High-density Water Research Articles

Interannual deep-water renewal in the tropical fjord of Kao Bay of Halmahera Island, eastern Indonesia, linked to ocean dynamics in western equatorial Pacific

Ocean dynamics in western equatorial Pacific (WEP) controls interannual deep-water renewal in the tropical fjord of Kao Bay, Halmahera Island of Indonesia. Processes such as boreal winter coastal upwelling at north New Guinea, New Guinea Coastal Undercurrent (NGCUC) and Halmahera Eddy (HE) were hypothesized to supply high density water at the vicinity of Kao Bay fjord to subsequently replenish the bottom of the fjord. To test the hypothesis, a large temporal dataset of temperature and salinity from HYCOM reanalysis model (1/12o) complemented by observations from TRITON T13 and T16 moorings and World Ocean Database (WOD) was employed within the NGCUC pathway from north New Guinea (T13) to Halmahera Island at T16 and offshore Kao Bay. Oceanic Niño Index (ONI) was used to unveil the connection between the coastal upwelling and ENSO. Additionally, tidal suction model was used to investigate when high density water from WEP can overflow the sill of Kao Bay. HYCOM simulation outputs were reasonably validated by the observations (RMSE: 0.37-1.67oC; 0.02-0.28 psu). The signal of the interannual variation of boreal winter coastal upwelling linked to ENSO variability (r=0.92) at the north New Guinea (at T13) was evident at offshore Kao Bay and T16, indicated by the concurrent of the shoaling of the 25oC isotherm between these locations. Pacific water mass reaching offshore Kao Bay and T16 resulting from the ocean teleconnection of the coastal upwelling was characterized as a mixture of North Pacific Tropical Water (NPTW) and South Pacific Tropical Water (SPTW). The upper layers of offshore Kao Bay and T16 showed similarity regarding a comparable mixture between NPTW and SPTW. The deep layers of these locations indicate the SPTW predominance (70-100% for offshore Kao Bay; 60% for T16).The comparable NPTW-SPTW mixture water at the upper layers of offshore Kao Bay fjord was identified to eligibly replenish the bottom of the fjord due to its temperature and salinity characteristics and its location within the range of local vertical tidal excursion based on tidal suction model – these two aspects of the intruding water were only achieved during boreal winter of normal and El Niño years. Due to this interannual nature, the deep layers of Kao Bay fjord can only be completely flushed via the cumulative effects of series of deep-water renewal intrusions spanning some El Niño years. This study has added an essential insight into the existing knowledge of deep-water renewal in Kao Bay fjord by demonstrating the more likely occurrence of interannual renewal than annual renewal, proposed by the early study of Van Aken and Verbeek (1988).

Study of Protein Hydration Water with the V4S Structural Index: Focus on Binding Site Description.

V4S, a new structural indicator for water specially designed to be suitable for hydration and nanoconfined contexts, has been recently introduced and preliminarily applied for water in contact with self-assembled monolayers and graphene-like systems. This index enabled an accurate detection of defective high local density water molecules (called HDA-like given their structural resemblance with the high-density amorphous ice, HDA). In the present work, we shall apply this new metric to characterize protein hydration water with particular interest in protein binding sites. As a first result, we shall find that protein hydration water has a higher concentration of HDA-like molecular arrangements compared to the bulk. Significantly, we shall show that the concentration of HDA-like molecules sharply decreases beyond the first hydration layer. Finally, we shall also reveal a highly nonuniform spatial distribution of the V4S values for the first hydration shell on the protein surface, where the higher hydrophobicity inherent to the ligand binding site will be evident from an enrichment in HDA-like molecules as compared to the population exhibited by the global protein surface.

