Closed-loop liquid-vapor equilibrium in a one-component system

Almarza, N. G.

doi:10.1103/physreve.86.030101

Cited by 17 publications

(31 citation statements)

References 34 publications

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“…The thermodynamic stability at low T is shown to arise from the building up of non interacting clusters of particles with low energy and low entropy. The theory also provides a theoretical foundation of the behavior numerically observed recently in models of Janus particles in three dimensions [15] and in 2D-simulations of limited valence particles on lattice [21]. In both cases, the gas reentrance is connected to the self assembly into weakly or non interacting saturated aggregates (micelles for the Janus particles and rings for the patchy particles).…”

Section: Discussionmentioning

confidence: 99%

Self-Assembly in Chains, Rings, and Branches: A Single Component System with Two Critical Points

2013

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We study the interplay between phase separation and self-assembly in chains, rings and branched structures in a model of particles with dissimilar patches. We extend Wertheim's first order perturbation theory to include the effects of ring formation and theoretically investigate the thermodynamics of the model. We find a peculiar shape for the vapor-liquid coexistence, featuring re-entrant behavior in both phases and two critical points, despite the single-component nature of the system. The emergence of the lower critical point is caused by the self-assembly of rings taking place in the vapor, generating a phase with lower energy and lower entropy than the liquid. Monte Carlo simulations of the same model fully support these unconventional theoretical predictions. PACS numbers:Understanding the competition between self-assembly and phase-separation is central in today's research in different fields encompassing biology, soft-matter, material science, statistical mechanics. Self-assembly of finitesize aggregates requires strong interaction energies compared to the thermal energy to guarantee that the generated structure is persistent. As a result, self-assembly competes with the ubiquitous macroscopic phase separation, the low-temperature tendency common to atoms, molecules and larger particles to maximize the number of bonded neighbours and minimize the potential energy, giving rise to a condensed (liquid) state [1]. When particles can arrange themselves into low energy and weakly interacting finite size aggregates, self-assembly can completely suppress phase separation [2][3][4]. Soft matter and biology offers several examples of three-dimensional stable aggregates (e.g. micelles, vesicles, capsids [5,6]) which constitute the stable phase in wide temperature and density regions.The possibility of hampering the formation of large amorphous aggregates in favor of ordered structures is often facilitated by the presence of strong, directional and saturable interactions (limited valence) [7][8][9]. The renewed focus on the role of directional interactions, stimulated by the synthesis of new-generation patchy colloids [10][11][12][13], has deepened our understanding not only of the role of the valence on the gas-liquid phase separation [14] but also on the competition between selfassembly and phase separation. Two recent investigations have provided insights particularly relevant for this work: (i) a numerical study of Janus colloids in which a gas-liquid critical point and a self-assembly process are simultaneously observed [15,16]. In this model, the formation of energetically stable vesicles stabilizes at low temperature T the gas-phase; (ii) a study of particles with dissimilar patches [17][18][19], promoting respectively chaining and branching, specifically designed to reproduce a mean-field model introduced by Safran and Tlustly [20] to describe the phase behavior of dipolar fluids. Here branching produces a gas-liquid critical point, but on cooling the formation of energetically favored chains stabilizes, thi...

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Section: Discussionmentioning

confidence: 99%

Self-Assembly in Chains, Rings, and Branches: A Single Component System with Two Critical Points

2013

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“…A related study of the generic phase diagram of 2A4B models on the triangular lattice with r > 1 3 , reports that orientational correlations between the A patches that promote ring formation have a profound effect on the phase equilibria. 18 No phase coexistence is observed when short rings are formed. Closed miscibility loops are found if larger rings are formed while the usual reentrant behavior is observed if no rings are formed.…”

Section: Introductionmentioning

confidence: 99%

Three-dimensional patchy lattice model for empty fluids

Almarza

Tavares

Noya

et al. 2012

The Journal of Chemical Physics

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The phase diagram of a simple model with two patches of type A and ten patches of type B (2A10B) on the face centred cubic lattice has been calculated by simulations and theory. Assuming that there is no interaction between the B patches the behavior of the system can be described in terms of the ratio of the AB and AA interactions, r. Our results show that, similarly to what happens for related off-lattice and two-dimensional lattice models, the liquid-vapor phase equilibria exhibit reentrant behavior for some values of the interaction parameters. However, for the model studied here the liquid-vapor phase equilibria occur for values of r lower than 1 3 , a threshold value which was previously thought to be universal for 2AnB models. In addition, the theory predicts that below r = 1 3 (and above a new condensation threshold which is < 1 3 ) the reentrant liquid-vapor equilibria are so extreme that it exhibits a closed loop with a lower critical point, a very unusual behavior in singlecomponent systems. An order-disorder transition is also observed at higher densities than the liquidvapor equilibria, which shows that the liquid-vapor reentrancy occurs in an equilibrium region of the phase diagram. These findings may have implications in the understanding of the condensation of dipolar hard spheres given the analogy between that system and the 2AnB models considered here.

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“…Comparing the two cases α AB = 60 • and 80 • , it is clear that cycle formation decreases both the critical temperature T c and critical density ρ c . Lattice simulations 8 have also shown that cycle formation has a substantial influence on phase equilibria. Decreasing α AB further to α AB = 50 • , double bonding becomes significant which results in a further decrease in T c and ρ c as compared to the α AB = 60 • case.…”

Section: Resultsmentioning

confidence: 99%

“…There has also been an extensive number of theoretical and simulation studies on the thermodynamics, phase behavior, and self-assembly of patchy colloid fluids. [8][9][10][11][12][13][14][15][16][17][18][19][20][21] Patchy colloids are typically modeled using Wertheim's first order perturbation theory (TPT1) and a potential model for conical association sites introduced by Bol 22 and later Chapman 23 that became widely used in the patchy colloid community after Kern and Frenkel 24 introduced this potential as a primitive model for patchy colloids. a) Author to whom correspondence should be addressed.…”

Section: Introductionmentioning

confidence: 99%

Molecular theory for the phase equilibria and cluster distribution of associating fluids with small bond angles

Marshall

Chapman

2013

The Journal of Chemical Physics

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We develop a new theory for associating fluids with multiple association sites. The theory accounts for small bond angle effects such as steric hindrance, ring formation, and double bonding. The theory is validated against Monte Carlo simulations for the case of a fluid of patchy colloid particles with three patches and is found to be very accurate. Once validated, the theory is applied to study the phase diagram of a fluid composed of three patch colloids. It is found that bond angle has a significant effect on the phase diagram and the very existence of a liquid-vapor transition. © 2013 AIP Publishing LLC. [http://dx

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Closed-loop liquid-vapor equilibrium in a one-component system

Cited by 17 publications

References 34 publications

Self-Assembly in Chains, Rings, and Branches: A Single Component System with Two Critical Points

Self-Assembly in Chains, Rings, and Branches: A Single Component System with Two Critical Points

Three-dimensional patchy lattice model for empty fluids

Molecular theory for the phase equilibria and cluster distribution of associating fluids with small bond angles

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