Aggregation Of Water Molecules Research Articles

The Adsorption of Benzo-15-Crown-5 Ether from Water onto Carbon Surfaces

Isotherms are reported for the adsorption of water vapor and benzo-15-crown-5 ether from aqueous solution onto one nonporous and three porous carbons. Specific adsorption of water at oxygen-containing sites on the porous carbons was followed by adsorptive aggregation of water molecules on the carbon surfaces and in pores. The adsorption of benzo-15-crown-5 ether was impeded by coadsorbed water and by the steric requirements of narrow pore entrances which denied the large molecules access to surface within the carbon micropore structure.

Vibrational spectroscopic studies on the state of aggregation of water in carbon tetrachloride, in dioxane and in the mixed solvents

A detailed infrared study of the vibrational modes of water in dioxane, carbon tetrachloride and a mixed solvent as a function of concentration is reported. H 2O/D 2O mixtures have been used in order to isolate the uncoupled v(OH) and v(OD) modes. The data have been interpreted in terms of the state of aggregation of water molecules in a hydrophobic solvent and in a solvent to which hydrogen bonding can occur. It is shown that at very low concentrations ( x H 2O = 5×10 −4) water exists in the monomeric form and can rotate rather freely. However, water is strongly self aggregated in a hydrophobic organic solvent for concentrations greater than x H 2O = 5×10 −3 (ie if there are more than 5 water molecules in a 1000 solvent molecule ‘bath’). Evidence of distinct (dioxane) m(water) n complexes is found in dioxane solution and in the mixed solvent. However, as the water concentration is increased it is clear that a water/solvent ‘network’ is formed. The aggregation processes involving water depend critically, however, on the hydrophobicity of the solvent mixture.

The effects of bilayer thickness and tension on gramicidin single-channel lifetime

Measurements have been made of gramicidin single-channel lifetimes in monoacylglycerol bilayers chosen so that their thickness ranged from above to below the length of the gramicidin channel. Contact angles, electrical capacities and bulk-phase interfacial tensions have also been determined for these systems. The mean channel lifetime decreased with the hydrocarbon thickness of the membrane until the latter reached 2.2 nm, after which the lifetime was relatively constant. A theoretical model has been proposed which relates the mean channel lifetime (or dissociation constant) to both the thickness and the tension of the bilayers. The analysis of the present results and of those of previous studies has led to the idea that aggregates of water molecules may play an important rǒle in the dissociation of the gramicidin channel.

Pulse Radiolysis of Formamide and Formamide–Water Mixtures

From the optical absorption spectrum observed by a sub-nanosecond pulse radiolysis method it is concluded that irradiated pure liquid formamide (dielectric constant = 109) does not yield solvated electrons with lifetimes >10−11 s. In formamide–water mixtures the hydrated electron is formed in low yield and the position of the absorption band of eaq− is not altered by changing the composition. Apparently formamide reacts much more rapidly with thermalized electrons than it does with hydrated electrons. The latter may be formed in formamide–water mixtures due to aggregates of water molecules.

Conductance and transport numbers of acidified sodium aluminate solutions and the zero point of charge of aluminium hydroxide

Conductance measurements of acidified sodium aluminate solutions showed a gradual drop as the alumina content of the solution increases. This behaviour was explained by adsorption of H+ ions, as visualised from linear plots of (κ0−κ) per mole of alumina against\(\Gamma _{{\rm H}^ + }\) (whereκ0 is the specific conductance of the corresponding (NaOH + HCl),κ is the specific conductance of (sodium aluminate + HCl) and\(\Gamma _{{\rm H}^ + }\) is the amount of H+ ions adsorbed per mole of alumina). Transport number experiments showed that alumina behaves as a non-electrolyte and that the transport number of the Cl− ion increases with increase in alumina content. This behaviour was explained on the basis of aggregation of water molecules around alumina.

Studies of ultrasonic velocity in aqueous solutions of electrolytes

Measurements of sound velocity in aqueous solutions of sodium formate, sodium acetate, sodium propionate, sodium iso-valerate, calcium formate, calcium acetate, calcium propionate, lead acetate and zinc sulphate support Eucken’s theory which envisages a decrease in the number of aggregates of water molecules as the temperature rises. The other derived characteristics such as adiabatic compressibility, apparent molal compressibility and apparent molal volume conform to Gucker’s theoretical expressions based on the Debye-Huckel theory in the entire concentration range.