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Related Concept Videos

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Polymer Classification: Crystallinity

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Unlike ionic or small covalent molecules, polymers do not form crystalline solids due to the diffusion limitations of their long-chain structures. However, polymers contain microscopic crystalline domains separated by amorphous domains.
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Step growth polymerization involves bi or multifunctional monomers. Bifunctional monomers react to form linear step growth polymers, whereas multifunctional monomers react to form non-linear or branched polymers.
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Step-Growth Polymerization: Overview01:03

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Heating a crystalline solid increases the average energy of its atoms, molecules, or ions, and the solid gets hotter. At some point, the added energy becomes large enough to partially overcome the forces holding the molecules or ions of the solid in their fixed positions, and the solid begins the process of transitioning to the liquid state or melting. At this point, the temperature of the solid stops rising, despite the continual input of heat, and it remains constant until all of the solid is...
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The cationic polymerization mechanism consists of three steps: initiation, propagation, and termination. In the initiation step of the polymerization process, the π bond of a monomer gets protonated by the Lewis acid catalyst, which is formed from boron trifluoride and water. The protonation of the π bond generates a carbocation stabilized by the electron‐donating group. In the propagation step, the π bond of the second monomer acts as a nucleophile and attacks the...
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Cooling Rate Dependent Ellipsometry Measurements to Determine the Dynamics of Thin Glassy Films
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Dynamic phase transitions in freestanding polymer thin films.

Robert J S Ivancic1, Robert A Riggleman2

  • 1Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104.

Proceedings of the National Academy of Sciences of the United States of America
|October 3, 2020
PubMed
Summary

Investigating dynamics in freestanding polymer films reveals how interfaces influence molecular mobility. Thin films exhibit a single dynamic transition, unlike thicker films, suggesting capillary condensation-like behavior in glass formers.

Keywords:
glassthin filmtrajectory phase transitionwetting transition

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Area of Science:

  • Materials Science
  • Condensed Matter Physics
  • Polymer Physics

Background:

  • Fundamental questions persist regarding the dynamics of glass-forming materials in thin films.
  • Free interfaces are known to enhance dynamics, with effects intensifying at lower temperatures, but their precise influence remains debated.
  • Understanding these dynamics is crucial for applications involving thin-film materials.

Purpose of the Study:

  • To explore the nonequilibrium phase transition in dynamics within freestanding model polymer films.
  • To investigate how film thickness influences the transition between high- and low-mobility states.
  • To compare the observed dynamic transitions with phenomena like thermodynamic capillary condensation.

Main Methods:

  • Utilized molecular dynamics simulations of model polymer freestanding films.
  • Analyzed the nonequilibrium phase transition in trajectory space, focusing on mobility basins.
  • Examined the local coexistence points of the transition relative to film thickness and distance from surfaces.

Main Results:

  • Thick films show a broader film-averaged mobility transition than the bulk, with distinct surface and center transitions.
  • Thin films exhibit a single, shifted mobility transition throughout the film, resembling bulk behavior but with higher bias.
  • Observed transitions are analogous to thermodynamic capillary condensation, suggesting a similar effect in dynamic trajectory transitions.

Conclusions:

  • The study demonstrates a trajectory phase transition in glass-forming dynamics within freestanding polymer films.
  • Results suggest that confinement and interfaces induce capillary condensation-like phenomena in the dynamics of structural glass formers.
  • Findings align with experimental observations of anomalous glass transition behavior in thin films, including broadened transitions and homogenized temperatures.