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Method for estimating the cooperativity length in polymers.

Marco Pieruccini1, Andrea Alessandrini2

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Summary
This summary is machine-generated.

This study estimates cooperatively rearranging region (CRR) sizes in polymers using relaxation experiments. It details a two-step mechanism for CRR configuration changes, applicable to various polymer systems.

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Area of Science:

  • Polymer Physics
  • Materials Science
  • Statistical Mechanics

Background:

  • Supercooled polymeric melts exhibit complex relaxation dynamics.
  • Estimating the size of cooperatively rearranging regions (CRRs) is crucial for understanding these dynamics.
  • Existing models like Donth's scheme provide a framework for analyzing large-scale rearrangements.

Purpose of the Study:

  • To address the problem of estimating CRR size in polymeric melts from relaxation experiments.
  • To propose a two-step mechanism for CRR configuration changes, encompassing both local and large-scale rearrangements.
  • To analyze the influence of configurational degrees of freedom on relaxation processes.

Main Methods:

  • Analysis of the α-process in ordinary relaxation experiments.
  • Canonical formalism for describing local monomer rearrangements.
  • Modeling large-scale configurational changes as spontaneous processes.
  • Application of stress relaxation experiments using atomic force microscopy.

Main Results:

  • A two-step mechanism for CRR configuration changes is detailed: initial local rearrangement followed by larger-scale rearrangements.
  • Two regimes are identified based on the significance of configurational degrees of freedom in energy fluctuation regression.
  • Consistency with Donth's scheme is demonstrated, particularly when configurational degrees of freedom are relevant.
  • CRR size and temperature fluctuations were estimated for poly(n-butyl methacrylate).

Conclusions:

  • The proposed model provides a consistent framework for analyzing polymer relaxation and estimating CRR sizes.
  • The study highlights the importance of configurational degrees of freedom in relaxation dynamics.
  • Analysis of poly(dimethyl siloxane) in nanopores suggests that combining temperature fluctuation measurements with this analysis offers a more complete view of configurational constraints.