Library

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Microphase separation in poly(isoprene-b-ethylene oxide) diblock copolymer melts. I. Phase state and kinetics of the order-to-order transitions (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 652-663 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The phase state and the kinetics of the order-to-order transitions have been studied in a series of poly(isoprene-b-ethylene oxide) (PI-PEO) diblock copolymers with a PI volume fraction in the range 0.25〈fPI〈0.92, using small angle x-ray scattering (SAXS), and rheology. The mean-field theory (MFT) structure factor is used to describe the SAXS profiles in the disordered phase and to extract the temperature dependence of the interaction parameter χ(T). In general, an agreement is found with the phase diagram proposed by an extended MFT, except at fPI=0.61 where the following sequence of phases was found: Lc→Hex→Gyroid→Dis (Lc is the crystalline lamellar phase, Hex signifies hexagonally packed cylinders, Gyroid is the bicontinuous cubic network with the Ia3¯d symmetry, and Dis is the disordered phase). We found that crystallization disrupts the amorphous ordered morphologies and imposes a layered structure (Lc). The study of the kinetics of the Hex to Lc and the Hex to Gyroid transitions is facilitated by the different viscoelastic contrast and the distinctly different scattering patterns of the three phases involved (Lc, Hex, Gyroid). Our studies show that it is possible to undercool and overheat ordered phases just as we can undercool the disordered phase. The transformation from the Hex to the Lc phase proceeds via a heterogeneous nucleation and growth process and results in the formation of a spherulitic superstructure composed from stacks of lamellar crystals. The transformation of the Hex to the Gyroid phase involves two steps. The first step—which is too fast to be picked up by rheology—involves fluctuations of the hexagonal phase. The second "slow" step involves a nucleation and growth process of elongated objects. The transformation proceeds nearly epitaxially and has an activation energy of 47 kcal/mol which is typical for a collective process. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478122
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Dynamics of polyisoprene in star block copolymers confined in microstructures: A dielectric spectroscopy study (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 5502-5509 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Dielectric spectroscopy has been employed to study selectively the local and global dynamics of polyisoprene (PI) in three microphase separated star diblock copolymers (SI)4, where PI and polystyrene (PS) form the core and corona, respectively. The thermally induced order-to-disorder transition (ODT) has been identified by rheology and small-angle x-ray scattering (SAXS). All dielectric measurements were made at temperatures well below the ODT and the polystyrene glass transition temperatures, where the four PI chain ends are tethered by the glassy polystyrene domains. The ordered state morphology, studied by SAXS, revealed the formation of PS spheres (fPS=0.25, where fPS is the polystyrene volume fraction), polyisoprene cylinders (fPS=0.68), and a lamellar structure (fPS=0.41) in the three copolymers. In contrast to the local segmental motions, the chain orientational dynamics associated with the amplitude and the characteristic relaxation time are strongly influenced by the spatial confinement. The main effects are the suppressed amplitude and the enhanced chain mobility, which are predicted and found to be stronger if the star topology is accompanied by topological (entanglement) effects of the PI block, irrespective of the ordered star morphology. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474255
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Microphase separation in block copolymer/homopolymer blends: Theory and experiment (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 3318-3328 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The process of microphase separation in diblock copolymer/homopolymer blends is studied both theoretically and experimentally for an asymmetric diblock copolymer and for homopolymer concentration less than 25%. The degree of polymerization of the added homopolymer (Nh) covered all possible cases; N(approximate)Nh, N〉Nh, and N〈Nh. SAXS and rheology are employed and provide the order–disorder transition temperature through the discontinuous changes of the structure factor and the storage modulus. The minority phase can solubilize only a small amount of added homopolymer; addition of a higher amount results in the formation of nonequilibrium structures. Theoretical calculations performed in the strong segregation limit provide the period and the critical value of χN for the stability of the disordered phase. The theory predicts that (χN)c always increases with the addition of the majority phase. When the minority phase is added, (χN)c can increase (N(very-much-greater-than)Nh and N≥Nh) or decrease (N(very-much-less-than)Nh). The experimental results are in good agreement with the theoretical predictions for the two extreme cases; N(very-much-greater-than)Nh and N(very-much-less-than)Nh, but differ when the minority component is added with N≥Nh. These results demonstrate that the degree of compatibility between the two blocks of the diblock AB can be effectively controlled by adding a small amount of homopolymer A or B. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473080
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Effect of pressure on the segmental and chain dynamics of polyisoprene. Molecular weight dependence (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 9847-9852 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report on the effect of pressure on the relaxation modes of the type-A polymer polyisoprene as a function of the chain length for M/Me ratio's (Me is the entanglement molecular weight): 〈fraction SHAPE="CASE"〉15, 〈fraction SHAPE="CASE"〉12, 〈fraction SHAPE="CASE"〉23, 2, and 5. We find that the spectral shape of the segmental and normal modes is invariant under temperature (T) and pressure (P) variations, but the time–pressure superposition fails as a consequence of the stronger P dependence of the segmental mode. The segmental mode activation volume for the different molecular weights was found to scale with the temperature difference from the respective glass transition temperature. Pressure is found to slow down both modes in a quantitatively similar way, irrespective of the chain length, implying that Me is largely independent of pressure. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480327
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Pressure dependence of the local and global dynamics of polyisoprene (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 5201-5204 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report on the pressure dependence of the local segmental and normal modes of a type-A polymer (polyisoprene) using dielectric spectroscopy. We find that external pressure exerts a stronger influence on the dynamics of the segmental mode as compared to the longest normal mode which results in the crossing of the two modes at higher pressures. The predictions of the Rouse model are not adequate to explain the different shift factors even at elevated temperatures. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479774
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Equilibrium order-to-disorder transition temperature in block copolymers (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 6498-6501 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The process of order-to-disorder transition (ODT) has been studied in a symmetric diblock copolymer AB and in an asymmetric miktoarm star block copolymer of the AB3 type. We find that the TODT depends on the ordering temperature just as the melting temperature in semicrystalline homopolymers depends on the crystallization temperature. In this work we show, for the first time, the existence of an equilibrium transition temperature (TODT0) and we demonstrate how this can be obtained. The dependence of the apparent TODT′ on the supercooling is attributed to grains of different sizes. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476056
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    Pressure-induced dynamic homogeneity in an athermal diblock copolymer melt (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 9129-9132 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report on the effect of pressure on the dual segmental relaxation of an athermal poly(isoprene-b-vinylethylene) (PI-PVE) diblock copolymer melt using dielectric spectroscopy. The quantity (∂ log τ/∂P)T is employed as a probe of the state of dynamic miscibility in the system. We find that pressure, unlike temperature, induces dynamic homogeneity. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479387
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    Optical anisotropy as an index of polymer microstructure in poly(phenylmethylsiloxane) chains (1990)
    s.l. : American Chemical Society
    Macromolecules 23 (1990), S. 498-501 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00204a023
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    Electronic Resource
    Electronic Resource
    Density and concentration fluctuations in plasticized poly(cyclohexyl methacrylate) (1990)
    s.l. : American Chemical Society
    Macromolecules 23 (1990), S. 1104-1109 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00206a032
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 10
    Electronic Resource
    Electronic Resource
    Optical anisotropy and conformational analysis of styrene-methyl methacrylate block copolymers in dilute solutions (1991)
    s.l. : American Chemical Society
    Macromolecules 24 (1991), S. 5796-5800 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00021a011
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...