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Chloride molten salts have become a potential heat storage material for the design of a new generation of concentrating solar power (CSP) (>700 °C) due to its abundant reserves and low cost. The difficulty of measuring the high-temperature thermal properties of chlorides can be effectively solved by using molecular dynamics simulation. However, it is challenging to get the thermophysical properties of multi-component molten salts containing CaCl2 due to the lack of Born–Mayer–Huggins (BMH) potential parameters of CaCl2. Through comparative analysis of the structure and thermal properties of CaCl2, including density and thermal conductivity, a set of Born–Mayer–Huggins (BMH) potential parameters of CaCl2 named SP2 is determined in this study. The density, specific heat capacity, and thermal conductivity of nine eutectic molten salts are simulated, including NaCl-CaCl2, KCl-CaCl2, NaCl-CaCl2-MgCl2, and NaCl-CaCl2-KCl, and the simulation results are found to be in good agreement with the experimental results. It is also found that the SP2 parameters are able to predict the thermal properties and structure of molten multicomponent chlorides including calcium. [ABSTRACT FROM AUTHOR]

Mixed sex pigs (n = 720) were placed in 12 rooms (Purdue Swine Environmental Research Building) to measure the effect of reduced crude protein (CP), amino acid (AA)-supplemented diets on growth and the carcass. Pigs were blocked by body weight (BW) and gender and allotted to room and pen (10 mixed-sex pigs/pen). Pigs were fed a nine-phase, wean-finish program. Control pigs consumed corn-soybean meal-distiller's dried grains with solubles (DDGS) diets containing no to minimal (Met) synthetic AA. The 2X diet was formulated to meet the seventh most-limiting AA, and balanced using synthetic AAs to meet all AA needs. The 1X diet was formulated to meet a CP value halfway between the control and 2X diet, and also balanced using synthetic AAs to meet all AA needs. Diets were formulated to identical net energy concentrations and balanced to meet standard ileal digestible NRC 2012 AA requirements. Pit vacuum samples were collected at the end of each growth phase for analyses of nitrogen, C and dry matter (DM). Pigs fed the Control and 1X diet grew faster (P < 0.005), had greater gain:feed (P < 0.001), and were heavier at market (P < 0.001) than animals fed the 2X diet. No consistent effects of diet were observed on average daily feed intake. Carcass data were analyzed for sex, diet and sex*diet effects. Reductions in dietary CP resulted in a linear reduction in ammonium nitrogen excretion per kg of BW gain in Nursery (P < 0.001) and Grow-Finish (P < 0.001) phases. Reductions in dietary CP, with synthetic AA supplementation resulted in a linear reduction in total nitrogen excreted per kg BW gain in the Grow-Finish phase (P < 0.001) and overall (P < 0.001). Total mineral excretion per kg gain was reduced in pigs fed 1X and 2X diets compared with control-fed pigs (P < 0.005). Reductions in dietary CP of ~3 and 5%-units from wean-finish result in reductions of total N excretion of 11.7 and 24.4%, respectively. Reduced performance and carcass characteristics observed in pigs fed the 2X diets indicates an inaccurate estimate of NRC 2012 AA requirements or ratios to lysine in a low CP diet. [ABSTRACT FROM AUTHOR]

The solvation structure and dynamics of small organic molecules at the methanol–silica interface are important for understanding the reaction dynamics in heterogeneous catalysis as well as the transport mechanisms in liquid chromatography. The role of solute polarity in interfacial solvation at the methanol–silica interface has been investigated via umbrella sampling molecular dynamics (MD) simulations and 1,3-propanediol and n-pentane were selected as representative species of polar and apolar solutes. Free energy calculations reveal that it took a similar free energy cost to transfer both solute molecules from the interface to the bulk, despite the huge difference in their polarities. The 1,3-propendiol molecule can penetrate the adsorbed methanol layer and form hydrogen bonds with the silica surface with its backbone perpendicular to the silica surface, resulting in a significant slowdown of translational and rotational dynamics. Further analysis of solvent density and solute orientations suggest that at the minimum of the adsorption free energy curve, the 1,3-propanediol molecule is in a desolvated state, while n-pentane is in a solvated state. The collective effect of solute concentration has also been studied by unbiased MD simulations, and the free energy barriers of transferring the solute molecule from the interface to bulk, as well as the parallel diffusion coefficients at the interface, show a non-monotonic dependence on solute concentration, which can be related to the crowded environment in the interfacial layers. [ABSTRACT FROM AUTHOR]

