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Related Experiment Videos

Diffusion and viscosity in a supercooled polydisperse system.

Rajesh K Murarka1, Biman Bagchi

  • 1Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore, India 560 012.

Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
|June 6, 2003
PubMed
Summary
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Molecular dynamics simulations reveal that supercooled polydisperse liquids exhibit fragile behavior. Particle diffusion and viscosity follow the Vogel-Fulcher-Tammann equation, with diffusion decoupling from viscosity at low temperatures.

Area of Science:

  • Condensed Matter Physics
  • Computational Chemistry
  • Materials Science

Background:

  • Supercooled liquids exhibit complex dynamics deviating from simple Arrhenius behavior.
  • Understanding the temperature dependence of transport properties is crucial for characterizing liquid states.
  • Polydispersity in particle size and mass introduces additional complexity to liquid dynamics.

Purpose of the Study:

  • To investigate the temperature dependence of dynamical properties in a supercooled polydisperse Lennard-Jones liquid.
  • To analyze the relationship between viscosity and self-diffusion coefficients for particles of varying sizes.
  • To characterize the fragility and diffusion mechanisms in this complex liquid system.

Main Methods:

  • Extensive molecular dynamics simulations were performed on a supercooled polydisperse Lennard-Jones system.

Related Experiment Videos

  • Simulations were conducted at a fixed pressure across a wide temperature range.
  • Dynamical properties, including viscosity (eta) and self-diffusion coefficients (D(i)), were calculated.

    • Main Results:

    • Both viscosity and diffusion coefficients displayed super-Arrhenius temperature dependence, fitting the Vogel-Fulcher-Tammann equation.
    • The system was classified as a very fragile liquid (Angell's fragility parameter D ≈ 1.4).
    • Critical temperatures for diffusion (T(D(i))(o)) increased with particle size, and T(eta)(o) exceeded T(D(i))(o), indicating decoupling.

    Conclusions:

    • Deeply supercooled polydisperse liquids show decoupling of translational diffusion from viscosity, especially for smaller particles.
    • Particle diffusion exhibits non-Stokesian behavior at low temperatures with a nonlinear size dependence.
    • Particle motion transitions from continuous Brownian to discontinuous jump-type at low temperatures, with smaller particles showing this crossover at shorter timescales.