Nonequilibrium hyperuniform fluids

• Main Author: Lei, Yusheng
• Other Authors: Ni Ran
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2024
• Subjects: Engineering; Physics; Hyperunifromity; Nonequilibrium system
• Online Access: https://hdl.handle.net/10356/181663
• Institution: Nanyang Technological University

Disordered hyperuniform structures are an exotic state of matter with vanishing long-range fluctuations in many-particle systems, which have recently drawn attention from researchers in various fields such as mathematics, physics, materials sciences, etc., due to their unusual structural properties. This thesis aims to provide an in-depth discussion on hyperuniform structures observed in various nonequilibrium many-particle systems, mainly focusing on those without long-range interactions, where hyperuniformity emerges through self-organization due to their nonequilibrium nature. In Chapter 2, we review a number of typical out-of-equilibrium dynamic hyperuniform systems found numerically and experimentally in the recent decade. And we divide them into three main parts. The first one is the systems stemmed from random organization (RO) dynamics, which is a model originally proposed to describe the chaotic particle motion in sheared non-Brownian suspensions. The subsequent one is the hyperuniform systems found in active particle systems, including hyperuniform reactive particle fluids and the chiral active brownian systems and biological algae systems, etc. The last one is hyperuniform systems found in phase separating structures via spinodal decomposition. Overall, these recent progress deepen and broaden our understanding on nonequilibrium hyperuniform states in different systems of various mechanisms. In Chapter 3, we generalize the random organization (RO) model with center-of-mass conservation (CMC) onto spherical surfaces via numerical simulation and theoretical analysis. We found that the hyperuniformity in the critical point and active states still remains despite of the curvature on the curved manifold, and the hyperuniform structure factor shows similar forms comparing to the one on flat spaces. It is noteworthy that the hyperuniform structures are long-range correlated, while the random organization excitation between particles are local dynamic rules, and it is non-trivial that the emergent long-range hyperuniform correlation does not significantly affected by the topology of the space. Besides, we also consider the impact of inertia in realistic nonequilibrium hyperuniform fluids, and it is found only by adding an extra length-scale, above which hyperuniform scaling appears. Our finding suggests a new method for creating non-equilibrium hyperuniform structures on closed manifolds to avoid boundary effects with self-healing properties. In Chapter 4, we explore the discontinuous freezing transition in barrier-controlled nonequilibrium reactive particle systems by molecular dynamics simulations. We find a metastable hyperuniform state with a new scaling, and the survival time of this metastable state is increasing with system size which seems to be kinetically stable in the thermodynamic limit. Moreover, we find that the discontinuous freezing transition of the metastable hyperuniform fluid into an absorbing state does not have the kinetic pathway of nucleation and growth, and the transition is triggered by long-wavelength fluctuations. We also validate our finding in a similar lattice model called the facilitated Manna model, and ``metastable yet kinetically stable" hyperuniform states with the same structure factor scaling are also found. Our result suggests that the phase transformations in nonequilibrium systems can be fundamentally different from the ones in equilibrium. In Chapter 5, we study nonequilibrium reactive particle systems with additional short-ranged attractive interactions using molecular dynamics simulations. Comparing to original reactive particle systems, we find that a liquid-gas-like phase separation occurs due to this extra attractive force between particles, and we measure the phase diagram of the liquid-gas mixture. Besides, by rapidly quenching the system from the homogeneous phase to the coexistence region, we observe a series of time-evolved self-similar phase-separating patterns growing via spinodal decomposition, where the patterns are found to exhibit strong hyperuniformity with scaling properties similar to equilibrium Model-B and nonequilibrium active field theories. Our results indicate that the hyperuniformity observed in systems via spinodal decomposition could be universal, suggesting a robust approach for obtaining strongly hyperuniform structures.