Bottom water hypoxia enhanced by vertical migration of the raphidophyte Chattonella sp. in the Ariake Sea, Japan

In general, the formation of hypoxic water masses in coastal waters is caused by the restriction of vertical oxygen transport due to enhanced stratification, and the increase in oxygen consumption due to the decomposition of organic matter supplied from phytoplankton blooms. However, the direct relationship between phytoplankton blooms and hypoxia has been rarely reported. In this study, we clarified the relationship between the development of a hypoxic water mass (< 3 mg L−1) and a bloom of the raphidophyte Chattonella sp. in the Ariake Sea, Japan through field surveys and experiments to measure the water oxygen demand. The process of development of and recovery from the hypoxic water mass in a spring-neap tidal cycle was observed. From the spring to the neap tide, high-salinity, high-density water from offshore intruded into the bottom layer of the inner part of the bay, strengthening the stratification and developing a hypoxic water mass. In this period, the bacterial oxygen demand was dominant during the day in the bottom layer. At night, oxygen consumption increased due to the respiration of Chattonella that had accumulated in the bottom layer, reaching five times the amount during the day. In the following spring tides, the stratification weakened and the hypoxic water mass disappeared. However, water oxygen demand was the highest, suggesting the influence of the decay of Chattonella that caused the bloom. These results indicate that the increase in oxygen consumption at night due to the diurnal vertical migration of Chattonella greatly influenced the development of the hypoxic water mass.

Cooperative and Local Molecular Motion of High-Density Water in Glycerol Aqueous Solutions.

The glass-to-liquid transition of water, particularly in high-density water (HDW), has long been a controversial topic due to challenges posed by inevitable crystallization. In this study, we addressed this issue by creating homogeneous high-density glass from a dilute glycerol aqueous solution under high pressure. Using dielectric spectroscopy, we explored the glass transition of HDW in glycerol solutions across the full concentration range under high pressures. HDW was found to exhibit two distinct relaxation modes: one linked to cooperative motion and the other to noncooperative local motion. The fragility index classification of HDW, derived from the cooperative motion of water, suggests that HDW behaves as a "fragile" liquid, contradicting previous suggestions. Extrapolation to pure HDW indicates that the dielectric relaxation observed in pure HDW originates from noncooperative local water motion.

Mexico city’s decline in per capita domestic water use: a comprehensive spatial-temporal study

ABSTRACT Facing the growing challenges in water supply in urban areas, characterized by high demand and water scarcity, Mexico City, with its high population density and limited water resources, exemplifies the challenges in ensuring equitable management and water supply in complex urban environments. This study combines GIS tools, statistical analysis and spatial regression to analyze the spatiotemporal changes in per capita water consumption in Mexico City households between 2010 and 2019. The results show a 40% decrease in average consumption and a spatial reconfiguration that reflects an increase in inequalities in access to drinking water. The influence of five key factors in the reconfiguration is identified: intermittent supply, economic income, water feasibility, households without piped water, and an increase in dwellings. The findings are essential for developing equitable and effective water policies, emphasizing the need to address inequalities in water access in urban planning to achieve the Sustainable Development Goals.

Analyzing urban water metabolism of Adama city using water mass balance method for advancing water sensitive interventions

Urban water metabolism focuses on measuring water inflows and outflows within a defined urban system. As an emerging concept, it provides valuable understandings into water flow dynamics, supporting evidence-based decision-making. One approach to quantify these flows is the urban water mass balance method, which accounts for both human-induced and natural water resources. By equating these flows, it identifies whether water movement within the system is linear or circular. The primary goal of water mass balance analysis is to assess how closely a city aligns with water-sensitive management approaches. However, urban metabolism studies are rare in developing countries, where cities often lack the experience to estimate water inflows and outflows for informed water-sensitive interventions. This study addresses this gap by analyzing Adama city in Ethiopia using the water mass balance method to measure its water metabolism. The result revealed that the city faces a negative water balance with outflows exceeding inflows by 46.89 million cubic meters annually. The results indicated that Adama’s water flow follows a linear “take-make-use-dispose” model. The imbalance in Adama’s water cycle is driven by urbanization, impervious surfaces, and climate change, which increase runoff and evaporation. The study found that 61.3% of the city’s water comes from a centralized system, with 90% sourced from distant rivers through a telecoupling system. In the city, inadequate water harvesting, high population density and intensive water use are worsening water scarcity. Urban water metabolism indicators reveal significant losses and indicating the need for water conservation efforts. Despite the reliance on centralized systems, the study identifies strong potential for decentralized solutions and alternative water harvesting. To tackle these challenges, the research recommends adopting water-sensitive strategies such as low-impact development, sustainable urban drainage systems, and water-sensitive urban design and planning. These approaches can reduce the negative effects of urbanization, mitigate urban water scarcity risks and improve water management through water sensitive management approach. The study also emphasizes the need for collaborative learning, community involvement, and innovative technologies, supported by legal frameworks to ensure effective water wise interventions. Shifting toward circular water management and decentralized water systems will boost Adama’s resilience and promote sustainable water resource management, making the city more internally self-sufficient.

