Young's moduli of the pre-oriented copolymers are highly anisotropic. Specimens were then subject to uniaxial deformation along the Extensional flow direction and at the same time microstructural changes induced by the deformation were investigated by SANS. It was found that the deformation of the bcc lattice is affine, and that the deformation of the microstructure is reversible. For the triblock copolymer with a cylindrical microdomain structure the deformation of the lattice was found to be non-affine. In this case, SANS patterns suggest a “micronecking” and a breaking of the cylindrical domains without any change in the domain spacing.

  • Effect of Planar Extension on the structure and mechanical properties of polystyrene–poly(ethylene-co-butylene)–polystyrene triblock copolymers
    Polymer, 2000
    Co-Authors: Christophe Daniel, Ian W. Hamley, Kell Mortensen
    Abstract:

    Abstract Two thermoplastic poly(styrene)–poly(ethylene- co -butylene)–poly(styrene) triblock copolymers containing either spherical or cylindrical poly(styrene) microdomains were pre-oriented through Extensional flow. Small angle neutron scattering (SANS) measurements revealed that the pre-oriented triblock with a spherical microstructure adopts a body-centred cubic (bcc) structure with a [111] orientation along the flow direction. For the pre-oriented triblock with a cylindrical microstructure, the cylinder axis is aligned along the Extensional flow direction. Investigation of the mechanical properties showed that Young's moduli of the pre-oriented copolymers are highly anisotropic. Specimens were then subject to uniaxial deformation along the Extensional flow direction and at the same time microstructural changes induced by the deformation were investigated by SANS. It was found that the deformation of the bcc lattice is affine, and that the deformation of the microstructure is reversible. For the triblock copolymer with a cylindrical microdomain structure the deformation of the lattice was found to be non-affine. In this case, SANS patterns suggest a “micronecking” and a breaking of the cylindrical domains without any change in the domain spacing.

Shi-qing Wang - One of the best experts on this subject based on the ideXlab platform.

  • Inhomogeneous chain relaxation of entangled polymer melts from stepwise Planar Extension in absence of free surface
    Journal of Rheology, 2020
    Co-Authors: Ruchao Yuan, Shi-qing Wang
    Abstract:

    In this work, we apply lubricated squeezing to perform Planar Extension of styrene-butadiene rubbers (SBRs) and illustrate how large step-strained SBR undergo chain relaxation. When the imposed step strain is moderate or the stepwise Planar Extension is imposed sufficiently slowly, the stress relaxation is spatially uniform. Upon a large stepwise Extension imposed over a period much shorter than the overall chain relaxation time, the strained SBR undergo spatially inhomogeneous molecular relaxation, plausibly due to localized chain disentanglement that results from the molecular force imbalance. As a manifestation of localized elastic yielding, the SBR specimen appears wrinkled upon unloading in the middle of stress relaxation. In situ birefringence measurements confirm that uneven chain relaxation is ongoing during stress relaxation that involves keeping the sample height H fixed after squeezing from the initial height H0 to H. Thus, localized chain relaxation is shown to take place even in the presence of geometrical constraint, i.e., the absence of any free surface or meniscus. In comparison, homogenous stepwise deformation was found to result in nonquiescent relaxation for simple shear and filament breakup for uniaxial melt stretching.

  • characterizing effects of fast melt deformation on entangled polymers in their glassy state
    Journal of Chemical Physics, 2019
    Co-Authors: Zhichen Zhao, Xinyang Zhao, Jianning Liu, Weiyu Wang, Jimmy W Mays, Shi-qing Wang
    Abstract:

    Fast deformation of entangled melts is known to cause chain stretching due to affinelike straining of the entanglement network. Since the chain deformation may also result in perturbations of covalent bond angles and bond length, there are always possible enthalpic effects. In this study, we first subject polystyrene and PMMA of different molecular weights to either uniaxial melt Extension or Planar Extension and subsequently impose rapid thermal quenching to preserve the chain deformation. Then, such pre-melt-deformed samples are annealed at various temperatures below the glass transition temperature Tg. During annealing, these samples can undergo appreciable contraction on a time scale much shorter than the alpha relaxation time. Significant retractive stress is observed when such contracting samples are held fixed during the annealing. The stress level can be nearly as high as the Cauchy stress produced during melt stretching. These observations not only allowed us to investigate glassy chain dynamics as well as the molecular nature of mechanical stress but may also suggest that pre-melt-stretched polymers can cause segmental mobilization in the glassy state. The available evidence indicates that the retractive stress is enthalpic in origin, associated with the conformational distortion at the bond level produced by melt stretching.

Vlasis G. Mavrantzas - One of the best experts on this subject based on the ideXlab platform.

  • Tension thickening, molecular shape, and flow birefringence of an H-shaped polymer melt in steady shear and Planar Extension.
    The Journal of chemical physics, 2010
    Co-Authors: Chunggi Baig, Vlasis G. Mavrantzas
    Abstract:

    Despite recent advances in the design of Extensional rheometers optimized for strain and stress controlled operation in steady, dynamic, and transient modes, obtaining reliable steady-state elongational data for macromolecular systems is still a formidable task, limiting today’s approach to trial-and-error efforts rather than based on a deep understanding of the deformation processes occurring under elongation. Guided, in particular, by the need to understand the special rheology of branched polymers, we studied a model, unentangled H-shaped polyethylene melt using nonequilibrium molecular dynamics simulations based on a recently developed rigorous statistical mechanics algorithm. The melt has been simulated under steady shear and steady Planar Extension, over a wide range of deformation rates. In shear, the steady-state shear viscosity is observed to decrease monotonically as the shear rate increases; furthermore, the degree of shear thinning of the viscosity and of the first- and second-normal stress co...