We use Molecular Dynamics simulations to study how the nanopore and the fluid structures affects the dynamic, thermodynamic and structural properties of a confined anomalous fluid. The fluid is modeled using an effective pair potential derived from the ST4 atomistic model for water. This system exhibits density, structural and dynamical anomalies and the vapor-liquid and liquid-liquid critical points similar to the quantities observed in bulk water. The confinement is modeled both by smooth and structured walls. The temperatures of extremum density and diffusion for the confined fluid show a shift to lower values while the pressures move to higher amounts for both smooth and structured confinement. In the case of smooth walls, the critical points and the limit between fluid and amorphous phases show a non-monotonic change in the temperatures and pressures when the the nanopore size is increase. In the case of structured walls the pressures and temperatures of the critical points varies monotonicaly with the porous size. Our results are explained on basis of the competition between the different length scales of the fluid and the wall-fluid interaction.
We investigate the structural, thermodynamic and dynamic behavior of of a two dimensional core-corona system using Langevin Dynamics simulations. The particles are modeled using a core-softened potential that exhibits waterlike anomalies for the 3D case. For quasi-2D systems we have observed previously a new region of structural anomaly. Now, our results show that a new region of structural, density and diffusion anomalies arises for the 2D system. Our findings indicates that while the anomalous region at lower densities observed is due the competition between the two length scales in the pote…
Water-like Anomalies and Breakdown of the Rosenfeld Excess Entropy Scaling Relations for the Core-Softened Systems: Dependence on the Trajectory in Density-Temperature Plane
In a recent work [\textit{J. Mol. Liq}, 2020, \textbf{320}, 114420], using molecular dynamics simulations and a core-softened potential approach, we have shown that adding a simple solute as methanol can "kill" the density anomalous behavior as the LLCP is suppressed by the spontaneous crystallization in a hexagonal closed packing (HCP) crystal near the LLPT. Now, we extend this work in order to realize how longer-chain alcohols will affect the complex behavior of water-alcohol mixtures in the supercooled regime. Besides core-softened (CS) methanol, ethanol and 1-propanol were added to a syste…
Amorphous Radial Frustration and Water-Like Anomalies in a Ramp-Shoulder Fluid
Universidade Federal do Oeste da Bahia（巴伊亚联邦大学）；Universidade Federal do ABC（ABC联邦大学）；Universidade Federal de Pelotas（佩洛塔斯联邦大学）；Universität Konstanz（康斯坦茨大学）
Water is an unique material with a long list of thermodynamic, dynamic and structural anomalies, which are usually attributed to the competition between two characteristic length scales in the intermolecular interaction. It has been argued that a potential liquid-liquid phase transition (LLPT) ending at a liquid-liquid critical point (LLCP) lies at the core of the anomalous behavior of water. This transition which has been evidenced in multiple simulation studies seems to be preempted experimentally by spontaneous crystallization. Here, in order to expose the connection between the spontaneous…
2D competitive systems shows a large variety of solid and aggregate patterns, re-entrant fluid phase, a continuous melting as predicted by the KTHNY theory and, in some cases, waterlike anomalies. In this paper, we employ Langevin Dynamics simulations of a ramp-like core-softened fluid that have two characteristic length scales and all the features mentioned above. Analyzing the fluid phase of this system, Bordin and Barbosa [Phys. Rev. E 97, 022604 (2018)] reported the existence of two waterlike anomalous region. Now, we revisit this problem focusing in the low temperature regime and a larger…
Activity and Competing Length Scales in an Anomalous Core-Softened Fluid
Programa de Pós-Graduação em Física, Instituto de Física e Matemática, Universidade Federal de Pelotas（佩洛塔斯联邦大学物理与数学研究所）；Departamento de Física, Centro de Ciências Exatas e Naturais, Universidade Federal de Santa Maria（圣玛丽亚联邦大学自然科学与中心物理系）；Programa de Pós-Graduação em Modelagem Matemática, Instituto de Física e Matemática, Universidade Federal de Pelotas（佩洛塔斯联邦大学物理与数学研究所数学建模研究生项目）；Centro de Ciências, Tecnologias e Saúde, Campus Araranguá, Universidade Federal de Santa Catarina（圣卡塔琳娜联邦大学阿拉兰瓜校区科学技术与健康中心）；Fachbereich Physik, Universität Konstanz（康斯坦茨大学物理学系）；Departamento de Física, Instituto de Física e Matemática, Universidade Federal de Pelotas（佩洛塔斯联邦大学物理与数学研究所物理系）
In this work, a two dimensional system of polymer grafted nanoparticles is analyzed using large-scale Langevin Dymanics simulations. Effective core-softened potentials were obtained for two cases: one where the polymers are free to rotate around the nanoparticle core and a second where the polymers are fixed, with a $45^\circ$ angle between them. The use of effective core-softened potentials allow us to explore the complete system phase space. In this way, the $PT$, $Tρ$ and $Pρ$ phase diagrams for each potential were obtained, with all fluid and solid phases. The phase boundaries were defined…
We present a study using molecular dynamics simulations based on the Fermi-Jagla potential model, which is the continuous version of the mono-atomic core-softened Jagla model [J. Y. Abraham, S. V. Buldyrev, and N. Giovambattista, J. Phys. Chem. B, 115, 14229 (2011)]. This model shows the water-like liquid-liquid phase transition between high-density and low-density liquids at the liquid-liquid critical point. In particular, the slope of the coexistence line becomes weakly negative, which is expected to represent one of anomalies of liquid polyamorphism. In this study, we examined the density, …
We have established the detailed phase diagram of the prototypical deep eutectic solvent ethaline (ethylene glycol / choline chloride 2:1) as a function of the hydration level, in the bulk state and confined in the nanochannels of mesostructured porous silica matrices MCM-41 and SBA-15, with pore radii $R_P$ = 1.8 nm and 4.15 nm. For neat and moderately hydrated DESs, freezing was avoided and glassforming solutions were formed in all cases. For mass fraction of water above a threshold value $W_g'\approx30\%$, crystallization occurred and led to the formation of a maximally-freeze concentrated …
Nanoconfinement can drastically change the behavior of liquids, puzzling us with counterintuitive properties. Moreover, it is relevant in applications, including decontamination and crystallization control. It still lacks a systematic analysis for fluids with different bulk properties. Here we fill this gap. We compare, by molecular dynamics simulations, three different liquids in a graphene slit pore: (A) A simple fluid, such as argon, described by a Lennard-Jones potential; (B) An anomalous fluid, such as a liquid metal, modeled with an isotropic core-softened potential; (C) Water, the proto…
