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Jun 30, 2018
06/18

by
Santi Prestipino; Gianmarco Munaò; Dino Costa; Carlo Caccamo

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We investigate the structure of a dilute mixture of amphiphilic dimers and spherical particles, a model relevant to the problem of encapsulating globular "guest" molecules in a dispersion. Dimers and spheres are taken to be hard particles, with an additional attraction between spheres and the smaller monomers in a dimer. Using Monte Carlo simulation, we document the low-temperature formation of aggregates of guests (clusters) held together by dimers, whose typical size and shape...

Topics: Condensed Matter, Soft Condensed Matter

Source: http://arxiv.org/abs/1702.07318

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Jun 30, 2018
06/18

by
Santi Prestipino; Alessandro Laio; Erio Tosatti

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In standard nucleation theory, the nucleation process is characterized by computing $\Delta\Omega(V)$, the reversible work required to form a cluster of volume $V$ of the stable phase inside the metastable mother phase. However, other quantities besides the volume could play a role in the free energy of cluster formation, and this will in turn affect the nucleation barrier and the shape of the nucleus. Here we exploit our recently introduced mesoscopic theory of nucleation to compute the free...

Topics: Mesoscale and Nanoscale Physics, Statistical Mechanics, Condensed Matter

Source: http://arxiv.org/abs/1402.3934

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Jun 28, 2018
06/18

by
Gianpietro Malescio; Santi Prestipino

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The phase behavior of stabilized dispersions of macromolecules is most easily described in terms of the effective interaction between the centers of mass of solute particles. For molecules like polymer chains, dendrimers, etc., the effective pair potential is {\em finite} at the origin, allowing "particles" to freely interpenetrate each other. Using a double-Gaussian model (DGM) for demonstration, we studied the behavior of the system as a function of the attraction strength $\eta$....

Topics: Soft Condensed Matter, Condensed Matter

Source: http://arxiv.org/abs/1511.04924

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Sep 18, 2013
09/13

by
Franz Saija; Santi Prestipino; Paolo V. Giaquinta

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We test the validity of some widely used phenomenological criteria for the localization of the fluid-solid transition thresholds against the phase diagrams of particles interacting through the exp-6, inverse-power-law, and Gaussian potentials. We find that one-phase rules give, on the whole, reliable estimates of freezing/melting points. The agreement is ordinarily better for a face-centered-cubic solid than for a body-centered-cubic crystal, even more so in the presence of a pressure-driven...

Source: http://arxiv.org/abs/cond-mat/0605492v1

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Sep 18, 2013
09/13

by
Santi Prestipino; Franz Saija; Paolo V. Giaquinta

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We study a two-dimensional fluid of particles interacting through a spherically-symmetric and marginally soft two-body repulsion. This model can exist in three different crystal phases, one of them with square symmetry and the other two triangular. We show that, while the triangular solids first melt into a hexatic fluid, the square solid is directly transformed on heating into an isotropic fluid through a first-order transition, with no intermediate tetratic phase. In the low-pressure...

Source: http://arxiv.org/abs/1209.2608v1

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4.0

Jun 30, 2018
06/18

by
Santi Prestipino; Franz Saija

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Two-dimensional crystals of classical particles are very peculiar in that melting may occur in two steps, in a continuous fashion, via an intermediate hexatic fluid phase exhibiting quasi-long-range orientational order. On the other hand, three-dimensional spheres repelling each other through a fast-decaying bounded potential of generalized-exponential shape (GEM4 potential) can undergo freezing into cluster crystals, allowing for more that one particle per lattice site. We hereby study the...

Topics: Soft Condensed Matter, Condensed Matter

Source: http://arxiv.org/abs/1411.4403

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Sep 23, 2013
09/13

by
Cristina Speranza; Santi Prestipino; Paolo V. Giaquinta

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We investigated the equilibrium properties of a one-dimensional system of classical particles which interact in pairs through a bounded repulsive potential with a Gaussian shape. Notwithstanding the absence of a proper fluid-solid phase transition, we found that the system exhibits a complex behaviour, with "anomalies" in the density and in the thermodynamic response functions which closely recall those observed in bulk and confined liquid water. We also discuss the emergence in the...

