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Disorder induced melting and glass formation in a one-component Lennard-Jones system

Saumya Suvarna, Prabhat K. Jaiswal, Madhu Priya

Abstract

Identifying the conditions under which glass formation occurs is crucial for a fundamental understanding of the glass transition mechanism. Pure liquids devoid of any frustration avoid glass transition and undergo crystallization. In this work, we investigate a one-component liquid interacting via the Lennard-Jones potential in two dimensions, where disorder is introduced through pinning, a protocol in which a fixed fraction of particles is immobilized at positions selected from an equilibrium configuration. By employing molecular dynamics simulation, we systematically study the influence of pinning concentration on both structural and dynamical properties. Structural properties quantified by radial distribution function and hexatic-order parameter display a systematic decrease with a rise in pinning concentration. However, the dynamical properties such as the fragility index and the late-time mean squared displacement exhibit a non-monotonic trend as the concentration of pinned particles increases. A moderate concentration of pinned particles helps prevent crystallization and facilitates particle motion. A further rise in the number of pinned particles suppresses particle mobility, leading to a reduction in the overall dynamics of the system. These simulation results are in good agreement with experimental observations on colloidal suspensions confined between glass coverslips, where particles are immobilized. Our findings demonstrate the pivotal role of pinning in controlling the phase behavior of simple liquids and validate the unique dynamical features of two-dimensional liquids with pinned particles.

Disorder induced melting and glass formation in a one-component Lennard-Jones system

Abstract

Identifying the conditions under which glass formation occurs is crucial for a fundamental understanding of the glass transition mechanism. Pure liquids devoid of any frustration avoid glass transition and undergo crystallization. In this work, we investigate a one-component liquid interacting via the Lennard-Jones potential in two dimensions, where disorder is introduced through pinning, a protocol in which a fixed fraction of particles is immobilized at positions selected from an equilibrium configuration. By employing molecular dynamics simulation, we systematically study the influence of pinning concentration on both structural and dynamical properties. Structural properties quantified by radial distribution function and hexatic-order parameter display a systematic decrease with a rise in pinning concentration. However, the dynamical properties such as the fragility index and the late-time mean squared displacement exhibit a non-monotonic trend as the concentration of pinned particles increases. A moderate concentration of pinned particles helps prevent crystallization and facilitates particle motion. A further rise in the number of pinned particles suppresses particle mobility, leading to a reduction in the overall dynamics of the system. These simulation results are in good agreement with experimental observations on colloidal suspensions confined between glass coverslips, where particles are immobilized. Our findings demonstrate the pivotal role of pinning in controlling the phase behavior of simple liquids and validate the unique dynamical features of two-dimensional liquids with pinned particles.
Paper Structure (12 sections, 9 equations, 12 figures)

This paper contains 12 sections, 9 equations, 12 figures.

Table of Contents

  1. INTRODUCTION
  2. METHODOLOGY
  3. RESULTS
  4. RADIAL DISTRIBUTION FUNCTION
  5. HEXATIC-ORDER PARAMETER
  6. SELF-INTERMEDIATE SCATTERING FUNCTION
  7. RELAXATION MECHANISM
  8. MEAN-SQUARED DISPLACEMENT
  9. DIFFUSION COEFFICIENT AND ACTIVATION ENERGY
  10. NON-GAUSSIAN PARAMETER
  11. STOKES-EINSTEIN RELATION WITH TEMPERATURE
  12. CONCLUSIONS

Figures (12)

  • Figure 1: Radial distribution function at $T=0$ for a monodisperse system interacting via LJ$(12,6)$ potential and constituting 0%, 1%, 5%, 10%, 20% and 50% pinned particles. add c%
  • Figure 2: Hexatic-order parameter for an identical particle system with increasing concentration of pinned particles $c\%$. We observe a systematic decrease in orientational ordering with a rise in the concentration of pinned particles.
  • Figure 3: Snapshots showing hexatic-order parameter for one-component system composed of $c=0\%, 1\%, 5\%, 10\%, 20\%$ and $50\%$ pinned particles. The maroon color dots mark the particles surrounded by a group of perfect hexagons of neighboring particles. As we proceed from systems composed of $0\%$ to $50\%$ pinned particles, the number of maroon color particles decreases, indicating the monotonic decrease of the hexatic-order parameter.
  • Figure 4: Self-intermediate scattering function for a group of particles interacting with LJ$(12,6)$ potential and consisting of various concentrations of pinned particles (a) at $T = 5$ and (b) at $T = 0.5$.
  • Figure 5: The VFT fit to relaxation time $\tau$ with inverse of temperature for different pinning concentrations. Particles here are subjected to the LJ$(12,6)$ potential. The fitting extracts the value of fragility.
  • ...and 7 more figures