Fluids and fluid mixtures containing square-well diatomics: Equations of state and canonical molecular dynamics simulation

Gulati, Harpreet S.; Hall, Carol K.

doi:10.1063/1.474749

Cited by 42 publications

(22 citation statements)

References 42 publications

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“…[23][24][25] This method is a fast alternative to traditional Molecular Dynamics (MD) simulations, where the forces on the particles are computed in each (constant) time step. In DMD, on the contrary, we compute the forces only when two particles collide.…”

Section: Model and Simulation Methodsmentioning

confidence: 99%

“…Specifically, we consider a model which was recently proposed in ref. 23 to simulate dipole-like systems via the so-called Discontinuous Molecular Dynamics (DMD) method, [23][24][25] a special form of (event-driven) MD. In this context, the true, continuous, longrange dipolar potential is approximated by a discontinuous, three-step potential which (roughly) preserves the directional dependence of the original interaction, particularly the preference of head-tail-arrangements, but restricts its range.…”

Section: -12mentioning

confidence: 99%

“…Details of the DMD method in the canonical ensemble can be found in ref. 25,38,39. Here we consider mainly system sizes of N ¼ 576, 1024, and 1600 particles.…”

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confidence: 99%

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Phase diagram of two-dimensional systems of dipole-like colloids

et al. 2012

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Based on Discontinuous Molecular Dynamics (DMD) simulations we present a phase diagram of twodimensional nano-particles with dipole-like short-ranged interactions. Similar to systems with true, long-ranged dipolar interactions the present system undergoes a transition from an isotropic fluid phase into a polymer-like fluid, characterized by an association of most particles into clusters. Further decrease of the temperature leads to a percolated system which, moreover, displays dynamical properties reminiscent of a gel. Specifically, we find a plateau in the mean-squared displacement and a non-gaussian behavior of the self-part of the van Hove correlation function. In the high density region we observe crystallization from the isotropic fluid into a solid phase with hexagonal order. Surprisingly, the crystallization is accompanied by a global parallel ordering of the dipole moments, i.e., a ferroelectric phase. This behavior is in marked contrast to what is found in 2D systems with longranged dipolar interactions. Our results allow insights into the design of gel-like or highly ordered structures at interfaces, shells around droplets and bubbles and new-sheet like materials.

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Section: Model and Simulation Methodsmentioning

confidence: 99%

Section: -12mentioning

confidence: 99%

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Phase diagram of two-dimensional systems of dipole-like colloids

et al. 2012

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“…The central idea is motivated by the observation from molecular simulations that, under equilibrium conditions, key dimensionless "reduced" quantities for confined fluids closely correspond to those of homogeneous bulk fluids with the same excess entropy [33][34][35][36][37] (relative to an ideal gas at the same density and temperature). The excess entropy can be computed using Monte Carlo methods 36 or predicted from classical density-functional theories 35,38 . An open question is whether this observed correspondence between dynamics and excess entropy applies for fluids in deeply supercooled liquid states approaching the glass transition, where highly nontrivial dynamic effects of confinement are observed.…”

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confidence: 99%

Predicting How Nanoconfinement Changes the Relaxation Time of a Supercooled Liquid