Molecular Probing Coupled with Density Functional Theory Calculation to Reveal the Influence of Fe Doping on Fe-NiOOH Electrode for High Current Density of Water Splitting.

Fe-doped NiOOH electrocatalysts have attracted wide interest for the exceptional oxygen evolution reaction (OER) performance, but the precise role of Fe doping on the improved intrinsic activity remains unclear. Herein, the molecular probe technique combined with density functional theory calculation is used to reveal the influence of the Fe atom on the rate-determining step of the OER reaction, where the pre-catalyst of hierarchical self-supporting NiFe layered double hydroxide [LDH] nanosheets equipped on nickel foam (NiFe LDH/NF) is generated via a facile and industrially well-matched one-pot corrosion method. The physical characterization results reveal the reconstruction of NiFe LDH into Fe-doped NiOOH for promoted OER, which has a lower OH* adsorption energy with fast subsequent steps that help in obtaining an improved charge injection efficiency compared to NiOOH. In addition, more exposed electroactive species and facile delivery of mass/electron inside the catalytic procedure actually have a high-quality contribution to the outstanding catalytic activity. Therefore, the NiFe LDH36/NF electrocatalyst provides high catalytic activities of 241 and 320mV at 10mA cm-2 toward the OER and overall water-splitting in 1m KOH. This work provides a promising avenue for the rational design of durable self-supporting electrodes toward large-scale water splitting.

Electrochemical Migration Study on Sn-58Bi Lead-Free Solder Alloy Under Dust Contamination.

With the development of electronic packaging technology toward miniaturization, integration, and high reliability, the diameter and pitch of solder joints continue to shrink. Adjacent solder joints are highly susceptible to electrochemical migration (ECM) due to the synergistic effects of high-density electric fields, water vapor, and contaminants. Dust has become one of the non-negligible causal factors in ECM studies due to air pollution. In this study, 0.2 mM/L NaCl and Na2SO4 solutions were used to simulate soluble salt in dust, and the failure mechanism of an Sn-58Bi solder ECM in the soluble salt in dust was analyzed by a water-droplet experimental method. It was shown that the mean failure time of the ECM of an Sn-58Bi solder in an NaCl solution (53 s) was longer than that in an Na2SO4 solution (32 s) due to the difference in the anodic dissolution characteristics in the two soluble salt solutions. XPS analysis revealed that the dendrites produced by the ECM process were mainly composed of Sn, SnO, and SnO2, and there were precipitation products-Sn(OH)2 and Na2SO4-attached to the dendrites. The corrosion potential in the NaCl solution (-0.351 V) was higher than that in the Na2SO4 solution (-0.360 V), as shown by a polarization test, indicating that the Sn-58Bi solder had better corrosion resistance in the NaCl solution. Therefore, an Sn-58Bi solder has better resistance to electrochemical migration in an NaCl solution compared to an Na2SO4 solution.

