Structural properties of the dipolar hard-sphere fluid at low temperatures and densities

Rovigatti, Lorenzo; Russo, John; Sciortino, Francesco

doi:10.1039/c2sm25192b

Cited by 85 publications

(107 citation statements)

References 56 publications

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“…Despite the model's apparent simplicity, the low T behavior of this system is still object of controversial interpretations. The early predictions [38,39] of a normal liquid vapor phase separation originated by an effective isotropic attractive potential, were challenged by numerical simulations [40,41] that showed that dipoles self assemble in chains, branched chains [39,42,43] and (at low T ) in rings [22,23,44], the same structures reproduced in the presently investigated patchy particle model. The similarity between the interactions and the self assembled structures formed in the DHS and those of the patchy model under study [19], can be hopefully used to establish a quantitative mapping between both models.…”

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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“…As T is further lowered, T < 0.2, the DHS fluid enters in the proper self-assembly region and it is made of persistent chain-like clusters which, depending on density, are more or less connected together by branching points. 19,20,26 For T < 0.2, the number of s = 1 defect clusters decreases with T and the curves have a non-monotonic behaviour. We ascribe the qualitative difference between defect cluster size distributions at temperatures higher and lower than T = 0.2 to the onset of the chaining process.…”

Section: A Identification Of the Defect Clusters And Their Spatial Cmentioning

confidence: 99%

“…In this work, we analyse equilibrium configurations generated via Monte Carlo simulations 18,26 of the DHS fluid in the NV T ensemble. Aggregation-volume-bias MC moves, 35 specifically adapted for the DHS model, had been implemented to facilitate breaking and reforming of the strong head-to-tail bonds.…”

Section: Methodsmentioning

confidence: 99%

“…Aggregation-volume-bias MC moves, 35 specifically adapted for the DHS model, had been implemented to facilitate breaking and reforming of the strong head-to-tail bonds. 26 Long range interactions were taken into account using Ewald sums with conducting boundary conditions. 36 We analyze simulations at T = 0.125, 0.140, 0.155, 0.170, 0.250, 0.50 and in the density range ρ ∈ [0, 0.14].…”

Section: Methodsmentioning

confidence: 99%

“…21 At low temperature T and density ρ, dipolar particles tend to form chain-like structures, 16,22 giving rise to a fluid made up of long, transient, and weakly interacting chains (structures in which all particles, except two, have two neighbours aligned in the nose-to-tail configurations) and rings (structures in which all particles are doubly bonded). 18,23,24 As the density increases, inter-cluster interactions start to rise and, eventually, chains and rings merge together to form branched clusters [25][26][27][28] via the emergence of junctions, i.e., of particles which have more than two neighbours. The analysis of equilibrium configurations confirms that, for any reasonable criterion for classifying two neighbour particles as bonded, a significant number of branching points exists, 15,18 providing a mechanism for connecting chains and rings in a percolating three-dimensional network.…”

Section: Introductionmentioning

confidence: 99%

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Branching points in the low-temperature dipolar hard sphere fluid

Rovigatti

Kantorovich

Иванов

et al. 2013

The Journal of Chemical Physics

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Branching points in the low-temperature dipolar hard sphere fluid In this contribution, we investigate the low-temperature, low-density behaviour of dipolar hardsphere (DHS) particles, i.e., hard spheres with dipoles embedded in their centre. We aim at describing the DHS fluid in terms of a network of chains and rings (the fundamental clusters) held together by branching points (defects) of different nature. We first introduce a systematic way of classifying inter-cluster connections according to their topology, and then employ this classification to analyse the geometric and thermodynamic properties of each class of defects, as extracted from state-of-the-art equilibrium Monte Carlo simulations. By computing the average density and energetic cost of each defect class, we find that the relevant contribution to inter-cluster interactions is indeed provided by (rare) three-way junctions and by four-way junctions arising from parallel or anti-parallel locally linear aggregates. All other (numerous) defects are either intra-cluster or associated to low cluster-cluster interaction energies, suggesting that these defects do not play a significant part in the thermodynamic description of the self-assembly processes of dipolar hard spheres.

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Structure, Dynamics, and Thermodynamics of Ferrofluids

Camp

2017

Springer Proceedings in Physics

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A survey of recent work on the structure, dynamics, and thermodynamics of ferrofluids is given. The emphasis is on new theoretical descriptions and computer simulations of simple models of colloidal ferromagnetic nanoparticles, but some favourable comparisons with experiments are shown to justify the choices of models. The survey summarises combined theoretical and computational studies of field-induced microstructure in ferrofluids, magnetisation curves, static and dynamic initial magnetic susceptibilities, thermodynamic properties, and sedimentation profiles.

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Structural properties of the dipolar hard-sphere fluid at low temperatures and densities

Cited by 85 publications

References 56 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

Branching points in the low-temperature dipolar hard sphere fluid

Structure, Dynamics, and Thermodynamics of Ferrofluids

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