et al. 2013

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The properties of nanoconfined fluids can be strikingly different from those of bulk liquids. A basic unanswered question is whether the equilibrium and dynamic consequences of confinement are related to each other in a simple way. We study this question by simulation of a liquid comprising asymmetric dumbbell-shaped molecules, which can be deeply supercooled without crystallizing. We find that the dimensionless structural relaxation times − spanning six decades as a function of temperature, density, and degree of confinement − collapse when plotted versus excess entropy. The data also collapse when plotted versus excess isochoric heat capacity, a behaviour that follows from the existence of isomorphs in the bulk and confined states.That confined liquids microscopically relax and flow with different characteristic time scales than bulk liquids is hardly surprising. Confining boundaries bias the spatial distribution of the constituent molecules and the ways by which those molecules can dynamically rearrange. These effects play important roles in the design of coating, nanopatterning, and nanomanufacturing technologies 1,2 . As a result, they have already been experimentally characterized for a wide variety of material systems, including small-molecule fluids 3-10 , polymers 11-16 , ionic liquids 17 , liquid crystals 18 , and dense colloidal suspensions [19][20][21][22][23] , and studied extensively via molecular simulations 22,24-31 . Recent reviews of confined-liquid behavior may be found in, e.g., Refs. 10,32 .Unfortunately, successful theories for predicting the dynamics of inhomogeneous fluids have been slower to emerge. Here, we explore the possibility of a novel approach for predicting how confinement affects the dynamics of viscous fluids. The central idea is motivated by the observation from molecular simulations that, under equilibrium conditions, key dimensionless "reduced" quantities for confined fluids closely correspond to those of homogeneous bulk fluids with the same excess entropy 33-37 (relative to an ideal gas at the same density and temperature). The excess entropy can be computed using Monte Carlo methods 36 or predicted from classical density-functional theories 35,38 . An open question is whether this observed correspondence between dynamics and excess entropy applies for fluids in deeply supercooled liquid states approaching the glass transition, where highly nontrivial dynamic effects of confinement are observed. Another open question is whether thermodynamic properties other than the excess entropy can be used to predict the dynamics in confinement.To investigate these questions we study the behavior of a glass-former comprising asymmetric dumbbell-shaped molecules 39 . This model is perhaps the simplest singlecomponent system that avoids freezing upon cooling or compression in confinement, allowing for a systematic comparison of the properties of supercooled states in both bulk and confined geometries. The latter is modeled as a slit-pore, i.e., a sandwich geometry, using a 9-3 LennardJo...

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“…A numerical calculation of such integrals is often omitted in engineering applications for practical reasons. In PC-SAFT one follows an approach previously proposed for monomers and dimers 45,46 and approximates these integrals by a power series of sixth order in the packing fraction:…”

Section: B Attractive Interactionsmentioning

confidence: 99%

A global investigation of phase equilibria using the perturbed-chain statistical-associating-fluid-theory approach

Yelash

Müller

Paul

et al. 2005

The Journal of Chemical Physics

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The recently developed Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) is investigated for a wide range of model parameters including the parameter m representing the chain length and the thermodynamic temperature T and pressure p. This approach is based upon the first-order thermodynamic perturbation theory for chain molecules developed by Wertheim [ M.S. Wertheim, J. Stat. Phys. 35, 19-46 (1984); ibid. 42, 459-492 (1986) Chem. Phys. 47, 4714 (1967)]. We systematically study a hierarchy of models which are based on the PC-SAFT approach using analytical model calculations and Monte Carlo simulations. For one-component systems we find that the analytical model in contrast to the simulation results exhibits two phase-separation regions in addition to the common gas-liquid coexistence region: One phase separation occurs at high density and low temperature. The second demixing takes place at low density and high temperature where usually the ideal gas phase is expected in the phase diagram. These phenomena, which are referred to as "liquid-liquid" and "gas-gas" equilibria, give rise to multiple critical points in one-component systems, as well as to critical end points (CEP) and equilibria of three fluid phases, which can usually be found in multicomponent mixtures only. Furthermore, it is shown that the "liquid-liquid" demixing in this model is not a consequence of a "softened" repulsive interaction as assumed in the theoretical derivation of the model. Experimental data for the melt density of polybutadiene with molecular mass M w = 45000 g/mol are correlated here using the PC-SAFT equation. It is shown that the discrepancies in modeling the polymer density at ambient temperature and high pressure can be traced back to the "liquid-liquid" phase separation predicted by the equation of state at low temperatures. This investigation provides a basis for understanding possible inaccuracies or even unexpected phase behavior which can occur in engineering applications of the PC-SAFT model aiming at predicting properties of macromolecular substances.

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Fluids and fluid mixtures containing square-well diatomics: Equations of state and canonical molecular dynamics simulation

Cited by 42 publications

References 42 publications

Phase diagram of two-dimensional systems of dipole-like colloids

Phase diagram of two-dimensional systems of dipole-like colloids

Predicting How Nanoconfinement Changes the Relaxation Time of a Supercooled Liquid

A global investigation of phase equilibria using the perturbed-chain statistical-associating-fluid-theory approach

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