The influence of the Biobio Canyon on the circulation and coastal upwelling/downwelling off central Chile

The influence of Biobio Canyon on the circulation and coastal upwelling and downwelling was evaluated by using high-resolution hydrodynamic simulations of the coastal ocean off central Chile, a highly productive zone of the Southern Humboldt Current System that supports important coastal ecosystem services. The model bathymetry was GEBCO 2020 with a spatial resolution of 500 m, which allows a relatively fine representation of the complex topography of the region. To understand the role of the Biobio Canyon, contrasting experiments were run. A Reference Simulation (RS) considering the canyon bathymetry and the Biobio River discharge, a Simulation Experiment 1 (SE1) considering only the canyon bathymetry without the Biobio River discharge, and a Simulation Experiment 2 (SE2) only with the Biobio River discharge (without the canyon). During upwelling conditions, the characteristic asymmetry in the along-canyon circulation was observed, with onshore flow over the northern side of the canyon and most of the upper water column, and offshore flow over the upstream canyon wall. In contrast, the cross-shore flow was limited to a narrow band over the northern wall of the canyon in RS and SE1 during downwelling conditions. Not many differences were detected between the RS and SE1 during both upwelling and downwelling conditions, which suggest that the canyon imposes a major effect on the circulation in comparison to the river discharge. Our results exhibit a net onshore transport onto the continental shelf during coastal upwelling and, net offshore transport restricted to the area south of the canyon during downwelling conditions. Finally, the advection of high-density waters on the northern shelf dominates during upwelling conditions in RS and SE1. Similarly, presence of the canyon promotes higher bottom density over the shelf even during downwelling conditions, as compared to the no-canyon experiment.

Hydrogen Bond Network Shaping Proton Penetration Behavior across Two-Dimensional Nanoporous Materials.

In this study, we investigate aqueous proton penetration behavior across four types of two-dimensional (2D) nanoporous materials with similar pore sizes using extensive ReaxFF molecular dynamics simulations. The results reveal significant differences in proton penetration energy barriers among the four kinds of 2D materials, despite their comparable pore sizes. Our analysis indicates that these variations in energy barriers stem from differences in the hydrogen bond (HB) network formed between the 2D nanoporous materials and the aqueous environment. The HB network can be classified into two categories: those formed between the surface of the 2D nanoporous materials and the aqueous environment, and those formed between the edge atoms of the nanopores and the water molecules inside the pores. A strong HB network formed between the surface of the 2D nanoporous materials and the aqueous environment induces an orientational preference of water molecules, resulting in an aggregated water layer with high density. This high-density water region traps protons, making it difficult for them to escape and penetrate the nanopores. On the other hand, a strong HB network formed between the edge atoms of the nanopores and the water molecules inside the pores impedes the rotation and migration of water molecules, further inhibiting proton penetration behavior. To facilitate the proton penetration process, in addition to a sufficiently large pore size, a weak HB network between the 2D nanoporous material and the aqueous environment is necessary.

Ecological Network Construction in High-Density Water Network Areas Based on a Three-Dimensional Perspective: The Case of Foshan City

The acceleration of urbanization has resulted in varying degrees of impact on the stability and health of high-density urban ecosystems. Building urban ecological networks is crucial for safeguarding biodiversity and sustaining ecosystem vitality. In this study, the city of Foshan was selected as the study area, which is a prime representative of a high-density water network city. Additionally, a morphological spatial pattern analysis was employed to identify the ecological source. We built an ecological resistance surface using geographic, natural, and behavioral elements, adjusting it based on the density of the water network and the building height. Following this, the circuit theoretical model was utilized to create an ecological network by identifying ecological corridors. There were three key findings. First, the ecological network consisted of 30 ecological source sites and 53 ecological corridors, and 103 ecological “pinch points” and 193 ecological barrier points were identified. Second, the ecological sources were predominantly situated in the southwestern and northern parts of Foshan City. Meanwhile, the suburbs of Foshan City contained the primary ecological barrier points, mainly stemming from new construction sites, while the key ecological “pinch points” were concentrated at river junctions. The third outcome was the recommendations to (a) boost the connectivity of the ecological network in the suburbs, (b) improve the connection of the water network in urban areas, and (c) focus on enhancing landscape connectivity. The objective was to develop approaches for optimizing urban ecological networks, leading to better connectivity and improved ecological network quality.

