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  • 1
    Digitale Medien
    Digitale Medien
    Frequency Dependence of Orientation in Dynamically Sheared Diblock Copolymers (1995)
    s.l. : American Chemical Society
    Macromolecules 28 (1995), S. 778-781 
    Details
    ISSN: 1520-5835
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie , Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1021/ma00107a015
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  • 2
    Digitale Medien
    Digitale Medien
    Diffusion of Tracer Molecules within Symmetric Diblock Copolymers (1995)
    s.l. : American Chemical Society
    Macromolecules 28 (1995), S. 8287-8294 
    Details
    ISSN: 1520-5835
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie , Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1021/ma00128a044
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  • 3
    Digitale Medien
    Digitale Medien
    Symmetric diblock copolymers under large amplitude oscillatory shear flow: Entanglement effect (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 4784-4793 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The effect of large amplitude oscillatory shear flow on the morphology of two nearly symmetric polystyrene–polyisoprene diblock copolymers of intermediate molecular weights has been studied. Using two dimensional SAXS experiments and electron microscopy micrographs the orientation of the lamellae after shear flow has been determined. It has been shown that under the appropriate experimental conditions an orientation component can be observed with the unit normal of the lamellae parallel to the flow which on the timescale of hours is not observed in low molecular weight samples. It has been proposed that this orientation is the result of topological constraints, i.e., entanglement effects, on the diblock copolymer dynamics, as evidenced by dynamic mechanical experiments on the samples before flow. With the help of mechanical data collected during the flow, the orientation dynamics has been studied. Using concepts from the tube model of entangled polymer melts and characteristic features of the chain conformational statistics of diblock copolymers, a mechanism for the formation of this orientation component is suggested. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.470613
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  • 4
    Digitale Medien
    Digitale Medien
    Symmetric diblock copolymers under large amplitude oscillatory shear flow: Dual frequency experiments (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 2961-2969 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Conceptually new experiments are described in which the effects of the superposition of two large amplitude oscillatory shear components on the morphology of a lamellar PS-b-PI diblock copolymer of low molecular weight close to TODT are investigated. First results of such dual frequency experiments are presented for the coupling of two shear components from the lower and intermediate frequency regimes I and II of the shear viscosity leading to parallel and perpendicular orientation behavior, respectively, in single frequency experiments. The employed frequencies were separated by more than two orders of magnitude, rendering possible coupling terms unimportant. Using two-dimensional small-angle x-ray scattering (2D-SAXS) measurements, it is shown that for large rim strain values the perpendicular orientation mechanism completely governs the behavior. In experiments where the applied strain for shear component II leading to perpendicular orientation is significantly reduced with respect to that of component I leading to parallel orientation, a characteristic flip from parallel to perpendicular orientation is observed along the radius of the sample disk. It is further demonstrated that the position of the flipping point along the radius can be altered by varying the amplitude of deformation component II. In these experiments regions of parallel as well as perpendicular orientation exhibiting high order parameters can be achieved. The results are interpreted using concepts for the orientation mechanisms developed in earlier single frequency studies, thereby corroborating the underlying ideas. Furthermore, the results of the dual frequency experiments supply valuable information concerning the competition between different orientation mechanisms not directly obtained from single frequency experiments. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.473795
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  • 5
    Digitale Medien
    Digitale Medien
    Probe diffusion in homogeneous diblock copolymers (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 1739-1746 
    Details
    ISSN: 0887-6266
    Schlagwort(e): block copolymers ; molecular diffusion ; Forced Rayleigh scattering ; free volume ; Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Forced Rayleigh scattering was used to investigate the diffusion of a photoreactive dye molecule in two homogeneous poly(styrene-b-isoprene) (SI) diblock copolymers with overall molecular weights of approximately 2000. Although diffusion rates were intermediate to TTI transport in homopolymer polystyrene (PS) and polyisoprene (PI), system dynamics appear to be largely dictated in each case by the PI block. The size of the polymer jumping unit, on the other hand, is evaluated from a free-volume analysis of the data, and is found to be governed predominantly by the PS component of the copolymer. The mechanism for tracer diffusion in low-molecular-weight block copolymers appears analogous to transport in a high molecular weight SI diblock copolymer (Mn = 13,600) that has been solvated sufficiently in toluene to be microstructurally disordered. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1739-1746, 1998
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Rheology of lamellar polystyrene-block-polyisoprene diblock copolymers (1998)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 199 (1998), S. 1771-1784 
    Details
    ISSN: 1022-1352
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The linear viscoelastic properties of symmetric polystyrene-block-polyisoprene diblock copolymers (PS-b-PI) were studied over a range of molecular weights between 20 000 and 200 000 using dynamic mechanical spectroscopy. For all samples the low frequency rheological response can be divided into two frequency regimes in agreement with previous reports on this subject, indicating the onset of a third relaxation process at very low frequencies related to the microphase separated microstructure. Various methods to determine two characteristic frequencies, ωc and ωd, separating different orientation regimes of the lamellar microstructure observed under large amplitude oscillatory shear flow in the vicinity of TODT (T 〈 TODT) are compared. It is further shown that for PS-b-PI diblock copolymers an apparent entanglement effect sets in at molecular weights which are much lower than those expected from the corresponding homopolymer data. A microscopic picture is proposed to account for the experimental results.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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