Effect of water-wall interaction potential on the properties of nanoconfined water

Much of the understanding of bulk liquids has progressed through study of the limiting case in which molecules interact via purely repulsive forces, such as a hard-core potential. In the same spirit, we report progress on the understanding of confined water by examining the behavior of water-like molecules interacting with planar walls via purely repulsive forces and compare our results with those obtained for Lennard-Jones (LJ) interactions between the molecules and the walls. Specifically, we perform molecular dynamics simulations of 512 water-like molecules which are confined between two smooth planar walls that are separated by 1.1 nm. At this separation, there are either two or three molecular layers of water, depending on density. We study two different forms of repulsive confinements, when the interaction potential between water-wall is (i) $1/r^9$ and (ii) WCA-like repulsive potential. We find that the thermodynamic, dynamic and structural properties of the liquid in purely repulsive confinements qualitatively match those for a system with a pure LJ attraction to the wall. In previous studies that include attractions, freezing into monolayer or trilayer ice was seen for this wall separation. Using the same separation as these previous studies, we find that the crystal state is not stable with $1/r^9$ repulsive walls but is stable with WCA-like repulsive confinement. However, by carefully adjusting the separation of the plates with $1/r^9$ repulsive interactions so that the effective space available to the molecules is the same as that for LJ confinement, we find that the same crystal phases are stable. This result emphasizes the importance of comparing systems only using the same effective confinement, which may differ from the geometric separation of the confining surfaces.Comment: 20 pages, 10 figure

Effect Of Water Soluble Fraction Of Cotton Banana (Musa Paradisiaca L.) Ethanolic Extract On The Blood Glucose Levels In Vivo And Active Compounds Identification

Banana is one of Indonesian food which has many pharmacological activities. Pisang kapas (Musa paradisiaca L.), one of Indonesian banana, is well known empirically as laxative, so it can be used in the treatment of constipation. It has been reported that both of chloroformic and ethanolic extract of pisang kapas have antidiabetic activities. However, fractination of those are not yet performed and report about their antidiabetic activities are not yet available. Here we investigated the effect of water-dissolved fraction of ethanolic extract of cotton banana to reduce the blood glucose level in rat model and identified its active ingredient. The oral glucose tolerance method with 60 min glucose loading time was used to induce hyperglicemic condition in rats, either in control group or treatment group. Glibenclamid (positive control), sodium carboxymethyl cellulose (negative control) and the fraction were orally given to the rats in a single dose. To measure blood glucose level photometrically, enzimatic reaction by using diagnostic reagent Glucose GOD FS is applied. Paper chromatography was utilized to identify the ingredient of the fraction qualitatively. The fraction in dose of 0.25 g/kg reduced blood glucose level by 22.28 ± 0.76 %. The fraction contained reductants in addition to glucose, amino acids, and the acids in plants

Preferential sorption versus preferential permeability in pervaporation

Transport of liquids by pervaporation takes place by a solution—diffusion mechanism. In order to investigate the “solution part” of this transport model, preferential sorption has been compared with preferential permeability. Sorption equilibria and pervaporation experiments for the systems water—ethanol—cellulose acetate, water—ethanol—polyacrylonitrile and water—ethanol—polysulfone have been investigated. Theoretical values of preferential sorption have been derived from Flory—Huggins thermodynamics, extended with concentration dependent interaction parameters. These calculated sorption values show a reasonable agreement with experimental values. The large difference in molar volumes between water and ethanol determines the preferential sorption of water in these systems to a great extent, and this effect increases with decreasing swelling value. Comparison of preferential sorption experiments with pervaporation experiments indicates that, apart from the effect of differences in diffusivity for the permeating components, preferential sorption contributes to a major extent to selective transport

A new atmospheric aerosol phase equilibrium model (UHAERO): organic systems

In atmospheric aerosols, water and volatile inorganic and organic species are distributed between the gas and aerosol phases in accordance with thermodynamic equilibrium. Within an atmospheric particle, liquid and solid phases can exist at equilibrium. Models exist for computation of phase equilibria for inorganic/water mixtures typical of atmospheric aerosols; when organic species are present, the phase equilibrium problem is complicated by organic/water interactions as well as the potentially large number of organic species. We present here an extension of the UHAERO inorganic thermodynamic model (Amundson et al., 2006c) to organic/water systems. Phase diagrams for a number of model organic/water systems characteristic of both primary and secondary organic aerosols are computed. Also calculated are inorganic/organic/water phase diagrams that show the effect of organics on inorganic deliquescence behavior. The effect of the choice of activity coefficient model for organics on the computed phase equilibria is explored

Kosmotropes and chaotropes: modelling preferential exclusion, binding and aggregate stability

Kosmotropic cosolvents added to an aqueous solution promote the aggregation of hydrophobic solute particles, while chaotropic cosolvents act to destabilise such aggregates. We discuss the mechanism for these phenomena within an adapted version of the two-state Muller-Lee-Graziano model for water, which provides a complete description of the ternary water/cosolvent/solute system for small solute particles. This model contains the dominant effect of a kosmotropic substance, which is to enhance the formation of water structure. The consequent preferential exclusion both of cosolvent molecules from the solvation shell of hydrophobic particles and of these particles from the solution leads to a stabilisation of aggregates. By contrast, chaotropic substances disrupt the formation of water structure, are themselves preferentially excluded from the solution, and thereby contribute to solvation of hydrophobic particles. We use Monte Carlo simulations to demonstrate at the molecular level the preferential exclusion or binding of cosolvent molecules in the solvation shell of hydrophobic particles, and the consequent enhancement or suppression of aggregate formation. We illustrate the influence of structure-changing cosolvents on effective hydrophobic interactions by modelling qualitatively the kosmotropic effect of sodium chloride and the chaotropic effect of urea.Comment: 13 pages, 12 figures; inclusion of review material, parameter analysis and comparison of kosmotropic and chaotropic effect

Effect of Water Price on the Multicrop Production Decision: Appling Fixed Allocatable Input Model in Georgia

This study applies the fixed allocatable input model to test the effect of water price on the multiple production decision in Georgia, U.S. The limited dependent variable models are applied and intensive data are analyzed in this study to estimate the decision for crop choice, land allocation, product supply, and water demand functions at crop-level. In order to investigate the effect of water price on crop-level demand, the total water price effect on farm water demand is decomposed the intensive margin and extensive margin.Resource /Energy Economics and Policy,

Measurement of the Cotton Mouton effect of water vapour

In this paper we report on a measurement of the Cotton Mouton effect of water vapour. Measurement performed at room temperature ($T=301$ K) with a wavelength of 1064 nm gave the value $\Delta n_u = (6.67 \pm 0.45) \cdot 10^{-15}$ for the unit magnetic birefringence (1 T magnetic field and atmospheric pressure)