Solution-state self-assembly of novel poly(carbamoyl methacrylate)s synthesized via combining Passerini three-component reactions and free radical polymerizations

Coupling multicomponent reactions (MCRs) with other polymerizations has excellent advantages in inducing multifunctionality and syntheses of complex macromolecular structures. Herein, a straightforward combination method using aqueous Passerini three-component reaction (P3CR(aq)) and conventional free radical polymerization (FRP) (termed as P3CR(aq)-Є-FRP) was applied using mild conditions. Firstly, an environmental-friendly and efficient aqueous P3CR was applied to synthesize various carbamoyl methacrylate (CMA) monomers from methacrylic acid, cyclohexyl isocyanide, and four different aldehydes with high yield (ca. 90 %) and purity. This is plausibly prompted by the key factors of high cohesive energy density of water and facile isolation by the poor solubility of CMAs in aqueous. Then, poly(carbamoyl methacrylate)s (PCMAs) were obtained via FRP with 2,2′-azobis(isobutyronitrile) (AIBN) in dimethylformamide (DMF). Characterizations of both synthesized noble monomers, polymers, solubilities in different solvents, and thermal properties, as well as the solution-state self-assembly behaviors of the polymers by dynamic light scattering (DLS), scanning electron microscope (SEM), and small-angle X-ray scattering (SAXS), including micellized particle sizes, critical micelle concentrations (CMCs), and micelle morphology, were investigated. PCMAs can self-assemble into stable globular micellar nanoparticles (ca. 170–310 nm) with low CMC values (1.6 × 10−5–4.0 × 10−9 mg/mL).

Modulation of the multiphase phosphorus/sulfide heterogeneous interface via rare earth for solar‐enhanced water splitting at industrial‐level current densities

AbstractPhotoelectrically coupling water splitting at high current density is a promising approach for the acquisition of green hydrogen energy. However, it places significant demands on the photo/electrocatalysts. Herein, rare earth elements doping NiMoO4‐based phosphorus/sulfide heterostructure nanorod arrays (RE‐NiMo‐PS@NF [RE = Y, Er, La, and Sc]) are obtained for solar‐enhanced electrocatalytic water splitting at high current densities. The results of the experiment and density‐functional theory studies illustrate that the Y element as a dopant not only makes the NiMoP2/NiMo3S4/NiMoO4 heterostructure exhibit excellent solar‐enhanced electrocatalytic activity (hydrogen evolution reaction [HER]: η1000 = 211 mV, oxygen evolution reaction [OER]: η1000 = 367 mV) but also optimizes the heterostructure interfacial electron density distributions and HER free energy. In addition, Y‐NiMo‐PS@NF achieves 18.64% solar‐to‐hydrogen efficiency. This study not only provides a new way to synthesize heterostructure electrocatalysts but also inspires the application of solar enhancement strategies for high current density water splitting.

Design Strategies of Hydrogen Evolution Reaction Nano Electrocatalysts for High Current Density Water Splitting.

Hydrogen is now recognized as the primary alternative to fossil fuels due to its renewable, safe, high-energy density and environmentally friendly properties. Efficient hydrogen production through water splitting has laid the foundation for sustainable energy technologies. However, when hydrogen production is scaled up to industrial levels, operating at high current densities introduces unique challenges. It is necessary to design advanced electrocatalysts for hydrogen evolution reactions (HERs) under high current densities. This review will briefly introduce the challenges posed by high current densities on electrocatalysts, including catalytic activity, mass diffusion, and catalyst stability. In an attempt to address these issues, various electrocatalyst design strategies are summarized in detail. In the end, our insights into future challenges for efficient large-scale industrial hydrogen production from water splitting are presented. This review is expected to guide the rational design of efficient high-current density water electrolysis electrocatalysts and promote the research progress of sustainable energy.

