Cooperative strings in glassy nanoparticles.

@article{Arutkin2016CooperativeSI,
  title={Cooperative strings in glassy nanoparticles.},
  author={Maxence Arutkin and {\'E}lie Rapha{\"e}l and James A. Forrest and Thomas J. Salez},
  journal={Soft matter},
  year={2016},
  volume={13 1},
  pages={
          141-146
        }
}
Motivated by recent experimental results on glassy polymer nanoparticles, we develop a minimal theoretical framework for the glass transition in spherical confinement. This is accomplished using our cooperative-string model for supercooled dynamics, that was successful at recovering the bulk phenomenology and describing the thin-film anomalies. In particular, we obtain predictions for the mobile-layer thickness as a function of temperature, and for the effective glass-transition temperature as… 

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References

SHOWING 1-10 OF 129 REFERENCES
String model for the dynamics of glass-forming liquids.
TLDR
A living polymerization theory quantitatively describes the interrelation between the average string length L, configurational entropy Sconf, and the order parameter for string assembly Φ without free parameters and is used to predict the relaxation time τ in a lower temperature T range than accessible by current simulations.
Cooperative strings and glassy interfaces
TLDR
A minimal analytical model is introduced, which invokes only the ideas of molecular crowding and string-like cooperative rearrangement, before addressing the key effects of interfaces, and suggests that dynamics in glass-forming materials might be understood from elementary arguments.
Structures and Dynamics of Glass-Forming Colloidal Liquids under Spherical Confinement.
TLDR
A colloidal system is designed, where particles are confined inside spherical cavities with an amorphous layer of particles pinned at the boundary, and a simple relation for the change of the configurational entropy of confined colloidal liquids is proposed, which quantitatively explains the experimental findings and illustrates a divergent static length scale during the colloidal glass transition.
Crossover to surface flow in supercooled unentangled polymer films.
  • C. Lam, O. Tsui
  • Physics
    Physical review. E, Statistical, nonlinear, and soft matter physics
  • 2013
TLDR
A mobile layer is found responsible for the surface transport, as previously conjectured, and it is shown that it has a velocity profile decaying exponentially into the bulk.
Heterogeneous dynamics at the glass transition in van der Waals liquids, in the bulk and in thin films
Abstract:It has been shown over the last few years that the dynamics close to the glass transition is strongly heterogeneous, both by measuring the diffusion coefficient of tagged particles or by NMR
Reduction of the glass transition temperature in polymer films: a molecular-dynamics study.
TLDR
Results of molecular-dynamics simulations for a nonentangled polymer melt confined between two completely smooth and repulsive walls, interacting with inner particles via the potential U(wall)=(sigma/z)(9), are in qualitative agreement with that of the glass transition temperature observed in some experiments on supported polymer films.
The shapes of cooperatively rearranging regions in glass-forming liquids
The cooperative rearrangement of groups of many molecules has long been thought to underlie the dramatic slowing of liquid dynamics on cooling towards the glassy state. For instance, there exists
Effect of Free Surfaces on the Glass Transition Temperature of Thin Polymer Films.
TLDR
The concept of cooperative rearrangement was introduced in an attempt to unify these two views of the glass transition by demonstrating that such cooperativity, coupled with a thermodynamic glass transition, resulted naturally insystem dynamics such as those described by the WLFequation for temperatures near freezing.
Reduction of the glass transition temperature of confined polystyrene nanoparticles in nanoblends.
  • Y. Rharbi
  • Materials Science
    Physical review. E, Statistical, nonlinear, and soft matter physics
  • 2008
TLDR
The role of nanoconfinement on the glass transition temperature (T(g)) of polymers has been extensively studied in the thin film geometry and the general trend of T(g) depression in nanospheres was found to be similar to the results onthin film geometry.
The glass transition of thin polymer films: some questions, and a possible answer
Abstract:A simple and predictive model is put forward explaining the experimentally observed substantial shift of the glass transition temperature, Tg, of sufficiently thin polymer films. It focuses
...
...