Liquid structure and particle interactions
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Liquid Structure: Molecular Arrangements and Interactions
The structure of liquids is shaped by the interactions between their constituent particles. In simple liquids like water and low molecular weight alcohols, hydrogen bonding leads to unique structural features such as cage-like arrangements and temperature-dependent properties. These interactions can be effectively modeled using mesoscopic simulation techniques, such as dissipative particle dynamics (DPD), which incorporate experimental thermodynamic data to capture both the structure and temperature-dependent behavior of the liquid. The radial distribution function and angular distributions from these simulations closely match those from atomistic models, confirming the accuracy of the approach in representing liquid structure and hydrogen bond effects 1.
In systems where particles interact through ultrasoft, harmonic-repulsive potentials, the liquid structure can change significantly under varying pressures. For example, as pressure increases, the pair distribution function (PDF) shows a splitting of the first peak, indicating the emergence of significant interactions with second neighbors and a rearrangement of the local structure. These changes can lead to unusual properties, such as negative thermal expansion and increased stability against crystallization 2.
Particle Interactions: Effects on Liquid Structure and Dynamics
Particle interactions in liquids are not limited to simple pairwise forces. The presence of pinned (immobile) particles, for instance, can alter the structural parameters of a liquid. When pinned particles are treated as a separate species, their interactions with mobile particles have a greater impact on structural order parameters and excess entropy than interactions between mobile particles themselves. This effect becomes more pronounced as the density of pinned particles increases, leading to a decrease in structural order and a continued correlation between structure and dynamics, even at higher pinning densities 5.
The dynamics of structural transitions in liquids are governed by the movement between different stable particle packings, or "inherent structures." These transitions, which can be tracked using molecular dynamics simulations, are linked to phenomena such as self-diffusion and viscous flow. In supercooled or amorphous states, transitions can occur intermittently, highlighting the complex relationship between structure and particle motion 8.
Fluid-Structure-Particle Interactions: Simulation and Modeling
Simulating the interactions between fluids, particles, and structures is essential for understanding many engineering and environmental processes. Advanced computational methods, such as hybrid immersed boundary techniques and coupled CFD-DEM-CSD frameworks, enable detailed modeling of these interactions. These methods can accurately capture particle-particle and particle-structure interactions, including contact and lubrication effects, and are validated against experimental data for scenarios like particle-laden flows and fluid-structure deformation 34.
Coherent Structures and Particle Behavior in Liquids
In certain flow conditions, such as those found in liquid bridges, particles can organize into coherent structures due to the interplay between flow dynamics and particle properties. Experiments and simulations reveal that multiple types of particles can form distinct, coexisting structures within the same flow, with the arrangement influenced by factors like particle size and flow parameters. The competition between different attractors in the flow can lead to complex, sometimes asymmetric, particle distributions 79.
Particle Impact and Liquid Surface Interactions
When a particle impacts a liquid surface, the interaction involves complex coupling between the particle, liquid, and surrounding gas. This process can result in phenomena such as splashing, bubble formation, and surface deformation. The dynamics of the contact line—the boundary where the particle, liquid, and air meet—play a crucial role in determining the outcome of the impact. Key parameters like particle size, impact velocity, and angle influence the resulting structures and behaviors, and understanding these interactions is essential for applications ranging from material processing to environmental science 10.
Conclusion
The structure of liquids and the interactions between their particles are deeply interconnected, influencing both static properties and dynamic behaviors. Advances in simulation and experimental techniques have provided new insights into how molecular arrangements, particle pinning, and external forces shape liquid structure and dynamics. These findings are crucial for both fundamental science and practical applications involving complex fluids and particle-laden systems.
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