Unexpected Self-Assembly of Nanographene Oxide Membranes upon Electron Beam Irradiation for Ultrafast Ion Sieving.

Nanographene oxide (nGO) flakes-graphene oxide with a lateral size of ≈100nm or less-hold great promise for superior flux and energy-efficient nanofiltration membranes for desalination and precise ionic sieving owing to their unique high-density water channels with less tortuousness. However, their potential usage is currently limited by several challenges, including the tricky self-assembly of nano-sized flakes on substrates with micron-sized pores, severe swelling in aqueous solutions, and mechanical instability. Herein, the successful fabrication of a robust membrane stacked with nGO flakes on a substrate with a pore size of 0.22µm by vacuum filtration is reported. This membrane achieved an unprecedented water permeance above 819.1 LMH bar-1, with a high rejection rate of 99.7% for multivalent metal ions. The nGO flakes prepared using an electron beam irradiation method, have uniquely pure hydroxyl groups and abundant aromatic regions. The calculations revealed the strong hydrogen bonds between two nGO flakes, which arise from hydroxyl groups, coupled with hydrophobic aromatic regions, greatly enhance the stability of stacked flakes in aqueous solutions and increase their effective lateral size. The research presents a simple yet effective approach toward the fabrication of advanced 2D nanographene membranes with superior performance for ion sieving applications.

Exploring ice Ic nucleation and structural relaxation in supercooled water

Despite intensive research efforts, understanding how water freezes remains an open and relevant question with profound implications. In this study, we examine ice Ic nucleation and water relaxation at the atomic level, employing molecular dynamics (MD) simulations and Classical Nucleation Theory (CNT). Our key findings address the following foundational issues: (i) Routes to cubic ice. Ice Ic seeding liquid water results in equal amounts of ice Ic and Ih structures at T<235K, while ice Ic predominates at T⩾235K along zero isobar. Moreover, ice produced from spontaneous nucleation at T=205-215K is more cubic compared with that grown on ice Ic seeds; (ii) CNT validity. Using MD-generated data, CNT accurately predicts ice nucleation rates without any fitting parameter, thereby bridging the gap between simulations and experiments; (iii) Kinetic crossroads. We determined a kinetic spinodal for high-density water as an intersection of relaxation and nucleation time curves at TKS=199K for a MD sample and TKS=233K for a macroscopic sample, which coincides with the experimental homogenous freezing limit; (iv) Kauzmann conundrum. Finally, we indicated that if the Kauzmann temperature exists, estimated as TK=190K, it might be inaccessible for high-density water due to the kinetic spinodal at a higher temperature, TKS>TK, thus resolving the long-standing entropy paradox. Overall, this research provides valuable insights into fundamental aspects related to water crystallization.

Intelligent Devices Harnessing Underwater Superoleophobic and Underoil Superhydrophobic Quartz Sands for the Separation of Diverse Stratified and Emulsified Water-Oil Mixtures.

To achieve the green, sustainable, and controllable recovery of oil-water resources and to address the limited functionality of single superwet materials in oil-water separation, this study reports a multifunctional oil-water separation strategy by compositing the underwater superoleophobic and underoil superhydrophobic materials (HS). The underwater superoleophobic quartz sands with an oil contact angle of 152.68° were prepared by adjusting the particle size. This material demonstrated a water flux of 4688 L m-2 h-1 and a low-density oil and water mixture separation efficiency of 98.6%, which remained above 97.9% over 50 cycles. It was effective in separating oil-in-water emulsions with a separation efficiency of >99%. For HS, quartz sands were modified with dodecyltrimethoxysilane. The optimized HS-4 exhibited superhydrophobic properties with a water contact angle of 157.06°. It achieved an oil flux of 5775 L m-2 h-1 and a water and dichloromethane mixture separation efficiency of 98.4%. Additionally, they exhibited significant potential in the separation of water-in-oil emulsions. Furthermore, by placing the underwater superoleophobic and underoil superhydrophobic units at the bottom of the filter, we achieved cyclic separation of high-density oil and water mixtures, low-density oil and water mixtures, water-in-oil emulsions, and oil-in-water emulsions. The separation efficiency consistently exceeded 96.5% over 10 cycles. In addition, the oil-water separation mechanism of underwater oleophobic and underoil hydrophobic materials was demonstrated by the relative concentration distribution of water and oil with molecular dynamics simulations. This intelligent oil-water separation method marks a significant advancement in the sustainable separation of diverse oil-water mixtures.