The interfacial properties of the acetonitrile (ACN)–water–silica interface have great implications in both liquid chromatography and heterogeneous catalysis. We have performed molecular dynamics (MD) simulations of ACN and water binary solutions to give a comprehensive study of the collective effect of silica surface polarity and ACN concentration on interfacial structures and dynamics by tuning both surface charges and ACN concentration. MD simulation results indicate that many properties in the liquid–solid interface region undergo a monotonic change as the silica surface is tuned from polar to apolar due to the weakening of hydrogen bonding, while their dependence on ACN concentration is presumably governed by the preferential adsorption of water at the silica surface over ACN. However, at apolar surfaces, the interfacial structures of both water and ACN behave like the liquid–vapor interface, and this resemblance leads to an enrichment of ACN at the interface as well as accelerated dynamics, which is very different from that in the bulk solution. The organization of ACN molecules at both polar and apolar surfaces can be attributed to the amphiphilic nature of ACN, by which the micro-heterogeneity domain formed can persist both in the bulk and at the liquid–solid interface. Moreover, extending diffusion analysis to the second layer of the interface shows that the interfacial transport pathways at polar surfaces are likely very different from that of apolar surfaces. These simulation results give a full spectrum description of the ACN/water liquid–solid interface at the microscopic level and will be helpful for explaining related spectroscopic experiments and understanding the microscopic mechanisms of separation protocols in current chromatography applications. [ABSTRACT FROM AUTHOR]

We have performed molecular dynamics simulations to study the structure and dynamics of liquid ethanol at the α-Al2O3 surface. We scale the surface charges by a dimensionless parameter k, ranging from 0 to 1, which allows us to model the surface changing from apolar to polar. Compared with previous studies on hydrophilic surfaces, interfacial ethanol molecules form less densely packed layering structures and show less preferential orientational ordering as the alumina surface gradually becomes more apolar. Further analysis of hydrogen bonds and density correlation functions suggest that both hydrogen bonding between ethanol and the alumina surface and the interdigitation of alkyl groups control the interfacial structures collectively. Rotational dynamics and in-plane diffusion analysis show an acceleration of interfacial dynamics as the surface is switched to nonpolar, whereas interfacial rotational dynamics does not follow a monotonic trend during polarity tuning. Extending in-plane diffusion analysis to the second layer of the interface shows a strong enhancement of diffusion from the first layer at the polar interface in comparison to the apolar surfaces, suggesting different surface diffusion mechanisms at polar surfaces that may play an important role in the mobile phase transport in liquid chromatography. [ABSTRACT FROM AUTHOR]

Long-standing problems associated with long-ranged electrostatic interactions have plagued theory and simulation alike. Traditional lattice sum (Ewald-like) treatments of Coulomb interactions add significant overhead to computer simulations and can produce artifacts from spurious interactions between simulation cell images. These subtle issues become particularly apparent when estimating thermodynamic quantities, such as free energies of solvation in charged and polar systems, to which long-ranged Coulomb interactions typically make a large contribution. In this paper, we develop a framework for determining very accurate solvation free energies of systems with long-ranged interactions from models that interact with purely short-ranged potentials. Our approach is generally applicable and can be combinedwith existing computational and theoretical techniques for estimating solvation thermodynamics. We demonstrate the utility of our approach by examining the hydration thermodynamics of hydrophobic and ionic solutes and the solvation of a large, highly charged colloid that exhibits overcharging, a complex nonlinear electrostatic phenomenon whereby counterions from the solvent effectively overscreen and locally invert the integrated charge of the solvated object. [ABSTRACT FROM AUTHOR]

Molten chloride salt is recognized as a promising heat transfer and storage medium in concentrating solar power in recent years, but there is a serious lack for thermal property data of molten chloride salts. In this work, local structures and thermal properties for molten chloride salt—including NaCl, MgCl2, and ZnCl2—were precisely simulated by Born–Mayer–Huggins (BMH) potential in a rigid ion model (RIM) and a polarizable ion model (PIM). Compared with experimental data, distances between cations, densities, and heat capacities of molten chloride slats calculated from PIM agree remarkably better than those from RIM. The polarization effect brings an extra contribution to screen large repulsive Coulombic interaction of cation–cation, and then it makes shorter distance between cations, larger density and lower heat capacity. For NaCl, MgCl2, and ZnCl2, PIM simulation deviations of distances between cations are respectively 3.8%, 3.7%, and 0.3%. The deviations of density and heat capacity for NaCl between PIM simulation and experiments are only 0.6% and 2.2%, and those for MgCl2 and ZnCl2 are 0.7–10.7%. As the temperature rises, the distance between cations increases and the structure turns into loose state, so the density and thermal conductivity decrease, while the ionic self-diffusion coefficient increases, which also agree well with the experimental results. [ABSTRACT FROM AUTHOR]