1,721,040 research outputs found
Tuning the liquid-liquid transition by modulating the Hydrogen-bond angular flexibility in a model for water
Full text linkWe propose a simple extension of the well known ST2 model for water [F. H. Stillinger and A. Rahman, J. Chem. Phys. 60, 1545 (1974)] that allows for a continuous modification of the hydrogen-bond angular flexibility. We show that the bond flexibility affects the relative thermodynamic stability of the liquid and of the hexagonal (or cubic) ice. On increasing the flexibility, the liquid-liquid critical point, which in the original ST2 model is located in the no-man’s land (i.e., the region where ice is the thermodynamically stable phase) progressively moves to a temperature where the liquid is more stable than ice. Our study definitively proves that the liquid-liquid transition in the ST2 model is a genuine phenomenon, of high relevance in all tetrahedral network-forming liquids, including water
Dataset for "A simple and accurate method to determine fluid-crystal phase boundaries from direct coexistence simulations"
No full text<p>This is a dataset for the article "A simple and accurate method to determine fluid-crystal phase boundaries from direct coexistence simulations", available at https://arxiv.org/abs/2403.10891 (Full citation data will be added upon final publication of the article.)</p>
<p>This package provides figure data and representative configuration files associated with the systems studied in the article above. Additionally, for the hard sphere system, this package includes direct coexistence data for all reported system sizes and crystal orientations.</p>
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Liquids more stable than crystals in particles with limited valence and flexible bonds
No full textAll liquids (except helium owing to quantum effects) crystallize at low temperatures, forming ordered structures. The competition between disorder, which stabilizes the liquid phase, and energy, which leads to a preference for the crystalline structure, inevitably favours the crystal when the temperature is lowered and entropy becomes progressively less relevant. The liquid state survives at low temperatures only as a glass, an out-of-equilibrium arrested state of matter. This textbook description holds inevitably for atomic and molecular systems, where particle interactions are set by quantum-mechanical laws. The question remains whether it holds for colloidal particles, where interparticle interactions are usually short-ranged and tunable. Here we show that for patchy colloids with limited valence(1), conditions can be found for which the liquid phase is stable even in the zero-temperature limit. Our results offer fresh cues for understanding the stability of gels(2) and the glass-forming ability of molecular network glasses(3,4)
Patchy Particle Model for Vitrimers
No full textVitrimers-a recently invented new class of polymers-consist of covalent networks that can rearrange their topology via a bond shuffling mechanism, preserving the total number of network links. We introduce a patchy particle model whose dynamics directly mimic the bond exchange mechanism and reproduce the observed glass-forming ability. We calculate the free energy of this model in the limit of strong (chemical) bonds between the particles, both via the Wertheim thermodynamic perturbation theory and using computer simulations. The system exhibits an entropy-driven phase separation between a network phase and a dilute cluster gas, bringing new insight into the swelling behavior of vitrimers in solvents
Phase diagram of the ST2 model of water
No full textWe evaluate the free energy of the fluid and crystal phases for the ST2 potential with reaction field corrections for the long-range interactions. We estimate the phase coexistence boundaries in the temperature–pressure plane, as well as the gas–liquid critical point and gas–liquid coexistence conditions. Our study frames the location of the previously identified liquid–liquid critical point relative to the crystalline phase boundaries, and opens the way for exploring crystal nucleation in a model where the metastable liquid–liquid critical point is computationally accessible
Understanding tetrahedral liquids through patchy colloids
No full textWe investigate the structural properties of a simple model for tetrahedral patchy colloids in which the patch width and the patch range can be tuned independently. For wide bond angles, a fully bonded network can be generated by standard Monte Carlo or molecular dynamics simulations of the model, providing a good method for generating defect-free random tetrahedral networks. This offers the possibility of focusing on the role of the patch angular width on the structure of the fully bonded network. The analysis of the fully bonded configurations as a function of the bonding angle shows how the bonding angle controls the system compressibility, the strength of the pre-peak in the structure factor, and ring size distribution. Comparison with models of liquid water and silica allows us to find the best mapping between these continuous potentials and the colloidal one. Building on previous studies focused on the connection between angular range and crystallization, the mapping makes it possible to shed new light on the glass-forming ability of network-forming tetrahedral liquids. (C) 2013 AIP Publishing LLC
Gels of DNA nanostars never crystallize
No full textUsing state-of-the-art numerical techniques, we show that, upon lowering the temperature, tetravalent DNA nanostars form a thermodynamically stable, fully bonded equilibrium gel. In contrast to atomic and molecular network formers, in which the disordered liquid is always metastable with respect to some crystalline phase, we find that the DNA nanostar gel has a lower free energy than the diamond crystal structure in a wide range of concentrations. This unconventional behavior, here verified for the first time in a realistic model, arises from the large arm flexibility of the DNA nanostars, a property that can be tuned by design. Our results confirm the thermodynamic stability of the recently experimentally realized DNA hydrogels
Liquid-liquid phase transitions in tetrahedrally coordinated fluids via Wertheim theory
No full textNetwork interpenetration has been proposed as a mechanism for generating liquid−liquid phase transitions in one component systems. We introduce a model of four coordinated particles, which explicitly treats the system as a mixture of two interacting interpenetrating networks that can freely exchange particles. This model can be solved within Wertheim’s theory for associating fluids and shows liquid−liquid phase separations (in addition to the gas−liquid) for a wide range of model parameters. We find that originating a liquid−liquid transition requires a small degree of interpenetrability and a preference for intranetwork bonding. Physically, these requirements can be seen as controlling the softness of the particle−particle interaction and the bond flexibility, in full agreement with recent findings [Smallenburg, F.; Filion, L.; Sciortino, F. Nat. Phys. 2014, 10, 653]
Phase Diagram of One-Patch Colloids Forming Tubes and Lamellae
No full textWe numerically calculate the equilibrium phase diagram of one-patch particles with 30% patch coverage. It has been previously shown that in the fluid phase these particles organize into extremely long tubelike aggregates (G. Munao et al. Soft Matter 2013, 9, 2652). Here, we demonstrate by means of free-energy calculations that such a disordered tube phase, despite forming spontaneously from the fluid phase below a density-dependent temperature, is always metastable against a lamellar crystal. We also show that a crystal of infinitely long packed tubes is thermodynamically stable, but only at high pressure. The full phase diagram of the model, beside the fluid phase, displays four different stable crystals. A gas-liquid critical point, and hence a liquid phase, is not detected
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