The MD study of water short-range order during liquid-liquid transition: Toward the second critical point

Full-scale thermodynamic experimental investigations of the liquid-liquid transition and different water phases remain challenging due to spontaneous crystallization and the complexity of studies on the nanosecond time scale. Moreover, the specific position of the second critical point in water is still unclear. This study used molecular dynamics to reproduce the structural properties of both low- and high-density waters and to characterize changes in the order parameters, average number of hydrogen bonds, and ordering of neighboring molecules during liquid-liquid transitions and in regimes of supercooled waters. A rapid change in calculated parameters under increased pressure could be attributed to a first-order phase transition. In addition, we provided evidence that low-density water becomes dissolved in high-density water inclusions as the temperature or pressure increases. The presumed location of the second critical point has been identified as TC ≈ 220 K, PC ≈ 1.5 kbar, and ρC ≈ 1.02 g/cm3.

Prediction of water anomalous properties by introducing the two-state theory in SAFT.

Water is one of the most abundant substances on earth, but it is still not entirely understood. It shows unusual behavior, and its properties present characteristic extrema unlike any other fluid. This unusual behavior has been linked to the two-state theory of water, which proposes that water forms different clusters, one with a high density and one with a low density, which may even form two distinct phases at low temperatures. Models incorporating the two-state theory manage to capture the unusual extrema of water, unlike traditional equations of state, which fail. In this work, we have derived the framework to incorporate the two-state theory of water into the Statistical-Associating-Fluid-Theory (SAFT). More specifically, we have assumed that water is an ideal solution of high density water molecules and low density water molecules that are in chemical equilibrium. Using this assumption, we have generalized the association term SAFT to allow for the simultaneous existence of the two water types, which have the same physical parameters but different association properties. We have incorporated the newly derived association term in the context of the Perturbed Chain-SAFT (PC-SAFT). The new model is referred to as PC-SAFT-Two-State (PC-SAFT-TS). Using PC-SAFT-TS, we have succeeded in predicting the characteristic extrema of water, such as its density and speed of sound maximum, etc., without loss of accuracy compared to the original PC-SAFT. This new framework is readily extended to mixtures, and PC-SAFT-TS manages to capture the solubility minimum of hydrocarbons in water in a straightforward manner.

A close look at the hydration layer and at the premelting layer of K-feldspar

In this work, we perform molecular dynamics simulations to investigate the structural properties of water at the interface with K-feldspar. We aim at understanding the modifications induced on water structure by the presence of this mineral. We analysed both the hydration layer of K-feldspar in supercooled water and the premelting layer at the interface between K-feldspar and hexagonal ice. We studied the density profile, the orientational tetrahedral order parameter, the distribution of the cos ⁡ ( γ ) function, the hydrogen bond distribution, the number of water molecules belonging to different phases close to the surface of the feldspar. We focused on the interplay between high-density water and low-density water to inquire on local modifications of water structure with respect to the bulk phase. We investigated four different pressures where the structure of bulk water spans from high-density liquid (locally more disordered) to low-density liquid (locally more ordered). The investigation showed that both the hydration and the premelting layers present a low-density liquid water component and similarities as a function of pressure with the corresponding bulk. We also find that the premelting layer shows structural features intermediate between the liquid and the crystalline state acting as a matching layer.