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DNA Nanotubes as a Versatile Tool to Study Semiflexible Polymers
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Published on: October 25, 2017

Rheological complexity in simple chain models.

Taylor C Dotson1, Julieanne V Heffernan, Joanne Budzien

  • 1Department of Materials and Metallurgical Engineering, New Mexico Institute of Mining and Technology, Socorro, NM 87801, USA.

The Journal of Chemical Physics
|June 6, 2008
PubMed
Summary
This summary is machine-generated.

Molecular dynamics simulations reveal that freely jointed chains exhibit simple rheological behavior, while freely rotating chains show complex dynamics. This study enhances understanding of glass formers and chain dynamics.

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Combining Microfluidics and Microrheology to Determine Rheological Properties of Soft Matter during Repeated Phase Transitions
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Combining Microfluidics and Microrheology to Determine Rheological Properties of Soft Matter during Repeated Phase Transitions
11:38

Combining Microfluidics and Microrheology to Determine Rheological Properties of Soft Matter during Repeated Phase Transitions

Published on: April 19, 2018

Area of Science:

  • Polymer Physics
  • Materials Science
  • Computational Chemistry

Background:

  • Understanding the rheological complexity of polymer chains is crucial for predicting material properties.
  • Previous studies have explored chain dynamics, but a comprehensive assessment of rheological complexity in simplified models is needed.

Purpose of the Study:

  • To investigate and compare the dynamical properties and rheological complexity of short freely jointed chains (FJC) and freely rotating chains (FRC) using molecular dynamics simulations.
  • To assess the validity of the Kohlrausch-Williams-Watts (KWW) function in describing rotational relaxation and track the KWW stretching exponent (beta) across various state points.
  • To compare simulation results with experimental data for small molecular glass formers.

Main Methods:

  • Molecular dynamics simulations were employed to study the dynamical properties of FJC and FRC.
  • An improved analysis procedure focused on the rotational relaxation of the end-to-end vector using the KWW function.
  • The study analyzed translational and rotational motion, length-scale dependencies, and time-temperature superposition behavior.

Main Results:

  • The KWW stretching exponent (beta) was tracked accurately over a wide range of packing fractions (eta), showing smooth variation.
  • Freely jointed chains closely approximated simple rheological behavior, while freely rotating chains exhibited distinctly complex dynamical features.
  • Simulation results for beta and relaxation times align with experimental observations for small molecular glass formers.

Conclusions:

  • Freely jointed chains serve as a good approximation for simple rheological models, whereas freely rotating chains display significant complexity.
  • The study validates the use of (eta(0)-eta) as a measure of distance to the glass transition and confirms the accuracy of the analytical methods.
  • The findings contribute to a deeper understanding of the relationship between molecular structure, dynamics, and macroscopic rheological properties in glass-forming systems.