Source: http://arxiv.org/abs/1110.6730v2

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Sep 18, 2013
09/13

by
Franz Saija; Santi Prestipino

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We investigated numerically the high-temperature/high-pressure phase diagram of Xenon as modelled through the exp-6 interaction potential, which is thought to provide a reliable description of the thermal behaviour of rare gases under extreme conditions. We performed a series of extensive NVT Monte Carlo simulations which, in conjunction with exact computation of the solid free energy by the Frenkel-Ladd method, allowed us to precisely locate the freezing and the melting thresholds at each...

Source: http://arxiv.org/abs/cond-mat/0504468v3

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Sep 21, 2013
09/13

by
Santi Prestipino; Franz Saija; Gianpietro Malescio

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Effective pair interactions with a soft-repulsive component are a well-known feature of polymer solutions and colloidal suspensions, but they also provide a key to interpret the high-pressure behaviour of simple elements. We have computed the zero-temperature phase diagram of four different model potentials with various degrees of core softness. Among the reviewed crystal structures, there are also a number of non-Bravais lattices, chosen among those observed in real systems. Some of these...

Source: http://arxiv.org/abs/0905.1224v1

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Jul 20, 2013
07/13

by
Santi Prestipino

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An ongoing problem in the study of a classical many-body system is the characterization of its equilibrium behaviour by theory or numerical simulation. For purely repulsive particles, locating the melting line in the pressure-temperature plane can be especially hard if the interparticle potential has a softened core or contains some adjustable parameters. A method is hereby presented that yields reliable melting-curve topologies with negligible computational effort. It is obtained by combining...

Source: http://arxiv.org/abs/1203.0134v1

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Sep 19, 2013
09/13

by
Santi Prestipino; Franz Saija; Gianpietro Malescio

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We present evidence that the concurrent existence of two populations of particles with different effective diameters is not a prerequisite for the occurrence of anomalous phase behaviors in systems of particles interacting through spherically-symmetric unbounded potentials. Our results show that an extremely weak softening of the interparticle repulsion, yielding a single nearest-neighbor separation, is able to originate a wide spectrum of unconventional features including reentrant melting,...

Source: http://arxiv.org/abs/1009.4331v1

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Sep 18, 2013
09/13

by
Santi Prestipino; Franz Saija

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We study a simple model of a nematic liquid crystal made of parallel ellipsoidal particles interacting via a repulsive Gaussian law. After identifying the relevant solid phases of the system through a careful zero-temperature scrutiny of as many as eleven candidate crystal structures, we determine the melting temperature for various pressure values, also with the help of exact free energy calculations. Among the prominent features of this model are pressure-driven reentrant melting and the...

Source: http://arxiv.org/abs/0704.0056v1

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Sep 19, 2013
09/13

by
Franz Saija; Santi Prestipino; Gianpietro Malescio

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We study the phase behavior of a classical system of particles interacting through a strictly convex soft-repulsive potential which, at variance with the pairwise softened repulsions considered so far in the literature, lacks a region of downward or zero curvature. Nonetheless, such interaction is characterized by two length scales, owing to the presence of a range of interparticle distances where the repulsive force increases, for decreasing distance, much more slowly than in the adjacent...

Source: http://arxiv.org/abs/0909.0468v1

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Sep 22, 2013
09/13

by
Santi Prestipino; Alessandro Laio; Erio Tosatti

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We focus on the Gibbs free energy $\Delta G$ for nucleating a droplet of the stable phase (e.g. solid) inside the metastable parent phase (e.g. liquid), close to the first-order transition temperature. This quantity is central to the theory of homogeneous nucleation, since it superintends the nucleation rate. We recently introduced a field theory describing the dependence of $\Delta G$ on the droplet volume $V$, taking into account besides the microscopic fuzziness of the droplet-parent...

Source: http://arxiv.org/abs/1302.3712v1

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Jul 20, 2013
07/13

by
Santi Prestipino

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I employ the van der Waals theory of Baus and coworkers to analyze the fast, adiabatic decay of a supercooled liquid in a closed vessel with which the solidification process usually starts. By imposing a further constraint on either the system volume or pressure, I use the maximum-entropy method to quantify the fraction of liquid that is transformed into solid as a function of undercooling and of the amount of a foreign gas that could possibly be also present in the test tube. Upon looking at...

Source: http://arxiv.org/abs/1304.7593v1