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
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 117 (2002), S. 2389-2396 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The radial local dynamics in poly(1,4-trans-butadiene) melts is studied using molecular dynamics simulations. In this work, the hopping peak is observed in the Van Hove space-time correlation function Gs(r,t) for the first time in polymeric systems. The hopping motion, observed only for methine hydrogen, is also identified in the mean-square displacement 〈Δr2(t)〉 and the intermediate scattering function Fs(k,t) through the relative dynamics of the hopping methine hydrogen and the nonhopping methylene hydrogen. The hopping motion is found to cause an unusual broadening of the dispersion width in the dynamic structure factor Sinc(k,ω). Active free volume is proposed in terms of Gs(r,t) at a short time, which offers a consistency to the relationship between free volume and local dynamics. Fast counterrotation at a pair of CH(Single Bond)CH2 bonds across a CH(Double Bond)CH bond is found responsible for the hopping peak in this polymer, and a new hopping criterion modified for polymeric liquids is proposed. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 2
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 3
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dynamic rotational isomeric state (DRIS) formalism has been utilized to predict the local dynamics of amorphous cis- and trans-polybutadiene at bulk density from short-time molecular dynamics (MD) simulations at 425 K. The rates for transitions between rotational isomeric states have been calculated from the initial slopes of time-delayed transition (conditional) probability curves extracted from the MD simulation. First- (independent), second- (pairwise dependent), and third- (triplewise dependent) order conformational transitions have been incorporated into the DRIS formalism. Conformational and orientational correlation functions have been evaluated. The comparison of DRIS results with MD simulations indicates that this approach may be advantageously used to predict the time evolution of bond isomeric states and the contribution of transitions between these states to conformational correlation functions. The first-order conformational kinetics is the major factor controlling the relaxation in the latter. Cross-correlation functions are not reproduced as well, because they are dominated by torsional librations within rotational isomeric states, and such librations are not incorporated in the DRIS analysis. The prediction of anisotropic character of the segmental motions is also satisfactory to an important extent, but it still awaits some more consideration in the choice of the size of the kinetic segment, along with the accurate input of cooperative motions arising from both intra- and intermolecular interactions in a MD simulation. Information which would otherwise be extracted from the statistical analysis of very long trajectories of MD simulations may become readily obtainable from DRIS. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 6242-6254 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The local motions of bulk amorphous polybutadienes (PBDs) have been studied by a molecular dynamics simulation. Fully atomistic models of PBDs have been obtained at a realistic bulk density under periodic boundary conditions. Local chain motions are examined for poly(cis-1,4-butadiene) (cis-PBD) and poly(trans-1,4-butadiene) (trans-PBD) well above the glass transition temperature, where the only structural difference is imposed by the different conformational states at the double bond. The local motions are found to be strikingly different in the two polymers. Intramolecular cooperative conformational transitions occur at second-neighbor bond pairs of CH–CH2 in both PBDs. In trans-PBD, both CH2–CH2 and CH=CH triplets undergo cooperative counterrotations. In cis-PBD, CH2–CH2 triplets undergo counterrotations while CH=CH triplets undergo corotations. Intermolecular cooperativity, probed by the local free volume, has little influence on local relaxation processes. The effect of libration on the shape of autocorrelation functions (ACFs) is significant over the entire time range. A universality is found in the time evolution of the Kohlrausch–Williams–Watts exponent regardless of the type and order of the ACF. On the other hand, the single exponential decay regarded as common at short times is only due to the discreteness of conformational states.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...