Viscosity aqueous solvent mixtures

Table 4.3 lists the viscosities of pure solvents. For non-aqueous solvent mixtures they can be calculated with Eq. 4.1 from the viscosities of the pure solvents and their mole fractions XA and XB (Snyder et al., 1997). 

An example of the calculation including the conversion factors is given in section 2.2.S. The viscosities for various HPLC solvents are also listed in Section 2.2.5, including aqueous solvent mixtures. The influence of buffers and salts on the viscosity of an aqueous mixture is typically small, and we can use the viscosity of the solvent mixture without the buffer for an estimation of the pressure. 

Thickeners. Thickeners are added to remover formulas to increase the viscosity which allows the remover to cling to vertical surfaces. Natural and synthetic polymers are used as thickeners. They are generally dispersed and then caused to swell by the addition of a protic solvent or by adjusting the pH of the remover. When the polymer swells, it causes the viscosity of the mixture to increase. Viscosity is controlled by the amount of thickener added. Common thickeners used in organic removers include hydroxypropylmethylceUulose [9004-65-3], hydroxypropylceUulose [9004-64-2], hydroxyethyl cellulose, and poly(acryHc acid) [9003-01-4]. Thickeners used in aqueous removers include acryHc polymers and latex-type polymers. Some thickeners are not stable in very acidic or very basic environments, so careful selection is important. 

Effects of solvent mixtures can be seen in biochemical systems. Ligand binding to myoglobin in aqueous solution involves two kinetic components, one extramolecular and one intramolecular, which have been interpreted in terms of two sequential kinetic barriers. In mixed solvents and subzero temperatures, the outer barrier increases and the inner barrier splits into several components, giving rise to fast intramolecular recombination. Measurements of the corresponding solvent structural relaxation rates by frequency resolved calorimetry allows the discrimination between solvent composition and viscosity-related effects. The inner barrier and its coupling to structural relaxation appear to be independent of viscosity but change with solvent composition (Kleinert et al., 1998). 

For relatively porous nanofiltration membranes, simple pore flow models based on convective flow will be adapted to incorporate the influence of the parameters mentioned above. The Hagen-Poiseuille model and the Jonsson and Boesen model, which are commonly used for aqueous systems permeating through porous media, such as microfiltration and ultrafiltration membranes, take no interaction parameters into account, and the viscosity as the only solvent parameter. It is expected that these equations will be insufficient to describe the performance of solvent resistant nanofiltration membranes. Machado et al. [62] developed a resistance-in-series model based on convective transport of the solvent for the permeation of pure solvents and solvent mixtures ... 

The viscosity of concentrated solutions can be quite different from that of the pure solvent. Many models have been proposed to calculate the viscosity of liquid mixtures from the viscosity of the pure components. These models rely on interpolation. As is often the case, mixtures of components that can exhibit intermolecular hydrogen bonding and especially aqueous solutions must be considered separately. 

The catalytic activity and selectivity in the hydrocyanation also depend on the method of purification. When the catalyst was purified by a non-aqueous solvent, high catalytic activity and asymmetric induction were realized. In addition, viscosity and thixotropy of the reaction mixture were also reported to influence the enantioselectivity [28]. Thus, it seems difficult to explain how the asymmetric induction occurs on a unimolecular level. Mechanistic studies on the asymmetric catalysis by NMR [29,30,31],calculation [30,31],andX-ray diffraction patterns [25] were reported by several groups. 

In all these calculations we need to know the viscosity of the mobile phase. Table 2.2 contains the data for the solvents commonly used in HPLC. Most mobile phases, however, are mixtures of solvents. For nonpolar solvents, one can estimate the viscosity of a mixture by linear interpolation between the viscosities of the component solvents. This is not true for aqueous mixtures due to the strong association of polar solvents. Since aqueous mixtures are the mobile phases for reversed-phase chromatography, it is important to know their viscosity. Figure 2.9 ows the viscosity of the aqueous mixtures of the polar organic solvents commonly used in reversed-phase chromatography. Note that the water-alcohol mixtures exhibit a pronounced viscosity... 

The chemical resistance of polyester amide glass fibre composite is excellent [126]. A solvent mixture of CF3COOH/CHCI3 was used as a solvent for thermotropic LC polyester, based on 4-chlorocarbonyl phenyl esters of aromatic dicarboxylic acids and phenols or aliphatic diols for viscosity measurement. This indicates thermal stability in various organic solvents. [127]. Unsaturated aromatic LC polyesters, synthesized with the aim to fix the LC state, can be crosslinked by using styrene. The crosslinked matrix can be degraded by refluxing in 3 M aqueous sodium hydroxide solution and methanol in a vol. ratio of 3 2 [128]. 

Cordless, rechargeable electro-pneumatic reagent sprayers that can apply solutions that are viscous (e.g., aqueous sulfuric acid) or of normal viscosity (water-organic solvent mixtures) in an even, fine (0.3-10 pm), reproducible aerosol are commercially available (e.g., from Camag and Desaga) to facilitate application of detection reagents (Figure 8.3). 

Polybutene resins. These liquid resins are obtained by cationic polymerization of petroleum C4 streams in the presence of AICI3 at relatively low temperature. Temperature and AICI3 concentration are important factors as they influence the molecular weight and viscosity of the final resin. After reaction, the mixture is deactivated with water, methanol, ammonia or aqueous sodium hydroxide. The organic layer is separated and distilled to remove solvent and unconverted material. 

Solutions in organic solvents may, with certain reservations, be used directly, provided that the viscosity of the solution is not very different from that of an aqueous solution. The important consideration is that the solvent should not lead to any disturbance of the flame an extreme example of this is carbon tetrachloride, which may extinguish an air-acetylene flame. In many cases, suitable organic solvents [e.g. 4-methylpentan-2-one (methyl isobutyl ketone) and the hydrocarbon mixture sold as white spirit ] give enhanced production of ground-state gaseous atoms and lead to about three times the sensitivity... 

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